[draft parallel baseline risk assessment for the … · 2018. 9. 8. · the variogram using curve...

W a s t e M a n a g e m e n t o f N o r t h A m e r i c a , inc.Centra! Region1320 Greenwav D r i v e - .-inc. ~ a J t 3 3 7 5 D 3 3S u t t e 900 -214 550-1 77;

March 14, 1991

Ms. Monica C h a p a ( 6 H - E O )M o s l e y Road P r o j e c t C o o r d i n a t o rO k l a h o m a / N e w Mexico Enforc ement S e c t i o nU. S. Environmental Protection Agency, Region VI1445 Ross AvenueDallas, Texas 75202-2733R E : " D R A F F P A R A L L E L R I S K A S S E S S M E N T " F O R T H E M O S L E Y ROAD S A N I T A R YL A N D F I L LDear Ms. C h a p a :Enclo s ed i s t h e " D r a f t P a r a l l e l Risk Ass e s smen t" f o r t h e M o s l e y Road S a n i t a r y L a n d f i l lR I / F S s u b m i t t e d o n b e h a l f o f W a s t e Managemen t o f Oklahoma. I n c . ( W M O ) f o r E P Areview. The " D r a f t P a r a l l e l Risk Ass e s sment" was p r e p a r e d by T e t r a T e c h , Inc. on b e h a l fo f WMO.As you are aware, the "Draf t R e m e d i a l I n v e s t i g a t i o n Repor t" s u b m i t t e d to EPA for r e c e i p ton J a n u a r y 14, 1991 included a section de s cr i b ing the risks associated wi th p o t e n t i a le xpo sur e to c o m p o u n d s d e t e c t e d in the various media in the s t u d y area. As r e q u i r e d , therisk assessment in the "Draft Remedial I n v e s t i g a t i o n Report" con forms wi th EPA RiskA s s e s s m e n t G u i d a n c e f o r S u p e r f u n d ( R A G S : V o l u m e I , H u m a n H e a l t h E v a l u a t i o n M a n u a l ;Volume I I , Environmental Evaluation Manual) .As you are al so aware, a number of the a s s u m p t i o n s and methods mandated by RAGS arecon trover s ia l . W a s t e M a n a g e m e n t has spon sor ed o r i g i n a l risk as se s sment research t h a t hasled to a l t e r n a t i v e m e t h o d o l o g i e s . T h e s e a l t e r n a t i v e m e t h o d o l o g i e s were d i s c u s s e d in ap r e s e n t a t i o n to A g e n c y H e a d q u a r t e r s and Region VI staff on N o v e m b e r 27, 1990 inW a s h i n g t o n , D.C. The two a p p r o a c h e s a d d r e s s e d in the research are: 1) a t r u l y a c c u r a t e"reasonable maximum exposure" scenario; and 2) a g e o s t a t i s t i c a l ( k r i g i n g ) a p p r o a c h to morea c c u r a t e l y charac t e r i z e t h e risk f r o m g r o u n d w a t e r c o n t a m i n a n t s , a s a c k n o w l e d g e d in RAGSand by A g e n c y s taff a t t e n d i n g the m e e t i n g as a val id t e chn ique for q u a n t i t a t i v e riskassessment. At the end of that m e e t i n g , c op i e s o f the research r e p o r t s were p r o v i d e d .By l e t t e r da t ed J a n u a r y 10, 1991, EPA acknowledged "...there is merit in the a l t e r n a t i v e sWMNA proposed...," al though the Agency was unable at that time to authorize the use ofthese a l t e r n a t i v e m e t h o d o l o g i e s f o r t h e M o s l e y Road S a n i t a r y L a n d f i l l . E P A d i r e c t e dWMO to submit a risk assessment for the S i t e conforming with current Agency gu idance ,but invi t ed WMO to submit a p a r a l l e l s i t e ri sk assessment u s ing the k r i g i n g t e chn ique w h i c hthe Agency would evaluate.

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Ms. Monica C h a p aMarch 14, 1991

The "Draft P a r a l l e l Risk Assessment" is be ing s u b m i t t e d to the EPA for rece ipt on March14, 1991. If a p p r o v e d , EPA comments could be incorporat ed into the " F i n a l R e m e d i a lI n v e s t i g a t i o n Report" without s i g n i f i c a n t l y a f f e c t i n g t h e d e l i v e r a b l e s c h e d u l e . C o n s e q u e n t l y ,WMO is reque s t ing that EPA c o m p l e t e its review of th i s document as e x p e d i t i o u s l y asp o s s i b l e .If you have any que s t i ons , p l e a s e do not h e s i t a t e to c a l l me.Very t r u l y yours,W A S T E M A N A G E M E N T O F N O R T H A M E R I C A , I N C .

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M a r k S n y d e rS e n i o r P r o j e c t E n g i n e e rEnclo surecc: C h i e f o f S u p e r f u n d E n f o r c e m e n t BranchRobert M e l t o n , PRC Environmenta lDavid G u i e r , W M N ARich O ' H a r a , W M N ALisa S e g l i n , W M N ADavid Dolan, W M N ADennis H r e b e c , O S D HH a l C a n t w e l l , O S D HV i n c e L o p e z , A F C R E / R O V

O C T 1 7 1 9 9 1REGION 6

«45 ROSS AVENUE SUfTE 1200D A L L A S T E X A S 75202-2733

Mr, Lou BarinkaW a s t e Management at Oklahoma, I n c .1320 Greenway Dr. S u i t e #900I r v i n g , T e x a s 75038K e : M o s l e y Road S a n i t a r y L a n d f i l lP a r a l l e l Basel ine Risk Asses smentDear Mr* Barinks:T h a n k you for submi t t ing the P a r a l l e l Basel ine Risk Asse s sment(PBRA). EPA has c ompl e t ed its review of the PBRA and is f o r w a r d i n gt h e enclosed comments* I t should b e no t ed , that E P A ' s riskmanagement dec i s ions w i l l be based upon the Risk Asse s sment whichwas submitted as a part of the approved F i n a l RemedialI n v e s t i g a t i o n R e p o r t ,

If you should have any questions r egarding this l e t t e r , I can becontacted at ( 2 1 4 ) 655-6730.S i n c e r e l y ,

in•5JCCI T ' ,Co

Monica -.^O K / N K S u p e r & n d Enfor c ement S e c t i o n ( 6 H - E O )Enclosurecc: Mary D r a k e - Vff lNA Rich 0 - K a r a - WMNA

M e l t ° n - P*C Dennis Hreb.c - OSDH

PARALLEL B A S E L I N E R I S K A S S E S S M E N TMOSLEY ROAB S A H X T A R Y L A N D F I L L

Page 1, 1st Paragraph: Delete the phrase "The PBRA employs mores t a t i s t i c a l l y re f ined methods ... than those used in the RIbaseline risk assessment ,,." The methodology used in PBRA is notnecessarily a "more r e f ined method1 1.Page 9, T a b l e isof concern. Vinyl chloride was not indicated as a chemical

Sect i on 3.2.2 Using G e o s t a t i s t i c s to Estimate EPCs: Thes ta t i s t i ca l analysis of kriged grid squares used in the PBRA tocalculate the exposure point concentration (EPC) violates a basicassumption of parametric s ta t i s t i c s - Parametric s ta t i s t i c s assumesthat s a m p l i n g units are independent of each other. To per formkriging analys i s , the s a m p l i n g data is modeled using a varlogram."The variograin model is then fit to the da ta p l o t t e d inthe variogram using curve f i t t i n g techniques. Using thevariogram mode l , kriging equations can be used toestimate an average concentration for each grid squarein an evenly spaced grid. When e s t imat ing the averageconcentration for a s p e c i f i c grid square, more weight isgiven to s a m p l i n g data point s closest to the square beingconsidered."

T h e r e f o r e , the concentrations estimated for each grid square aredependent on each other. To p e r f o r m parametric s ta t i s t i c s onkriged grid squares violates the assumption that s a m p l i n g units areindependent of each other. The "Reasonable Maximum Exposure (RME)case" concentrations calculated in the PBRA do net represent anupper bound est imate of po t en t ia l exposure to site chemicals. The"maximum case" presents a better representation of an upper boundestimate of p o t en t i a l exposure.f l e c t i o n 3.3.2 Using Monte Carlo S i m u l a t i o n To Estimate ChronicDai ly Intake s: At the present time, i n s u f f i c i e n t data on exposureparameters exists to accurately estimate the chronic d a i l y intakevalues using the Mont© carlo S i m u l a t i o n method. The Monte carloS i m u l a t i o n method is not a p p l i c a b l e for risk management decisionper ta in ing to the M o s l e y Road S a n i t a r y L a n d f i l l .

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D R A F T P A R A L L E LB A S E L I N E R I S K A S S E S S M E N T

F O R T H EM O S I i B Y nOAO S A N I T A R Y L A N D F I L t S I T EOklahoma city. Oklahoma

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Prepared f o r :W a s t e Management o f N o r t h Ameri ca , I n c3003 B u t t e r f i e l d Roadoak Brook, I l l i n o i s 60521

Prepared by:T E T R A T E C H , I N C ,10306 Eaton P l a c e , S u i t e 340F a i r r & x , V i r g i n i a 22030

March 13,

T A B L E OF CONTENTS

S e c t i o n £age1.0 INTRODUCTION . . . . . . . . . . . . . . , . , . . . . , . 12.0 S E L E C T I O N OF CHEMICALS OF CONCERN . . . . . . . . . . . . 4

2.1 M e t h o d s f or E v a l u a t i n g a n d _ A n a l y z i n g . M o n i t o r i n g _ D _ a t a 42.2 M e t h o d s for. S e l e c t i n g .Chemicals _ Q f _ C _ o n c e r n . . . . . 62.3 A l l u v i a l A c r u i f e r . . . . . . . . . . . . . . . . . . 82.4 Garber-Wel l inq. tpn , f tqu i f er . . . . .......... 123.0 E X P O S U R E ASSESSMENT . . . . . . . . . . . . . . . . . . 16

3.1 Exposure.Assessment A p p r o a c h . . . . . . . . . . . 173.2 Environmental S e t t i n g . . . . . . . . . . . . . . . 173.1.2 Exposure Pathways of Concern . . . . . . . . 183.2 Es t imat ion of Exposure Point .Concentrations . . . 203.2.1 Commonly A p p l i e d Methods for Es t imat ing EPCs 213.2.2 Us ing G e o s t a t i s t i c s to Est imate EPCs . . . » 263.3 Est imat ion o f Chronic. D a i l y I n t a k e s . (GDIs) . . . . 323.3.1 Commonly A p p l i e d M e t h o d s f o r E s t i m a t i n gchronic D a i l y I n t a k e s . . . . . . . . . . . . 373 . 3 . 2 U s i n g M o n t e C a r l o S i m u l a t i o n t o E s t ima t eChronic D a i l y I n t a k e s . . . . . . . . . . . . 404 . 0 T O X I C I T Y A S S E S S M E N T . . . . . . . . . . . . . . . . . . 4 7

4.1 T o x i c i t v . Cri t er ia .for Eva lua t ing Pot en t ia lCarcinogenic: E f f a c t s . . . . . . . . . . . . . . . 504.2 T_oxic.ltv: Criteria fo.r Evaluat ing Potent ialNoncarc inocrenic_ E f f e c t s . . . . . . . . . . . . . . 535 . 0 R I S K C H A R A C T E R I Z A T I O N . . . . . . . . . . . . . . . . . 5 7

5.1 M_ethod.5_£or_Estimatina Carcinogenic., and...Koncarcinogenic Risks . . . . . . . . . . . . . . . 575-2 Alluv ia l . A q u i f e r . . . . . . . . . . . . . . . . . 605.3 S a r b e r - W g H i n g t o n _ Aqui f er . . . . . . . . . . . . . 656 . 0 U N C E R T A I N T Y A N A L Y S I S . . . . . . . . . . . . . . . . . . 7 0

6.1 Environmental S a m p l i n g and A n a l y s i s . . . . . . . . 706.2 E s t i m a t i o n j a f Exposure . . . . . . . . . . . . . . 736.3 ^o jd , cJ±VL_Asse s sn i en t . . . . . . . . . . . . . . . . 74

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T A B L E O F C O N T E N T S ( c o n t . )S e c t i o n7 . 0 S U M M A R Y A N D C O N C L U S I O N S

8.07.3

R E F E R E N C E S

als .of. Conceriure .Asse s sment . . . . . . .7.2.1 Exposure Pathway S e l e c t i o n . . . . . . .7.2.2 E s t i m a t i n g Exposure Point Concen tra t i on s7.2.3 E s t i m a t i n g chronic D a i l y I n t a k e s . „ . .R g s i u l t s o f t h e H u ' * ^ ~*~*- "

7979808031828288

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February 1991 DRAFT REPORT

1.0 INTRODUCTION

T n i s d r a f t P a r a l l e l Baseline Risk Assessment Report (PBRA)q u a n t i f i e s p o t e n t i a l human h e a l t h risks as sociated with use ofgroundwater at the M o s l e y Road S a n i t a r y L a n d f i l l S i t e located inOklahoma ci ty, Oklahoma, The baseline risk assessment presented inSec t i on 4 of the Mosley Road Sani tary L a n d f i l l RemedialI n v e s t i g a t i o n ( R I ) Report prepared b y C o l d e r A s s o c i a t e s , I n c . a n dsubmit ted to EPA in d r a f t f o r m on J a n u a r y 11, 1991 ( h e r e i n a f t e rr e f e rr ed to as the MRI baseline risk as se s sment"), i d e n t i f i e dinges t ion of groundwater under p o t e n t i a l f u tur e land-use conditionsof the s i t e as the exposure p a t h w a y of concern. In a d d i t i o n , theRI ba s e l ine risk assessment i d e n t i f i e d s p e c i f i c chemicals ofconcern that s i g n i f i c a n t l y contributed to p o t e n t i a l risks. ThePBRA employ s more s t a t i s t i c a l l y re f ined methods ( i . e . , Monte carlos i m u l a t i o n and g e o s t a t i s t i c s [ k r i g i n g ] ) than those used in the RIba s e l in e risk assessment for e s t i m a t i n g exposure via thegroundwater ingestion exposure pathway for s e l e c t ed chemicals o fconcern. As a r e s u l t , the risks presented in this report moreaccurately characterize the p o t e n t i a l human hea l th risks associatedwith f u t u r e use of groundwater in and around the M o s l e y RoadS a n i t a r y L a n d f i l l .

OI T .CCL T ,OO

The PBRA was prepared in keep ing with avai lable EPA guidance forc onduc t ing S u p e r f u n d risk as se s sments ( E P A 1990, I 9 8 9 a , b , c ) .S p e c i f i c a l l y , th e report q u a n t i f i e s th& p o t e n t i a l i m p a c t s t o humanhea l th f r o m inges t ion of groundwater f r o m the A l l u v i a l A q u i f e r andG a r b e r - W e l l i n g t o n A q u i f e r under the no-action remedial al ternative(EPA 1 9 9 0 ) . The s t a t i s t i c a l techniques employed in this report( i . e . , Monte Car lo s imula t i on and k r i g i n g ) are accepted me thod s foruse in baseline risk assessments, as discussed in Risk AssessmentGuidance f o r S u p e r f u n d ( R A G S ) ( E P A , 1 9 8 9 a ) . T h e s p e c i f i c

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a p p l i c a t i o n of these s t a t i s t i c a l techniques is discussed in Sec t i on4 of thi s report and are based on research sponsored by W a s t eManagement o f N o r t h A m e r i c a , Inc . ( C l e m e n t I 9 9 0 a , b ) .

The risk assessment process consists of f o u r basic s t eps which f ormthe outl ine of this report,

S T E P 1 . I D E N T I F I C A T I O N ..OF. C H E M I C A L S O F C O N C E R N . ( S e c t i o n 2 )Chemica l s of p o t e n t i a l concern i d e n t i f i e d in the RIbaseline risk assessment are summarized and discussed forboth the A l l u v i a l A q u i f e r and G a r b e r - W e l l i n g t o n A q u i f e r .only a subset of these chemicals are se lec ted for fur th ereva lua t i on in th i s report based on the r e s u l t s of the RIbas e l ine risk assessment and a d d i t i o n a l s e l e c t i o ncriteria.

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S T E P 2 . E X P O S U R E . . A S S E S S M E N T . ( S e c t i o n 3 ) T h e s t a t i s t i c a lmethods ( i . e . , Monte Carlo s imu la t i on and k r i g i n g ) fore s t i m a t i n g expo sure po in t c oncentra t ions ( E P C s ) a n de xpo sur e for the groundwater inge s t i on p a t h w a y arediscussed in this section. Pot en t ia l exposure toh y p o t h e t i c a l f u t u r e residents that ingest groundwaterf r o m th e A l l u v i a l A q u i f e r and G a r b e r - W a l l i n g t o n A q u i f e rare e s t imated .

S T E P 3 . T - O X I C I T Y A S S E S S M E N T . ( S e c t i o n 4 ) T o x i c i t y criteria f o rassessing carcinogenic and noncarcinogenic risk for theselected chemicals of concern are presented andevaluated.

S T E P 4 . & I S K ^ _ C K A E ^ C T E R . I 2 A T I Q N . ( S e c t i o n 5 ) T h e exposureestimates presented in Sec t i on 3 and the t ox i c i ty

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F e b r u a r y 1991 DRAFT REPORT

criteria presented in Sec t i on 4 are combined to estimatep o t e n t i a l carcinogenic and noncarcinogenic risks for thegroundwater ingestion pathway. Thes e risks characterizethe p o t e n t i a l human h e a l t h impact as soc iated with f u t u r euse of groundwater from the A l l u v i a l A q u i f e r and Garber*-W e l l i n g t o n A q u i f e r .

In a d d i t i o n , the uncertainties associated with the risk assessmentproce s s and the conc lu s ions of the PBRA report pre s en t ed in S e c t i o n6 and S e c t i o n 7, r e sp e c t iv e ly .

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2 . 0 I D E N T I F I C A T I O N O F C H E M I C A L S O F C O N C E R N

T h i s section s e l e c t s chemicals of concern that wi l l be eva lua t edf u r t h e r in this report for the groundwater media. The chemicals ofp o t e n t i a l concern in the RI basel ine risk assessment werereevaluated in the PBRA. As discussed in S e c t i o n 4 of the RIbasel ine risk assessment, several fa c t or s were considered whenevaluat ing the RI monitoring data inc lud ing p o t e n t i a l blankcontaminat ion, Q A / Q C procedures and codes, t e n t a t i v e l y i d e n t i f i e dcompounds , and background concentrations. Pursuant to EPA ( I 9 8 9 a )guidance , common laboratory contaminants ( e . g . , acetone, 2-butanone, methylene ch l or id e , p h t h a l a t e s , and t o lu ene) detected inon-site sample s which were within ten times the concentrationde t e c t ed in f i e l d or t r i p b lank sampl e s were treated as non-d e t e c t s . Likewise , uncommon laboratory contaminants ( i . e . ,chemicals not considered above) detected in on-site sample s whichwere within f i v e times the concentration detec ted in f i e l d or t r i pb lank s ampl e s were treated as non-detects (EPA 1 9 8 9 a ) .

A s recommended i n E P A ( I 9 8 9 a ) gu idance , t e n t a t i v e l y i d e n t i f i e dc ompound s were not s e l e c t ed as chemical s of p o t e n t i a l concern.I n o r g a n i c chemical s considered to be w i th in background al so werenot s e l e c t ed as chemical s of concern. In a d d i t i o n , inorganicc o m p o u n d s considered e s s ent ial human nutrient s ( i , e . , c a l c i u m ,iron, magnes ium, p o t a s s i u m , and s o d i u m ) were not s e l ec t ed aschemicals of p o t e n t i a l concern. Based on these da ta evaluationprocedure s , twenty-eight chemicals were selected as chemicals ofp o t e n t i a l concern in groundwater at th© M o s l e y Road S a n i t a r yL a n d f i l l site (see S e c t i o n 4.1.1 ©f the RI baseline riskas s e s sment).

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February 1 S 9 1 DRAFT REPORT

2*1 M e t h o d s , for Evaluat ing and A n a l v g i n g .As di scus sed in the RI/FS, 14 moni tor ing w e l l s (12 on-site anddowngradient we l l s and 2 upgradi ent w e l l s ) were i n s t a l l e d in theA l l u v i a l A q u i f e r and 8 monitoring w e l l s (6 on-site and downgradientw e l l s and 2 upgrad i en t w e l l s ) were i n s t a l l e d in the deeper Garber-W e l l i n g t o n A q u i f e r . Two rounds o f sample s were c o l l e c t ed f r o mthese monitoring w e l l s in May 1990 and J u l y / A u g u s t 1990. The RImonitoring data were analyzed using the f o l l o w i n g procedures , inorder to derive a da taba s e s u i t a b l e for risk assessment p u r p o s e( E P A 1 9 8 9 a ) .

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Monitor ing data q u a l i f i e d with a "R" based on datav a l i d a t i o n procedure s were d e l e t e d f r o m the RI moni t or ingdatabase.

Detec t i on l i m i t s (DL) that exceeded two times the maximumde t e c t ed concentrat ion of a chemical were not in c ludedwhen e s t imat ing mean concentrations for the s i t e , butwere included when e s t imat ing the frequency of de tec t ion.For e x a m p l e , if a chemical was not d e t e c t ed in one s a m p l eand the DL was 100 u g / L and the maximum de t e c t edconcentration at the site was 10 u g / L , then the DL wasnot included when c a l c u l a t i n g various s t a t i s t i c s sincethe DL would bias the r e su l t s .

One-hal f the s a m p l e q u a n t i f i c a t i o n l imit (SQL) was usedas the concentration for monitoring data q u a l i f i e d witha U ( i . e . , a non-dot ed:).

Concentrations of s p l i t and d u p l i c a t e samples werecombined using an arithmetic mean. If a ehamieal wa£ not

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detec ted in one s a m p l e but de t ec t ed in the s p l i t s a m p l e ,then the chemical was considered to be detec ted in thecombined sampl e f or th e p u r p o s e o f c a l c u l a t i n g f r e q u e n c yof de t ec t ion.

a Chemical concentrations f rom the two s a m p l i n g rounds werecombined for each s a m p l e l o ca t i on using an ari thmet icmean. The two s a m p l i n g rounds were combined since theydo not represent independen t s a m p l i n g events. If achemical was not de tec ted in one s a m p l i n g round at onep a r t i c u l a r l o ca t i on but was de t e c t ed in another s a m p l i n ground, then the chemical was considered to be detec ted inthe combined s a m p l e f or the p u r p o s e o f c a l c u l a t i n gfrequency of de t e c t ion.

2.2 M e t h o d s , for Se l e c t ing . .Chemi ca l s , of _c_oD.c_er_n

Of the twenty-eight chemicals of p o t e n t i a l concern se lec ted in theRI base l ine risk a s s e s sment , o n l y tho s e that may s i g n i f i c a n t l ycontribute to carcinogenic and noncarcinogenic risks were se lec tedfor f u r t h e r e v a l u a t i o n in th i s report ( h e r e i n a f t e r r e f e r r e d to a schemicals of concern). Chemical s which would s i g n i f i c a n t l yc on t r i bu t e to e s t i m a t e d risk were i d e n t i f i e d by c a l c u l a t i n g thepercent contribution of carcinogenic risk and noncarcinogenic risk(EPA 1 9 8 9 a ) . C h e m i c a l s which s i g n i f i c a n t l y c on t r i bu t e t o th e t o t a lcarcinogenic risk or noncarcinogenic risk ( e . g . , greater than 1percent [EPA 1 9 8 9 a ] ) were s e l e c t ed a s ch emica l s o f concern. T h i smethod can be used for any exposure pa thway, since th@ sameexposure parameters would b& a p p l i e d to al l ch emi ca l s . 1

The o n l y e x e m p t i o n to t h i s rule is when the expo sure e s t imate iod e p e n d e n t on the p h y s i e o c h e m i e a l p r o p e r t i e s o f each chemical ( e . g - »dermal p e r m e a b i l i t y ) .

T E T R A T E C H


The resul t s of the RI baseline risk assessment also were evaluatedt o se lect chemical s o f concern f or f u r t h e r evaluat ion. If apo t en t ia l carcinogenic chemical did not s i g n i f i c a n t l y contribute tot o ta l carcinogenic risk, but re su l t ed in a p o t e n t i a l carcinogenicrisk that exceeded the point of departure for carcinogens ( i . e . ,10"6 cancer risk, as e s t ab l i sh ed by EPA [ 1 9 9 0 ] ) as q u a n t i f i e d inthe RI baseline risk assessment, this chemical was evaluated in thePBRA.

The percent contribut ion of carcinogenic risk for each chemical ofconcern was c a l c u l a t e d using the f o l l o w i n g equation:

100MAX, * SFJ - l

where:%CCR

MAXS F ,

Percent c on tr i bu t i on o f carc inogenic risk f or c h e m i c a l , ;Maximum concentration for chemical ,; andS l o p e F a c t o r f o r c h e m i c a l j .

The d enomina tor of the equation sums the risk scores ( i . e . , maximumconcentration for c h e m i c a l j m u l t i p l i e d by the s l o p e f a c t o r f orc h e m i c a l j ) f o r a l l ch emica l s with a v a i l a b l e t o x i c i t y cri teria.The percent contribution of noncarcinogenic risk for each chemicalof concern was c a l c u l a t e d using the f o l l o w i n g equation:

% C M R ,blAXj/RfDj

* 100

T E T R A T E C H

February 1991 3

where:%CNKj « Percent contribution o f noncarcinogenic risk for c h e m i c a l f ;= Maximum concentration for chemical^* andRfD.- Reference dose for c h e m i c a l f .

The denominator o f the equation SHIPS the noncarcinogenic riskscores ( i . e . , maximum concentration for chemical, d ivided by theRfD f o r chemica l ,) f o r a l l chemicals with ava i lab l e t ox i c i tycriteria. T o x i c i t y criteria for chemicals of po t en t ia l concern aresummarized in S e c t i o n 4.1.3 of the RI bas e l ine risk assessment.

Chemica l s of concern selected for the A l l u v i a l A q u i f e r and Garber-W e l l i n g t o n A q u i f e r are discussed in Sec t i on s 2.3 and 2 , 4 ,r e s p e c t i v e l y .

2 - 3 A l l u v i a l A q u i f e r

T h i s s e c t ion s e l e c t s chemica l s o f concern f o r t h e A l l u v i a l A q u i f e rwhich are q u a n t i t a t i v e l y evaluated in thi s r epor t . T a b l e 1 p r e s e n t ssummary s t a t i s t i c s for chemicals of p o t e n t i a l concern se lec ted inthe RI basel ine risk assessment for the A l l u v i a l A q u i f e r .M o n i t o r i n g re su l t s f r o m w e l l s located on-site or p o t e n t i a l l yd o w n g r a d i e n t of s i t e were used to c a l c u l a t e summary s t a t i s t i c spresented i n T a b l e l ( M o n i t o r i n g W e l l s : M W - i l R , M W - 1 2 R , M W - 1 3 R ,M W - 1 4 R , M W - 1 5 R , M W - 2 0 1 , M f f - 2 0 4 , M W - 2 0 6 , M W - 2 0 7 , M W - 2 1 1 , M W - 2 . 1 2 , a n dM W - 2 1 4 ) . T w e n t y organic chemicals and f o u r inorganic chemicalswere s e l e c t ed by the RI ba s e l in e risk assessment as ch emi ca l s ofp o t e n t i a l concern for the A l l u v i a l A q u i f e r . Organic chemicals were

r-ITorinco

T E T R A T E C H

T a b l e 1

C h e m i e a TPercent C o n t r i b u t i o n

nm«u^-__-T^-1^J^-J-t$Hr- -r- - - - —— -C a r c i n o g e n i c H o n c a r c mogen icf t i s f c s ( b ) R i s k s ( c ) f r e q u e n c y o fD e t e c t i o n ( d )o fDete c t edC o n c e n t r a t i o n s ( e )

( W / U

4 - C M < 3 r o - 3 - M e t h y l p n e n o I4 , 4 ' - O D D1 , 1 - D i c h l o r o e t h a n et o t a l 1 , 2 - D i c h l o r o e t h e n e*1 , 2 - D i c h l o r o p r o p a n e

' B e n z e n e* b i s ( 2 - £ t h y ! h e x y l ) p h t h a l a t eC h l o r c o e n z e n eC h l o r o e t h a n e

D i - n - B u t y l p h t h a l a t es u l f a t e

P e n t a c h l o r o p n e n o 1Pheno 1Pyrene

' T e t r a c n l o r o e t h e n eT V i c h l o r o e t h e n eV i n y l c h l o r i d e

' A r s e n i c' B a r i u m" M a n g a n e s eS e l e n i u m

o 4

( a )( b )( c )

C d )

98

f u r £ h a r

7.00.06

1.9II3 70.3

0.040.8i fti .00.050.15

0.08

442617

1 / 1 11 / 1 11/12

HI Itf>f 1C5 / 1 ?2 / 1 21 / 1 15/124/122 / 1 22 / 1 2 ,1/122/12I / I 21 / 1 11/111/121 / 1 23 / 1 1s/ i:

1 1 / 1 212/121 2 / 1 2

7 / 1 2

55630.07

0.95 - 101 1 - 3 4

1 - 3.251101.5 - 3.5

5 - 250.75 - 1 1 . 2 52.5 - 6

6.50.06 0.16

95558

1.53 - 62 - 2

1 . 5 - 3 0238 - 3.200250 - 3.0002 - 5.1

IT-. Boc i^ mBEc 1<3 1

BE1•MR!mis?iBo f nsks

( d a t a

February 1991 DRAFT REPORT 10

detected i n f r e q u e n t l y along the perimeter of the Mosl ey RoadS a n i t a r y L a n d f i l l site. Many of the organic chemicals wered e t e c t e d at concentrat ions below the S Q L .

Only seven chemicals of po t ent ia l concern had oral carcinogenict o x i c i t y criteria ( i . e . , s l o p e f a c t o r s ) a v a i l a b l e f o r q u a n t i f y i n gthe percent contr ibut ion of carcinogenic risk (EPA has not repor t edan oral carcinogenic t o x i c i t y cri teria for arsenic as d i s cus s ed inS e c t i o n 4 . 1 ) . Vinyl chloride accounted for 98 percent of theest imated carcinogenic risk based on the l evel s of vinyl ch l or id ed e t e c t ed and the EPA upper-bound cancer scope f a c t o r . T h u s , theremaining chemical s accounted for o n l y 2 percent of the e s t imat edcarcinogenic risk. The quanti tat ive risk analysis presented in theRI basel ine risk assessment also found that vinyl chloride was thepr imary chemical of concern. T h e r e f o r e , vinyl ch l or id e wass e l e c t e d as a chemical of concern for f u r t h e r eva lua t i on .

inocinoc

The Rl baseline risk assessment also indicated that 1,2-d i c h l o r o p r o p a n e , benzene, b i s ( 2 ~ e t h y l h e x y l ) p h t h a l a t e , andt e t r a c h l o r o e t h e n e had p o t e n t i a l carcinogenic risks that exceededthe p o i n t of d e p a r t u r e ( i . e . , a 10"6 cancer risk e s t a b l i s h e d by theEPA [ 1 9 9 0 ] ) . T h e r e f o r e , these chemicals also were s e l ec ted aschemicals of concern. The remaining chemicals witn ava i lab l e oralcarcinogenic t o x i c i t y criteria ( i . e . , 4 , 4 ' - O D D a n d t r i c h l o r o e t h e n e )had e s t imat ed carcinogenic risks that were le s s than 10*6 asq u a n t i f i e d for the groundwater inge s t i on pathway in the RI baselinarisk assessment. In a d d i t i o n , these chemicals did not contributes i g n i f i c a n t l y to e s t imated risks ( l e s s than 1 percent [EPA 1 9 8 9 a ] ) ,as pre s ented in T a b l e 1 . T h e r e f o r e , 4 ,4'*DOD and t r i ch l oro e thanewere not s e l ec t ed as chemicals of concern. Chemical s with noavai lable carcinogenic toxic i ty criteria ware not selected aschemicals of concern since the po tent ia l carcinogenic risks (if

T E T R A T E C H


any) f r o m exposure to these chemical s could not be q u a n t i f i e d .

F o u r t e e n of the t w e n t y - f o u r chemical s se lected as chemica l s ofpo t en t ia l concern in the A l l u v i a l A q u i f e r , as presented in the RIba s e l in e risk assessment, had oral noncarcinogenic t o x i c i t ycri teria ( i . e . , R f D s ) f o r eva lua t ing t h e percent contribut ion o fnoncarcinogenic e f f e c t s . 2 -Chloropheno l ( 7 % ) , arsenic ( 4 4 % ) ,barium ( 2 6 % ) , and manganese ( 1 7 % ) contributed 94 percent of thet o ta l noncarcinogenic risks. Arsen i c , barium, and manganese a l s owere i d e n t i f i e d in the RI base l ine ,r i sk assessment as pr imarychemica l s of concern* T h e r e f o r e , these chemicals were s e l e c t ed aschemica l s o f concern for quant i ta t ive evaluation.

OCI T .CC

Each of the remaining chemicals with a v a i l a b l e oral noncarcinogenict o x i c i t y cr i t er ia contributed between 0.04 to 1.9 percent of thet o t a l noncarcinogenic risk ( i . e . , 1 , 1 - d i c h l o r o e t h a n e , t o ta l 1,2-d i c h l o r o e t h e n e , b i s ( 2 - e t h y l h e x y l ) p h t h a l a t e , ch lorobensene , di-n-b u t y l p h t h a l a t e , n a p h t h a l e n e , p e n t a c h l o r o p h e n o l , p h e n o l , pyrene , a n dt e t r a c h l o r o e t h e n e ) „ T h e s e chemical s a l so did not contr ibutes i g n i f i c a n t l y to e s t imat ed noncarcinogenic risks as pr e s en t ed inthe RI b a s e l i n e risk as se s sment. 2 T h e r e f o r e , these chemical s werenot s e l e c t ed as chemical s of concern. The remaining ten chemical swith no a v a i l a b l e noncarcinogenic t o x i c i t y cri teria were nots e l e c t e d as chemicals of concern since the p o t e n t i a lnoncarcinogenic risks f r o m exposure to these chemicals could not beq u a n t i f i e d .

In summary, the f o l l o w i n g chemical s were s e l e c t ed as chemica l s o f

As pr e s en t ed in the RI base l ine risk a s s e s smen t , th& t o ta lnoncarc inogenic risk f r o m these 10 chemica l s was an order ofmagni tude l e s s than the level considered to b*a o£ concern [ i . e . ,hazard index - 0 . 1 ] ,

T E T R A T E C H


any) f r o m exposure to these chemicals could not be q u a n t i f i e d .

F o u r t e e n of the t w e n t y - f o u r chemicals s e l ec ted as chemical s ofp o t e n t i a l concern in the A l l u v i a l A q u i f e r , as pr e s en t ed in the RIbase l ine risk as s e s sment , had oral noncarcinogenic t o x i c i t ycriteria ( i . e . , H f D s ) f o r eva luat ing t h e percent contr ibu t ion o fnoncarcinogenic e f f e c t s . 2 - C h l o r o p h e n o l ( 7 % ) , arsenic ( 4 4 % ) ,barium ( 2 6 % ) , and manganese ( 1 7 % ) contributed 94 percent of thet o t a l noncarcinogenic risks. Arsen i c , barium, and manganese a l sov / t r e i d e n t i f i e d in the RI bas e l ine risk assessment as pr imarychemica l s of concern. T h e r e f o r e , these chemicals were s e l e c t ed asch emi ca l s o f concern for q u a n t i t a t i v e evaluat ion.

OC\T\Co

Each of the remaining chemical s with a v a i l a b l e oral noncarcinogenict o x i o i t y criteria contributed between 0.04 to 1.9 percent of thet o t a l noncarcinogenic risk ( i . e . , 1 ,1-d i ch l oro e thane , t o t a l 1,2*d i c h l o r o e t h e n e , b i s ( 2 - e t h y l h e x y l ) p h t h a l a t e , chloroben.r.^ne, di-n-b u t y l p h t h a l a t e , n a p h t h a l e n e , p e n t a c h l o r o p h e n o l , p h e n o l , pyrene , a n dt e t r a c a l o r o e t h e n e ) . T h e s e chemical s a l s o d id not c on tr ibu t es i g n i f i c a n t l y to e s t imat ed noncarcinogenic risks as pr e s en t ed inthe RI ba s e l ine risk a s s e s sment . 2 T h e r e f o r e , these c h e m i c a l s wertnot s e l e c t ed as chemical s of coneam. The remaining ten chemical swith no a v a i l a b l e noncarcinogenic t ox i c i ty criteria wer** notse lected as chemicals of concern since the po t en t ia lnoncarcinogenic risks f rom exposure to thssa chemicals could not beq u a n t i f i e d .

In summary, the f o l l o w i n g chemicals were selected as chemicals ot

As p r e s e n t e d in the RI base l ine risk as s e s sment , the t o ta lno&darcinogenic risk from thesa 10 chemicals was an order offm a g n i t u d e l e s s than the level cons idered to be of concern [ i . e . ,hazard index - 0 . 1 J .

T E T R A T E C H


concern for evaluating po t en t ia l risks associated with ingestion ofgroundwater f r o m t h e A l l u v i a l A q u i f e r .

Potential -CarcinQaejiic Risks• BenzeneM 1,2"Dichloropropanem b i s ( 2 - E t h y l h e x y l ) p h t h a l a t ea Tetrachloroe thene• V i n y l C h l o r i d e

Po-tent_ial_.Noncarcinocrenic Risks• 2-Chloropheno lB ArsenicB Bariuma Manganese

2.4 G.arbe_rrWell_ington_ A q u i f e r

T h i s s e c t ion s e l e c t s chemical s o f concern f o r t h e G a r b e r - W e l l i n g t o nA q u i f e r which are quant i ta t iv e ly evaluated in this report. T a b l e2 pr e s en t s summary s t a t i s t i c s for chemical s o f p o t e n t i a l concernse lected by the RI baseline risk assessment for the Garber-W e l l i n g t o n A q u i f e r , Moni t or ing r e su l t s f r o m w e l l s l o ca t ed on-siteor p o t e n t i a l l y downgradient of site were used to ca l cu la t e summarys t a t i s t i c s pre s ent ed i n T a b l e 2 ( M o n i t o r i n g W e l l s : M W - 2 0 2 , M W - 2 0 3 ,M W - 2 0 5 , M W - 2 0 S , M W - 2 1 3 , a n d M W - 2 1 5 ) . Eight organic chemicals a n df o u r inorganic chemicals were selected by the RI baseline riskassessment as chemical s of p o t e n t i a l concern for the Garber-W e l l i n g t o n A q u i f e r . Far fewer organic chemicals ware detected int h e G a r b e r - W e l l i n g t o n A q u i f e r than t h e A l l u v i a l A q u i f e r . I na d d i t i o n , several of the chemicals of concern wera detected atlower concentrations in the G a r b e r - W e l l i n g t o n A q u i f e r than in the

CM\CccI T .cC

T E C H

T a b l e 2Summary o f C h e m i c a l s o f P o t e n t i a l Concern in th eG a r b e r W e l l i n g t o n A q u i f e r a t t h e M o s l e y Road S a n i t a r y L a n d f i l l S i t e ( a )

Range o fPercent C o n t r i b u t i o no f R i s k

C h e m i c a l

r

*8en2@neCarbon d i s u ' f i d eC h l o ( * o b e n ^ e n eC h l o r o e thane1 , 1 - D i c f i l o r o e t h a n et o t a l 1 , 2 - Q i c h l o r o e t h e n e/ m y ! ace ta teX y l e o e s

I n o r d a n i c s '' A r s e n i c' B a r i u m' H a n g a n e s f iV a n a a i u m

Ca re i nogen i c N o n c a r c i nogen i cRisks ( b ) R i s k s ( c )

100. 0 O . I2.4j a .

0.11.2^0.1

487.6

25I S

F r e o u e n c y o fD e t e c t i o n ( d )

2/61/61 / 61 / 61 / 61 / 61/61/6

5/66/66/66 / 6

D e t e c t e dC o n c e n t r a t i o n s ( e j( W / U

vOcc? - $ <;£ b.b4 5 u »19 OS 5 ^3 0

4.563

7.8 - 1939 - 21062 - 9904.3 - 42

* C h e m i c a l s o f concern that w i l l b e f u r t h e r e v a l u a t e d i n t h i s r e p o r t .N o t o x i c i t y da ta a v a i l a b l e f o r e v a l u a t i n g t h e percent c o n t r i b u t i o n o f r i s k s .

( j ) T h e c h e m i c a l s p r e s e n t e d i n t h i s t a b l e were s e l e c t e d a s c h e m i c a l s o f p o t e n t i a l concern i n t h e R l / F S S R A .( 5 ) S e e S e c t i o n 2 . 2 f o r t h e c a l c u l a t i o n o f t h e percent c o n t r i b u t i o n o f c a r c i n o g e n i c I - J S K S .( c j S e a S e c t i o n 2 . 2 f o r t h e c a l c u l a t i o n o f t h e percent c o n t r i b u t i o n o f noncare inogenic r i s k s .( a ) T n c nmncer o f d e t e c t e d c o n c e n t r a t i o n s d i v i d e d b y t h e number o f w e l l s l o c a t e d a n - s i t e a n d d o w n g r a d i e n to f t h e s i t e ( d a t a f r j m t h e t w o s a m p l i n g r ound s were a v e r a g e d t o g e t h e r ) .( e ) Range o f d e t e c tad c o n c e n t r a t i o n s obtained f r o m i*el I s located on- s i t e a n d d o w n g r a d i e n t o f t h e s i t e ( d a t af r o m th e two s a m p l i n g '•ound s were averaged t o g e t h e r ) .

February 1991

T a b l e 2DRAFT REPORT

OCinCc

T E T R A T E C H


A l l u v i a l A q u i f e r . Carbon d i s u l f i d e , vinyl acetate, xy l ene s , andv a n a d i u m / however/ were d e t e c t e d only in the G a r b e r - W e l l i n g t o nA q u i f e r . Organic chemicals of po t en t ia l concern were detectedon ly in monitoring w e l l s M W - 2 0 2 and M W - 2 0 8 , which are located alongthe northeast corner of the M o s l e y Road S a n i t a r y L a n d f i l l s i te. Asin the A l l u v i a l A q u i f e r , many of the organic chemicals werede t e c t ed at concentrations below the S Q L .

Benzene was the only chemical of po t en t ia l concern detec ted in theG a r b e r - W e l l i n g t o n A q u i f e r w i th an ora l^ carcinogenic t o x i c i t ycriteria ( i . e . , s l o p e f a c t o r ) . T h e r e f o r e , this chemical accountedfor 100 percent of the p o t e n t i a l carcinogenic e f f e c t s associatedwith i n g e s t i o n o f groundwater f r o m t h e G a r b e r - W e l l i n g t o n A q u i f e r .Chemica l s with no a v a i l a b l e carcinogenic t ox i c i ty criteria were nots e l e c t ed as chemical s of concern since the p o t e n t i a l carcinogenicrisks (if any) f r o m exposure to these chemica l s could not beq u a n t i f i e d .

I T .vCcctnoc

N i n e of the twelve chemicals selected as chemicals of p o t e n t i a lconcern in the RI base l ine risk assessment had oral noncarcinogenict o x i c i t y cr i t er ia ( i . e . , R f D s ) f o r e v a l u a t i n g t h e percentcontr ibut ion o f noncarcinogenic e f f e c t s f o r th e G a r b e r - W e l l i n g t o nA q u i f e r . A r s e n i c ( 4 8 % ) , barium ( 7 . 6 % ) , manganese ( 2 5 % ) , a n dvanadium ( 1 5 % ) contributed 96 percent of the total noncarcinogenicrisks. The RI baseline risk assessment al so i d e n t i f i e d thesech emi ca l s as the p r i m a r y chemicals of concern, but f o u n d noa p p r e c i a b l e risk associated with exposure to these chemicals.T h e r e f o r e , these chemical s were se lec ted as chemicals of concernt or f u r t h e r eva lua t i on- The remaining chemical s with a v a i l a b l eoral noncarcinocfenic t ox i c i ty criteria ( i . e . , carbon d i s u l f i d e ,eh lorobenzene , 1 , l - d i c h l o r o & t h a n @ , t o ta l 1 , 2 - d i c h l o r a e t h e n e , andx y l e n e s } contributed between 0.1 to 2.4 percent of the total

T E T R A T E C H


noncarcinogenic risk. In a d d i t i o n , these chemical s pre s ented noa p p r e c i a b l e noncarcinogenic risks from ingestion of groundwater asdi scus sed in the RI basel ine risk assessment . T h e r e f o r e , thesechemica l s were not s e l e c t ed as chemical s of concern. The threechemicals with no avai lable noncarcinogenic tox i c i ty criteria(i . e . , benzene, ch loroe thane , and vinyl a c e t a t e ) were not s e l e c t edas chemicals of concern since the po t ent ia l noncarcinogenic risksf r o m exposure to these chemicals could not be q u a n t i f i e d .

In summary, the f o l l o w i r g chemicals were se lec ted as chemicals ofconcern for eva lua t ing p o t e n t i a l risks associated with ing e s t i on ofgroundwater f r o m t h e G a r b e r - W e l l i n g t o n A q u i f e r .

Po ten t: i.a 1 Ca r c i n ogen i c _ H i sks& Benzene

. H o n u a r c i n o f f e n i c .RisksArsen i cBariumMangane s eVanadium

T E T R A T E C H


3 . 0 E X P O S U R E A S S E S S M E N T

T h i s section q u a n t i f i e s th e m a g n i t u d e , f r e q u e n c y , and dura t i on o fexposure f r o m use of groundwater in the vicinity of the M o s l e y RoadS a n i t a r y L a n d f i l l s i t e . T h e exposure assessment f o r t h e M o s l e yRoad sanitary L a n d f i l l was conducted in accordance with avai lab l eEPA ( 1 9 9 0 , 1 9 8 9 a , b / c , and 1 9 8 8 a ) guidance.

The f i r s t s t ep in the exposure assessment process is characterizingthe environmental s e t t i n g o f the s i te . Tne environmental s e t t i n gconsi s t s of the p h y s i c a l environment and p o t e n t i a l l y exposedp o p u l a t i o n s . The p h y s i c a l environment and expo s ed p o p u l a t i o n s werecharacterized in Sec t ions 2 and 4.1.2.1 of the RI/FS, r e s p e c t i v e l y .A summary of the environmental s e t t i n g is p r e s e n t e d in S e c t i o n3,1.1 of this report.

I d e n t i f y i n g expo sure pa thways i s the second s t e p o f the exposureassessment process which inc lude s: 1) evaluat ing chemical sources,re l ea s e mechani sms , a n d t r a n s p o r t ; 2 ) i d e n t i f y i n g p o s s i b l e expo surep o i n t s ; and 3) i d e n t i f y i n g the exposure routes. Chemical sources,re l ea s e mechanisms, and t r a n s p o r t were d i s cu s s ed in S e c t i o n 3 oft h e R I / F S . S e c t i o n 3.1.2, o f this report , reviews p o s s i b l ee xpo sur e routes evaluated in the RI base l ine risk assessment( S e c t i o n 4 .1 .2.1 o f the RI) and i d e n t i f i e s the exposure pa thway s o fconcern.

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The f i n a l s t e p in the exposure assessment process is q u a n t i f y i n gexposure f or the i d e n t i f i e d exposure routes. Exposure i sq u a n t i f i e d in Sec t ions 3.2 and 3,3 of this report for the exposurep a t h w a y s of concern. S e c t i o n 3.2 describes the methods used toe s t imate exposure point concentrations ( E P C s ) and q u a n t i f i e s EPCafor chemicals of concern i d e n t i f i e d in S e c t i o n 2. Sec t ion 3.3describes the methods used to e s t imate exposure ( i . e . , chronic

T E T R A T E C H

F e b r u a r y 1991 DRAFT REPORT 17

d a i l y intakes [ G D I s ] ) f o r t h e exposure pathways evaluated i n thisreport. The C D I s wi l l be used in c on junc t i on with t o x i c i tycriteria ( i d e n t i f i e d in S e c t i o n 4) to characterize the po t en t i a lrisk associated with use of groundwater in the vicinity of theM o s l e y Road Sani tary L a n d f i l l site.

3 . 1 Expgs_ur_e_ Asse s sment A p p r o a c h

3.1.1 Environmental S e t t i n g

The M o s l e y Road S a n i t a r y L a n d f i l l s i te is a 72 acre f a c i l i t ylocated in Oklahoma County, Oklahoma. The f a c i l i t y is locatedp r i m a r i l y in a rural s e t t ing. The active East Oak S a n i t a r yL a n d f i l l i s l o ca t ed a l o n g the western border o f the M o s l e y RoadS a n i t a r y L a n d f i l l . S o u t h w e s t o f the l a n d f i l l i s an inactive sandand gravel p i t . A sewage treatment p l a n t operat ed by the ci ty ofMidwes t i s located 1/4 miles northeast of the l a n d f i l l .

As discussed in S e c t i o n 3 of the RI, groundwater in the v i c ini ty ofthe l a n d f i l l is separated into two d i s t inc t a q u i f e r systems: theA l l u v i a l A q u i f e r and the deeper G a r b e r - W e i l i n g t o n A q u i f e r . Botha q u i f e r s may be used as a p o t e n t i a l dr ink ing water resources,Eight e en pr iva t e w e l l s are c u r r e n t l y lo ca t ed within 1 m i l e of theM o s l e y Road S a n i t a r y L a n d f i l l , As di scus sed in S e c t i o n 4.1.2.1 ofthe RI, f i f t e e n of these w e l l s are not considered to bedowngradient of the l a n d f i l l . Of the remaining three privatew e l l s , one is located at the Mos l ey Road S a n i t a r y L a n d f i l l and oneis located at the East Oak S a n i t a r y L a n d f i l l . The s e wa l l s are notused as a p o t a b l e water s u p p l y . The remaining well is locateda p p r o x i m a t e l y 350 f e e t northeast of the M o s l e y Road Sani taryL a n d f i l l . Based on th© h y d r o g e o l o g y of the s i te , it is u n l i k e l ythat this well is located downgradient of the site ( G o l d e rAssoc ia t e s 1990) .

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S u r f a c e water bodie s located within the vic inity of the l a n d f i l li n c l u d e : N o r t h Canadian River ( 1 / 2 mile west o f the s i t e ) ; CrutchoCreek (a tributary of N o r t h Canadian River, south of the s i t e ) ;N o r t h Pond (nor th o f t h e s i t e ) ; S o u t h S w a m p (sou th o f t h e s i t e ) ;inactive sand and gravel pit (southwest of the s i t e ) ; and a smalls ed imentat ion pond (northeas t corner of the l a n d f i l l ) . Groundwatero r i g i n a t i n g f r o m the site may di scharge to the N o r t h CanadianRiver, Crutcho Creek, and N o r t h Pond. The N o r t h Canadian River andCrutcho creek are used for i n d u s t r i a l p ro c e s s ing , i r r iga t i on , warmwater f i s h i n g , recreation, and emergency water use ( N o r t h CanadianRiver o n l y ) ( C o l d e r A s s o c i a t e s , 1 9 9 0 ) . It i s u n l i k e l y that theremaining s u r f a c e water bodies are h y d r o g e o l o g i c a l l y downgrad i en tof p o t e n t i a l l y contaminated groundwater at the l a n d f i l l .

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3.1.2 Exposure Pathways of Concern

The RI ba s e l ine risk assessment has evaluated p o t e n t i a l l y c o m p l e t eexposure pa thways of concern and selected certain pathways forq u a n t i t a t i v e e v a l u a t i o n . As discussed in the RI base l ine riskas s e s sment , use of groundwater and s u r f a c e water ( g r o u n d w a t e rseepage to the N o r t h Canadian River) were the only exposurep a t h w a y s s e l e c t e d f o r e va lua t i on . T h e H a z a r d Ranking S y s t e m ( H R S )report prepared for the M o s l e y Road Sani tary L a n d f i l l i d e n t i f i e dexposure to groundwater as the only s i g n i f i c a n t pathway of concern.Expo sur e routes evaluated in the RI base l ine risk assessmentincluded inge s t i on , inha la t i on , and dermal absorpt ion.

As prev iou s ly di s cus s ed, p o t e n t i a l l y contaminated groundwater inthe vicinity of the Mos l ey Road Sani tary L a n d f i l l is not currentlybeing used as a source of drinking water. H y p o t h e t i e a l l y , it isp o s s i b l e that groundwater at the Mosley Road Sani tary L a n d f i l l andd i r e c t l y downgradient of the l a n d f i l l may be used as a source ofdrinking water. T h e r e f o r e , f u t u r e hypo th e t i ca l r e s ident s may be

T E T R A T E C H


exposed to chemical s of p o t e n t i a l concern via i n g e s t i o n ,inha la t i on , and dermal ab sorpt ion. In a d d i t i o n , s u r f a c e water f r o mthe N o r t h Canadian River may be used under emergency condit ions( e . g . , in the event of a drough t) as a source of drinking water.

T h u s , exposure to re s idents who may use groundwater ( f r o m theA l l u v i a l A q u i f e r o r G a r b e r - W e l l i n g t o n A q u i f e r ) a n d / o r s u r f a c e water( f r o m t h e N o r t h Canadian River) f o r d r i n k i n g , showering, a n d / o rb a t h i n g were q u a n t i t a t i v e l y evaluated in the RI ba s e l ine riskassessment.

The presence of the c lay cap, erosion-reducing vegetat ion coveringt h e l a n d f i l l , a n d f e n c i n g around t h e f a c i l i t y s i g n i f i c a n t l y l imitthe p o s s i b i l i t y of coming in direct contact wi th contaminated soilor i n h a l i n g contaminated dust p a r t i c l e s or vapors. T h e r e f o r e ,exposure to chemica l s of p o t e n t i a l concern via direct contact wi thso i l s and inha la t i on of dust or vapors were not considered compl e t eexposure pathways.

T h i s PBRA evaluat e s o n l y expo sure p a t h w a y s f r o m the RI bas e l inerisk assessment which may re su l t in a s i g n i f i c a n t risk to humanh e a l t h . The conc lu s ions o f the q u a n t i t a t i v e risk assessmentpresented in the RI are summarized in T a b l e 3. The RI baselinerisk assessment q u a n t i f i e d po t en t ia l noncarcinogenic risks andcarcinogenic risks associated with inges t ion, i n h a l a t i o n , anddermal contact with chemicals of p o t e n t i a l concern in the A l l u v i a lA q u i f e r , G a r b e r - W e l l i n g t o n A q u i f e r , a n d s u r f a c e water. I t w a sassumed that s u r f a c e water was used as an emergency water resourceon ly (3 months per year over the dura t i on of the exposure p e r i o d ) .As presented in T a b l e 3, ingestion accounted for 97 to nearly 100percent of the total estimated risk (carcinogenic andnoncarcinogenie) for aach media evaluated. T h u s , inhalat ion anddermal contact exposure routes did not s i g n i f i c a n t l y contribute tooverall risk. T h e r e f o r e , the PBRA evaluate s only the inge s t i on

T E T R A T E C H

Or-ccIAoO

T a b l e 3S u m m a r y o f t h e Q u a n t i t a t i v e R i s k A n a l y s i s P r e s e n t e d i n t h eR l / f S B a s e l i n e R i s k A s s e s s m e n t

Carc inogeni c g f f g c t g

M e d i a PathwayP o t e n t i a lCarc inogen i c

R i s k s% C o n t r i b u t i o no f T o t a lR i s k Comments

H a r a r dI n d e x

% C o n t r i b u t i o no f T o t a lR i s k Comment s

f e a r Round I n g e s t i o nof GroundwaEer

6E-4

rear Round I n h a l a t i o n o f ° £ - 6 1Chemica l s in Groundwaterrear Round DerataE 9i-7 *1C o n t a c t w i t h Sroundwater

The ingescion pat t iway accounts for 98percent o f t h e t o t a l r i s k , v i n y l , c h l o r i d ei s the p r i m a r y c h e m i c a l o f concern.I n h a l a t i o n an dermal exposure routes do notc o n t r i b u t e s i g n i f i c a n t l y t o t o t a t r i s k .

too-4 <T

The ingest ton pathway eccourtts fornear ly 700 percent of the t o t a l hazardindex. Uo noncarc tnogenic r i s k sa s so c ia t ed w i t h i n h a l a t i o n or dermalcontact. A r s e n i c , barium, andmanganese account for th* m a j o r i t y ofthe noncarctnogentc ri sks.

T o t a i R i s k 6E:4fiarber • Ma t _H n g . t j p j i_ _Year Round I n g e s c i o n of

GroundwaCer3 E - 6 97

rear Round I n h a l a t i o n of t £ - 7 5C h e j a i c a t s in GroundwaterY e a r Round Oernsat 5E-9 <1C o n t a c t w i c h S r o u n d w & c e r 1

T o s a t RiskS u r f a c e

S n g e s t f o n o f S u r f a c et n h a l a t i o n o f C h e m i c a l sin S u r f a c e waterDermal C o n t a c t w i t hS u r f a c e W a t e r

2E5£ 12

4 6 - 1 1

T o t a l Risk 2£-3

i s the o n l y chemica l o f concernEh<at cot iEd be q u a n t i t a t i v e l y evacuated .R i s k f o r i n g e s t i o n s l i g h t t v exceeds t h ep o t r v t of d epar tur e ( i . e . , 10" >. I n g e s t i o npathway accounts for 97 percent of t o t a tr i sk . I n h a l a t i o n and dermat exposureroutes do no t c o o t H b u t e s i g n i f t c a n t E y t ot o t a t r i s k .

M o s i g n i f i c a n t r i s k s a s s o c i a t e d w i t h u s e o fs u r f a c e w a t e r . C a r c i n o g e n i c r i s k s w e l tb e & o w t h e p o i n t o f d e p a r t u r e ( 1 0 ) .

2£-5

5 E - 5 <\

T o t a t R i s k 7E-1

tOO

21 f

T o t a E R i s k / E - 2

I n g e s t i o n exposure accounts f o r meantyTOO percent of the t o t a E hazard index.H o adverse noncarc inogenic r i s k sas soc ia t ed w:th use of groundwater.

t n g e s t i o n exposure accounts f or n e a r t y100 percent of the t o t a l hazard index.No. adverse noncarc inag*n;c r i s k sa s s o c ia t ed w i t h use of groundwater.

00 58 7 1


exposure route.

As presented in T a b l e 3, the po t ent ia l carcinogenic total riskassoc iated with use of s u r f a c e water ( i . e . , 2 x l o ~ 6 ) was below thepoint o f departure ( i . e . , 10 ' 6 ) e s tabl i shed by the EPA ( 1 9 9 0 ) . Thet o ta l noncarcinogenic risk as sociated with use of s u r f a c e water( i . e . , 7 x l O " 2 ) was not of concern ( i . e . , the hazard index was belowuni ty, see S e c t i o n 4.1.4 of the RI base l ine risk assessment forf u r t h e r d i s cu s s i on of these r e s u l t s ) . S i n c e the use o f s u r f a c ewater did not result in an a p p r e c i a b l e risk to human h e a l t h , thisexpo sure pa thway w i l l not be evaluated in the PBRA.

T h e r e f o r e , the exposure pa thways q u a n t i t a t i v e l y evaluated in thePBRA include:

H i n g e s t i o n o f groundwater f r o m the A l l u v i a l A q u i f e r underf u t u r e land-use c ond i t i on s; and

M inge s t ion of groundwater from the G a r b e r - W e l l i n g t o n A q u i f e runder f u t u r e land-use c ond i t i on s .

3.2 Estimat_io_n_o_f Exposure Point. Concentrat ions

To c a l c u l a t e exposure and u l t i m a t e l y risk for the reasonablemaximum exposure ( R M E ) case (see S e c t i o n 3 . 3 ) , c h e m i c a l - s p e c i f i cconcentrations that a receptor could contact over tha durat ion oft h e exposure per iod ( i . e . . , exposure po in t concentrat ions [ E P C s j )must be e s t imated. T h i s section describes the methods used toe s t imate EPCs for the groundwatar inge s t ion pathway. Commonlya p p l i e d methods for e s t imating EPCs using avai lab l e EPA ( 1 9 8 9 a )guidance are discussed in Sec t ion 3.2.1. The a p p l i c a t i o n ofk r i g i n g to e s t imat e EPCs is discussed in S e c t i o n 3.2.2.

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TEURA T E C H


3.2.1 Commonly A p p l i e d M e t h o d s f o r E s t i m a t i n g E P C s

The most commonly a p p l i e d method for e s t imating EPCs for thegroundwater ingest ion pathway involves ca l cu la t ing the 95th upperconf idence limit (UCL) on the arithmetic mean concentration usingthe ava i lab l e monitoring data. EPA ( 1 9 8 9 a ) guidance recommendsa p p l y i n g a 95 th UCL on the ari thmetic mean concentration because ofthe uncertainty as soc iated with a v a i l a b l e moni tor ing d a t a . TWOa l t e r n a t i v e methods for c a l c u l a t i n g the 95 th UCL on the ar i t hme t i cmean have been recommended by EPA ( G i l b e r t 1987, as cited in EPA1 9 8 9 a ) . One of the methods assumes that the individual chemicalconsti tuent concentrations are normal ly d i s t r i bu t ed and c a l c u l a t e sa 9 5 t h UCL on the a r i t hme t i c mean f r o m the t - d i s t r i b u t i o n ( G i l b e r t1 9 8 ? ) , 3 The other m e t h o d , based on Land ( 1 9 7 1 , 1 9 7 5 ) , i s used forchemical cons t i tuent concentration da ta that are l o g n o r m a l l yd i s t r i bu t ed ( G i l b e r t 1 9 8 7 ) . Most chemical d i s t r ibu t ions in naturetend to be l o g n o r m a l l y d i s t r i bu t ed except for abundant metal s suchas aluminum and iron (Connor and S h a c k l e t t e 1975, Dean 1981, Esmenand H a m m a d 1977, and Ott 1 9 8 8 ) , T h e r e f o r e , between the two methodsrecommended by E P A , the method d e v e l o p e d by Land ( 1 9 7 1 , 1 9 7 5 )shou ld be used in v i r t u a l l y all cases to c a l c u l a t e the 9 5 t h UCL onthe ar i t hme t i c mean.

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The equation for c a l c u l a t i n g the 95th UCL on the arithmetic mean aspresented in Land ( 1 9 7 1 , 1975) and G i l b e r t ( 1 9 8 7 ) is presentedbelow:

UCL 0.95

th i s method was used in the RX base l ine risk asses sment

T E T R A TECH

F e b r u a r y 1991 D R A F T REPORT 23

where:

U C L 0 > 9 S «• The 9 5 t h upper c o n f i d e n c e l i m i t on the ar i thme t i c meanconcentration ( i . e . , exposure point concentrat ion);

= natural log base ( 2 . 7 1 8 ) ;« arithmetic mean of the natural log trans formed da ta;= s tandard dev ia t i on of the natural log t r a n s f o r m e d d a t a ;

tabular value which depends on the degrees of f r e e d o m ,a l p h a , and s; and

N = sampl e size.0.95

EPA ( 1 9 8 9 a ) guidance recommends us ing the maximum de t e c t edconcentration as the EPC if the 95th UCL on the arithmetic meanexceeds the maximum d e t e c t ed concentration. However , the 9 5 t h UCLon the ari thmet ic mean exceeds the maximum detected concentrationin most cases for a t y p i c a l NPL s i te based on research pre s en t ed inClement ( 1 9 9 0 a , b ) . T h e r e f o r e , the maximum concentration wi l l beused in most cases as tM EPC for the RME case. T h i s , however, isi n t e r n a l l y inconsistent with another Agency recommendation on EPCsthat " . . .a s suming long-term contact with the maximum d e t e c t e dconcentrations is not reasonable" (EPA 1 9 8 9 a ) .

S i m u l a t i o n m o d e l i n g r e su l t s presented in Clement ( 1 9 9 0 a ) show thatthe m e t h o d s pre s ented above for e s t imat ing EPCs are not a p p r o p r i a t efor the groundwater inge s t i on pa thway. T h e s e methods may bea p p r o p r i a t e when evaluating exposure where an individual has ane q u a l l y l i k e l y chance of c o n t a c t i n g any area at a site overnumeroi s independent exposure events. T h i s a s sumpt ion may holdtrue when eva lua t ing the s o i l , s u r f a c e watsr, and sedimentingestion pathways , sine© the individual may contact numerouslo ca t i ons across the sit® over the durat ion of the exposure per iod .However, this as sumption does not hold true when evaluatinggroundwater exposure. For a groundwater inge s t ion p a t h w a y / it is

ocincc

T E T R A T E C H


assumed that a hypothe t i cal resident may ins ta l l a well anywherewith in a given s tudy area. If a well were i n s t a l l e d near a "hotspot" loca t ion, then an individual may contact r e la t iv e ly highconcentrat ions in the general v i c ini ty of the wel l and not anaverage of concentration from the entire study area. Likewise, ifa well is i n s t a l l e d in an area with much lower l e v e l s ofcontamination far from the suspected source area, then thei n d i v i d u a l wi l l l i k e l y contact concentrations character i s t i c o fthat locat ion and not an average of chemical concentrations fromthe entire s tudy area. The extent to which groundwater may bedrawn into a well f rom locations in the general vic inity of thewel l is de termined by several f a c t o r s i n c l u d i n g p u m p i n g rate,hydrogeo log i ca l parameters , and i n f i l t r a t i o n rate.

Inherent problems with the methods used to e s t imate EPCs for thegroundwater inge s t i on pathway have sparked debate between EPAregional o f f i c e s and EPA headquarters. C u r r e n t l y , one EPA regionis recommending using the maximum detected concentration for eachchemical of concern as the EPC for e s t i m a t i n g exposure. Otherregions are recommending using the 95th UCL on the arithmetic meanfor w e l l s that characterize the general extent of c on taminat ion ofthe site when e s t imat ing EPCs. T h i s l a t t e r approach involvese l i m i n a t i n g moni tor ing w e l l s f r o m the ana ly s i s that may notadequate ly r e f l e c t the concentrations of chemicals characteristicof the site. U s i n g such an a p p r o a c h , however, would result inestimates of the 95th UCL on the arithmetic mean that exceeded themaximum de t e c t ed concentration in most cases (based on researchf i n d i n g s presented in Clement [ 1 9 9 0 b ] ) . T h u s , th© maximum detectedconcentrat ion would be used in most cases as th© EPC to es t imateexposure which would give the same results as the f i r s t methoddiscussed above ( i , ® , , using ths maximum detec ted concentration foreach chemical of po t en t ia l concern as the EPC, as recommended byone EPA r e g i o n ) ,

ocinco

T E T R A T E C H


There are two primary l i m i t a t i o n s to the EPA recommendeda p p r o a c h e s . F i r s t , as discussed above, using the maximum de t e c t edconcentration is in t erna l ly inconsistent with Risk AssessmentG u i d a n c e f o r S u p e r f u n d ( R A G S ) ( E P A 1 9 8 9 a ) which s t a t e s that"...assuming long-term contact with the maximum detec tedconcentration is not reasonable," S e c o n d / it would bei n a p p r o p r i a t e to sum c h e m i c a l - s p e c i f i c risks e s t imat ed us ing th i sapproach , since an individual would not be exposed to the maximumconcentration for chemicals that were in ent ire ly d i f f e r e n tl o c a t i o n s . For e x a m p l e , a t th i s s i t e , the maximum de t e c t edconcentration of manganese and arsenic were detected in monitoringw e l l s in excess of 1000 f e e t f r o m each other. It would bei n a p p r o p r i a t e to assume that an ind iv idua l u s ing a wel l i n s t a l l e dnear the arsenic "hot spot" also would be exposed to the maximumd e t e c t e d concentrat ion of manganese which wac d e t e c t e d over 1000f e e t away. T h e r e f o r e , it would be i n a p p r o p r i a t e to assume that anind iv idua l would be exposed to the maximum detec ted concentrationfor that chemical over the d u r a t i o n of an assumed e xpo sur e p e r i o d *

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It s h o u l d be a l s o noted that RI ac t iv i ty at the s i t e used apurpo s iv e s a m p l i n g de s ign for characterizing the extent o fgroundwater contamination at the Mos l ey Road L a n d f i l l , Variousg e o p h y s i c a l t echniques , h y d r o g e o l o g i c a l i n v e s t i g a t i o n s usingp i e zome t e r s , and historical data were used to f o c u s monitoringe f f o r t s in areas of s u s p a c t e d source areas. Such a s a m p l i n g p l a nwould result in higher concentrations of chemicals of concern thantypi ca l s a m p l i n g p lan s employed at NPX, sit@s using random oru n i f o r m s a m p l i n g de s igns . M o n i t o r i n g r e su l t s obtained f r o m th esite already r e f l e c t upper-bound estimates of groundwatercontamination. EPCs estimated using ths methods outlined above,

T E T R A T E C H


given their l i m i t a t i o n s , would result in u n r e a l i s t i c e s t imates ofE P C s , and t h e r e f o r e exposure and risk.

3.2.2 Using Geo s ta t i s t i c s to Est imate EPCs

G e o s t a t i s t i e s can be a p p l i e d to address the l i m i t a t i o n s of thesemethods for e s t i m a t i n g E P C s . G e o s t a t i s t i e s can be used to e s t imatethe s p a t i a l d i s t r i bu t i on of chemical concentrations over an evenlyspaced grid us ing unevenly spaced moni t or ing d a t a . G e o s t a t i s t i c a lmethods ava i lab l e for c a l c u l a t i n g concentrations over an evenlyspaced grid i n c l u d e kr ig ing ( B e l l and Reeves 1979, G i l b e r t andS i m p s o n 1985, Matheron 1973, R i p l e y 1983, and Zirs chky 1 9 8 5 ) ,d i s t a n c e weighted least-squares (McLain 1 9 7 4 ) , three dimensionalnegat ive e x p o n e n t i a l i n t e r p o l a t i o n (Akima 1978, M c L a i n 1 9 7 1 ) , threedimensional quadratic curve f i t t i n g , and bicubic s p l i n e s ( B r o d l i e1980, F o l e y 1 9 8 1 ) . Of th e ava i lab l e g e o s t a t i s t i c a l me thod s ,krig ing has been the method of choice for p e r f o r m i n g g e o s t a t i s t i c sf o r R I / F S a p p l i c a t i o n s . I n f a c t , kr ig ing i s recommended i n E P A( 1 9 8 9 a ) guidance as ". . .another method that p o t e n t i a l l y can be used[ f o r e s t i m a t i n g E P C s ] . " I n a d d i t i o n , t h e E P A ( 1 9 8 8 b ) h a s d e v e l o p e dk r i g i n g s o f t w a r e (GEOEAS) which was used in the PBRA to es t imateE P C s .

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The a d v a n t a g e of u s ing kr ig ing is that it can c a l c u l a t e averageconcentrations for each grid square across an evenly spaced gridusing unevenly spaced monitoring data re sul t s . The averageconcentrat ion c a l c u l a t e d for a s i n g l e grid square may represent theEPC for an individual who i n s t a l l s a well in the center of the gridsquare. The area of each grid square can be set to equal the areaof groundwat&r that may eventual ly be drawn into a w e l l , assumingthe well was i n s t a l l e d in the center of the gr id . The p u m p i n gaction of the well would create a l o c a l i z e d gradient toward thew e l l , thereby p u l l i n g water f r o m surrounding areas into th& well .

T E T R A T E C H


over a long period of time. The extent of groundwater drawn intothe wel l is de termined by several f a c t o r s i n c l u d i n g p u m p i n g rate,h y d r o g e o l o g i c a l c ond i t i on s , and i n f i l t r a t i o n rate.

The d i s t r i b u t i o n o f kr ig ing r e su l t s ( i . e . , average concentrat ionsestimated for all grid squares) would represent the d i s t r i bu t i on ofp o s s i b l e E P C s . A n a p p r o p r i a t e s t a t i s t i c f r o m thi s d i s t r i b u t i o ncould be used as the EPC for the RME case. In this assessment, twoapproa ch e s were used to e s t i m a t e E P C s using the k r i g i n g r e su l t s .T h e s e approaches r e f l e c t recent regional gu id e l in e s discussed inS e c t i o n 3 .2.1 f o r e s t i m a t i n g E P C s f o r t h e groundwater i n g e s t i o npathway. The f i r s t approach involved c a l c u l a t i n g EPCs for the RMEcase us ing the t r a d i t i o n a l EPA ( 1 9 8 9 a ) approach . The RME caser e f l e c t s the reasonable maximum exposure for the entire s tudy area.For the RME case, the 9 5 t h UCL on the ar i thme t i c mean of the krigeddata for all the gr id s or the maximum kriged concentration,whichever is l e s s , was used as the E P C . Grid squares that were on-site or d i r e c t l y downgradient of the site were inc luded inc a l c u l a t i n g these s t a t i s t i c s .

The second a p p r o a c h involved c a l c u l a t i n g E P C s f or a maximum case.The maximum case r e f l e c t s the p l a u s i b l e maximum exposure for ani s o l a t e d "hot spo t" at the s i te . For the maximum case, the maximumkriged concentration for each chemical of concern was used as theE P C . The c h e m i c a l - s p e c i f i c risks e s t imated for the maximum casewere not summed d i r e c t l y , however, since the maximum kriged valueswere not a lways l o ca t ed w i th in the same grid square. Rather , theto ta l risk for the maximum case was derived using the maximum totalrisk e s t imated for a*;y grid square. T h u s , the t o ta l risk for themaximum case calculated in this report may b«s lower than the sum ofthe c h e m i c a l - s p e c i f i c risks for the maximum case ca l cu la t edf o l l o w i n g the t radi t i onal EPA risk assessment approach.

CCr-ccmoo

T E T R A T E C H


To p e r f o r m kriging ana ly s i s , the underlying correlation structiireof the da ta must be mode l ed using a variogram. A variogram is ap l o t of the variance of paired s a m p l e measurements as a f u n c t i o n ofdistance. The variogram model is then fit to the data p l o t t e d inthe variogram using curve f i t t i n g techniques. U s i n g the variogramm o d e l , kr ig ing equations can be used to e s t imate an averageconcentration for each grid square in an evenly spaced grid. Whene s t imat ing the average concentration for a s p e c i f i c grid square,more weight is given to s a m p l i n g data p o i n t s closest to the gridsquare being considered.

If an a p p r o p r i a t e variogram model cannot be derived using ordinarykr ig ing for data that tend to be l o g n o r m a l l y d i s t r i b u t e d , thenlognormal kr ig ing may be the pr e f e r r ed kr ig ing method. Lognormalk r i g i n g can be a p p l i e d in such cases to ob ta in a b e t t e r fit of thevariogram model (see C a n d e l a et al. 1988, G i l b e r t and S i m p s o n 1985,and Zirs cky 1 9 8 5 ) . To p e r f o r m lognormal kriging the input datamust be l o g - t r a n s f o r m e d using natural l og s . The averageconcentrat ion for each grid square e s t imated us ing l o g n o r m a lkr ig ing must then be t rans f ormed using an approach out l ined byC a n d e l a et al. ( 1 9 8 8 ) to estimate arithmetic mean concentration foreach grid square.

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The methods used to e s t imate EPCs for chemicals of concerni d e n t i f i e d in S e c t i o n 2 using kr ig ing are o u t l i n e d below.

B K r i g i n g re su l t s were estimated using groundwater monitoringd a t a for the chemical s of concern d i s cu s s ed in S e c t i o n 2* Thadata screening procedures discussed in Sec t i on 2 w*ra usad toderive a s ingle concentration for &ach chemical of concern foreach monitoring wal l l o ca t i on . For vinyl c h l o r i d e , benzene,and l , 2 * d i c h l o r o p r o p a n e p a s i g n i f i c a n t p r o p o r t i o n of thadetected concentrations in the A l l u v i a l A q u i f e r were found

T E T R A T E C H


below the Contract Required Q u a n t i f i c a t i o n Limit ( C R Q L ) . Thes p a t i a l d i s t r i bu t i on for these chemicals would be incorrectlyportrayed by the kriging ana ly s i s if one-ha l f the CRQL wereused for nondetec t s . A more accurate and robust a s sumpt ionwould be to use the method detect ion l imit ( M D L ) in theseinstances. In lieu of the M D L , the lowest detectedconcentration is a conservative surrogate measure (1 u g / L ingroundwater was reported for each of these c o n t a m i n a n t s ) . Ina d d i t i o n , the instrument detec t ion l imi t tor these VOCs iswell below their respective CRQLs (e.g.. , 0.1 u g / L ) .T h e r e f o r e , the a s sumpt ion that the concentration of acontaminant reported as a nondetec t is equal to its lowestde t e c t ed concentration is based on r e l i ab l e , yet conservative,data. For the purpose of this risk assessment, the lowestdetected concentration for these three chemicals (1 u g / L ) wasused f or nonde t e c t s . For a l l other c h e m i c a l s , o n e - h a l f th eCRQL was used as the concentration for nondetec t s .

OCO00inOO

• X~Y coordinate data for each well derived f r o m a land-surveyof the M o s l e y Road L a n d f i l l were merged wi th the chemicalconcentrat ion d a t a .

« The g e o s t a t i s t i ca l package GEOEAS ( G e o s t a t i s t i c a lEnvironmenta l Ass e s smen t S o f t w a r e ) d e v e l o p e d by EPA ( 1 9 8 8 b )was used to p e r f o r m kr ig ing on all data sets. V a r i o g r a mmodel s were deve loped for all chemicals of concern in theA l l u v i a l A g u i f e r and G a r b e r - W e l l i n g t o n A q u i f e r . Based on thecurve f i t t i n g exercise, the best variogram models ware fit tou n t r a n s f o r m e d chemical concentration d a t a for the inorganicchemicals ©f concern ( i . e . , arsenic, barium, manganese, and

T E T R A T E C H

February 1.991 DRAFT REPORT 30

vanadium). T h e r e f o r e , ordinary kriging was used to deriveaverage grid concentrat ions for the inorganic chemical s ofconcern. For the organic chemicals of concern ( i . e . , benzene,2 - c h l o r o p h e n o l , 1 , 2 - d i c h l o r o p r o p a n e , b i s ( 2 -e t h y l h e x y l j p h t h a l a t e , a n d vinyl c h l o r i d e ) , l o g - t r a n s f o r m e dchemical concentrat ion d a t a provided the best variogram modelf i t . T h u s , lognormal k r i g i n g was used to e s t imate averageconcentrat ions for each grid square for organic chemical s o fconcern.

The variogram m o d e l s for each chemical of concern were used tokrige the data. The kr ig ing grid size was derived using amass ba lance equation that equates the water d emand s of are s ident ial well with the volume of water added to the a q u i f e rby recharge ( i . e . , by p r e c i p i t a t i o n and other source s).Accord ing to EPA ( 1 9 8 6 b ) , 150 g a l l o n s of water per day ( 7 , 3 0 0cubic f e e t o f water per y e a r ) i s a s u f f i c i e n t q u a n t i t y ofwater to meet the needs of an average f a m i l y . Thei n f i l t r a t i o n rate at the M o s l e y Road L a n d f i l l was e s t imated tobe between 0.005 to 0.009 inches of water per year using theHELP model d i s cu s s ed in S e c t i o n 2.1.1.8 o f th e RI. To beconservative ( i . e . , to ensure that E P C s are notu n d e r e s t i m a t e d ) , it was assumed that the i n f i l t r a t i o n rate wasa p p r o x i m a t e l y 0 .1 inches- per year ( 0 . 0 0 8 f e e t / y e a r ) f or th ep u r p o s e o f d e f i n i n g the kr iging grid square size. The kriginggrid square s ize was c a l c u l a t e d using the f o l l o w i n g equation:

OCCCinco

Grid Size (ft) 7300nfil tr a tion Rate

T E T R A T E C H

February 1991 D R A F T REPORT 31

The e s t imated grid s ize used f or th e M o s l e y Road S a n i t a r y L a n d f i l ls i t e was a p p r o x i m a t e l y 1000 f e e t x 1000 f e e t .

The lognormal kriging results were trans formed back intoari thmet i c mean concentrations using the f o l l o w i n g equation( C a n d e l a e t a l . 1 9 8 8 ) ;

where:

AJ. i thme td. c Mean = e (KM

CMccocincc

A r i t h m e t i c Mean « The arithmetic mean concentration of the gridsquare;

e = N a t u r a l l og base ( 2 . 7 1 7 ) ;KM ~ Kr: T i e a n concentration for a s i n g l e grid square derived

f r o m k r i g i n g equat ions; andKE - K r i g i n g error of the kriged mean concentra t ion.

a The 95th UCL on the arithmetic mean and maximum concentrationof the kriged d a t a for all grid squares l o ca t ed at the s i t e ord i r e c t l y d o w n g r a d i e n t o f th e s i t e were c a l c u l a t e d ( t h e 9 5 t hUCL on the arithmetic mean was ca l cu la t ed using the equationpre s en t ed i n S e c t i o n 3 , 2 . 1 ) .

s E P C s were e s t imated for a RMF case and maximum case. The 9 5 t h0CL on the ari thmetic mean or th© maximum of the kriged d a t a ,whichever was l e s s , was used as the BPC for RME case. The RMEcase r e f l e c t s the reasonable maximum exposure associated withthe entire study area since the EPC was based on th© 95th UCLon the ar i thmet i c mean concentration for the entire studyarea. Th© maximum concentration of th& kriged data was used

T E T R A T E C H


as the EPC for the maximum case. The maximum case r e f l e c t sthe maximum p l a u s i b l e exposure associated with the "hot spots"of the site since the EPC was based on the maximum kriged datapoint for each chemical of concern. EPCs derived forchemicals of concern in the A l l u v i a l A q u i f e r for the RME caseand maximum case are presented in T a b l e s 4 and 5,r e sp e c t i v e ly . EPCs derived for chemicals of concern in theG a r b e r - W e l l i n g t o n A q u i f e r for the RME case and maximum caseare pre s en t ed in T a b l e s 6 and 7, r e s p e c t i v e l y . T h e s e EPCswere used to e s t imat e exposure ( i . e . , chronic d a i l y i n t a k e s )pre s en t ed below in S e c t i o n 3.3.

3.3 E s t i m a t i o n o f Chronic ...Daily. I n t a k e s

A c c o r d i n g t o t h e N a t i o n a l C o n t i n g e n c y P l a n ( N C P ) ( E P A 1 9 9 0 ) , t h eb a s e l i n e risk assessment should eva lua t e exposure to p o p u l a t i o n sp o t e n t i a l l y exposed to chemica l s of concern under current andf u t u r e land-us e o f the s i te. F u r t h e r m o r e , the expo sure e s t ima t e sshou ld be based on a r ea sonabl e maximum expo sure ( R M E ) scenario.T h e N C P d e f i n e s "reasonable maximum" such that "only p o t e n t i a lexpo sure s that are l i k e l y to occur w i l l be inc luded in theassessment of exposure" ( E P A 1 9 9 0 ) . Exposure is r e f e r r e d to as thechronic d a i l y intake ( G D I ) which i s expre s s ed in terms o fm i l l i g r a m s o f contaminant contac t ed per k i l o g r a m o f body weight perday ( i . e . , m g / k g / d a y ) . The GDI i s c a l c u l a t e d by c omb in ing E P C s andexposure parameter e s t i m a t e s us ing a s i m p l e chemical intake

orccincc

T E T R A T E C H

T a b l e 4c r n ? C o n c e n t r a t i o n s ( E P C s ) a n d C h r o n i c D a i l yI n t a k e s ( G D I s ) f o r E v a l u a t i n g G r o u n d w a t e r Q u a l i t yf r o m t h e A l l u v i a l A q u i f e r f o r t h e R M E C a s e

S a n g e o f 9 5 t h U C L a n t h e<r igea C o n c e n t r a t i o n s A r i t h m e t i ci ) M e a n

6etuenea i s ( 2 - E t h y i h e x y D p h t h a l a t e1 , 2 - D i c h i o r o o r a o a n e" e t r a c n i o r o e c n a n e; i r w i C h l o r i d e

0.694.91.0

3ME EPC

1.76.21.2

1.76.21 . 2

RHE CDI{ r r . g / k g / d a y )( d )

1 .3E-054.7E-059.0E-06I . I E - O S3 .6E-05

OCcct T ico

A r s e n i c2 - C h l o r o n n e n o IM a n g a n e s e

1.4 * -UI7C - 1.3004.3 - 7.5

250 - 1,300

20i .SOO5.7

640

201.6005.7

540

4 . 0 E - Q 43.2E-021. 16-041.3E-02

' a n g e o f k r i g e d c o n c e n t r a t i o n s e s t i m a t e d f o r g r i d s l o c a t e d a t t h e s i t e a n d d i r e c t l y d o w n g r a c f t e n t o f t h es i t e .

" H e 9 5 t h uocer c o n f i d e n c e l i m i t ( U C L ) o n c h a a r i t h m e t i c mean c o n c e n t r a t i o n e s t i m a t e a f o r g r i d s l o c a t e da t t h e s i t e a n a d i r e c t l y d a w n g r a a t e n t c f t h e s i t e .~^e 9 5 t h UCL on th e a r u n m e t i c mean or th e max irrum c o n c e n t r a t i o n (from the k r i g e d d a t a ) . *mcn ever i s' e s s . * a s used a s t h e r e a s o n a b l e m a x i m u m e x o o s u r e i S M E l £ . ° C , a s recontnenoea b y E P A ( I 9 8 9 a ) g u i d a n c e ." n e R H t C O I w a s c a l c u l a t e d u s i n g t h e R M E £ P C a n a t h e 9 5 t h o e r c e n t i l e o f w a t e r i n t a k e v a l u e s i L / k g / d a y )a s t i m a t e a u s i n g M o n t e C a r l o s i m u l a t i o n ( s e e t s x t f o r f u r t h e r a i s c u s s i o n ) .

T a b l e 5E x p o s u r e P o i n t C o n c e n t r a t i o n s ( E P C ) a n d C h r o n i c D a i l yI n t a k e s ( C D I s ) f o r E v a l u a t i n g G r o u n d w a t e r Q u a l i t yf r o m t h e A l l u v i a l A q u i f e r f o r t h e M a x i m u m Cas e

E f f e c t / C o m p o u n dR a n g e o fK r i g e d C o n c e n t r a t i o n s

C a r e i n o g e n i c E f f e_ct_s:B e n z e n eb i s ( 2 - E t h y l h e x y l ) p h t h a i a t e1 , 2 - D i c h l o r o p r o p a n eT e t r a c h l o r o e t h a n eV i n y l C h l o r i d e

0.694.91.0

2.33.61.75

M a x i m u m C O I( m g / k g / d a y )( b )

I . I - 7 . 3

1 . 7 E - 0 56 . 5 E - 0 51.3E-051 . I E - 0 55 . 5 E - 0 5

CCCOinco

NQJI c arc in g_gg nl c £ f f e c t sA r s e n i c2 - C h l o r o p h e n o lM a n g a n e s e

1.4 - 43170 - 1,8004.8 - 7.5250 - 1,900

8.6E-043.6E-021.5E-043 . 8 E - 0 2

( a ) Range o f k r i g e d c o n c e n t r a t i o n s e s t i m a t e d f o r g r i d s l o c a t e d a t t h e s i t e a n dd i r e c t l y d o w n g r a a i e n t o f t h e s i t e .{ b ) T h e m a x i m u m C D I w a s c a l c u l a t e d u s i n g t h e m a x i m u m E P C ( f r o m t h e k r i g e d d a t a )a n d t h e 9 5 t h p e r c e n t i l e o f w a t e r i n t a k e v a l u e s ( L / k g / d a y ) e s t i m a t e d u s i n gM o n t e C a r l o s i m u l a t i o n ( s e e t e x t f o r f u r t h e r d i s c u s s i o n ) .

a b l e 6

f r n r n t h of i o m t h e( E P C S ) a n d

m g G r o u n a w a t e r Q u a l i t yl i n g t o n A q u i f e r f o r t h e R M E C a s e

i f f e c t / C o m o Q u n

' l a f ] c a .re; " r j j g n L j . £ _ t _ f f e e t s i

A r s e n i cran un

' J a n g a n e s ev a n a a i L , n

o r ? 5 t h UCL on the< r t g e a C o n c e n t r a t i o n s A r i t h m e t i c( w g / L ) ( a j M e a n ( . u g / L j ( b )

1.0 - 3.0

5 . S

2.7

EPC

700

«ME CO!( a g / k g / d a y j

2.0E-05

vCOCCCincc

f a ) 4 » f l g e o r k r . g e o c a n c e n t r a t ^ o r - s e s t i m a t e d f o r gr-.as l o c a t e d A t > h « . . * -s--e . g r a s I Q c a t e d a t t h e s i t e ana d i r e c t l y d o w n g r a d l e n t o f t h e> e 9 S t h u p p e r c o n f i d e n c e l i m i t ( U C 1 J o n t h p Ar-rh. .^a t t h e s u e a n a d i r e c t l y d o w n g r a d l e n t o f t h e s i t e

"? '& 9 5 t h UCL on tne a r i t h m e t i c mean' « . . N « used , s t h e r e a s o n a b l e

C o n c e n t r a t l ° n e s t i m a t e d f o r g r i a s i o c a t ed

" e « M £ C O ! w a s c a l c u l a t e d u s i n g t h e R H £ E P C d i r t r h »u s i n g M o n t e C a r l o a , m u l a t , o n ( s e e t e ' x t f o r

d 3 t a ) ' w f l l c h ever 5a s reconmenaed b y £ P A ( 1 9 8 9 a ) g u i d a n c e .

T a b l e 7E x p o s u r e P M n t C o n c e n t r a t i o n s ( E P C s ) a n a C h r o n i c D a i l yI n t a k e s ( C D I s ) f o r E v a l u a t i n g G r o u n d w a t e r Q u a l i t yf r o m t h 2 G a r b e r - W e l l i n g t o n A q u i f e r f o r t h e M a x i m u m C a s e

E f f e c t / C o m p o u n dRange o fK r i g e d C o n c e n t r a t i o n s M a x i m u m C D !( m g / k g / d a y j( b )

C a c l n Q . g e n i c . . E f f e c t s :B e n z e n e

Nonc a r c i n o g e n i c._Ef f e_c.t_s :A r s e n i cB a r i u mM a n g a n e s eV a n a d i u m

1.0 - 3.0

4.8801706.6

1218065040

2 . 3 E - 0 5

2.4E-043.6E-031.3E-02

ocITCO

( a ) Range o f k r i g e d c o n c e n t r a t i o n s e s t i m a t e d f o r g r i d s l o c a t e d a t t h e s i t e a n dd i r e c t l y d o w n g r a d i e n t o f t h e s i t e .( b ) T h e m a x i m u m G D I w a s c a l c u l a t e d u s i n g t h e m a x i m u m £ P C ( f r o m t h e k r i g e d d a t a )a n d t h e 9 5 t h p e r c e n t i l e o f water i n t a k e v a l u e s ( L / k g / d a y ) e s t i m a t e d u s i n gM o n t e C a r l o s i m u l a t i o n ( s e e t e x t f o r f u r t h e r d i s c u s s i o n ) .


equation. For the groundwater ingestion pa thway, the CDI isc a l c u l a t e d a s f o l l o w s (EPA 1 9 9 0 ) :

(BftO (AT)

where:

CDI - Chronic D a i l y I n t a k e ( m g / k g / d a y ) ;EPC - Expo sur e Point Concentra t ion ( m g / L ) ;IR = I n g e s t i o n Rate ( L / < 3 a y ) ;ED - Exposure Duration ( y e a r s ) ;EF - Exposure Frequency ( y e a r s ) /BW - Body W e i g h t (kg)/ andAT = A v e r a g i n g T i m e ( d a y s ) [number o f days in a l i f e t i m e for

carcinogens, number of days in the exposure period forn o n c a r c i n o g e n s ] ,

T h i s s ec t ion de s cr ibe s t h e me thod s used t o e s t imat e G D I s f o r t h egroundwater inges t ion pathway for chemicals of concern. Commonlya p p l i e d methods f o r e s t i m a t i n g R M E G D I s using a v a i l a b l e E P A ( 1 9 8 9 a )guidance wi l l be discussed in S e c t i o n 3.3.1. The a p p l i c a t i o n ofM o n t e C a r l o s imula t i on to e s t imate RME and maximum GDIs w i l l bediscussed in Sec t i on 3 .3 ,2 .

OCacc

3.3.1 Commonly A p p l i e d Method f o r Es t imat ing chronic D a i l y Intake s

The most commonly a p p l i e d method f or e s t i m a t i n g RME CDIs for th egroundwater ingestion pathway involves combining the EPC,c a l c u l a t e d us ing the methods pre s ented in S e c t i o n 3 , 2 . 1 , and point

T E T R A T E C H


e s t imate s f r o m intake parameter d i s t r i b u t i o n s using the equationpre s en t ed above. Certain RME parameters are based on u p p e rp e r c e n t i l e s o f the d i s t r i b u t i o n of p o s s i b l e values ( e . g . , 90th and95th p e r c e n t i l e s ) inc luding: ingestion rate (2 L / d a y ) , exposureduration (70 y e a r s ) , and exposure frequency (365 d a y s / y e a r ) . EPArecommends using the median body weight ( i . e . , 50th p e r c e n t i l e ) inorder to minimize po t en t ia l error due to the intercorre la t ionbetween inge s t i on rate and body weight ( i , e . , 70 kg) (EPA I 9 8 9 a ) .For the averaging t i m e , the exposure is averaged over the number ofdays in the exposure dura t i on when e v a l u a t i n g noncarcinogenice f f e c t s and the number of days in a l i f e t i m e when e v a l u a t i n gcarc inogenic e f f e c t s . T a b l e 8 pr e s en t s EPA recommended paramet ervalue s for the RME case. T h e s e values a l s o were used in the RIbase l ine risk assessment for e s t imat ing exposure for thegroundwater ingest ior- ^=>thway.

In g enera l , RME GDIs estimated using the approach described abovemay r e f l e c t an upper-bound on the p o t e n t i a l risks as sociated withuse of g r o u n d w a t e r at a s i t e . H o w e v e r , there are severala n a l y t i c a l d e f i c i e n c i e s a s so c ia t ed wi th th i s m e t h o d , a s d i s cu s s edi n C l e m e n t ( 1 9 9 0 b ) . F i r s t o f a l l , t h e p r o b a b i l i t y o f t h e exposureevent occurring cannot be q u a n t i f i e d using th i s me thod .Q u a n t i t a t i v e uncer ta in ty a n a l y s i s should be an impor tant part ofthe baseline risk assessment process. Xn f a c t , EPA ( 1 9 8 9 a )guidance recommends using Monte Carlo s imulat ion and othertechniques for conducting such an analysi s . S e c o n d l y , thep r o b a b i l i t y of the exposure event occurring may be h i g h l y u n l i k e l yand unreasonable . S i m u l a t i o n m o d e l i n g r e su l t s pre s ent ed in Clement( 1 9 9 0 b ) reveal that a p p r o x i m a t e l y 60 percent of the RME CDJse s t imated using thi s a p p r o a c h w i l l overest imate th© tru<a 9 S t hp a r c e n t i l e of p o s s i b l e exposures by at least on© ord^r ofm a g n i t u d e - F i n a l l y , the l i k e l i h o o d of th© RME CDI occurring mayd i f f e r s i g n i f i c a n t l y f r o m chemical to chemical d e p e n d i n g on the

T E T R A T E C H

CTcca.ince

Table c5E R A R e c o m m e n d e d P a r a m e t e r V a l u e s f o r t h e R M E C a s e

P a r a m e t e r

I n g e s t i o n R a t e ( L / d a y ) ( a )E x p o s u r e D u r a t i o n ( y e a r s ) ( b )E x p o s u r e F r e q u e n c y ( d a y s / y e a r ) ( c )B o d y W e i g h t ( k g ) ( d )A v e r a g i n g T i m e ( d a y s ) ( e )

R e a s o n a b l e M a x i m u mE x p o s u r e ( R M E ) C a s e

270

36570

70 x 365

Oerocincc

( a ) R e p r e s e n t s t h e 9 0 t h p e r c e n t i l e o f w a t e r i n g e s t i o n r a t e s ( E P A 1 9 8 9 a ) .( b ) L e n g t h o f a n a v e r a g e l i r e t i m e u s ed f o r e x p o s u r e d u r a t i o n s i n rural areas( E P A 1 9 8 9 a ) .( c ) N u m b e r o f d a y s i n a year.( d ) A v e r a g e b o d y w e i g h t f o r a n a d u l t ( E P A 1 9 8 9 a ) .( e ) A v e r a g i n g t i m e i s t h e number o f d a y s i n a l i f e t i m e f o r a s s e s s i n gc a r c i n o g e n i c e f f e c t s a n d t h e number o f d a y s i n t h e e x p o s u r e d u r a t i o n f o ra s s e s s i n g n o n c a r c i n o g e n i c e f f e c t s ( w h i c h i n t h i s case a r e e q u i v a l e n t ) .


d i s t r i b u t i o n of the chemical. T h e r e f o r e , risk management dec i s ionsmay not be a p p l i e d c o n s i s t e n t l y .

3 .3 .2 U s i n g Monte C a r l o S i m u l a t i o n t o E s t ima t e Chronic D a i l yI n t a k e s

M o n t e C a r l o s i m u l a t i o n can be a p p l i e d to addre s s the l i m i t a t i o n swith the me thod s d i s cu s s ed in S e c t i o n 3 .3.1, Monte C a r l os i m u l a t i o n is a numerical s t o cha s t i c process that can be used toq u a n t i t a t i v e l y evaluate uncertainty, Monte Carlo s imulat ion hasbeen a p p l i e d to characterize d i s t r i bu t i on s of p o s s i b l e exposuresand risks for various pathways in risk assessment (Burmaster andvon S t a c k e l b e r g 1988, Eschenroeder and Faeder 1988, Iman and H e l t o n1988, and M c K o n e and Ryan 1 9 8 9 ) . In a d d i t i o n , Monte C a r l os i m u l a t i o n is endorsed by EPA ( I 9 8 9 b ) in RAGS as a s u i t a b l e methodf o r q u a n t i t a t i v e l y e v a l u a t i n g u n c e r t a i n t y , Mont e C a r l o s i m u l a t i o ntheory and p r o g r a m m i n g a l g o r i t h m s are de scr ibed in K a l o s andW l i i t l o c k ( 1 9 8 6 ) , R u b i n s t e i n ( 1 9 8 1 ) , a n d F e d r a ( 1 9 8 3 ) .

M o n t e C a r l o s i m u l a t i o n was used to e s t imat e GDIs for the RME caseand maximum case. In th i s r e p o r t , tha 9 5 t h p e r c e n t i l e o f p o s s i b l eCDIs were vised to correspond to the RME case and maximum case. Asp r e v i o u s l y d i s c u s s e d , the RME case CDI represents tha reasonablemaximum exposure associated with the s tudy area. The maximum caseCDI repre sent s the maximum p l a u s i b l e exposure associated withexposure to tha worst "hot spot" at the site.

F i g u r e 1 i l l u s t r a t e s how a M o n t a C a r l o s i m u l a t i o n is used toe s t imat e CDIs. During each i t e ra t i on o f th e Monta C a r l os i m u l a t i o n , a value f r o m each at tha input parameters ( F i g u r e 1 -l e f t s i d e ) is a a l a c t e d at random and combined in tha chemicalintake equat ion pr e s en t ed above. T h i s process i s r & p e a t a dthousands o f times untLl a s tab l e d i s t r i b u t i o n of p o s s i b l e GDIs i s

T E T R A T E C H

E x p o s u r e P o i n tC o n c e n t r a t i o n( m a x i m u m o r 9 5 t h U C Uon a r i t h m e t i c mean)

F i g u r e 1E x a m p l e o f M o n t e C a r l o S i m u l a t i o n

I n g e s t i o n R a t e

LA.E x p o s u r e D u r a t i o n

E x p o s u r e rrequeney

Body W e i g h t

A v e r a g i n g Tliv

1. T a k e a random s a m p l ef r o m each d i s t r i b u t i o n2. C a l c u l a t e an e x p o s u r ee s t i m a t e

3. R e p e a t s t e p s 1 & 2numerous t ime s(e.$., S O O O I t e r a t i o n s )

4. G e n e r a t e a d i s t r i b u t i o n ofp o s s i b l e e xpo sur ee s t i m a t e s

M a x i m u mG D I E s t i m a t e

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COIE s t i m a t e


f o rmed ( F i g u r e 1 - right s i d e ) . F r o m this d i s t r i b u t i o n , C D I s thatcorrespond to a d e f i n e d upper-bound p e r c en t i l e can be determined.The f a c t that the GDI estimates are based on a 95th perc ent i l e ofp o s s i b l e C D I s i m p l i e s that the GDI estimates are upper-bounds onintake. Furthermore , since the GDI for every chemical is based onthe same p r o b a b i l i t y of occurrence, it means that ths e s t imate s arecons i s t ent and commensurate. T h e r e f o r e , the a p p l i c a t i o n of thesetechniques a l l o w s for more t e c h n i c a l l y sound and b e t t e r i n f o r m e drisk management dec i s ions .

The f i r s t s t ep in conducting a Monte Carlo s imulat ion involvescharacterizing each of the input parameter d i s tr ibut ions . T a b l e 9pr e s en t s d i s t r i b u t i o n s t a t i s t i c s for each-* of the exposureparamet er s . All of the parameter d i s t r i b u t i o n s are assumed to benormal, a l t h o u g h some are truncated f r o m be low ( e . g . , at zero forwater i n g e s t i o n r a t e ) and some f r o m above ( e . g . , at 365 days peryear f r o m exposure f r e q u e n c y ) . The average inge s t ion rate o f 1*4L / d a y , which is recommended by EPA ( 1 9 8 9 a ) and reported by cantorat al. ( 1 9 8 7 ) , was used in this assessment. The average exposureduration of nine years represents the average number of years aperson in the U n i t e d S t a t e s remains at a s i n g l e re s idence ( E P A1 9 8 9 b ) . The average exposure f r e q u e n c y was c a l c u l a t e d -bym u l t i p l y i n g 365 days by the average p e r c e n t a g e of time that ani n d i v i d u a l w i l l be awake at home. The average per son s p e n d s 68percent of their waking hours at home ( E P A 1 9 8 9 b ) . The averageexposure frequency assumes that an individual ingests water at af a i r l y constant rate during the port ion of tha day that the personis awake. For e x a m p l e , w h i l e at work the ind iv idua l drinksa p p r o x i m a t e l y the same amount of water per unit time as at home.S t a n d a r d d e v i a t i o n s for inges t ion rata, exposure durat ion, andexposure frequency were c a l c u l a t e d for raach parameter by usingper c en t i l e d a t a pre s ented i n various s tudies (see T a b l e 9 ) . T h i s

was used because no studies were avai lable that presented aT E T R A T E C H

ocinco

T a b l e 9E x p o s u r e P a r a m e t e r D i s t r i b u t i o n S t a t i s t i c s U s e d t o E s t i m a t e E x p o s u r eU s i n g M o n t e C a r l o S i m u l a t i o n ( a )

M o n t e C a r l o S i m u l a t i o nParameter D i s t r i b u t i o nS t a t i s t i c sP a r a m e t e rI n g e s t i o n R a t e ( I / d a y ) ( b )E x p o s u r e D u r a t i o n ( y e a r s ) ( c )E x p o s u r e F r e q u e n c y ( d a y s / y e a r ) ( d )Body W e i g h t ( k g ) ( e )L i f e t i m e ( d a y s )C a r c i n o g e n i c R i s k s ( f )N o n c a r c i n o g e n i c R i s k s ( g )

A r i t h m e t i cM e a n1.4

9250

71.8

70 x 365ED x 365

S t a n d a r dD e v i a t i o n0.47

167015

00

ccI T ,CO

( a ) A d a p t e d f r o m C l e m e n t ( 1 9 9 0 o ) .( b ) P l / e r a g e a d u l t i n g e s t i o n p r e s e n t e d i n E R A ( 1 9 8 9 a ) . S t a n d a r d d e v i a t i o nc a l c u l a t e d f r o m E R A a v e r a g e a n d 90th p e r c e n t i l e p a r a m e t e r s a s s u m i n g t h ed i s t r i b u t i o n o f i n g e s t i o n r a t e s i s n o r m a l , t h u s { 2 . 0 - 1 . 4 I J / 1 . 2 8 * 0.47.( c j A v e r a g e number o f years a n a d u l t w i l l l i v e a t a g i v e n r e s i d e n c e p r e s e n t e di n E P A ( 1 9 8 9 a ) . S t a n d a r d d e v i a t i o n d e r i v e d i n t h e same manner a s d i s c u s s e dabove (30 - 9 ) / i . 2 8 « 16.( d ) A v e r a g e e x p o s u r e f r e q u e n c y c a l c u l a t e d b y m u l t i p l y i n g 3 6 5 d a y s b y t h e a v e r a g ep e r c e n t a g e o f t i m e that an i n d i v i d u a l w i l l b e awake at home (68 p e r c e n t )( E P A , 1 9 8 9 b ) . T h e s t a n d a r d d e v i a t i o n w a s c a l c u l a t e d b y a s s u m i n g t h a t 2 5 0d a y s r e p r e s e n t s t h e mean , 3 6 5 d a y s i s t h e 9 5 t h p e r c e n t i l e , a n d t h ed i s t r i b u t i o n i s n o r m a l , t h u s 365 - 2 5 0 / 1 . 6 4 = 70.( e ) A v e r a g e body w e i g h t a n d s t a n d a r d d e v i a t i o n c a l c u l a t e d f r o m E P A ( 1 9 8 5 J .( f j 7 0 years x 3 6 5 d a y s / y e a r i s t h e a v e r a g i n g t i m e f o r e s t i m a t i n g c a r c i n o g e n i ce x p o s u r e s .( g ) S x p o s u r * d u r a t i o n ( E D ) x 3 6 5 d a y s / y e a r i s t h e a v e r a g i n g t i m e f o r e s t i m a t i n gn o n c a r c i n o g e n i c exposures .


f u l l s t a t i s t i c a l de s cr ip t ion o f the d i s tr ibut ions for these threeexposure parameters. The average adult body weight of 71.8 kg andthe s tandard deviation of 15 kg were, however, ca l cu la t ed f romd e t a i l e d da ta prov ided in EPA ( 1 9 8 5 ) . The inter-correlat ionbetween body weight and water inge s t i on rate, e s t ima t ed to bea p p r o x i m a t e l y 0.9 , was taken into account in the Monte C a r l os i m u l a t i o n . Body weight and i n g & s t i o n rate values were s e l ec tedf r o m a b ivar ia t e normal d i s t r i b u t i o n , in order that the inter-correlat ion of these parameters would be 0.9 (Clement I 9 9 0 b ) . Theaveraging time is assumed to be constant* When c a l c u l a t i n g C D I sfor noncarcinogenic e f f e c t s , the averaging time is equal to thenumber of days in the exposure dura t i on; thereby canc e l ing thev a r i a b i l i t y o f t h e exposure duration. W h e n c a l c u l a t i n g C D I s f o rcarc inogenic e f f e c t s , the averaging time is equal to the number ofdays in a l i f e t i m e , assumed to be 70 years x 365 d a y s .

In this report , C D I s corresponding to the 95 th p e r c e n t i l e for theRME case and maximum case were calculated by m u l t i p l y i n g the EPCsfor these case by the 95th p er c en t i l e of p o s s i b l e water-intakevalue s . W a t e r intake is d e f i n e d as l i t e r s of water inges t ed perk i l o g r a m o f body we igh t p e r day. T h e 9 5 t h p e r c e n t i l e o f exposurecan be c a l c u l a t e d us ing thi s a p p r o a c h since the EPC parameter is ac on s tan t . T h e M o n t e C a r l o s i m u l a t i o n derived wat er- in take valuesare p r e s e n t e d in T a b l e 10. In a d d i t i o n , wat er* in take valuesest imated using the EPA. ( 1 9 8 9 a ) method described in S e c t i o n 3.3.1are presented in T a b l u 10 for comparison sake. As shown in T a b l e10, the water-intake values derived using the EPA ( I 9 8 9 a ) methodwere 1.5 and 3.7 t imras higher than the actual 9 5 t h p e r c e n t i l e ofp o s s i b l e water-intake values for noncarcinogenic and carcinogenica f f e c t s , r e s p e c t i v e l y .

To e s t imat e noncarcinogenic CDIs for the RME case and Maximum case,the 95th p er c en t i l e o f water-intake value (0.02 L / k g / d a y ) for

T E T R A T E C H

T a b l e 1 0C o m p a r i s o n o f E s t i m a t e d W a t e r I n t a k e V a l u e s C a l c u l a t e d U s i n gM o n t e C a r l o S i m u l a t i o n a n d E P A ( 1 9 8 9 a ) G u i d a n c e

E f f e c t / M e t h o d W a t e r i n t a k e( L / k g / d a y )M o n c a r c i n o g e n i c E f f e c t s

M o n t e C a r l o S i m u l a t i o nE P A ( 1 9 8 9 a ) M e t h o dC a r c i n o g e n i c E f f e c t . s .

M o n t e C a r l o S i m u l a t i o nE P A ( 1 9 8 9 a ) M e t h o d

2 . 0 E - 22 . 9 E - 2

7 . 5 E - 32 . 8 E - 2

accu\co


e v a l u a t i n g noncarcinogenic e f f e c t s was m u l t i p l i e d by thea p p r o p r i a t e E P C s . T o e s t i m a t e carcinogenic G D I s f o r t h e R M E caseand Maximum case, the 95 th p e r c e n t i l e of water-intake value foreva lua t ing carcinogenic e f f e c t s (0.0075 L / k g / d a y ) w a s m u l t i p l i e d b ythe a p p r o p r i a t e EPCs (d iv id ed by 1000 to convert the units f r o mu g / L t o r n g / L ) . RME G D I s and maximum GDIs e s t imated f or chemicalsof concern present in the A l l u v i a l A q u i f e r are pre s en t ed in T a b l e4 and 5, r e s p e c t i v e l y . RME GDIs and maximum GDIs e s t imated forchemical s of concern present in the G a r b e r - W e l l i n g t o n A q u i f e r arep r e s e n t e d in T a b l e 6 and 7, r e s p e c t i v e l y .

T E T H A T E C H


4 . 0 T O X I C I T Y A S S E S S M E N T

T h i s section evaluates the carcinogenic and noncarcinogenict o x i c i t y of chemicals of concern selected in S e c t i o n 2. T o x i c i t yassessment is the process of e v a l u a t i n g the p o t e n t i a l for achemical to cause an adverse health e f f e c t in humans and, ifp o s s i b l e , to q u a n t i f y the r e la t i on sh ip between exposure l eve l s( i . e . , d o s e ) and th e adverse h ea l th e f f e c t * H a z a r d i d e n t i f i c a t i o nis the f i r s t s t e p in conduc t ing a t o x i c i t y assessment whichinvolves evaluat ing the p o t e n t i a l for a chemical to cause anadverse h e a l t h e f f e c t . Dose-response evaluation is the second s t epin the t o x i c i t y assessment proces s which a t t e m p t s to q u a n t i f y ther e l a t i o n s h i p between dose of the admini s t e r ed chemical and theincreased incidence of the adverse heal th e f f e c t .

OCa<rineo

The s l o p e f a c t o r i s used to evaluate the p o t e n t i a l carcinogenicri sks a s so c ia t ed wi th exposure to a chemical of concern. S l o p ef a c t o r s and s u p p o r t i n g t ox i c i ty data for chemicals of concern aresummarized in T a b l e 11 and discussed below in S e c t i o n 4.1. Ther e f e r e n c e dose ( i . e . , R f D ) i s used t o evaluate th e p o t e n t i a lnoncarc inogenic risks a s soc ia t ed wi th e xpo sure to a chemical ofconcern. R f D s and s u p p o r t i n g tox i c i ty data for chemicals ofconcern are summarized in T a b l e 12 and discussed below in Sec t i on4.2. T o x i c i t y cr i t er ia and s u p p o r t i n g t o x i c i t y d a t a used in thePBRA were obtained f r o m the I n t e g r a t e d Risk I n f o r m a t i o n S y s t e m( I R I S ) ( E P A 1 9 9 1 ) . T o x i c i t y criteria f o r chemicals o f concern n o tl i s t ed in IRIS ( i . e . , arsenic, 1 , 2 - d i c h l o r o p r o p a n e , b i s ( 2 -e t h y l h e x y l j p h t h a l a t e , t e t rach ioro e th eno , vanadium, and vinylc h l o r i d e ) were obtained f r o m t h e F o u r t h Quarter H e a l t h E f f e c t sAssessment Summary T a b l e s ( H E A S T ) (EPA 1990).

T E T R A T E C H

T a b l e I I

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C h r o n i c C a r c i n o g e n i c T o x i c i t y C r i t e r i a ( S F s )f o r C h e r n i c a ] s o f C o n c e r n

S ( o p « F a c t o r ( S f >C r a g / k g / d a y ) " 'C o r a t route>

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Cavage/H E A S T

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* I R I S data obtained February,** SEASf da ta used Sept ember , 1990.£ a > s e e t ex t f o r w e t g h t - a f - e v i d e n c e c E a s s i f i c a i c o n c f e s c r i p t i ion

0 0 5 8 9 9

T a b l e 1 2C h r o n i c N o n c a r c i n o g e n i c T o x i c i t y C r i t e r i a ( R F D s )f o r C h e m i c a l s o f C o n c e r n

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(oral route)

I E - 0 3

?£-02 H e d i t a n

5E-03 low

J E - O i M e d i u m

7 E - Q 3

C r i t t e a lE f f e c t

K e r a t o s i s a n dh y p e r p i g m e n t a t ion

in cr ea s ed b l o o dpressure

R e p r c J u c t wee f f e c t s

C e n t r a l N e r v o u sS y s t e m s E f f e c t sN o n e ob s erved

R f O B a s i s /R f D S o u r c e

W a t e r /H E A S P

W a t e rI R I S 1 "

W a t e r /I R I S

W a t e r /E R S S

W a t e rH £ A S T

U n c e r t a i n t y andH o d i f / t n g F a c t u r s

U f ' = i

U F - 3 f o r HK F » 1U t - 1 0 0 0 f o r H . A . SH E = !y f * iM F « IU F = 1 0 0 f o r A . S

No dataH E A S I da ta used f r c m S e p t e m b e r . J 9 9 0I R I S data obtained February. I & 9 1C o n f i d e n c e J e w e l a s given b y I R I SU n c e r t a i n t y a d j u s t m e n t s r e p r e s e n t t h e f o l l o w i n g combined e x t r a p o l a t i o n s :

ri = v a r i a t t o n in human sensU t v i t y ;A = a n i m a l to huraain e x t r a p o l a t i o n ;S = e x t r a p o l a t i o n f r o m s uh chron i c t o c h r o n i c N O A f L .

ft 0 5 9 0 0


4.1 T o x i c . i t Y C r i t e r i a for Evaluating. P o t e n t i a l carcinogenicE f f e c t a

The s l o p e f a c t o r , expressed in m g / k g / d a y ' 1 , q u a n t i f i e s t h e po t en t ia lcancer potency of a chemical for evaluating the carcinogenic risksassociated with exposure. U n l i k e noncarcinogenic e f f e c t s , a smallnumber of molecu lar events may a l t er a cel l in such a way as tocause uncon tro l l ed c e l l u l a r p r o l i f e r a t i o n , thereby r e s u l t i n g indi s ease ( i . e . , carcinogenic e f f , c t ) . T h e r e f o r e , a n y expo sure m a yresult in the m a n i f e s t a t i o n of a carc inogenic e f f e c t . T h u s , noexposure is considered risk f r e e -

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To evaluate the p o t e n t i a l carcinogenic t o x i c i t y of a chemical , EPAf i r s t determines the l i k e l i h o o d that the chemical is a humancarcinogen. EPA uses a c l a s s i f i c a t i o n system ( i . e . , w e i g h t ~ o f -evidence c l a s s i f i c a t i o n ) f o r charac t er i z ing t h e p o t e n t i a lcar c inogen i c i ty of a chemical based on the evidence pr e s en t ed inanimal and human s t u d i e s . The w e i g h t - o f - e v i d e n c e c l a s s i f i c a t i o nscheme is pr e s en t ed be low:

A - H u m a n C a r c i n o g e n ;Bl - Probable Human Carcinogen, based on l imi t ed human d a t a ;B2 - Probable Human Carcinogen, based on s u f f i c i e n t evidence

in animals and inadequate or no evidence in humans;C - P o s s i b l e Human Carcinogen;D - Not c l a s s i f i a b l e as to human car c inogen i c i ty; andE - Evidence of noncarc inogen i c i ty for humans.

If the chemical i s a human carcinogen ( G r o u p A) or a p r o b a b l e humancarcinogen ( G r o u p Bl or Group 8 2 } , then a s l o p e f a c t o r isc a l c u l a t e d for the chemical which q u a n t i f i e s i t s cancer potency.In certain cases, s l o p e f a c t o r s are derived for p o s a i b l & humancarcinogens ( G r o u p C compounds). S l o p © f a c t o r s are derived by

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e x t r a p o l a t i n g dose-re sponse r e l a t i o n s h i p s measured under high dosec o n d i t i o n s in labora tory animal s tud i e s or e p i d e m i o l o g i c a l s tud i e sto low dose conditions t y p i c a l l y encountered at S u p e r f u n d sites.The f i r s t s t e p in deriving a s l o p e f a c t o r involves f i t t i n g amathemat ical model to the e xper imenta l d a t a ( E P A 1 9 8 6 a ) , Of thea v a i l a b l e l o w dose e x t r a p o l a t i o n m o d e l s ( i . e . , W e i b u l l , p r o b i t ,l o g i t , one-hit, and gamma raul t ih i t m o d e l s ) , the more conservativel inearized m u l t i s t a g e model is t y p i c a l l y used to derive a s l o p ef a c t o r f r o m animal data. T h i s model assumes that the do s e-re sponser e l a t i o n s h i p at low doses is linear. Once the data are fit usingthe l inearized m u l t i s t a g e mode l , the 95th upper c o n f i d e n c e l imit onthe s l o p e of the l ine i s c a l c u l a t e d which r e p r e s e n t s the s l o p ef a c t o r . S l o p e f a c t o r s are then v e r i f i e d and v a l i d a t e d by theCarcinogen Risk Asses sment V e r i f i c a t i o n Endeavor (CRAVE) Workgroupb e f o r e being p lac ed on IRIS. S l o p e f a c t o r s based one p i d e m i o l o g i c a l da ta are fit on an ad hoc basis.

The carcinogenic t o x i c i ty of chemicals of concern evaluated in thePBRA are d i s cus s ed below.

4£genlc... The CRAVE W o r k g r o u p is currently reviewing thecarcinogenic p o t e n t i a l of arsenic for the oral exposure route.N e i t h e r I R I S ( M a r c h 1 9 5 1 ) n o r H E A S T ( 1 9 9 0 ) r epor t ed a n oral s l o p ef a c t o r f o r arsenic. T h e r e f o r e , t h e p o t e n t i a l carcinogenic riskassociated with exposure to arsenic could not be quan t i t a t i v e lyevaluated in accordance with EPA ( I 9 8 9 a ) guidance. The ScienceA d v i s o r y Board ( S A B ) reviewed t h e p o t e n t i a l c a r c i n o g e n i c i t y o farsenic in a l e t t er to W i l l i a m K. R e i l l y , EPA A d m i n i s t r a t o r( S e p t e m b e r 23, 1 9 8 9 ) . One of the m a j o r conclusions made by SAB was"that at dose l ev e l s below 200 to 250 ug A s 3 * / p e r s o n / d a y [ 2 . 9 E - 3 -3.5E to 3 m g / k g / d a y ] there is a p o s s i b l e d e t o x i f i c a t i o n mechanismthat may s u b s t a n t i a l l y reduce cancer risk f rom levels EPA hascalculated using l inear-quadratic model f i t to the T s e n g da ta ,"

OaLAao

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The exposure l e v e l s e s t imated f or inge s t i on o f arsenic f or both th eRME and maximum cases ( f o r po t ent ia l carcinogenic e f f e c t s ) werea p p r o x i m a t e l y an order of magnitude below this threshold level.T h e r e f o r e , the p o t e n t i a l carcinogenic e f f e c t s a^ «ociated withexposure to arsenic p r o b a b l y would not contribute s i g n i f i c a n t l y tothe carcinogenic e f f e c t s evaluated in this report.

Benzene. The huraan carc inogenic i ty of benzene has m a i n l y beenevident f r o m occupational exposure r e su l t ing in s i g n i f i c a n tincidence of non lymphoay t i c leukemia. Based on the re su l t s ofthese s t u d i e s , benzene has been c l a s s i f i e d as a Group A carcinogen-S t u d i e s on rodents exposed to benzene by gavage showed increasedincidence of various cancers (EPA 1 9 9 1 ) . A s l o p e f a c t o r of 2 . 9 X 1 0 " 2

( m g / k g / d a y ) - 1 was c a l c u l a t e d based on increased incidence ofl eukemia in rodent s f r o m d r i n k i n g water wi th varying l e v e l s ofbenzene.

OOI T ,

M s , ( 2 - E t h v l h e x y l l . p h t h a l _ a t e . EPA ha s c l a s s i f i e d b i s ( 2 -e t h y l h e x y l ) p h t h a l a t e as a probab l e human carcinogen ( G r o u p B 2 ) .B i s ( 2 - e t h y l h e x y l ) p h t h a l a t e induced carc inogeni c e f f e c t s( h e p a t o c e l l u l a r carcinomas and n e o p l a s t i c n o d u l e s when a d m i n i s t e r e do r a l l y to rats [NTP 1 9 8 2 ] ) . Retardat ion o f growth and the increasein liver and kidney weight may result f r o m a diet having highc onc en t ra t i on s o f b i s ( 2 - e t h y l h e x y l ) p h t h a l a t e ( N T P 1 9 8 2 , E P A 1980,C a r p e n t e r e t a l . 1 9 5 3 ) . A s l o p e f a c t o r ( S F ) o f l , 4 x i O ' 2

(mg/kg/day)' } was ca l cu la t ed based on increased h e p a t o c e l l u l a rcarcinomas in rats and mice (EPA 1 9 9 0 ) .

i1 .2-Dich lQropropane . Gavaga studies have shown that 1,2-d i c h l o r o p r o p a n e causes h e p a t i c tumors in mice (EPA 1 9 9 0 ) . It i sconsidered to be a h i g h l y toxic ch lor inated hydrocarbon and isregarded as a probable human carcinogen ( G r o u p B2) , An oral s l o p ef a c t o r o f e . S x l O " 2 (mg/kg/day)' 1 was ca l cu la t ed based on increased

tTORA TECH


hepat i c tumors in mice (EPA 1 9 9 0 } .

Tetrach loroe thene . . Tetra ch l oro e th ene was demons tra t ed to causehepat i c neop la s ims in rodents administered this chemical by gavageover a long-term exposure per iod (EPA 1 9 9 0 ) . T e t r a c h l o r o e t h e n e isconsidered a probable human carcinogen ( G r o u p B2) with the livermost l i k e l y the target organ as in the rodent bioassay. An orals l o p e f a c t o r o f S . l x l O * 2 ( i n g / k g / d a y } " 1 was computed based on dataf r c m the gavage study of mice (EPA 1 9 9 0 ) .

V i n v J L . , C h l o r i d e . « s .udy on rodents p e r f o r m e d u s ing 10-50 ppmdie tary vinyl chloride produced liver tumors (EPA 1 9 9 0 ) » Furthers t u d i e s ind i ca t e the c a r c i n o g e n i c i t y of vinyl c h l o r i d e asassociated with the s p l e e n , kidneys, hema^opoietic sys tem, andske l e ta l system (EPA 1984a)* An oral s l o p e f a c t o r for dr inkingwater o f 1 .9 ( m g / k g / d a y ) " 1 ha s r e c en t ly been v e r i f i e d ( E P A 1 9 9 0 ) ,r e p l a c i n g the earlier value of 2.3 ( m g / k g / d a y ) "*. An EPA workgroupi s c u r r e n t l y reviewing a v a i l a b l e da ta for d e r i v i n g the mosta p p r o p r i a t e s l o p e f a c t o r f o r vinyl ch l or id e ( E P A 1 9 9 0 ) .

4.2 t o x i c i ty Criteria . . fQr- .Evalua t . ing_PotQnt iaI N o n c a r c i n o a e n i c

catncc

The re f erence dose, expressed in m g / k g / d a y , is used to eva lua t e thep o t e n t i a l noncarcinogenic risks associated with exposure to achemical of concern at a S u p e r f u n d s ite. T h i s report eva luat e schronic exposure via inges t ion, thus chronic oral R f D s arenecessary for e v a l u a t i n g the p o t e n t i a l noncarcinogenic risks f orth i s pathway. An oral chronic RfD is d e f i n e d as an est imate of ad a i l y exposure level for the human p o p u l a t i o n , including sen0itives u b p o p u l a t i o n a , that is l i k e l y to be without an a p p r e c i a b l e risk ofde le t er ious e f f e c t s during a l i£®ti iae based on an oral administereddosa (EPA 1 9 8 S & ) * It is assumed that a protective machanism in the

T E C H


body must be overcome in order for a noncarcinogenie e f f e c t to ccur( i . e . , threshold e f f e c t ) . For e xampl e , numerous c e l l s in an organmust be damaged b e f or e an e f f e c t may be m a n i f e s t e d .

In general , R f D s are derived f rom animal laboratory studies orhuman e p i d e m i o l o g y s tudies . T h e s e s tudies are reviewed to derivea no-ob s e rvab l e -adver s e - e f f e c t level (NOAEL) for the chemical. Thel o w e s t ~ o b s e r v a b l e - a d v e r s e - e f f e e t level (LOAEL) is used when a NOAELcannot be derived f rom the study. In this case, an a d d i t i o n a luncertainty f a c t o r i s a p p l i e d to es t imate the R f D . Uncer ta in tyf a c t o r s (UF) are a p p l i e d to the NOAEL (or LOAEL) to account forvarious t y p e s of uncertainty inc luding: .. ^• variation in the human p o p u l a t i o n (UF - 1 0 ) ;• e x t r a p o l a t i o n f r o m animal to human s tudie s (UF - 1 0 } ;a derivation of a chronic RfD from a subchronic KOAEL (UF * 10) ;

anda der iva t i on of a chronic RfD f r o m a chronic L O A E L (UF * 10) .

An a d d i t i o n a l s a f e t y f a c t o r , referred to as the m o d i f y i n g f a c t o r(MF), ;ttay be a p p l i e d when deriving the RfD to account for othersources of uncertainty in the s tudy. The m o d i f y i n g f a c t o r is avalue that ranges f r o m 1 to 10 which is assigned based on aq u a l i t a t i v e evaluation of the study. R f D s are d eve l oped by theintra-agency RfD Workgroup in accordance with EPA guide l ine s (EPA1986b, EPA 1 9 8 9 b , c ) .

The noncarcinogenie t o x i c i t y of chemicals of concern evaluated inthe PBRA are discussed below.

tr.C

C

The most common non-carcinogenic e f f e c t s noted f romingest ion of arsenic are hyperkeratosis and hyperp igmenta t ion.Thes e skin lesions have been general ly found to deve lop on surface s

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not n o r m a l l y expo s ed to u l t r a v i o l e t l i g h t * Some e f f e c t s o f arsenicon the p e r i p h e r a l nervous sys t em i n c l u d e sensory-motor p r o b l e m swi th h igh l e v e l s of exposure and a decrease in nerve conduct ionv e l o c i t y under low exposure l e v e l s with long-term dura t i on . Ane p i d e i n i o l c g i c a l s tudy p e r f o r m e d on a T a i w a n e s e p o p u l a t i o n withpro trac t ed exposure to arsenic inge s t i or showed an increase in theincidence o f B l a c k f o o t d i s ease ( p e r i p h e r a l v a s c u l o p a t h y ) a l t h o u g hdirect causation is considered que s t ionable (EPA 1984b) . An oralRfD o f I x l O " 3 m g / k g / d a y in d r i n k i n g water ha s been c a l c u l a t e d usingan unc er ta in ty f a c t o r of l based on the T a i w a n s t udy ( E P A 1990,T s e n g 1 9 7 7 ) . An EPA workgroup is currently reevaluat ing the RfDf o r arsenic ( E P A 1 9 9 1 ) .

ccrincoBarium has been c l a s s i f i e d as a noncarcinogen by E P A .

Oral expo sure s t ud i e s conducted on human be ings have recorded avari e ty o f h e a l t h e f f e c t s f r o m t h e ing e s t i on o f s o l u b l e bariumcompounds i n c l u d i n g : g a s t r o e n t e r i t i s , muscular p a r a l y s i s ,h y p e r t e n s i o n , v en tr i cu lar f i b r i l l a t i o n , a n d C N S damage. A n i m a l so r a l l y e xpo s ed to barium showed an increase in blood pre s sure ( E P A1 9 8 4 c ) . I R I S repor t ed a n oral R f D f o r barium o f 7 x l O * 2 m g / k g / d a y( E P A 1 9 9 1 ) . T h e R f D w a s derived f r o m a N O A E L o f 1 0 m g / L ( 0 . 2 1

m g / k g / d a y ) and an u n c e r t a i n t y f a c t o r o f 3 ( t h e m o d i f y i n g f a c t o r wasequal t o 1) ( E P A 1 9 9 1 ) . The c o n f i d e n c e level o f th e oral RfD forbarium is medium.

2-_Cblo . ropheno l . The most s en s i t iv e targe t organ a s s o c ia t ed wi thexposure to 2 - c h l o r o p h e n o l is the r eproduc t i v e sys t em. Otheradverse e f f e c t s noted at higher doses i n c l u d e : l iver and kidneydamage, edema of the l u n g , d i g e s t i v e d i s turbance s , and centralnervous sys t em (CNS) e f f e c t s . A s tudy was p e r f o r m e d in which ratswere s u b c h r o n i c a l l y exposed to 2- ch loropheno l . The r e su l t s of thi ss tudy showed that 2 - c h l o r o p f c e n o l caused adverse r eproduc t ivee f f e c t s i n c l u d i n g increased s t i l l b i r t h s and decreased l i t t e r size

T E T R A T E C H


(EPA 1991) . An oral RfD of 5xlO* 3 m g / k g / d a y for drinking water wasc a l c u l a t e d based on the above s tudy using a NOAEL of 5 m g / k g / d a yand an uncertainty f a c t o r of 1000 (EPA 1991) . The conf idence levelof the oral RfD for 2-chlorophenol is low.

Manganese * E p i d e m i o l o g i c a l studies have shown that very high doses( > l l . 5 m g / d a y ) o f manganese d i s s o lved in drinking water causeprob l ems with the central nervous system (EPA 1991). These toxice f f e c t s are thought to be i n t e n s i f i e d by increased water a c i d i t yand the presence of iron. Chronic exposure to manganese indrinking water produced increased l e thargy, higher muscle tonus,tremor, and mental d i s turbance s . T h e s e symptoms were i n t e n s i f i e din e l d e r l y p e o p l e , oral s tudies on rodents and macaques were foundto cause prob l ems ranging f r o m biochemical changes in the brain tomuscular weakness. T h e oral R f D o f i x J O " 1 m g / k g / d a y w a s computedusing a NOAEL of 0.14 m g / k g / d a y for chronic human consumption ofmanganese. The unc er ta in ty f a c t o r and m o d i f y i n g f a c t o r wereassumed to be 1. T h i s RfD was ca l cu la t ed considering a totald i e t a r y intake of manganese. Because manganese f r o m d r i n k i n g wateralone is more b i o a v a i l a b l e , t h i s level may not be a c c e p t a b l e inthat case. Manganese is an essential human nutrient and therepor t ed p r o b l e m s occurred at l e v e l s above 9 m g / d a y (EPA 1 9 9 1 ) .

V a n a d i u m . The most common e f f e c t s o f exposure to vanadium inc ludethe inh i b i t i on of pu lmonary l e s ions , d e p r e s s i o n of cholesterolsynthe s i s , and the prevention of dental cavities. A chronic orals t u d y p e r f o r m e d on rats rece iving vanadium in their d r i n k i n g waterwas used to ca l cu la t e an oral RfD of 7xlO" 3 m g / k g / d a y using a NOAELof 0.77 m g / k g / d a y and an uncertainty f a c t o r of 100 (EPA 1 9 9 0 ) . Noadverse e f f e c t s ware noted in this study. The critical e f f e c tnoted f«sr vanadium puntoxide exposure at s imilar dose levels was adecrease in cystine content in hair (EPA 1 9 9 1 ) .

ccrv\Co

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5 . 0 R I S K C H A R A C T E R I Z A T I O N

The f i n a l s t e p in the ba s e l ine risk assessment proces s is riskcharacterization. In this section, tox i c i ty criteria i d e n t i f i e din S e c t i o n 4 are combined with exposure estimates presented inS e c t i o n 3 to q u a n t i f y p o t e n t i a l noncarcinogenic and carcinogenice f f e c t s as sociated with inge s t i on o f groundwater f r o m t h e M o s l e yRoad S a n i t a r y L a n d f i l l . Sec t i on 5.1 presents an overview of themethods for q u a n t i f y i n g po t en t ia l carcinogenic andnoncarc inogenic risks. P o t e n t i a l risks associated with inge s t i ono f groundwater f r o m t h e A l l u v i a l A q u i f e r a n d G a r b e r - W e l l i n g t o nA q u i f e r are presented in Sec t i on s 5.2 and 5.3, r e sp e c t i v e ly .

It should be r e cognized when .reviewing the r e s u l t s p r e s e n t e d int h i s s e c t ion that groundwater in th i s area is current ly not beingused as a source of drinking water. In a d d i t i o n , it is h i g h l yu n l i k e l y that groundwater within the perimeter of the M o s l e y RoadS a n i t a r y L a n d f i l l w i l l be used in the f u t u r e as a d r i n k i n g waterresource. T h e r e f o r e , t h i s a n a l y s i s should be i n t e r p r e t e d o n l y asan evaluat ion of groundwater qua l i ty at the site for determiningwhether remediation of the site is even necessary.

5.1 M e t h o d s for _E.s tima t i ncr Carc inoggni ,g a|K| N o j i c a r c j j i o g e n i c

COOCTinco

P o t e n t i a l carc inogenic ri sks are expres s ed as an increasedp r o b a b i l i t y o f d e v e l o p i n g cancer over a l i f e t i m e ( i . e . , excessind iv idua l l i f e t i m e cancer r i s k ) (EPA 1 9 8 9 ) . For e x a m p l e , a10'6 increased cancer risk can be in t erpre t ed as an increasedrisk of 1 in 1,000,000 for d e v e l o p i n g cancer over a l i f e t i m e ifan ind iv idua l is exposed as d e f i n e d by the pathways pre s ented inthis report. A 10*6 increased cancer risk is the point ofdeparture established in the HCP (EPA 1990). Xn add i t i on , the

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NCP ( E P A 1 9 9 0 ) s ta t e s that " f o r known or su spec t ed carcinogens,acc ep tab l e exposure level s are g enera l ly concentration l eve l sthat represent an excess per bound l i f e t i m e cancer risk to ani n d i v i d u a l o f between 10"4 and 10"6.11 In f a c t , v i r t u a l l y al lARARs ( e . g . , vinyl c h l o r i d e ) are based on po t en t ia l carcinogenicrisks that are within this range. It should also be noted thatmany CRQLs for chemicals of concern are within or even exceedth i s risk range. For e x a m p l e , the CRQL for vinyl c h l o r i d e ingroundwater corresponds to a carcinogenic risk o f 7xlO' 4 .

C a r c i n o g e n i c risks for chemica l s o f concern are q u a n t i f i e d usingthe equation below:

OaIAOc

Cancer Risk, CDI± * SFi

where:

Cancer R i s k j = The p o t e n t i a l carcinogenic risks a s so c ia t ed withexposure to chemical, ( u n i t l e s s ) ;

GDI ~ Chronic d a i l y intake f o r c h e m i c a l j ( m g / k g / d a y ) ; andS F « S l o p e F a c t o r f o r c h e m i c a l f ( m g / k g / d a y ) " 1 .

C h e m i c a l - s p e c i f i c cancer risks are summed in accordance with EPA( 1 9 8 9 , I 9 8 6 a , b ) guidance in order to q u a n t i f y the combined cancerri sk a s s o c ia t ed wi th exposure to a chemical mixture.

As discussed in S e c t i o n 4, the s l o p e f a c t o r is the 95 th UCL onthe l inear s l o p e that describes the cancer po t en cy of thechemical of concern. U s i n g th§ 9 5 t h UCL on the linear s l o p e is aconservative approach adopted by the EPA in ordar that the truerisks wi l l not be undere s t imated . T h u s , the "true carcinogenicrisk 1 1 may be several orders of magni tude le s s than the

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carcinogenic risks pre sented in this r epor t , given theconservative approaches used to derive s l o p e f a c t o r s .

Noncarcinogenic e f f e c t s are not q u a n t i f i e d as a p r o b a b i l i t y ofexh ib i t ing a p a r t i c u l a r e f f e c t . Rather, noncarcinogenic e f f e c t sare evaluated by comparing the est imated dose ( i . e . , CDI) with are f erence dose (RfD) . The hazard quotient is used to q u a n t i f ythe p o t e n t i a l for an adverse noncarcinogenic e f f e c t to occur andis ca l cu la t ed using the f o l l o w i n g equation;

C D J y

Ov~crineo

where :

HQ - H a z a r d quotient ( u n i t l e s s ) ;GDI,- - Chronic D a i l y Intake ( m g / k g / d a y ) ; and

« R e f e r e n c e Dose ( m g / k g / d a y ) ,

If th e hazard quotient exceeds uni ty ( i . e . , i) , then an adversehea l th e f f e c t may occur. The higher the hazard quotient the morel i k e l y that an adverse noncarcinogenic e f f e c t w i l l occur as aresult o f expo sure to the chemical o f concern. If the e s t imatedhazard quotient is lass than unity, then adverse noncarcinogenice f f e c t s are u n l i k e l y to occur.

E P A ( 1 9 8 9 , I 9 8 6 b ) recommends summing c h e m i c a l - s p e c i f i c hazardquotients to evaluate the combined noncarcinogenic risk f r o mexposure to a chemical mixture. The sum of the c h e m i c a l - s p e c i f i chazard quo t i en t s i s c a l l e d the hazard ind$x. U s i n g thi s a p p r o a c hassumes that c h e m i c a l - s p e c i f i c noncarcinogenic risks ar©

T . E T H A T E C H


addi t iv e . Limited data are avai lable for a c t u a l l y q u a n t i f y i n gt h e p o t e n t i a l s y n e r g i s t i c a n d / o r a n t a g o n i s t i c r e l a t i o n s h i p sbetween chemica l s in a chemical mixture. In a d d i t i o n , it isassumed that the target organisms and t o x i c o l o g i c a l mechanismsthat may result in the e f f e c t are the same for all chemicalsevaluated in the chemical mixture. If the l a t t e r a s s u m p t i o n i snot v a l i d , then hazard indices should be c a l c u l a t e d by targetorgan and mechanism, as recommended by EPA ( 1 9 8 9 ) guidance . Inthis assessment, none of the chemicals of concern have the sametarget organ for dose l e v e l s evaluated in th i s report .T h e r e f o r e , hazard indi c e s were not c a l c u l a t e d for exposure tononcarcinogenic chemical s of concern present in the A l l u v i a lA q u i f e r a n d G a r b e r - W e l l i n g t o n A q u i f e r .

Carc inogen i c risks and hazard quo t i en t s were e s t imat ed forch emi ca l s of concern in the A l l u v i a l A q u i f e r and Garber*-W e l l i n g t o n A q u i f e r for two cases: a RME case and maximum case.Risk e s t imates presented for the RME case represent reasonablemaximum risks ( i . e . , t h e a p p r o x i m a t e 9 5 t h p e r c e n t i l e o f p o s s i b l er i sk e s t i m a t e s ) as soc iated wi th the entire s t u d y area. Riske s t i m a t e s p r e s e n t e d f or th e maximum case represent p l a u s i b l emaximum risks associated with exposure to an i so la t ed "hot spot"at the s i t e and; t h e r e f o r e , represent an per-bound est imate ofrisk. Both exposure cases were evaluated in order to addre s s twoa p p r o a c h e s th e EPA i s c on s id e r ing f or q u a n t i f y i n g exposure f orthe groundwater ing e s t i on pa thway under f u t u r e land-usecondi t ions (di scus s ed f u r t h e r in Sec t i on 3 . 2 , 1 ) .

5 • 2 Alluv ia l , A q u i f e r

As discussed in Sect ions 2 and 3, f i v e chemicals were i d e n t i f i e das the p r i m a r y chemicals of concern for e v a l u a t i n g p o t e n t i a lcarcinogenic risks a s soc ia t ed with inge s t ion of groundwater f r o m

T E T R A T E C H

aLAO

F e b r u a r y DRAFT REPORT 61

the A l l u v i a l A q u i f e r inc luding: benzene, b i s(2~e t h y I h e x y 1 ) p h t h a l a t e , 1 ,2-d i ch loropropane , t e trachioroe thene, andvinyl c h l o r i d e . T h e s e chemical s were s e l e c t ed f or eva lua t i onbecause they contributed to over 99 percent of the t o t a lcarcinogenic risk associated with ingestion of groundwater fromthe A l l u v i a l A q u i f e r . Pot en t ia l carcinogenic risks associatedwith inge s t i on o f groundwater f r o m t h e A l l u v i a l A q u i f e r f o r boththe RME and maximum exposure cases are pre sented in T a b l e 13. Asshown in T a b l e 13, increased cancer risks associated withexposure to benzene, b i s ( 2 - e t h y l h e x y 1 ) p h t h a l a t e , 1,2-d i c h l o r o p r o p a n e , and t e t rach ioroe thene were below the p o i n t ofd e p a r t u r e ( i . e . , 1 0 ' 6 ) f o r both t h e R M E a n d maximum expo surecases. T h e r e f o r e , exposure to these chemicals does not presenta p p r e c i a b l e risk to p u b l i c heal th . N o n e of these chemical s wered e t e c t e d in o f f - s i t e m o n i t o r i n g w e l l s wi th th e e x c e p t i o n o fb i s ( 2 ~ e t h y l h e x y l ) p h t h a i a t e . P o t e n t i a l carcinogenic risksassociated with exposure to vinyl ch lor ide were 7xlO' 5 and ixiO* 4

for the RME case and maximum case ( i . e . , for the worst grids q u a r e ) , r e s p e c t i v e l y . A p p r o x i m a t e l y , 97 percent o f th e t o t a lcarcinogenic risks for the RME case ( 7 x l O " s ) and maximum case( i x l O " 4 ) was a t t r ibu t ed to p o t e n t i a l exposure to vinyl ch lor ide .P o t e n t i a l carcinogenic risk associated with exposure to vinylc h l o r i d e and the e s t imat ed t o ta l carcinogenic risk were w i t h i nthe a c c e p t a b l e risk range e s t a b l i s h e d by the NGP ( 1 9 9 0 ) .

A risk contour p l o t was derived in order to evaluate the s p a t i a ld i s t r i b u t i o n o f p o t e n t i a l carcinogenic risks a s soc ia t ed withinge s t ion of groundwater f rom the A l l u v i a l A q u i f e r . A riskcontour p l o t was derived by p e r f o r m i n g the f o l l o w i n g analyses.

n EPCs were e s t imated for each chemical of concern and gridsquare using kriging (discussed in Sec t i on 3).

Co?-GITCC

T E T R A T E C H

T a b l e 1 3P o t e n t i a l C a r c i n o g e n i c R i s k s A s s o c i a t e d w i t h I n g e s t i o n o fG r o u n d w a t e r f r o m t h e A l l u v i a l A q u i f e r b y H y p o t h e t i c a lR e s i d e n t s f o r t h e R M E a n d M a x i m u m C a s e s

C a s e / C h e m i c a i

a_se :

D i s ( 2 - £ t h y l h e x y ! ) p h t h a l a t e1 , 2 - D i c h l o r o o r o o a n eT e t r a c n i o r o e t h e n e; ; " y 1 C n 1 o r i de

S e n z e n et m U - t t h y l h e x y l J p h t n a l a t e1 . 2 - D i c h l o ^ o o r o o a n eT e t r a c n l o r o e t h e n eV i n y l C h l o r i d e

C h r o n i cD a i 1 y I n t a k e( m g / k g / d a y )

1 .3E-054 . / E - G 53.0E-061 . I E - 0 5

1 . 7 E - 0 56 . S E - 0 5L 3 E - 0 61 . I E - 0 55 . 5 E - 0 5

S l o p eF a c t o r

( m g / k g / d a y ) -1

2.3E-02I - 4 C - 0 26.8E-025 . I t - 0 21.9E+00

W e i g h t -o f - E v i a e n c e

AB28262AT o t a ! C a r i r t o g e m c R ; s k .

2 . 9 E - Q 21.4E-026.8E-0^5 . I E - 0 21.9E+00

A82B282A

P o t e n t i al anc er

7E-05

ince

T o t a l C a r c i n o g e n i c R i s k s ; I E - 0 4


B GDIs were derived for each chemical of concern and gridsquare by m u l t i p l y i n g the EPC wi th in each grid by the 9 5 t hperc en t i l e of po s s i b l e water-intake values derived usingMonte C a r l o s i m u l a t i o n (see S e c t i o n 3 .3 f o r f u r t h e rdi s cu s s i on on the derivation of exposure e s t ima t e s) .

• chemical and g r i d - s p e c i f i c risk e s t imates were c a l c u l a t e d bym u l t i p l y i n g G D I s for each chemical of concern within eachgrid square by the c h e m i c a l - s p e c i f i c s l o p e f a c t o r ,

• Chemical and g r i d - s p e c i f i c risk e s t imate s were then summedto c a l c u l a t e the t o ta l p o t e n t i a l carcinogenic riskassociated with inge s t ing groundwater f r o m each grid square.

s The to ta l carcinogenic risk estimates for the si te weredrawn by contouring s o f t w a r e (SURFER Vers ion 4 . 0 ) .

The risk contour p l o t for carcinogenic risks associated withi n g e s t i o n o f groundwater f r o m th e A l l u v i a l A q u i f e r i s p r e s e n t e din F i g u r e 2. As shown in F i g u r e 2, the t o ta l p o t e n t i a lcarc inogenic risks as sociated with inge s t i on of groundwater f r o many l o c a t i o n are all w i t h i n the a c c e p t a b l e risk range of10"6 to 10"4. The highest p o t e n t i a l carcinogenic risk est imatedwas I x l O " 4 . The s m a l l i s o l a t e d 10"4 cancer risk p l u m e i s l o ca t edwithin the boundary of the site in the northern por t ion of theM o s l a y Road S a n i t a r y L a n d f i l l . It should be noted that vinylc h l o r i d e , which contributed to the m a j o r i t y o f the e s t i m a t e drisks, was not detec ted in any o f f - s i t s monitoring w e l l s , Th©m a j o r i t y o f the p o t e n t i a l carcinogenic risks associated withingestion of groundwater in o f f - s i t e locations is an a r t i f a c tat t r i bu tab l e to assuming that vinyl chloride was present in o f f -s i te groundwater at a doncantrat ion of 1 u g / L . However, the only

ainco

T E T R A T E G H

F i g u r e 2C o n t o u r P l o t o f P o t e n t i a l C a r c i n g e n i c R i s k s A s s o c i a t e d w i t hI n g e s t i o n o f G r o u n d w a t e r f r o m t h e A l l u v i a ] A q u i f e r

M

2174000185000 2175000 2176000

184000

183000

2177000185000

S I T E B O U N D A R Y\ I

184000

182000 I2174000

183000

2177000182000

inf-aIAcc


chemical o f concern a c t u a l l y d e t e c t e d in o f f - s i t e moni tor ingw e l l s was b i s ( 2 - e t h y l h e x y l ) p h t h a l a t e .»

As d i s cu s s ed in S e c t i o n 3, f o u r chemicals of concern de t e c t ed inthe A l l u v i a l A q u i f e r were evaluated for noncarcinogenic e f f e c t s ,inc luding: arsenic, barium, 2-ch loropheno l , and manganese. Asdi s cu s s ed in S e c t i o n 2, these chemicals were s e l e c t ed aschemicals of concern for f u r t h e r evaluation because theycontributed to 94 percent of the total noncarcinogenic risk.P o t e n t i a l noncarcinogenic risks r s sociated with i n g e s t i o n ofgroundwater f r o m the A l l u v i a l A q u i f e r for both the RME andmaximum exposure cases are presented in T a b l e 14. All of thechemica l s pre s ent ed in T a b l e 14 had hazard quo t i en t s be low u n i t y ,T h e r e f o r e , adverse noncarcinogenic e f f e c t s are u n l i k e l y to occurf r o m use of groundwater f r o m the A l l u v i a l A q u i f e r . As shown inT a b l e 14, the target organs for each of these chemica l s ared i f f e r e n t at the concentrations reported f r o m the s i tegroundwater monitoring well data. T h e r e f o r e , in accordance withEPA ( 1 9 8 9 ) gu idance , it would be i n a p p r o p r i a t e to sum the hazardquot i ent s to e s t imate a hazard index.

5.3 Garber - W e l l i n g t o n . Aqul£erAs di scussed in S e c t i o n 3, benzene was the only p o t e n t i a l humancarcinogen de t e c t ed in t h e G a r b s r H t f e l l i n g t o n A q u i f e r . P o t e n t i a lcarcinogenic risks associated with inge s t i on of groundwater f r o mthe G a r b e r - W e l l i n g t o n A q u i f e r for both the RJME and maximumexpo sure cases ar& pr e s en t ed in T a b l e IS. As shown in T a b l e 15 ,the increased cancer risks associated with exposure to banzanawere 6x lO' 7 and 7X10' 7 f or the RME case and maximum ca s&,r e s p e c t i v e l y . T h u s , the estimated increased carcinogenic riskafor these cases were below the point of departure ( i , © . , 10" 6).

T E T R A T E C H

T a b l e 1 4P o t e n t i a l K o n c a r c i n o g e n i c R i s k s A s s o c i a t e d w i t h I n g e s t i o n o fG r o u n d w a t e r f r o m t h e A l l u v i a l A q u i f e r b y H y p o t h e t i c a l R e s i d e n t s f o r t h e R M E a n d M a x i m u m C a s e

C a s e / C h e m i c a l

RME Case:A r s e n i cB a r i u f n2 - C h J o r o p h e n a iManganese

K a x i w u m Case:A r s e n i cBarium2 - C h I o r o p f t s n o HManganese

C h r o r f i cD a t t y I n t a k e

( m g / k g / d d y ) .

4 . Q E - 0 43 . 2 E - Q 21 . I E - 0 41.3E-02

8 6E-043.6E-02

3 - Q E - O Z

R f 3£ m g / k g / d a y )

I E - 0 57E-025E-03I E - 0 1

I E - 0 3Z t - 0 25E-03U - O I

R f OU n c e r t a i n t yT s r g s t O r g a n F a c t o r

s k i n ( k e r a t o s i s a n d h y p e r p i g m e n t a t i o n ) Ic a r d i o v a s c u l a r S y s t e m (increased 3b l ood p r e s s u r e )r e p r o d u c t i v e E o x i c u y iOOOC N S i

s k i f l ' ( k e r a t o s i * « n d h y p e r p i g m e n t a t i u n ) 1c a r d i o v a s c u b r S y s t e a t ( incr ea s ed 3b l ood p r e s s u r e )reproduc t ive t o x t c i t y J O O OC M S i

H a z a r dQ u o t i e n t

4E-015E-012 E - ( »

96-015E-01

4E-01

C M S - C e n t r a l Mervoos iyatemw • , - -x--

0 0 5 * 5 1 7

T a b l e 1 5P o t e n t i a l C a r c i n o g e n i c R i s k s A s s o c i a t e d w i t h I n g e s t i o n o fG r o u n d w a t e r f r o m t h e G a r b e r - W e l l i n g t o n A q u i f e r b y H y p o t h e t i c a lR e s i d e n t s f o r t h e R H £ a n d M a x i m u m C a s e s

.-.ran ic

2 - K - 0 5

: 3 E - O S

S l o o aractor -1

2.9E-02

W « i g n t - P o t e n t 1 4 )e f - £ v 1 d a n c e Cancer

ee-o;

7E-07

ocT-aIAoo


T h e r e f o r e , exposure to benzene doss not present an a p p r e c i a b l erisk to p u b l i c h e a l t h .

As discussed in Sec t i on 3, f our chemicals of concern detected inthe G a r b e r - W e l l i n g t o n A q u i f e r ware evaluated for noncarcinogenice f f e c t s , in c lud ing: arsenic, barium, manganese, and vanadium.As discussed in S e c t i o n 2, these chemicals were s e l e c t ed aschemicals o f concern for f u r t h e r evaluat ion because theycontr ibuted to 96 percent of the t o ta l noncarcinogenic risk.P o t e n t i a l noncarcinogenic risks as soc iated with inge s t i on ofgroundwater f r o m the A l l u v i a l A q u i f e r for both the RME andmaximum exposure cases are presented in T a b l e 16* All of thechemicals presented in T a b l e 16 had hazard quotients well balowunity. T h e r e f o r e , adverse noncarcinogenic e f f e c t s a r e u n l i k e l yto occur f r o m inge s t i on of groundwater f r o m the G a r b e r - W e l l i n g t o nA q u i f e r . As shown in T a b l e 16, the target organs for each ofthese chemica l s are d i f f e r e n t at their re spec t ive chemicalconcen tra t i on s reported f r o m the s i te groundwater moni t or ing we l ld a t a ; t h e r e f o r e , it would be i n a p p r o p r i a t e to sum the hazardquot ient s to e s t imate a hazard index.

orIAOO

T E T R A T E C H

T a b l e 1 6P o t e n t i a l N o n c a r c i n o g e n i c R i s k s A s s o c i a t e d w i t h I n g e s t i o n o fG r o t m d w a t e r f r o m t h e G a r b e r - W e 1 1 i n g t e r n A q u i f e r b y H y p o t h e t i c a l R e s i d e n t s f o r t h e R M E a n d M a x i m u m C a s e s

C a s e / C h e m i c a lC h r o n i cD a i l y I n t a k e R f O( m g / k g / d a y ) ( r o g / k g / ^ y ) T a r g e t Organ

R f OU n c e r t a i n t y H a z a r dF a c t o r Q u o t i e n tRM£ Case:

ArsenicBariumManganeseV a n a d i u m

3.45-03S . 4 E - Q 28.0E-94

l i - O J7 E - G 2I E - 0 17E-03

skin ( f c e r a t o s i s and h y p e r p i g ( H e n t d t i a . o )C d r d i a v a s c u J a r sys tem ( i n c r e a s e db l o o d p r e s s u r e )C M SH o n e observed

131

I QO

?F-01S E - C t fI E - 0 1I E - 0 1

Max iguaaA r s e n i cBariumManganese

CHS = C e n t r a l Stepvou s S y s t e m

2 . 4 E -

1 .36-028.0E-04

!£-037 E - Q 2I E - 0 17E-03

s k i n f f c e r a t o s i s a n dc a r d i o v a s c u l a r s y s t e m { i n c r e a s e db lood pr e s s ur e !C H SN o n e observed

13I100

2 C - O I5E.-02I E - 0 1I E - 0 1

0 0 5 ^ 2 0


6 . 0 U N C E R T A I N T I E S I N T H E R I S K A S S E S S M E N T P R O C E S S

T h i s section out l ine s the uncertaint i e s associated with the re sul t so f th e M o s l e y Road S a n i t a r y L a n d f i l l PBRA. The pr imary areas o funcertainty include: 1) environmental s ampl ing and analy s i s ; 2)e s t imat ion of exposure; and 3) t o x i c i ty assessment. An overview ofthe pr imary areas of uncer ta in ty in the q u a n t i t a t i v e riskassessment is presented in T a b l e 17 and are discussed below,

6.1 Environmental . S a m p l i n g _and A n a l y s i s

As d i s cu s s ed in S e c t i o n 2, two rounds of s a m p l i n g r e s u l t s v/erec o l l e c t e d f r o m 14 moni tor ing well (12 on-sit© and downgradientw e l l s and 2 upgradi ent w e l l s ) i n s t a l l e d in the A l l u v i a l A q u i f e r and8 moni t or ing w e l l s (6 on-site and downgradient w e l l s and 2u p g r a d i e n t w e l l s ) were i n s t a l l e d in the d e ep er Garber W e l l i n g t o nA q u i f e r . S a m p l i n g re su l t s f r o m these w e l l s were assumed tocharac t er ize the extent of groundwater contaminat ion in the twoa q u i f e r systems. The degree to which the RI d a t a charac t er iz e ssite contamination is unknown. Two s a m p l i n g rounds were analyzedand used in this assessment to reduce some of the v a r i a b i l i t yas s o c ia t ed with s a m p l e c o l l e c t i o n me thod s and time v a r i a b i l i t y . Asp r e v i o u s l y d i s cu s s ed , RI ac t iv i ty at the site did not use a randoms a m p l i n g d e s i g n f o r groundwater moni tor ing w e l l s l o ca t i on s .Rather , a p u r p o s i v e s a m p l i n g technique is used that f o c u s e ss a m p l i n g intensi ty near suspected source areas. T h u s , themoni tor ing da ta p r o b a b l y characterizes the u p p e r d i s t r i b u t i o n o fchemical concentrat ions at the site.

CMCIP.OC

Another area of uncertainty concerns the treatment of noconcentrations in the quan t i ta t iv e assessment of risk. For moatchemicals of concern, one-half of the CRQL was used as thed e t e c t i o n l imi t . The actual concentration of the chemical may be

T E T R A T E C H

T a b l e 1 7U n c e r t a i n t i e s A s s o c i a t e d w i t h t h e M o s l e y Road S a n i t a r yL a n d f i l l P B R A

E f f e c t o n E s t i m a t e d R i s k U )

Source cfU n c e r t a i n t y

S a m p l i n g a n d ^ A n a l y s i sA v a i l a b l e s a m p l i n g d a t a used t oc h a r a c t e r i z e th e e x t e n t o fc o n t a m i n a t i o n at the s i t eI n o r g a n i c s ( i . e . , a r s e n i c ,S a r i u m . raanganese . a n d v a n a d i u m )were assumed to be e l eva t edabove b a c k g r o u n d

a n d / o r random errorsin a n a l y s i s -ma r e p o r t i n g

Expo sure saramater d i s t r i b u t i o ns t a t i s t i c s were assumed to oec h a r a c t e r i s t i c o f t h e p o t e n t i a l l ye x p o s e d c o p u l a t i o nThe amount of med ia i n t a k e i sas sumed to be c o n s t a n t andr e p r e s e n t a t i v e o f t h e e x p o s e d

icn

P o t e n t i a lf o rOver*E s t i m a t i o n

o f R i s k

P o t e n t i a lf o rUnder-E s t i m a t i o no f R i s k

P o t e n t i a l f o rOver or U n d e r -E s t i m a t i o n

o f R i s k

LowOJCV.Ctr

M o d e r a t e

LOW

Low

M o d e r a t e

o n o f h y p o t h e t i c a ls a i l y l i f e t i m e e x p o s u r e f o r- e s i d e n t s

M o d e r a t et o H i g h

A r e a ' . i c t a n l e m a x i m u m e x p o s e d: n d i v d . , a l «ul be e x p o s e d tothe maxi.man c o n c e n t r a t i o n att n e S ' t e over t ^ e d u r a t i o no f t h e e xpo sur e p e r i o d"ax_i c }_tyA n a d d i t i v e mode l i s used t oe v a l u a t e - - i s k f r o m a c h e m i c a l- i x t u r e

M o d e r a t et o H i g h

M o d e r a t e

y c r i t e r i a n o t a v a i l a b l ef o r c e r t a i n c h e m i c a l s o f p o t e n t i a l Low

C o n s a r v a t f y c m e t h o d s used t od er iva t o x r c i t y c r i t e r i a( p a r t i c u l a r l y s l o p e f a c t o r sCsee t e x t ] )

H e d a r a t at o h i g h

( a ) A s a g e n e r a l g u i d e l i n e , a s s u m p t i o n s marker) a s " low," m a y a f f e c t e s t i m a t e s o f e x p o s u r e b y l e s s than o n e orderof m a g n i t u f l e ; a s s u m p t i o n s marked "moderate" may a f f e c t e s t imat e s of exposure By between one and two orders ofi t t a g r n t u d e ; and a s s u m p t i o n s marked "high" may a f f e c t e s t i m a t e s of e xpo sur e by more than two orders of magni tud e .


zero to j u s t below the CRQL and p erhap s zero. In all p r o b a b i l i t y ,the actual concentration may be below one-hal f the CRQL given thatthe instrument de t e c t i on limit (IDL) is o f t e n much lower than one**h a l f the CRQL- In f a c t , vinyl ch lor ide , l , 2 ~ d i c h l o r o p r o p a n e , andbenzene were detec ted at concentrations of 1 u g / L which is wellbelow one-half the CRQL for these chemicals. For these chemical s ,the lowest detected concentration was used as the concentration fornon-detect s a m p l e s when e v a l u a t i n g the s p a t i a l d i s t r i bu t i on of thechemical. The methods used to evaluate non-detects in thisasses sment p r o b a b l y does not contribute s i g n i f i c a n t l y to theoverall uncertainty of the re sul t s ( p r o b a b l y less than a f a c t o r of2 ) .

In th i s a s s e s sment, several inorganic chemica l s of concern wereselected for evaluation in the quanti tat ive risk assessmenti n c l u d i n g : arsenic, barium, manganese, and vanadium. For thisasses sment, it was assumed that these chemicals were elevated abovebackground concentrations (based on the result s presented in the RIba s e l in e risk a s s e s s m e n t ) . H o w e v e r , not enough s a m p l e s ( l e s s thanthree s a m p l e s ) were ava i lab l e for p e r f o r m i n g a c o m p l e t e s t a t i s t i c a la n a l y s i s for d e t e rmin ing whether these inorganic chemical s weres i g n i f i c a n t l y elevated above background concentrations. The riskspr e s en t ed in thi s report would be overes t imated if any or all ofthe inorganic chemicals are a t t r ibu tab l e to background l ev e l s .

Another p o t e n t i a l source of uncertainty involves the analyt i ca lme thod s and used to q u a n t i f y the l e v e l s of ch emica l s of concern ingroundwater sample s c o l l e c t ed for the M o s l e y Road S a n i t a r yL a n d f i l l . T h e r e i s a certain degree of var iab i l i ty as soc iated withthe laboratory instruments ab i l i ty to q u a n t i f y the I f c v a l s of achemical in a sample . T h i s var iab i l i ty tends to be normallyd i s t r i bu t ed . The po t en t i a l contribution of this source of

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uncertainty, however, IB considered to be low given QA/QCrequirements for s a m p l e s and analys i s*

6.2 E s t i m a t i o n _o£ Exposure

The most commonly a p p l i e d method f o r e s t i m a t i n g exposure ( i . e . ,chronic d a i l y intake s) involves combining point estimates fromexposure parameter d i s t r i b u t i o n s using a s i m p l e chemical intakeequation (presented in Sec t i on 3 . 3 ) . As noted in S e c t i o n 3.3.1,there are several a n a l y t i c a l d e f i c i e n c i e s as soc iated with th i smethod that introduce a great deal of uncertainty into the resul t s .A M o n t e C a r l o s i m u l a t i o n was p e r f o r m e d to reduce the level ofuncertainty associated with the es t imation of exposure. The f i r s ts t e p in c o n d u c t i n g a M o n t e carlo s i m u l a t i o n involves charac t e r i z ingeach of the exposure parameter d i s t r ibu t ions . The EPA derivedexposure parameter d i s t r i b u t i o n s t a t i s t i c s were assumed tocharacterize the p o t e n t i a l l y exposed p o p u l a t i o n . To beconservative, the 95th p e r c e n t i l e of the exposure d i s t r i b u t i o n wasused to characterise the RME case. The degree of uncertaintyassoc iated with this ana ly s i s is assumed to be low.

For thi s a s s e s sment , it is assumed that a reasonable maximumexposed indiv idual would ingest the highest l eve l s currentlyde t e c t ed at the s i t e over the entire durat ion of the exposureperiod ( i . e . , close to a l i f e t i m e ) . Thes e are extremelyconservative as sumpt ions that may result in overe s t imate s ofp o t e n t i a l exposure and risk f rom one to two orders of magnitude.It is suspected that the concentrations of certain chemical s ofconcern would s t e a d i l y decrease overtime ( i . e . , 70 year p e r i o d ) dueto the reduction in release f r o m th® source, d i lu t i on andd i s p e r s i o n of concentrat ions f o u n d in groundwater, and p o s s i b l echemical degradat ion. T h e r e f o r e , it is conservative to assume thatan I n d i v i d u a l would be exposed to currently d e t e c t ed concentrations

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over the durat ion of the exposure per iod . In a d d i t i o n , it isd o u b t f u l that the groundwater inge s t i on exposure pa thway would evenoccur since residential development of the Mos l ey Road Sani taryL a n d f i l l i s h i g h l y u n l i k e l y .6 - 3 T o x i c i t v Assessment

EPA ( I 9 8 9 a , I 9 8 6 a , b ) recommends summing c h e m i c a l - s p e c i f i c risks inorder to q u a n t i f y the combined risk as soc iated with exposure to achemical mixture. Limited data are avai lable for a c t u a l l yq u a n t i f y i n g t h e p o t e n t i a l synerg i s t i c a n d / o r an tagon i s t i cr e l a t i o n s h i p s between chemical s in a chemical mixture. T h u s ,chemicals are assumed to act i n d e p e n d e n t l y in the body to causes ane f f e c t . In this a s s e s sment/ p o t e n t i a l carcinogenic risks weresummed for the chemical mixture. For e v a l u a t i n g p o t e n t i a lnoncarcinogenic e f f e c t s , none of the chemicals of concern have thesame target organ for dose l eve l s evaluated in this report.T h e r e f o r e , hazard indice s were not c a l c u l a t e d for exposure tononcarcinogenic chemicals of concern pre s ent in the A l l u v i a lA q u i f e r and G a r b e r - W e l l i n g t o n A q u i f e r . If these a s sumpt ions ar eincorrect r e g a r d i n g chemical in t erac t i on , then over- oru n d e r e s t i m a t i o n of p o t e n t i a l risk of the chemical mixture mayoccur.

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S e v e r a l chemical s o f p o t e n t i a l concern, pr e s en t ed in S e c t i o n 2, didnot have ava i lab l e f c o x i c i t y criteria. T h e r e f o r e , the p o t e n t i a lnoncarcinogenic and carcinogenic risks associated with ingest ion ofgroundwater may be u n d e r e s t i m a t e d . However , the chemical s ofprimary concern at tha Mosl ey Road Sani tary L a n d f i l l have avai lablet ox i c i ty criteria. T h e r e f o r e , the uncertainty associated with f ch ialack of t o x i c i t y criteria for othar chemicals of p o t e n t i a l concernis considered low.

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T h e r e is a high degree of uncer tainty associated with thed e r i v a t i o n o f a v a i l a b l e t o x i c i t y criteria. The pr imary sources o funcertainty associated with the derivation of t o x i c i ty criteria, assummarized by the EPA ( 1 9 8 9 a ) , include:

• using dose-response i n f o r m a t i o n f r o m e f f e c t s observed at highdoses to predic t the adverse health e f f e c t s that may occurf o l l o w i n g exposure to the low l eve l s expec t ed f r o m humancontact with the agent in the environment;

a using do s e-re sponse i n f o r m a t i o n f r o m short-term exposures t u d i e s to p r e d i c t the e f f e c t s o f long-term expo sur e s , andvice-versa;

vOCMCI T ,CC

i i u s ing do s e-r e spons e i n f o r m a t i o n f r o m animal s t ud i e s to p r e d i c te f f e c t s in humans; and

& using do s e-re sponse i n f o r m a t i o n f r o m homogeneous animalp o p u l a t i o n s or h e a l t h y human p o p u l a t i o n s to p r e d i c t thee f f e c t s l i k e l y to be observed in the general p o p u l a t i o nc o n s i s t i n g of i n d i v i d u a l s with a wide range of s en s i t i v i ty .

EPA ( I 9 8 9 a , b , c , I 9 8 6 a , b ) uses a conservative approach to derivet o x i c i t y cri teria given the uncer ta int i e s in the t o x i c i t y s tud i e sand do s e-re spons e i n f o r m a t i o n . For e x a m p l e , the s l o p e f a c t o r i sthe 95 th UCL on the linear s l ope that describes the cancer potencyof the chemical of concern. Using the 95th UCL on the linear s l o p eis a conservative a p p r o a c h a d o p t e d by the EPA in order that thetrue risks w i l l not be underest imated. T h u s , the "truecarcinogenic risk" may be s&varal orders of magnitude less than thecarcinogenic risks presented in this r epor t , given the conservativeapproache s used to derive s l o p e f a c t o r s .

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A thorough assessment of the high degree of uncer ta inty associatedwith the d er iva t i on of s l o p e f a c t o r s was presented in an EPA ( 1 9 8 5 )document e n t i t l e d "Technique s for the Asse s sment of theCarcinogenic Risk to the U . S . P o p u l a t i o n Due to Exposure f romS e l e c t e d V o l a t i l e organic Compounds f rom Drinking Water Via theI n g e s t i o n , I n h a l a t i o n , and Dermal Routes." The sources ofuncertainty ( a d a p t e d f r o m T a b l e 13 of the document) are summarizedbelow:

Category1) Choi c e o f e n d p o i n t

2 ) Personnel c a p a b i l i t i e s

3 ) Choice o f s p e c i e s , s t ra in ,

4 ) T e s t compound p u r i t y( c o n t a m i n a t i o n , decay andvehicle c on t r i bu t i on)5 ) I n a p p r o p r i a t e s t a t i s t i c a ltest methodology

Contribution, t o _ U n c e r t a i n t yLess than 10% of the t imethe wrong endpoint iss e l e c t edMay over- or under e s t imat eriskMay over- or u n d e r e s t i m a t erisk age and sex of animalsMay overe s t imate risk

May over- or u n d e r e s t i m a t erisk

r-<N0ir>cc

6 ) D i s t r i b u t i o n o f an imal samong doses and number used

7) s e lec t ion of dose l eve l s

8) Lack pr e l iminary tumorchange i n f o r m a t i o n suchas h y p e r p l a s i a9 ) Exper imenta l Surroundings

May over- or u n d e r e s t i m a t erisk by one or two orderso f m a g n i t u d eMay over- or underestimaterisk by one or two orderso f m a g n i t u d eMay underestimate risk byles s than 10 percent for VOCs

May av&rest imata risk bysev@ralord©rs of magni tude

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F e b r u a ? / y DRAFT REPORT 77

10) Die tary cons iderat ions

11) Good Laboratory Procedures

1 2 ) Time- t o- tumor

1 3 ) M i c r o s c o p i c t i s sueexamination14) Disea s e in test animal s

1 5 ) S t a t i s t i c a l noise

16) Outcomes o f cancer (i fi n c l u d e n o n - f a t a l cancers)17) Conventional choice ofp l evel ( e . g . , 0 . 0 5 )1 8 ) s y n e r g i s m / A n t a g o n i s m

1 9 ) N o c o r r e s p o n d i n g t i s su ein humans20) Mos t s en s i t i v e vs . average

21) Anima.l to man

22} Body weight vs . body s u r f a c earea

May over- or underest imaterisk by a f a c t o r of twoMay underestimate risk byone to two orders ofm a g n i t u d eMay miss the e f f e c t orundere s t imate risk by af a c t o r of twoMay over- or undere s t imaterisk by a f a c t o r of twoMay over- or under e s t imat eriskMay over- or under e s t imat erisk by a f a c t o r of twoMay overestimate risk by twoor more orders of magnitudeMay over- or underestimateriskMay over- or underestimaterisk by several orders ofm a g n i t u d eMay over- or u n d e r e s t i m a t eriskMay over*- or u n d e r e s t i m a t erisk by several orders ofmagnitude

cc(Ncrinco

May over- or undere s t imaterisk by two orders ofm a g n i t u d eMay over- or under e s t ima t erisk by one order ofmagnitude


23) use of 9 5 t h UCL on s l o p e for May overe s t imate risk bv ander iv ing s l o p e f a c t o r order o f m a g n i t u d e V

2 4 ) Choi c e o f do s e-re sponsemodel May over- or under e s t imat eriek (in thi s case p r o b a b l yover e s t imat e given themode l s u s e d ) by 5 to 6orders of m a g n i t u d e whencons ider ing risk l e v e l s inthe 10"* to 10"6 cancer riskrangeThe ri^ks pr e s en t ed in the H o s l e y Road S a n i t a r y L a n d f i l l PBRAshould not be construed as a b s o l u t e e s t imate s of risk given theh igh degree o f unc er ta in ty a s s o c ia t ed with the risk assessmentproce s s as described above, Rather, the PBRA characterizes thep o t e n t i a l for an adverse e f f e c t to occur if an i n d i v i d u a l isexpo s ed to g i o u n d w a t e r at the s i t e in the f u t u r e . In g e n e r a l , the"true risks" as soc iated with use of groundwatar at the M o s l e y RoadS a n i t a r y L a n d f i l l a r e p r o b a b l y several orders o f m a g n i t u d e lowerthan the r e s u l t s p r e s e n t e d in th i s r e p o r t , given the p o t e n t i a l f oro v e r e s t i m a t i o n of risk d i s cu s s ed above.

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7 . 0 S U M M A R Y A N D C O N C L U S I O N S

T h i s section summarizes th e f i n d i n g s o f th e PBRA for the M o s l e yRoad S a n i t a r y L a n d f i l l S i t e . The PBRA est imated risks andexposure to chemical s of concern for the groundwater ingea t ionpathway using more r e f i n e d a n a l y t i c a l techniques such asg e o s t a t i a t i c s ( i . e . , k r i g i n g ) a n d s t o chas t i c m o d e l i n g ( i . e . ,M o n t a C a r l o s i m u l a t i o n ) . T h e groundwater inge s t i on exposurep a t h w a y was i d e n t i f i e d as the primary exposure pa thway of concernbased on the results of the RX baseline risk assessment.

Chemica l s of concern se lec ted for evaluation in the PBRA. arediscussed in Sec t i on 7.1. Exposure pathways of concern selectedfor quanti tat ive evaluation in the PBRA are discussed in Sec t i on7.2. Pot en t ia l carcinogenic and noncarcinogenie risks estimatedfor the pa thways q u a n t i t a t i v e l y evaluated in this report aresummarized below in S e c t i o n 7,3

7.1 Chemicalg_Q£_ Concern

C h e m i c a l s of p o t e n t i a l concern i d e n t i f i e d in the Rl ba s e l in e riskasses sment were evaluated in the PBRA. Of the twen ty-e igh tch emi ca l s of p o t e n t i a l concern s e l e c t ed in the SI b a s e l i n e riskasses sment f o r groundwa t e r , only those that s i g n i f i c a n t l ycontr ibuted tc carcinogenic and noncarcinogenic risk weres e l e c t ed f o r f u r t h e r eva lua t i on i n t h e P B R A . T h e s a c h e m i c & l sweze i d e n t i f i e d by c a l c u l a t i n g the percent c on tr i bu t i on of t o t a lcarcinogenic and noncarcinogenic risk using an a l g o r i t h mpre s en t ed in EPA ( I 9 8 9 a ) . The chemicals presented below in T a b l e18 s i g n i f i c a n t l y contributed to t o ta l carcinogenic andnoncarcinogenic risk and thus w&ra s e l e c t ed as chemicals ofconcern for f u r t h e r evaluat ion in the PBRA.

T E T R A T E C H

February 1991 DRAFT REPORT S O

T a b l e 18% Contr ibut ion of Risk

E f f e c t / C h a m i c a l A l l u v i a lA q u i f e r G a r b a r - W e l l i n g t o nA q u i f e rCarcinogenic E f f e c t s :1 ,2-Dich loropropane 0,4Banzena 0.2b i s ( 2 - E t h y l h e x y l ) p h t h a l a t a 0.7Tetrach l oro e th ene 0.2V i n y l C h l o r i d e 98Noncarc inogenic E f f e c t s :2 - C h l o r o p h e n o l 7A r s e n i c 44Barium 26Mangane s e 17V a n a d i u m

100

7.2 Exposure Asse s sment

7 , 2 . 1 Exposure Pathway S e l e c t i o n

The PBRA evaluated only those exposure pathways that may resultin a s i g n i f i c a n t human hea l th risk. Exposure to chemicals ofconcern via direct contact with sur fac e and sub sur face so i l s andinhala t i on of vapors were not considered compl e t e exposurepathways given the presence of the c lay cap, erosion-reducingvegetation covering the l a n d f i l l , and f e n c i n g around thef a c i l i t y . Use of groundwater and sur fac e water were the exposurepathways evaluated quant i ta t iv e ly in the RI baseline riskassessment. Exposure routes evaluated in the RX baseline riskassessment included ingestion, inhalat ion, and dermal contact.The ingestion exposure route accounted for 97 to nearly 100percent of the total carcinogenic and noncarcinogenic riaksestimated. In add i t i on , us© of surface water did not result inan appre c iab l e risk to human health. T h e r e f o r e , ingestion of

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groundwater f r o m t h e A l l u v i a l A q u i f e r a n d G a r b e r - W e l l i n g t o nA q u i f e r under f u t u r e land-use c o n d i t i o n s were the only exposurep a t h w a y s q u a n t i t a t i v e l y evaluat ed in the PBRA. T h e s e a q u i f e r s arecurrent ly used as a source of dr inking water.

7.2.2 Es t imat ing Exposure Point Concentrations ( E P C s )

Several l i m i t a t i o n s to the EPA ( 1 9 8 9 a ) recommended approach werei d e n t i f i e d and discussed in Sec t i on 3.2.1 and in Clement( 1 9 9 0 a , b ) . In this r epor t , g e o s t a t i s t i c s ( i . e . , k r i g i n g ) wereused to e s t imate EPCs for the groundwater ingest ion pathway inorder to addre s s some of the l i m i t a t i o n s with the EPA ( I 9 8 9 a )recommended a p p r o a c h . K r i g i n g is recommended in EPA ( 1 9 8 9 a )gu idanc e as ".. .another method that p o t e n t i a l l y can be used ( f o re s t i m a t i n g E P C s ) . " EPA ( 1 9 8 6 ) s o f t w a r e and gu idance were usedwhen p e r f o r m i n g k r i g i n g .

As d i s cu s s ed in d e t a i l in S e c t i o n 3 . 2 . 2 , k r i g i n g was used toc a l c u l a t e average c onc en t ra t i on s of ch emica l s of concern in eachgrid square over an evenly spaced grid for each a q u i f e r . Theaverage c onc en tra t i on for a grid square r e p r e s e n t s theconc en tra t i on of water that may be drawn f r o m a h y p o t h e t i c a l we l li n s t a l l e d in the center of the grid (g iv en that the p u m p i n gact ion of the we l l draws in water f r o m the v i c i n i t y of the w e l l ) .The kriged data for a l l the grid squares r e f l e c t s thed i s t r i b u t i o n of p o s s i b l e EPCs that may be contacted*

In thi s assessment, exposures and risks were estimated for twocases: the RME case and maximum case. The RME case r e f l e c t s thereasonable maximum exposure associated with the entire s tudyarea. The maximum case r e f l e c t s the p l a u s i b l e maximum exposureassociated with an isolated "hot spot" at the site. The 95th UCLon the arithmetic mean of all the kriged data was used as the EPC

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for the RME case. The maximum kriged da ta point for eachchemical of concern was used as the EPC for the maximum case.

7 . 2 . 3 E s t i m a t i n g Chronic D a i l y I n t a k e s ( C D I s )

As d i s cu s s ed in S e c t i o n 3 .3 .1 , commonly used me thod s fore s t i m a t i n g exposure (GDIs) may result in s i g n i f i c a n tovere s t imat ion of exposure and u l t i m a t e l y risk. In a d d i t i o n , thep r o b a b i l i t y of the e s t imated exposure occurring is not known andmay d i f f e r s i g n i f i c a n t l y f r o m chemical t o chemical and f r o m siteto s i te. Monte carlo s i m u l a t i o n was a p p l i e d to addre s s thel i m i t a t i o n s o f the commonly used methods for e s t i m a t i n g exposure .M o n t e C a r l o s imu la t i on is endorsed by EPA ( 1 9 8 9 a ) guidance as as u i t a b l e method for q u a n t i t a t i v e l y e v a l u a t i n g u n c e r t a i n t y inba s e l ine risk asse s sments . Exposure parameter d i s t r i b u t i o ns t a t i s t i c s derived f r o m E P A cited s tudie s ( I 9 8 9 a , b , 1 9 8 5 ) wereused to p e r f o r m the Monte C a r l o s i m u l a t i o n . In the computers i m u l a t i o n , 5,000 C D I s were ca l cu la t ed by randomly s e l e c t i n gvalues f r o m each o f th e exposure parameter d i s t r i b u t i o n s ( e . g . ,i n g e s t i o n rate, expo sure d u r a t i o n , expo sure f r e q u e n c y , and bodyw e i g h t ) * The 9 5 t h p e r c e n t i l e o f p o s s i b l e CDIs was used as theGDI for the RME case and maximum case,

7.3 Resul t s _of_. the H u m a n . . _ H e a I f e h _ J a i a k _ Characterization

T o x i c i t y cri teria i d e n t i f i e d in S e c t i o n 4 and C D I s e s t imated inS e c t i o n 3 were combined to q u a n t i f y p o t e n t i a l noncarcinogenic andcarcinogenic e f f e c t s a s soc iated with inge s t i on o f groundwaterf r o m th e M o s l e y Road S a n i t a r y L a n d f i l l under f u t u r e land«usecondit ions. The risk e s t imate s should be in t erpre t ed only as anevaluat ion of groundwater qua l i ty at the site for de t erminingwhether remediat ion of the site is even necessary as the

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groundwater is not curren t ly being used as a source of d r i n k i n gwater.

P o t e n t i a l carcinogenic risk as soc iated with a p a r t i c u l a r chemicalwas q u a n t i f i e d by m u l t i p l y i n g i t s GDI by it s s l o p e f a c t o r .C h e m i c a l - s p e c i f i c cancer risks were summed in order to q u a n t i f ythe t o t a l cancer risk as soc iated with exposure to a chemicalmixture. It should be noted that the "true carcinogenic risk"may be several orders of magni tude le s s than the carcinogenicrisks pr e s en t ed in thi s r e p o r t , given the conservative a p p r o a c h e sused to derive s l o p e f a c t o r s .

P o t e n t i a l carc inogenic risks are expres s ed as an increasedp r o b a b i l i t y o f d e v e l o p i n g cc-~cer over a l i f e t i m e ( i . e . , excessi n d i v i d u a l l i f e t i m e cancer r i s k ) ( E P A 1 9 8 9 a ) . F o r e x a m p l e , a10"6 increased cancer risk can be i n t e r p r e t e d as an increasedrisk of 1 in 1,000,000 for d e v e l o p i n g cancer over a l i f e t i m e ifan i n d i v i d u a l is e xpo s ed as d e f : ' n e d by the pa thways pr e s en t ed int h i s r e p o r t . A 10"6 increased cancer risk is the p o i n t ofd e p a r t u r e e s t a b l i s h e d i n t h e N C P ( E P A 1 9 9 0 ) . I n a d d i t i o n , t h eNCP (EPA 1 9 9 0 ) s t a t e s that " f o r known or s u sp e c t ed carc inogens ,a c c e p t a b l e e xpo sur e l e v e l s ar e g e n e r a l l y concentrat ion l e v e l sthat r epre s ent an excess u p p e r bound l i f e t i m e cancer risk to ani n d i v i d u a l o f between 10"4 a n d 1 0 ' 6 . " T h u s , carcinogenic risksbelow a lo" 4 increased cancer risk are g e n e r a l l y cons idereda c c e p t a b l e .

N o n c a r c i n o g e n i c e f f e c t s a s soc iated with exposure to a chemicalwas q u a n t i f i e d by d i v i d i n g i t s CDI with i t s r e f e r enc e dose (RfD) .T h i s ratio i s c a l l e d the hazard quot ient . If the hazard quotientexceeds uni ty ( i . e . , l) , then an adverse h e a l t h e f f e c t may occur.If the e s t imated hazard quotient i s lees than uni ty , then adversenoncarcinogenic e f f e c t s are u n l i k e l y to occur. N o n e of the

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chemicals of concern evaluated in this report have the sametarget organ. T h e r e f o r e , hazard indices ( i . e . , the sum of thehazard q u o t i e n t s ) were not ca l cu la t ed for exposure tononcarcinogenic chemical s of concern present in the A l l u v i a l andG a r b e r - W e l i i n g t o n A q u i f e r s as recommended in EPA ( I 9 8 9 a )g u i d a n c e .

A swamary of the p o t e n t i a l carcinogenic and noncarcinogenic riskse s t ima t ed f o r t h e A l l u v i a l A q u i f e r a n d G a r b e r - W e l l i n g t o n A q u i f e rare pre s ent ed in T a b l e 19 and di s cus s ed below.

P o t e n t i a l Carcinogenic . . E f f e c t s . Increased cancer risksassociated with exposure to benzene, b i s ( 2 -e t h y l h e x y l j p h t h a l a t e , 1 , 2 - d i c h l o r o p r o p a n e , andt e t r a c h l o r o e t h e n e were below the po int o f d e p a r t u r e ( i . e . ,10" 6) for both the RME and maximum exposure cases.T h e r e f o r e , e xpo sur e to these chemical s do not pre s enta p p r e c i a b l e ri sk t o p u b l i c h e a l t h . T h e p o t e n t i a lcarc inogenic risks a s soc ia t ed wi th e xpo sur e to vinylc h l o r i d e was 7 x l O " 5 and I x l O * 4 for the RME case and maximumcase, r e s p e c t i v e l y . A p p r o x i m a t e l y , 97 percent of the t o t a lcarcinogenic risks for the RME case and maximum case wereattributed to exposure to vinyl chloride . The p o t e n t i a lcarcinogenic risk for vinyl ch lor ide and the total riskes t imates for the mixture, based on all f i v e chemicals ofconcern, were within the accep tab l e risk range e s tab l i sh edby the NCP (EPA 1 9 9 0 ) * It should be noted that thee s t imated carcinogenic risks may be much lower given theconservative a p p r o a c h e s usad to e s t imate the s l o p e f a c t o r .

T E T R A T E C H

T a b l e 1 9M a j o r C o n c l u s i o n s o f t h e S u p p l e m e n t a lB a s e l i n e R i s k A s s e s s m e n t f o r t h eM o s l e y Road S a n i t a r y L a n d f i l l

I n g e s t ion of Grounetwaterf r o m t h e A l l u v i a l A q u i f e r

M a n c a i r c i n o g e m cR i s k

R M E M a x i m u m l a r g e tC a s e Case Organ

< i < 1 ( S k i n )<1 M ( b l o o d p r e s s u r e )*1 «1 ( r e p r o d u c t i o n )< l < 1 ( C N S J

C a r c i n o g e n i cR i s k

R M E M ' d * imumC a s e C a s e

7 E - Q 5 I E - 0 4

Coanent s

N o n c a r c tnag«n i c e f f e c t s u n l i k e l y t o occur f r o mingest t a n o f groundwaEar f r o m t h e A l l u v i a l A q u i f e r .P o t e n t i a l c a r c t n o g e n f c r i s k w i t h i n t h e a c c e p t a b l er t s k range a s s t a t e d t o t h e N C P . ( E P A 1 9 9 0 J . T h »highest risk e sUnwte of 1 x 10 was fourtd w i t h i nt f i e s i t e boundary (see F i g u r e ? ) . V t n y i c h l o r i d ea c count ed for 93 percent o f the t o t a l c a r c i n o g e n i c

I n g e s t tort o f Sroundwat erf r o m th eA q u i f e r

<! ( s k i n )( b l o o d 6E-07 ?E-07

« I ( n o e f f e c t r e p o r t e d )

Noncarc inogenic e f f e c t s u n l i k e l y to occur f r o minge s t t o o o f gro tmdwater f r o m t h e S a r b e r - W e l l i n g t o nA q u i f e r . P a t e n t t a l c ar c inogen i c , r i s k s * r e b e l owth e p o i n t o f d e p a r t u r e ( i . e . . 10* ).

0 5 ^ 3 6

February 1991 D E A F T REPORT

The risk contour p l o t was derived in order to evaluate thes pa t ia l d i s t r i bu t i on of p o t en t i a l carcinogenic risksassociated with ingest ion of groundwater f r o m the A l l u v i a lA q u i f e r . The total p o t e n t i a l carcinogenic risks associatedwith ing e s t i on of groundwater f r o m any l o c a t i o n were allwi thin th e a c c e p t a b l e risk range o f 10 ' 6 t o 10~*. Thehighe s t p o t e n t i a l carc inogenic risk e s t imated was I x l O " 4 .T h i s sma l l i s o l a t e d p l u m e i s located w i t h i n the boundary o fthe s i t e in the northern - ort ion of the M o s l e y Road S a n i t a r yL a n d f i l l .

Nooc_ar_cinocrenic . E f f e c t s . A r s e n i c , barium, 2 - c h l o r o p h e n o l ,and manganese had hazard quo t i ent s below uni ty. T h e r e f o r e ,adverse noncarc inogenic e f f e c t s are u n l i k e l y to occur. Thetarge t organs for each o f these chemical s are d i f f e r e n t .T h e r e f o r e , in accordance with EPA ( 1 9 8 9 ) g u i d a n c e , i t wouldbe i n a p p r o p r i a t e to sum the hazard q u o t i e n t s to e s t imat e ahazard index.

G a r b e r - # e l l i n _ C T t o _ n A q u i f e r

P o t e n t i a l Carcinogenic E f f e _ c t s . Benzene was the onlyp o t e n t i a l human carcinogen detec ted in the G a r b e r - W e l l ingtonA q u i f e r with an ava i lab l e s l o p e f a c t o r . The increasedcancer risks associated with exposure to benzene were 6xlo' 7

and 7 x l ( T 7 for the RME case and maximum case, r e spe c t ive ly .T h u s , the estimated increased carcinogenic risks for thesecases were below the point of departure ( i . e . , 10"6) ,T h e r e f o r e , exposure to benzene does not present ana p p r e c i a b l e risk to p u b l i c health.

ni-C E f f e c t s . T h e hazard quot ient s f o r arsenic,barium, manganese, and vanadium were we l l be low unity

T E T R A T E C H


T h e r e f o r e , adverse noncarcinogenic e f f e c t s are u n l i k e l y tooccur f r o m inges t ion of groundwater f r o m the Garber-W e l l i n g t o n A q u i f e r . The target organs f o r each o f thesechemicals are d i f f e r e n t . T h e r e f o r e , in accordance with EPA( 1 9 8 9 a ) g u i d a n c e , it would be i n a p p r o p r i a t e to sum thehazard quot i ent s to e s t imate a hazard index.

In conclus ion, the K o s l e y Road Sani tary L a n d f i l l does not pose anunacc ep tab l e risk to human h ea l th under current or f u t u r e land-use c o n d i t i o n s . Most of the chemical s of concern were d e t e c t e di n f r e q u e n t l y , at concentrat ions below or near the d e t e c t i o nl i m i t . Based on these c onc en tra t i on s , use of groundwater f r o mthe s i t e does not pose a noncarcinogenic h e a l t h risk and thecarc inogenic ri sk f a l l s w i t h in t h e a c c e p t a b l e risk rangee s t a b l i s h e d by the EPA ( 1 9 9 0 ) . In a d d i t i o n , the "true risks"associated with use of groundwater at the K o s l e y Road S a n i t a r yL a n d f i l l are probab ly several orders of magnitude lower than ther e s u l t s p r e s e n t e d in thi s r e p o r t , given the h i g h l y conservativea s s u m p t i o n s and me thod s used to derive t o x i c i t y c r i t e r ia andexpo sure e s t i m a t e s d i s cu s s ed in S e c t i o n 6.

ocroctnco

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February id91 DRAFT REPORT

8.0 R E F B R E K C E S

S e c t i o n J .C L E M E N T I N T E R N A T I O N A L C O R P O R A T I O N . 1990a. Es t imat ion o f ExposurePoint Concentrations for S u p e r f u n d Baseline RiskAsses sments . D r a f t Report. Prepared for Wast e Management,Inc. Oak Brook, IL.C L E M E N T I N T E R N A T I O N A L C O R P O R A T I O N . 1990b. Es t imat ion o f Exposureand Risk for S u p e r f u n d Baseline Risk Asses sments . D r a f tReport. Prepared for W a s t e Management, I n c . Oak brook, IL.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989a. Risk A s s e s s m e n tG u i d a n c e f o r S u p e r f u n d . V o l u m e I : Human H e a l t h Evaluat ionManual (Part A ) . Inter im F i n a l . O S W E R Directive 9 2 8 5 . 7 - O l a *December, 1989.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) , 1989b. Expo sure F a c t o r sH a n d b o o k . O f f i c e o f H e a l t h a n d Environmental A s s e s s m e n t ,E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989c. ExposureA s s e s s m e n t s M e t h o d s H a n d b o o k . D r a f t . O f f i c e o f H e a l t h a n dEnvironmental A s s e s s m e n t .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1990. N a t i o n a lCont ingency P l a n . F e d e r a l Register. 5 5 : 8 6 6 6 . March 8,

1990.

0^;Cin\un,o

E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989a, Risk Asse s smentG u i d a n c e f o r S u p e r f u n d . V o l u m e I : H u m a n H e a l t h evaluat ionManual (Part A ) , I n t e r i m F i n a l . O S W E R Directive 9 2 8 5 . 7 - O l aE N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1990. N a t i o n a lC o n t i n g e n c y P l a n . F e d e r a l Regi s t e r . 5 5 : 8 6 6 6 . March 8 ,1990.

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February 1991 DRJtfT REPORT 89

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RIPLEY, B.D. 1983. S p a t i a l S t a t i s t i c s . W i l e y & sons, New Y o r k ,N Y .

RUBINSTEIN, R . Y . 1981. S i m u l a t i o n and the Monte Car lo Method.J o h n W i l e y & Sons, Inc. N e w York , W . Y .Z I R S C H K Y , J . 1985. G e o s t a t i s t i c s f o r Environmental M o n i t o r i n gand Survey Design. Enviro. I n t e r n a t i o n a l . 11:515-524.

sectian. 4C A R P E N T E R , C . P . , W E I L , C . S . , a n d S M Y T H , H . F . 1953. Chronic oralt o x i c i t y o f d i ( 2 - e t h y l h e x y l ) p h t h a l a t e f o r rats, guineap i g s , and dogs . Arch. Inaus t . H y g . Occup. Med. 8:219-226.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1930. Ambient WaterQual i ty criteria f o r p h t h a l a t e Esters. O f f i c e o f WaterRegula t i ons and S t a n d a r d s , Criteria and s tandards Division,W a s h i n g t o n , D . C . October 1980.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1984a. H e a l t h E f f e c t sAsse s sment f or V i n y l C h l o r i d e . Environmental C r i t e r i a andAss e s smen t O f f i c e , C i n c i n n a t i , Ohio. S e p t e m b e r , 1984.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1984b. H e a l t h Asse s smentDocument f o r I n o r g a n i c A r s e n i c , F i n a l Repor t . U S E P A , o f f i c eo f Research and D e v e l o p m e n t , O f f i c e o f H e a l t h andEnvironmental A s s e s s m e n t , Research T r i a n g l e P a r k , N . C .M a r c h , 1984.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1984C. H e a l t h E f f e c t sAssessment for Barium. Environmental Cri ter ia andAssessment O f f i c e , Cinc inna t i , Ohio. Sep t ember 1984.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986a. G u i d e l i n e s f o rCarcinogen Risk Assessment. 51 F e d e r a l Register 33992( S e p t e m b e r 24 , 1 9 8 6 ) .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986b. G u i d e l i n e s f o rthe H e a l t h Risk Asse s sment o f Chemical M i x t u r e s . 51 F e d e r a lRegis t er 34014 ( S e p t e m b e r 24, 1 9 8 6 ) .

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E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989a. Risk Asse s smentG u i d a n c e f o r S u p e r f u n d . V o l u m e I : Human H e a l t h E v a l u a t i o nM a n u a l , I n t e r i m F i n a l . o sWEil Directive 9 2 8 5 . 7 - O l a ,December 1989,E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989b. GeneralQuanti tat ive Risk Assessment G u i d e l i n e s for Noncancer H e a l t hE f f e c t s . External Review D r a f t . Risk Asse s sment FcrumT e c h n i c a l Panel on Risk Asse s sment G u i d e l i n e s for NoncancerH e a l t h E f f e c t s . E C A O - C I N - 5 3 8 .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) , 1989c. Reference Dose( R f D ) : Descr ip t i on and Use in H e a l t h Risk Asse s sment .A p p e n d i x A to the Integra t ed Risk I n f o r m a t i o n S y s t e m (IRIS) .

L T iooE N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) .A s s e s s m e n t Summary T a b l e s ( H E A S T )O S W E R , U . S . E P A

1990. H e a l t h E f f e c t sF o u r t h Quarter F Y - 1 9 9 0 .

E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1991. I n t e g r a t e d RiskI n f o r m a t i o n S y s t e m ( I R I S ) . H e a l t h Cr i t e r ia a n d Asse s smentO f f i c e , W a s h i n g t o n , D . C . Revised February l , 1991.N A T I O N A L T O X I C O L O G Y PROGRAM ( N T P ) . 1982. Carcinogenesi sbioassay of d i ( 2 ~ e t h y l h e x y l ) p h t h a l a t e in F 3 4 4 Rats andB 6 C 3 F , Mice . F i e l d S t u d y . N T P T e c h n i c a l Report S e r i e s N o . ,2 1 7 , U . S . Depar tment o f H e a l t h a n d H u m a n S e r v i c e s . N I HP u b l i c a t i o n N o . 82-1773. N T P - 8 0 - 3 7 .T S E N G , W . P . 1977. E f f e c t s a n d dose re sponse r e l a t i o n s h i p s o fskin cancer and b l a c k f o o t disease with arsenic.Environmental H e a l t h Perspect ives . 19: 109-119.W A S T E M A N A G E M E N T O F O K L A H O M A , I N C . 1990. D r a f t RemedialI n v e s t i g a t i o n s Report: M o s e l y Road S a n i t a r y L a n d f i l lRemedial I n v e s t i g a t i o n / F e a s i b i l i t y S t u d y . Vo l . 1 .

sectlo_n_ 5E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986a. Guide l ine s f o rCarcinogen Risk Asse s sment , 51 F e d e r a l Register 33992( S e p t e m b e r 2 4 , 1 9 8 6 ) .

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E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986b. G u i d e l i n e s f o rthe H e a l t h Risk Asse s sment of Chemical Mix tur e s . 51 F e d e r a lRegister 34014 ( S e p t e m b e r 24, 1 9 8 6 ) .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989. Risk AssessmentGuidance f o r s u p e r f u n d . Volume I : Human H e a l t h EvaluationManual (Part A ) . Inter im F i n a l , O S W E R Directive 9285 ,7-Ola. December 1989.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1990. N a t i o n a lCont ingency P l a n . F e d e r a l Regi s t er 5 5 : 8 6 6 6 . March 8, 1990.

s_Qction 6E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1985. T e c h n i q u e s f o r t h eAsse s sment o f th e Carc inogenic Risk t o th e U . S . P o p u l a t i o ndue t o Expo sur e f r o m S e l e c t e d V o l a t i l e Organic C o m p o u n d sf r o m Drinking water via the . T n g e s t i o n , I n h a l a t i o n and DermalRoutes. O f f i c e o f Drinking W a t e r . U . S . E P A . S e p t e m b e r1985.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986a. G u i d e l i n e s f o rCarcinogen Risk Assessment. 51 F e d e r a l Regis ter 33992( S e p t e m b e r 24 , 1 9 8 6 ) .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986b. G u i d e l i n e s f o rth e H e a l t h Risk Ass e s smen t o f Chemical M i x t i a r e s , 51 F e d e r a lRegi s t e r 34014 ( S e p t e m b e r 2 4 , 1 9 8 6 ) ,E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989a. Risk Ass e s smen tG u i d a n c e f o r S u p e r f u n d . V o l u m e I : H u m a n H e a l t h E v a l u a t i o nM a n u a l . I n t e r i m F i n a l . O S W E R Directive 9 2 8 5 . 7 - O l a .December 1989.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . I 9 8 9 b . GeneralQuanti tat ive Risk Assessment G u i d e l i n e s f or Honcencer H e a l t hE f f e c t s . External Review D r a f t . Risk Assessment ForumTechn i ca l Panel on Risk Assessment G u i d e l i n e s for NoncancerH e a l t h E f f e c t s . E C A O - C I N - 5 3 8 ,E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989C. Reference Dose(RfD): Descript ion and Use in H e a l t h Risk Asses sment,A p p e n d i x A t o t h e I n t e g r a t e d Risk I n f & g m a k l o n S y s t e m ( I R I S ) .

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C L E M E N T I N T E R N A T I O N A L C O R P O R A T I O N . 1990. Es t ima t i on o f ExposurePoint Concentra t i on s f or S u p e r f u n d Baseline Risk Ass e s sment .D r a f t Report. Prepared for Was t e Management, Inc. OakBrook, I L .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1985. ExposureAsse s sment M e t h o d o l o g i e s o f H a z a r d o u s W a s t e S i t e .Environmental Monitor ing Systems Laboratory/ Las V e g a s , NV.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1986. G u i d e l i n e s f o rCarcinogen Risk Ass e s smen t . 51 F e d e r a l Regi s t er 3 3 9 9 2( S e p t e m b e r 2 4 , 1 9 8 6 ) .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989a. Risk Asse s smentG u i d a n c e f o r S u p e r f u n d . Volume i : H u m a n H e a l t h E v a l u a t i o nManual ( P a r t A ) . I n t e r i m F i n a l . OSWER Directive 9285.7-O l a . December 1989.E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1989b. Exposure F a c t o r sH a n d b o o k . Ver sar I n c . contract N o . 68-02-4254. O f f i c e o fH e a l t h and Environmental Ass e s sment , E P A , W a s h i n g t o n , D . C .E N V I R O N M E N T A L P R O T E C T I O N A G E N C Y ( E P A ) . 1990. N a t i o n a lC o n t i n g e n c y P l a n . F e d e r a l Regi s t e r . 5 5 : 8 6 6 6 . March 8 ,1990.

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T E T R A T E C H

March 15, 1991

Mr. Mark SnyderW a s t e Management of N o r t h America, Inc.1320 Greenway Drive, S u i t e 900Irving, Texas 75038Re: Moslcy Road Sanitary L a n d f i l l S u p e r f u u d Si t eD r a f t Remedial Inve s t iga t i on ReportDear Mr. Snyde:;The Environmental Protection Agency (EPA), the Oklahoma S t a t e Department of H e a l t h ( O S D H ) andEPA's oversight contractor PRC, have comple t ed their reviews of the referenced report, lie format ofthe report (i.e. t e x t , table s , and f igure s were not located in the same volumes) was d i f f i c u l t tu read andf o l l o w . Based on the in format ion contained in the RI report, EPA, PRC and OSDH f o u n d technicaldeficiencies requiring explanation by Waste Management of Oklahoma (WMO) be fore WMO will receiveEPA's f ina l approval of the report. These deficiencies are presented as general and spec i f i c comments.General comments refer to the document as a whole. S p e c i f i c comments are referenced by section andpage. S p e c i f i c comments directed to t ab l e s and f igure s are referenced as such.Please ensure that all of the enclosed comments are addressed. If you should have any questionsregarding these comments, please contact me at (214) 655-6730.Sincere ly,

V,

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Monica ChapaO K / N M S u p e r f u n d Enfor c ement S e c t i o nEnclosurecc: Lisa S e g l i u - W M N A

Rich O'Hara-WMNADennis Hrebec-OSDHRobert M e l t o n - P R C

Received by: _.._ ._. _._WMO Representative Date

6 H - E O : m j c : C H A P A : M o s l e y 3.5:C060 i2ri

VOLUMEGeneral Comments

The approach takea in the RI report was to explain other possible sources of the contaminationdetected ia the Mosley Road Saniiary L a n d f i l l samples other than the waste pits. These include(1) laboratory contamination, (2) agricultural activities, (3) pumping oil wells, and (4) municipalrefuse, regardless of the fact that Mosley Road Sanitary L a n d f i l l contains municipal refuse. Thi sconcept of dividing sources of contamination between the waste pits and all others needs furtherexplanation and j u s t i f i c a t i o n , e spec ia l ly for those contaminants eliminated because of theassumption that the municipal r e fu s e is the source.The d a t a suopor l ing the Remedial I n v e s t i g a t i o n and F e a s i b i l i t y S t u d y (RI/FS) deviated from theproposed Level IV qual i ty for target ana ly t e l i s t (TAL) and target compound list (TCL)compounds because of two no tab l e instances. F i r s t , aqueous sample s , inc luding ground water,surface water and leachat~ were analyzed for dissolved me ta l s instead of total metals. S e c o n d , asa result of the d a t a v a l i d a t i o n , the ma jor i ty of the da ta for the l eachate sample s were q u a l i f i e dwith "R", indicating that the data were unusable.Using dissolved metal data exclusively could underestimate the risk, both of the baseline riskassessment and the ecological assessment. The portion of total metals which are dissolveddepends on the site and sample sp e c i f i c parameters. As stated in the Environmental ProtectionAgency (EPA) risk assessment guidance document (1989), Section 6.5.2 page 6-27, the use off i l t e r e d (dissolved) samples for estimating risk exposure is controversial because these data mayunderest imate chemical concentrations in water from an u n f i l t e r e d tap. T h e r e f o r e , da ta f rom( t o t a l ) u u f i l t e r e d s ampl e s should be used to es t imate exposure concentrations. Also, Sect ion 6.6.1of the EPA document (1989) s ta t e s that u n f i l t e r e d s ampl e s should be used to calculate intakesf rom surface water. Since metal s were the primary contaminants of concern, the use of thef i l t e r e d (di s s o lv ed) d a t a should be evaluated.S e d i m e n t d a t a was a p p a r e n t l y analyzed and reported in aqueous units instead of on a dry weightbasis. Because it was assumed that the sediment samples contained soil, a dry weight value wouldhave been more appropriate . The sediment samples were described as "water" on the chain-of-custody forms. The true nature of the sediment samples was not clearly stated.Most of the semivolatile o r g a m ' c s , pesticides, poiychlorinated biphenyls (PCB) and f o u r metalswere qual i f i ed with "R" for the leachate samples. The "R" q u a l i f i e r is def ined in the EPA datavalidation guidelines, and in the report, as "the data are unusable (compound may or may not bepresent). Resampl ing and reanalyuis is necessary for verification." The leachate sample s q u a l i f i e dwith "R" were sampled during the f i r s t round of sampl ing . They were not resampled during thesecond s a m p l i n g round or subsequent sampling. The leachate s ampl e s should have beenresampled since most of the d a t a for s emivo la t i l e p e s t i c id e s and PCBs were i d e n t i f i e d asthe leachate s ampl e s should have been resampled.The data reported above the instrument de t e c t ion linu't and below the contact requiredquanlitatiau limit (CRQL), or sample quaulitation limit (SQL), were apparently not used exceptto assist in determining dominant transport mechanisms. These "J" quali'fied values should havebeen used In the risk assessment^ as stated in the EPA pidauce document (1989),Background samples were not id en t i f i ed in the text. The criteria used to determine whether asample was representative of background was not presented. Background samples were discussedelsewhere in the report but were not supported or de f ined in Section 2.0.

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As outl ined in the EPA-approved work p l a n ( G o l d e r Associates, 1939), recommended remedialaction objectives were to be presented and discussed in the summary and conclusion section ofthe RI report. In reviewing the R! report, there was no mention of remedial action objectives.Since the remedial action ob j e c t ive s d epend oo this RI report, the revised ed i t i on should i n c l u d ethese objectives.Based on the i n f o r m a t i o n pre s ented in the RI report , f u r t h e r d e t a i l e d in format ion andexplanation is required to address anomalous conditions of the leachate interval of the l a n d f i l l .A p p e n d i x I contains the historical water level data for all of the wel l s existing at the site,i n c l u d i n g the da ta for l eachate risers (LR)-102, -103, and -106. As shown in the d a t a presented,an anomalous condition occurred between July 18 and July 29, 1990. The d i f f e r e n c e in waterlevels taken on these date s ranged from 7.77 f e e t in LR-102 to 8.08 f e e t in LR-103. Incomparing this d a t a to the hydrograph chart ( F i g u r e 2-13), the rise in leachate levels r e f l e c t s aperiod of prec ipi tat ion. The amount of p r e c i p i t a t i o n was about 1.5 inches. A l t h o u g h thehistorical d a t a i s l i m i t e d , the changes a p p a r e n t l y resulted '.com (1) i n f i l t r a t i o n through the claycap, (~) horizontal and vertical communication wi th the alluvial aqui f er , or (3) a combination of(1) and (2). Because the HELP model used to evaluate the e f f e c t i v e n e s s of the clay capindicated l i t t l e i n f i l t r a t i o n , and because the extent of horizontal and vertical communication thatmay be occurring between the l ea cha t e and the a l l u v i a l ground water is unclear, f u r t h e re x p l a n a t i o n is required.The human h e a l t h risks for use of a l luv ia l ground water were f o u n d to be equal to or s l i g h t l yexceed boaclimark risk levels - risk levels where the p o t e n t i a l concern for h e a l t h e f f e c t s requiredf u r t h e r evaluation. H.izard indices were 1 or 2, and carcinogenic risks exceeded 1 X 10"4 butwere loss than 1 X 10'3. The risk l eve l s associated wi th Gar h e r - W e l l i n g ton ground water, which isr • 4 as a community water s u p p l y , were de termined to be two or more orders of m a g n i t u d elowti . A review of the methods used to derive these risk level s r e su l t ed in the conclusions thatthey were f a i r l y derived and may represent & conservative e s t imate of the risks associated wi thdomestic use of ground water beneath the site. However, c j d t n i u m , l ead , and nickel wered e t e c t e d in a l l u v i a l ground water (p. 3-19, RI r epor t , 1991) but were omi t t ed f r o m the riskassessment c a l c u l a t i o n for ground water. Also, metal concentrations that were evaluated in therisk assessment were based on dis solved meta l s ra thrr than t o ta l metals. T o t a l metalconcentrat ions may more ac cura t e ly represent exposure concentrations for domestic water users.Dissolved metal concentrations may u n d e r e s t i m a t e exposure concentrat ions for domestic waterusers.Some of the conclusions of the report appear to contradict the data. For example, the reportindica t e s that migration of metal contaminant s is occurring f rom the waste p i t s to ground water,and po s s i b ly to sur fac e water. Tin's conclusion is s u p p o r t e d by the d a t a provided, however, therisk assessment generally evades the issue. The concentrations of metals in surface water inCrutcho Creek downstream of the site, however, may be approach ing or exceeding concentrationst h a t are toxic for a variety of aquatic organisms.The risk assessment should c l e a r l y s ta t e tha t risks f rom metal contaminants in the ground waterand sur face water are based on d i s s o lv ed , rather than t o t a l , metal concentrations. F u r t h e rsampling should be conducted to q u a n t i f y the uncertainty associated with the use of dissolved,rather than t o t a l , innta! concentrations in the risk assessment. It is requested that f u r t h e r ground-water s a m p l i n g be conducted to evaluate total metal concentrations. The da ta co l l ec t ed so farhas been based on water samples f i l t e r e d through a 0.45~micron f i l t e r . Because domestic waterusers are unl ike ly to use water f i l t e r e d through such a small pore f i l t e r , f i l t e r e d samples will l ik e lyunderes t imate exposure concentrations of metals for domestic water users, The us*? of f i l t e r e dsamples increases the uncertainty of the risk estimates, Tota l metal concentrations can be

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compared to the dissolved metal concentration data. The d i f f e r e n c e caa be used to evaluate themagnitude of uncertainty that may be associated w i th current risk estimates.Migration of metals from the sits waste pits to surface water in Crutcho Creek requires f u r t h e rinve s t igat ion to (1) fully evaluate the nature and extent of migration and (2) determine whetherconcentrations of l e a d , s e lenium, and cadmium de t e c t ed in the second s a m p l i n g round at SW-08are representative of ambient water concentrations downstream of the alluvia! ground-waterdischarge po in t .The risks associated with surface soils were noi evaluated. The potential for the area to be usedas recreational or open spa^e pub l i c laud and f u t u r e land use condit ions were not evaluated.A d d i t i o n a l evaluation of risks associated with s u r f a c e soil contaminants would provide a morecomplete assessment of site-associated risks.The v a l i d i t y of the assessment is undermined by the general lack of s u b s t an t ia t i on for impor tantstatements and conclusions. References are consistently omitted, background data is notreported for comparison wi th inorganic chemical s a m p l i n g -e su l l s on- and o f i - s i t e . Reference s ,s u p p o r t i n g d a t a , and the r a t i o n a l e should be provided for all s tatement^ assumptions, andconclusions critical to the assessment. The s p c c i f L comments note serious omissions. However,thi s is a general f a i l i n g throughout the report and is not l imi t ed to the noted s p e c i f i c comments.The p o t e n t i a l l y exposed p o p u l a t i o n is not characterized in the risk assessment. The currentguidance (EPA, I 9 8 9 a ) recoiuncnds characterizntion o f p o t e n t i a l l y exposed p o p u l a t i o n s i n c l u d i n g/I) t b e l o ca t ion re la t ive t o th e s i te , (2) current laud use, in c lud ing act ivi ty pa t t erns , (3) p o t e n t i a luture land use based on Bureau of Census pro j e c t i ons , and planning data, and (4) ident i f i ca t ionof sensitive s u b p o p u l a t i o n s . T h i s i n f o r m a t i o n is necessary to eva lua t e the exposure pauwayschosen for analysis.

I m p o r t a n t s a m p l i n g d a t a has been o m i t t e d f r o m the t a b l e s s u p p o r t i n g S e c t i o n 4.0. Cadmium hasbeen omit ted f r o m the table s p r e s e n t i n g s u r f a c e water s a m p l i n g re su l t s , and l e a d , cadmium, andnickel have been omitted f rom the ground-water sampling results tables. These contaminantswere omi t t ed f rom cons iderat ion in the risk assessment. Even if the concentrat ions of thesecontaminants are "low", as reported in the texi of S e c t i o n 3.0 ( p a g e 3-19, RI report, 1991) theirpresence or absence in ground vater and surface water is important in evaluating migration ofmetal* f r o m the landfil l . A l s o , the risks associated w i t h dome s t i c use of a l l u v i a l ground water areclose to benchmark rLk levels; even low concentrations of these toxic metals may add to thecumulative risk.Sec t i on 3.0 describes p o t e n t i a l contaminant f a t e and t ran spor t of site contaminant s and provide sa thorough discussion of these processes, with part icular at tention to s i t e- spec i f i c processes.However, the lack of regional and si t o - s p e c i f i c background d a t a l imi t s the conclusions that can bedrawn regarding the migration of contaminant s from the site, e s p e c ia l ly theThe report a p p e a r s to bo wri t t en in a manner which s eparate s the e f f e c t s o f ih ' j waste p i t s f romthe e f f e c t s of the landfill in general. T h i s may be a p p r o p r i a t e if only the piu were p r o m u l g a t e dto the NPJL but is not appropr ia t e if the entire site was ranked. The purpose of the RI is toassess the I m p a c t of the entire site, not j u s t the waste p i t s .The report should be mod i f i ed to include consideration of the fact that hydraulic gradient* in (hevicinity of the landfill may have been considerably d i f f e r e n t b e f o r e the cap was constructed andthe l a n d f i l l was open to i n f i l t r a t i o n . It is poss ible tha t the disturbed soils comprising the l a n d f i l l

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f a c i l i t a t e d i n f i l t r a t i o n and created mounding around the l a n d f i l l . T h e r e f o r e , in the vicinity of thelandfill , the u p g r a d i e n t / d o w n g r a d i c n t d e s i g n a t i o n s might have been d i f f e r e n t in the pas t .21. Oklahoma S t a t e Department o f H e a l t h (OSDH) i n f o r m a t i o n indicate s that OSDH d i d g r a i i t

nuhorizatioT on a t emporary basis for the landfill to accept the waste. However,OSDH has no in f ormat i on in our f i l e s i n d i c a t i n g that the l a n d f i l l owner was direc ted to acceptthe waste. A l e t t e r has been wri t t en to the current l a n d f i l l owner requesting this in f ormat i on .The document should be revised to s ta t e as such.

22. It was s tated in the D r a f t Technica l Memorandum on N i n e Criteria tha t "a concentrated sourceof hazardous waste was not i d c r t i f i e d during the RI." H o w e v e t , WMO has demons tra t edconf idence in its a b i l i t y to accurate ly locate tho waste p i t s , based on elevated vo la t i l e organiccompounds (VOC) scans and visible contamination, i d e n t i f i e d during the source characterization.T h i s s tatement contradict what has been stated ;,i previous documents. Are there any uns ta t edas sumptions by which this s ta t ement is made? Please i d e n t i f y the basis for this s ta t ement . A l s o , itis s tated in the d r a f t Remedial I n v e s t i g a t i o n Report tha t it is difficult to v i s u a l l y d i f f e r e n t i a t ebetween waste pit soils and municipal re fuse . Based on what in f ormat i on is this s tatement made?Plea s e c l a r i f y . Is there a p o s s i b i l i t y tha t the waste s t i l l exists in the waste p i t s ? If not, what i sW M O ' s basis f o r thi s thinking?

S p e c i f i c Comment sS e c t i o n l.t pflge 14 Change "a p r e d o m i n a n t l y ruralsetting." to "an undeveloped area on the eastern edge of Oklahoma City."S e c t i o n 2.1.1.5 p a g e 2-7 Change "The waste p i t s are under la in by up to 20 f e e t of r e f u s e overlying" to"Waste pit #1 is under la in by up to 8 f e e t of r e f u s e , waste pit #2 is u n d e r l a i n by up to 20 f e e t of r e fu s e ,and waste pit #1 rests direc t ly upon."

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S e c t i o n 2 .1 .1 .S_page_2-7 Changu "refuse ex t ends to e l evat ionsranging" to "elevations of the bottom of the l a n d f i l l underneath the waste p i t s range.'S e c t i o n 2_.t.i.5_p«ge_2-8 T a b l e de le t e the "Waste Pit Designation" column or add a note to the table toe x p l a i n tha t the elevations are the laudfill base and not the base of the waste p i t s , except in the case ofwaste pit #1 in which it is the same.Sect ion 2.!.l.S_pace.2-8 Change "underlain by low" tomeans waste p i t s , it and the rest ofthe paragraph are confl ic t with page 2-7, line 7, which states"the waste p i t s are under la in by up to 20 f e e l of refuse."S_cctioii_-£.l J J > J H i a e M C h a n g e ' a l t h o u g h this" t o "a l though

2-8 Change "beneath pit s" to beneath

underlain by sandy and low"

the."re fu s e u n d e r l y i n g pits."

S e c t i o n 2.1.1.6 p»ge.£-B These J'.acs arc in c o n f l i c t with page2-2, line 27-28. Please clarify.

S e c j i t e n 2.1.1.83. page 2-12 Because of poss ible i n f i l t r a t i o n , the r u n o f f curve value of 89 a p p a r e n t l ymay mot a d e q u a t e l y allow for evaluat ion of the e f f e c t s of rill and g u l l y deve lopment which current ly existon the clay cap cover. If this is the case, the H E L P model may not represent an adequate evaluation ofsite conditions, t h e r e f o r e rendering the H E L P model i n f o r m a t i o n provisional.Section .2.2.4.23 page 2-24 The discussion presented here describes the hydraulic conductivityt e s t ing of cohesive soil sample s as being non -representative due to the presence of worm holes. A l t h o u g hthe worm holes may not be found in every sample obtained (in part because they tend to be crushedduring s a m p l i n g ) these f e a t u r e s should not b«> di s counted because they act as the primary pathway ofground water f l o w through the soils. In f a c t , one of the primary problems with small scale labora to iypermeab i l i ty test s such as those conducted here, is that they t y p i c a l l y do not account for the e f f e c t s ofheterogenei t ie s which contribute s i g n i f i c a n t secondary p :rmeability. The sampl e containing thewormfaole s may be the most "representative 1 1 s a m p l e s since it contains f e a t u r e s t y p i c a l l y only observed in-situ. T h i s discussion should be rewritten.S e c t i o a 2.2.4.7 page 2-32 - W e l l d eve l opment should have continued unti l water q u a l i t y parameter s hajstabilized and turb id i ty levels were below 5 NTUs. The text docs not indicate whether the water wasclear when deve l opment was c o m p l e t e d . If the water remained turb id , r ed ev e l opmen t should beconsidered.S e c t i o n 2,2.6.2i_nage 2-38 It is s t a t e d tha t "the presence of the brecciated zones impl i e s thatprevious movement along structures in the Garber-Well ingtou may have occurred." If this is the case,what p o t e n t i a l e f f e c t s d o j s t h i s present in considerhg the horizontal and vortical g r a d i e n t s in the Garber-Welh'ngtou aquifer? In addi t ion, can these zones pos s ib ly represent permeable conduits which may a f f e c tthe f a t e and t r a n s p o r t a t i o n o f contaminant s? E x p l a i n .S e c t i o n 2 ! 2.7 .1 , l ._mjge 2-39 The I c a c h a t e levels a p p a r e n t l y represent perched condi t ions and may notbe d i r e c t l y r e la t ed to the a l luv ia l water levels. However, t h i s may only a p p l y to LU-102 and LR-103 sincethere was a c lay layer of unknown thickness encountered below the i n f e r r e d waste p i t s 1 and 2. Tin's maynot be the case for LR-106, however, because the l eacha t c l eve l s pre s en t ed in LU-106 a p p r o x i m a t e thealluvial water levels. Also, since a clay layer was not encountered below pit 3, there is no permeableboundary to prevent horizontal communication. Provide f u r t h e r e x p l a n a t i o n to c o n f i r m the b e l i e f t h a tthere is no horizontal communication between the leachate and the al luvial ground water.Section. 2JJ J.l.JLpage g-39 The ground water in the vicinity of the landfil l t y p i c a l l y f l o w s in a radialf a s h i o n towards the north, northwest and nor theas t . To only s ta t e t h a t ground water in thea l luv ium g e n e r a l l y f l o w s northward ov er s imp l i f i e s ava i lab l e d a t a ,Sect ion. -2.2*7 JJ« pa«c 2-41 It is s t a t e d tha t the north pond acts as a source of recharge to thesurrouading alluvial ground water when the north pond receives extensive pre c ip i ta t i on and r u n o f f from thelandfill. If t h i s i s the case, how does the I c a c h a t e interact at times of heavy p r e c i p i t a t i o n since the l eachatelevels are also raised, as inferred f r o m the da ta in A p p e n d i x I?S i ' C t i o M _ 1 . 2 . ? > L l i m « e J t - 4 2 It is not clear how ground water converges nt the northern edge of theInndfill. W h i l e there is a s l i g h t southern gradient between MW-215 and MW-205, there is a much steepergrad i en t towards the northeas t which would be the primary d i r e c t i on of f l o w or ig inat ing from the northeastcorner of the l a n d f i l l .

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ecto» -njU3L3._senfam£g .3 TTie bnsis for the conclusion drawn here that the amountof leakage necessary to transmit hydraul i c head changes f rom the alluvium to the Garbor-Wel l ing t on is notclear,, aad should be provided.

Sect ion 2JJ.7.2..1.. page 2-46 Vert i ca l hydraulic commum*C£?&ti% a p p a r e n t l y not good between LR-102,LR-103, and the al luvial ground water because there is a consistent hydraul i c head d i f f e r e n c e , general lyaveraging 2 and 15 f e e t , respectively. However, the data in A p p e n d i x I presents a complex s i tuation whenthe leachate levels are increased above those average levels. Since the levels have increased and decreased( A p p e n d i x I), there must be some type of communication. Expla in this occurrence, and provide technicallyadequate reasons to support this occurrence.Section .2-2.7.2.1, page 2-46 It is stated that " t i t t l e or no vertical gradient generally exists" in the area ofLR-106. The meaning of this statement is unclear. Does it mean that there is no communication betweenthe leachate and the alluvial water in this area?

•Sect ion _2.2.7.2.3_ paeg 2-47 The explanation of why the early water level data is questionable shouldbe provided here or referenced.Section. 2.2.7.2J page 2_-47 It is not clear if, or how, the convergent f l o w in the Garber-Wellingtonre la t e s to the downward f l o w w i t h i n the a l l uv ium discussed here. Perhap s this condit ion can be a t t r i b u t e dto recharge f rom the N o r t h Pond.S e c t i o n 2.2.7.2.3» page_2-48 The d a t a gathered from the p u m p test indicated tha t the al luvial and Garber-W e l l i n g t o n aqui fer s are not in s i g n i f i c a n t hydraul i c communication, yet it is suggested that there is s i gn i f i can tvertical hydraul i c communication between the two aqui f er s in the area north of the landfill i d e n t i f i e d as the"converging area." Since this is not In conformance with the p u m p test r e su l t s , has enough i n f o r m a t i o n beenobtained to a d e q u a t e l y (1) e x p l a i n th i s occurrence, (2) under s tand what will occur ,j the hydrologicalprocesses in r e la t i on to the l ea cba t e , a l l u v i a l a q u i f e r , and the G a r b e r - W e l l i n g t o n a q u i f e r if remedial ac t iv i t i e sare a p p l i e d to this area ( f o r e x a m p l e , p u m p and t r e a t ) , and (3) d e f i n e the l i fe for p o t e n t i a l remedialac t iv i t i e s?S e c t i o n 2,2.8.2, p j i g e 2-49 As described in the E P A - a p p r o v e d work p l a n ( G o l d c r Associate s , 1989), thep u m p test was conducted to obtain d a t a for analys i s to characterize (1) a q u i f e r hydrau l i c conductivity, (2)s p e c i f i c yield, (3) boundary e f f e c t s , and (4) in t e r-aqu i f e r hydraul i c communication. The r e su l t s of the p u m ptest did provide this in f ormat i on on a small-scale basis. However, these small-scale c h a r a c t e r ! _ J c s are notrepresentat ive of the overall site condit ions, thus making this d a t a i n s u f f i c i e n t to adequate ly characterize thecondit ions on the north side of the l a n d f i l l . If remediation is imp l emen t ed around the l a n d f i l l , what will eachaquifer's hydraulic conductivity be? What will each aquifer's s p e c i f i c yield be? Since the north and southpond s are direc t ly adjacent to ihe landfill, how will these act as boundary e f f e c t s ? How will the leachate,al luv ia l , and Garber-Wellington aquifers interact hydrologically?Section J L 3 . L 3 _ M g g 2-58 T a b l e 2-7 is not a table showing feachate collection depths .gection_2.3.2. page 2-_62 Hie text states that Level IV Contract Laboratory Program (CLP) methods wereused; however, the sampling and analysis methods deviated from CLP protocols. All aqueous samples weref i l t e r ed before analysis for TAL metal compounds. The parameter requested on the chain-of-custody formswas dissolved metals, which would result from the analysis of f i l t e r e d samples. Most chaiii-of-custody formsspe c i f i ed the samples had been f i l t e r e d .jjjfection_2.3AJt PQKe 1*6$ The data validation appeared to be consistent with EPA data validationguidelines (1988a, 1988b), with at least one exception. During the validation all laboratoiy "E" qua l i f i ed datawas validation qual i f i ed with "J." W h i l e this may have been appropriate for inorganics depending on thelaboratory explanation of "E," it was not appropr ia t e for organics. Changing the organic "E" quali f i er to "J"would greatly underestimate the concentration and the r'sk. A minority of samples were a f f e c t e d .

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S_ectj_Qns 2.3.2,_pnge 2 -62 There appeared to be a lot of laboratory blank contamination and poormatrix spike recoveries associated with the inorganics analyses. Thi s resulted in many inorganic results beingvalidated with T and "UJ," indicating estimated values and e s t imated detection limits associated withnondetects, respectively.T l i e surrogate recoveries for many of the semivolati les were low. The low surrogate recoveries resulted inthe corresponding data being q u a l i f i e d as T and "UJ," indicating estimated values aad estimated detectionlimits associated with nondetects, respectively.S e c t i o n 2.3.2.I3, page 2_-69 Most semivolati le organic, p e s t i c id e , and PCB d a t a for the leachate sample swere val idated as unusable. Resampling should have been conducted.S e c t i o n 23.1,l,S,_\>a&e 2~79 The term "Common Sediment TIC laboratory coo lamina a Is" was used, Areference should be provided to describe common sediment t e n t a t i v e l y i d e n t i f i e d compounds (TIC),S e c t i o n 23.2.2. page 2-83 The text discusses only those de t e c t ed values above the CRQL and S Q L .All "J" q u a l i f i e d da ta , p a r t i c u l a r l y those f a l l i n g between the instrument de t e c t ion l imit and the C R Q L / S Q L ,should also be addressed. The "J" q u a l i f i e d d a t a is a c c e p t a b l e for inclusion in a risk assessment and shouldhave been used (EPA, 1990),T a b l e 2-11 The p r e s e n t a t i o n of d a t a in T a b l e 2-11 was i n a p p r o p r i a t e . The pre sentat ion did not containnecessary informat ion. A p p e n d i x P had to be r e f e r r e d to in order to extract needed i n f o r m a t i o n . T a b l e 2-11,which is eight pages long and contains i n f o r m a t i o n on all seven s a m p l e media, should have been separatedinto several table s addre s s ing ind iv idua l s a m p l e types. Per t inen t i n f o r m a t i o n was not inc luded . It wasnecessary to r e f e r to A p p e n d i x P for a c ompl e t e l i s t of parameters analyzed and the corresponding CRQLsor SQLs. Also, i n f o r m a t i o n on values d e t e c t ed at level s below the CRQLs or S Q L s was not included.The maximum concentration values should have been in EPA CLP consis tent units. Tlie units presented werep a r t s per mill ion ( p p i i ? ) which could be mi l l igrams per l i t er ( m g / L ) or mil l igrams per kilogram (mg/kg) insteadof the units t y p i c a l l y used by EPA CLP for organics, CM'crograms per l i t e r (ug/L) and micrograms perkilogram ( u g / k j - x The non-matrix s p e c i f i c unit of ppm did not easily i d e n t i f y the matrix. For instancesediment samples were actuaMy nig/L and not mg/kg as might have been expected. TTie columns "Numberof S a m p l i n g Points" and "Number of Occurrences above CRQL" were misleading since the values presentedin the number of sampling points column included values which were validated as unusable. Since thesevalues were validated as unusable they should not have been included its a viable data point. For exampletor one leachate semivolattle* compounds l i s t ed , 4 - m c t h y i p f a e n o I , it was stated there were four sampling point swith one concentration greater than the CRQL or SQ£« A maximum value above the CRQL or SQL wasalso given. A c t u a l l y two of the four data values for the f o u r sampling points were validated as unusable. Theiatio was ac tual ly one out of two, instead of one out of f o u r , concentrations of 4-methylphenoI greater thani f a e CRQL or SQL._Sectij>n_2.3,2.2.4. page_2-g9 Figure 2-14 is a p p a r e n t l y not related to this discussion,SectiQn_2.3,2,2, The approach was to explain possible sources for the contamination detected in the MoslcyRoad Sani tary L a n d f i l l samples other than the waste pits. These include (1) laboratory contamination, (2)agricultural activities, (3) pumping oil wells, and (4) municipal refuse, regardless of the fact that Mosley RoadSanitary L a n d f i l l contains municipal refuse. Thi s concept of dividing sources of contamination between thewaste p i t s and all others needs fur th er explanation and j u s t i f i c a t i o n , especially for those eoatamimmtseliminated because the assumption that the source was the municipal refuse which is an integral part of thesite.

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Section! 2_4..2,1.6_frage_2-l 13 line. 3 Change "that" to "the."Sect ion 2 J.2.2.6 paee.2*117 It is not appropria t e to discount the elevated Se level just because it is belowone standard. Potential e f f e c t s on aquatic l i f e should be considered and the potential for bioaccumutationevaluated.Sect ion 2.4.5.8. page 2-144 The calculation for completeness was misleading, ilie calculation presentedaddresses overall completeness; it is generally calculated on a parameter group or sample location basis. Thecompleteness value for the leachate samples would probably not meet the 90 percent goal. Also if pesticides,PCBs, and semivolatiles were calculated separately they may not meet the 90 percent goal either.Section^ 3.3 page 3-2Jme 5 Change "may have been" to "were".

Section 3.2. page,3:4 It is stated that the organic acid compounds detected are "common degradationproducts." W h a t are the organic compounds from which these acids were degraded?.Section 33.1.1.1 page 3-6 It is not pos s ib le to draw the conclusion made here that s o l u b i l i t y is thecon tro l l ing f a c t o r ia contaminant mobi l i ty- The d a t a show t h a t , in many instances, less s o lub l e compoundsare present when more s o lub l e compounds are absent. T h i s text should ind i ca t e that s o l u b i l i t y is one f a c t o rwhich controls mobil i ty.S e c t i o n 33.1A page 3?7 It is assumed that wells located near the landfill not l i s t ed by the Association ofCentral Oklahoma Governments ( A C O G ) are c o m p l e t e d into the al luvium (page 2-17). Also , it is s tated t h a t"Flow direct ions in the a l luv ia l aqui f er vary due to seasonal e f f e c t s , as shown on Figure s 2-9 through 2-12,which creates uncer ta in ty in regards to the overall d ir e c t i on a dissolved compound might migrate throughtime." HP A requests t h a t the private wel l s currently lo ca t ed both u p g r a d i e u t and down gradient of the sitebe sampl ed and analyzed, to ensure the that contaminant s have not migrated to these areas.S_ection_3.3.2.I, Pflge_3-_16 It is suggested that benzene and xylene did not or ig inate f rom the waste p i t s .In prior responses to comments, G o l d e r has s ta t ed t h a t , in accordance with the EPA guidance documents,it i s required tha t i t i d e n t i f y all p o s s i b l e sources of comaminamts (for example municipal landfill contaminantsand indu s t r ia l hazardous waste contaminants). W h a t is the source of these contaminants?S e c t i o n 34.2.4._p«ge 3_-19 It is s t a t e d t h a t "concentrations of nickel, cadmium, and lead were alsog enera l ly low in a l luv ia l ground water and did not exceed SDWA standards." The guidance on riskassessment s t a t e s t h a t c o n t a m i n a n t . ' ) required to be addres s ed under A p p l i c a b l e or Relevant and A p p r o p r i a t eRequirements (ARAR), such as drinking water s t andard s , are not u s u a l l y a p p r o p r i a t e for exclusion f rom theq u a n t i t a t i v e por t i on of the risk assessment (EPA, 1989a). The s e contaminants should be evaluated, or af u r t h e r rationale for their exclusion should be provided. T h e i r presence in al luvial ground water and in wastep i t sample s sugges t s migration f rom th e l and f i l l .Section_3.4.2.1 p a g e 3-30 The p a r a g r a p h sections on " F i e l d measurements of a lka l in i ty" and hydrau l i c headdata" do not be long in th i s section on " V o l a t i l e Organic Compounds." Relocate to aii a p p r o p r i a t e section.S e c t i o n ,3.4.&1_n-8ge_3^3Q The same comment regarding section 33.1.1.1 page 3-6 a p p l i e s .S e c t f o i i - 3 * 4 4 . 4 - P - f l g e 3-32 The paragraphs explaining "field ph," "conductivity/ and "the dis tribution ofinorganic and organic compounds" do not belong in this section ent i t l ed "Inorganic compounds." Relocateto a p p r o p r i a t e sections, or create new sections.

Sect»n_3_.4.2.5 page 3-33 Wel l 217 inorganic data - Tlie discussion presented here correctly p o i n t s out tha tground water q u a l i t y at MW-217 d i f f e r s from nearby wel l s in both the alluvium and the Garber-WelHngton.It fur ther suggests an exp lanat ion for these d i f f e r e n c e s may be sorpt ion by mudstone in the vicinity of MW-217 is not a f f e c t e d by recharge from the overlying alluvium. The data presented does not support anyargument for the source of the anomalously high water levels since both downward and upward moving waterf lowing through the sorptive mudstone could cause the obseived lower concentrations of inorganics,Section 3.6.2,2 page 3_-4Q The f igure number should be 2-35 not 2-36,Sectiot3_3.8.1 page 3-47 The conclusion drawn here t h a t the waste p i t s did not act a source of inorganics toshal low ground water is not s uppor t ed by the barium, iron and manganese da ta for wells in the vicinity of thepi t s . These m e t a l s show elevated concentrations near the waste p i t s recognizing tha t historical grad i en t s werel ik e ly radial due to i n f i l t r a t i o n from the p i t s . F u r t h e r , any a t t e m p t io try and separate the e f f e c t s of the wastep i t s from the l a n d f i l l p r o p e r is not recommended, given the complex nature of both sources, the size of thestudy area and the limited number of data p o i n t s available to evaluation.Section. 3J{.l,__pflfiejM7 It ,'s stated that "inorganic results for alluvial ground water strongly suggest thatmigration of inorganic compounds from the waste pit has not occurred, al though it does appear that leachatefrom the l a n d f i l l refuse may have caused increased concentrations of inorganic compounds in alluvial groundwater." TTiis statement is contradictory. Lead, cadmium, and nickel were detected both in waste pit soilsample s (page 3-3, RI report, 1991) and al luvial ground water (page 3-19, RI report, 1991). Di s t ingu i sh ingbetween migration f rom "waste pits" and "landfill r e f u s e leachate" is not pos s ib le with the d a t a c o l l e c t e d .L a n d f i l l r e f u s e lies on top of and below the waste p i t s over the a l l u v i a l ground water.S e c t i o n _3.8,1 p a g e 3^47_jme 4 Change "arc" to "area."S e c t i o n _3.8.3 _ p f - a e 3^j8 No mention is made of impac t s to sur face water by sur fac e r u n o f f . However,surface impacts are a l lud ed io in section 3.8.4, line 2, but are addressed as no impacts on page 5-2,liue 24-25. Rewrite for consistency.S_ectji)n_4.1 page 4-1 Reword discussion to state that the Risk Assessment was performed to provide a basiswhether remediation is warranted, not to support the selection of the "no action" alternative.Sec t io i i_4--K1 p a g e J - 2 It does not seem a p p r o p r i a t e to discount a value of it is less than 10 time;*, the b lankconcentration. W h a t is basis for the "ten times" value used here?S e c t i o n 4.1.1.3 p a g e s 4-13_ -_4-_S4 Severa l of the p r o f i l e s for the inorganics (e.g. Chromium, Cobal t , Leadetc.) have addressed p o t e n t i a l carcinogenic action and the EPA/IARC ranking in the paragraph s di scus s ingenviron mental t r a n s p o r t , bioaccu mutat ion, etc. T h i s i n f o r j i a t i o n would more a p p r o p r i a t e l y be with thelexicological in format ion .Seciion_4.1_.1.3 sage 4-32 The chemical p r o f i l e for carbon tctrachloride l i s t s the EPA Carcinogenic Rankingas B3. T h i s is incorrect the correct ranking is B2. The corresponding tabular information is correct.S e c t i o n 4 , l . J L . . L p _ a g e 4-gO a a d j 1-51 The chemical p r o f i l e for heptachlor separates the statements oa EPAand IARC carcinogenic c las s i f i cat ion between two paragraphs; they should be discussed in the sameparagraph. H e p t a c h l o r [sic] is m i s s p e l l e d in the next to the la s t line on page 4-50.Sectit>o__4iJ.?-. pnge 4-54 Tin's section should inc lude an assessment of the p o t e n t i a l l y exposed p o p u l a t i o n .

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gectkm 41.2.1._i)age_4-56 Pathways of exposure to surface soil contamination were eliminated becauseof the "existing low-permeabi l i ty clay cap, f enc ing, and erosion-reducing vegetation . . . ." However, cyanidewas detected in 14 of 14 surface soil samples, chlorobenzene in 9 of 13, 1,1,2-trichtoroethane m 9/14, andt e t racJi loro e th ene in 5 of 13 sur fac e soil sample s ( T a b l e 4-1, RI report, 1991). Cyanide was also detected inwaste pit soil samples. The fencing may prevent direct contact with soils currently, but no possible fu tureconditions at the site were addressed. The contamination present m surface soils should be evaluated witnregard to risk.Section 4.1.2.1, .page 4-56 It is stated that "Future use pathways ... are essentially identical to currentuse pathways because conditions are not expected to change s i g n i f i c a n t l y in the future." Thi s statement isunsupported by any planning d a t a or Bureau of Census projec t ion data or by any other valid ju s t i f i ca t i on.The site is bordered by Oklahoma City, Midwest City, and Crutcho. While residential development may notbe likely, other uses of this site that may increase the likelihood of soil exposure pathways are possible. Theseshould be evaluated.S_ectioD_4_; 1,2.2! page, .4*58 It is not clear if only ground water concentrations from within the plumewere used to ca l cu la t e a repre s entat ive value for ground water. The values used to determine therepresentative ground water concentration should be providedSection .41,2.2 pjme_4^£ and 4-60_ The equation on the top of page 4-60 should more appropr ia t e ly read asfo l lows:

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Tafek-4-13 and.. T a b l e _4°14 The source for the T a b l e should probably be references U.S. EnvironmentalProtection Agency, 1990a and I990b rather than 1990c and 1990d, respectively.Section 4,1 J . l . p a j j e 4-jj4 In the Rfd discussion, change "conservative s a f e t y factors" to "uncertainly factors".Section .4.1.4. page 4-73 Unmodi f i ed oral reference doses (RfD) and s lope fac tors (SF) were used to calculatedermal risks. It is s tated tha t , "an impl i c i t a s sumpt ion was made that the relative dermal and oral absorptionfraction for humans is equivalent to ... (hat of the animals . . . used to derive the various toxicity factors,"No assumption was made regarding the "relative dermal and oral absorption fraction" between humans andanimals. When oral RfDs and SFs are modif i ed to calculate dermal risks, it is because s u f f i c i e n t data ondermal exposures is lacking in both animals and humans. The implici t a s sumpt ion that was made by usingoral RfDs and SFs without modi f i ca t ion is that an oral administered dose is equivalent in toxicity to a dermalabsorbed dose. In other words, 100 percent of the oral dose is absorbed. Thi s may be valid for somecompounds. The EPA guidance recommends m o d i f y i n g the RfDs and SFs by an oral absorption frac t ion forthe compound of interest (EPA, I989a j .Segt joa .j J .4. page 4-13 Inorganic compound-; were assumed to not be absorbed dermally. Lead andcadmium were de t e c t ed in ground water. Dermal absorpt ion of these contaminant s may be between 1 and9 percent of the a p p l i e d dose (Cassarret arid Doul l , 1980).

Section jJ-2f3T3. page_4*J)4 A short paragraph summarizing the reasons that e f f e c t s on endangered orthreatened species are not h'kely would be appropriate .

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Sec t i on 44A2. page 4-10Q It is stated that "toxic concentrations reported for laboratory animals ... areused as appropriate. I h e s e comparative values are summarized in Table 4-57 for chemicals of potentialconcern . . ." The values reported in T a b l e 4-57 are iiot "toxic concentrations," but they are toxic doses. TheLDjo « the dose of a compound that produces 50 percent mortali ty ia a test group of animals. It isinappropriate to compare LDJ O data with concentrations of contaminants in soil, sediment, and water. Nodoses have been calculated for terrestrial or aquatic organisms in this assessment.The statement that "this approach assumes that concentrations are transferred from soils through vegetationat 100 percent of the reported amount ..." is misleading. Direct exposure to contaminants in soils, surfacewater, and sediments may occur, depending on the organism. F u r t h e r m o r e , a p p a r e n t l y low concentrationsin these media may result in p o t e n t i a l l y toxic doses depending on the contact rate, exposure frequency andduration, and the size of the organism. As an example, a 20-gm (0.020 kg) mouse inges t ing 10 ml of waterper day from Crutcho Creek at the SW-08 location could receive, in 1 year, a dose of lead 30 percent higherthan the LDJ O for tetraethyl lead (assuming 100 percent absorption and retention). This example is notintended as an assessment of site contamination but i l l u s t r a t e s t ha t comparing doses with concentrations isinappropriate and can be extremely misleading,In addi t ion, even if doses were calculated from envuonmental concentrations, LD50 data provide noi n f o r m a t i o n concerning p o t e n t i a l adverse e f f e c t s at lowered doses. The dose-response curve may be such thatthe d i f f e r e n c e between a nontoxic dose and a lethal dose is very small or very large depending on thecontaminant, the species, and f a c t o r s such as contaminants and nutrit ional status.On page 4-107, it is s ta l ed that "tin's method . . ." (referring to comparison of LDJf) data with mediaconcentrat ions) "is a conventional way of addre s s ing w i l d l i f e risks . . . ." T h i s s tatement is f a l s e , for thereasons cited above. Acute toxicity tests, such as LQo (lethal concentrations producing 50 percent mortali ty)and LD50, are used to assess the toxicity of site contaminants and es tabl i sh a causal link to adverse e f f e c t snoted at a site (EPA, 1989b). The manner in which I,DJO d a t a are used in t h i s assessment, however, is notappropriate . It appears from the use of the term "LDSO concentration" on page 4-108 that the authorsmisunders tand the concept of LD50. All of the discussion relat ing media concentrations and LD40 da ta shouldbe dele ted from the report.S e c t i o n 4.2.63, _0_age 4_»1_Q9 As s t a t e d , lead does not b i o m a g n f f y . However, it bioconcentratess i g n i f i c a n t l y in lower organisms, such as algae, in which bioconcentration factors (BCF) as high as 92,000 havebeen reported (Eisler, 1988). B C F s of 49 have been reported in f i s h (EPA, 1988). Concentrations of leadless than the 36 ug/1 reported in Crutcho Creek have been shown to cause reproductive impairment inDaphnia species and s igni f i cant mor ta l i ty in snails, protozoans, and ampb ipod s (Eisler, 1988). Similarconcentrations have produced adverse e f f e c t s on pre- and pos t-hatch fry and small trout (Eisler, 1988). Thi sinformation indicates that the concentrations of lead and other metals in Crutcho Creek require f u r t h e revaluation. Crutcho Creek is described in the report as a "perennial stream tributary to the North CanadianRiver'1 and harbors at least 17 f i s h species (Sec t i ons 1.0 and 4.0, G o l d e r Assoc., Inc. 1991). T h i s assessmentdoes not appear to adequate ly assess contamination and po t en t ia l adverse e f f e c t s of the migration of metalsand other contaminants from the Moslcy Road l a n d f i l l .Section 4.2.63, P3ec_4~lQ9 The statement that "elevated lead and cadmium concentrations were bothdetec t ed at the downstream Crutcho Creek s a m p l i n g s ta t i on (SW-08) . . ." is s u p p o r t e d by the da ta presented.However, this statement is directly contradicted by the statement that "none of the inorganic compounds .. . are elevated in surface water . . ." which is made on page 3-39 (RI report, 1991). Thi s inconsistency shouldbe corrected.

4 63. pagp-4-109 The cadmium concentration in Crutcho Creek is reported in the text to be

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above chronic toxicity s tandards , but cadmium has been omitted from the tables at the end of Section 4.0.This should be corrected,

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Sec t i on 4.2.6.3, p a g e 4 _ ° 1 1 0 It is s ta t ed that "the individual sur face water values for cadmium, lead, , .. represent isolated detections suggesting no conspicuous pattern of widespread or excessive contamination."The elevated lead and cadmium concentrations were detected in the one sampling round conducted a f t e rsampling station SW-08 was moved to a downstream location where alluvial ground water from under thesite discharges into Cruicho Creek. It is not pos s ib le to evaluate whether a "pattern" of contamination exists,based on only one sampl ing round at one locat ion. Lead and cadmium were de t ec t ed in waste pit soilsamples and alluvial ground water. Contamina t i on of Crutcho Creek requires f u r t h e r evaluation. Thedismissal of the pos s ib i l i ty of any contamination in the creek resulting from the site is unsupported by thecurrent data.Sec t i on 4.2.6.3. page 4-110 References and s u p p o r t i n g data are lacking throughout the report and areabsent p a r t i c u l a r l y in the environmental evaluation section. I m p o r t a n t examples in this section include"aquatic p l a n t s are re la t ive ly u n a f f e c t e d by these general classes of chemicals ,. .,* "the highest sedimentconcentrations of chemicals of po t en t ia l concern are orders of magni tude lower than the levels usuallyassociated with toxic e f f e c t s on aquatic macroinvertebrates ...," and "the reported sediment levels are typicalof the n a t i o n ' s natural waterways." If appropriate references or suppor t ing data are not included* thesestatements and similar ones should be eliminated.S e c t i o n A2-6.3. page_4-11.4 Background d a t a and adequa t e r e f erence s are not presented to suppor t thes ta t ement that "sediment concentrations are within ranges reported for uncontani inated soils...." The lackof background data (site-speci f ic and regional) is a serious omission throughout the report and should becorrected.Sec_tiQ_n_4.2,6>4t Page_4-114 The LD50 discussions should be eliminated. Tile entire discussion of thep o t e n t i a l adverse e f f e c t s of the organic compounds in sur face water is a p p a r e n t l y based on suppo s i t i on . Itshould also be e l iminated.Scctjoo_4_.2.6.4, i > f t g c . 4 j l l 6 References and comparative data should be included to support s tatements(1) regarding theinsolubili ty of l ead, "low concentrations" of metals in sediments, and (2) that selenium is present inconcentrat ions similar to "average soil concentrations."Section_4.2.7.3. gage 4-U7 Dele t e the discussion of "LD30 concentrations," as discussed previously.Sect ion 44.7,4, page 4-U8 The statement that concentrations of lead and selenium are not above theContract Required Detection Limits (CRDL) contradicts the da ta presented in Tabl e 4-54.3^_b|e_4-5 The sediment d a t a reported in this t a b l e are reported in ug/I instead of mg/kg, Tliis isobviously erroneous and prevents any evaluat ion of the data. It should be corrected.S e c t i o n . . . S J L p a g g 5-tf It is not appropr ia t e to indicate that the shallow ground water ingestiou route isimprobable because only one well is located in the alluvium near the site. RAGS requires that the probablemaximum exposure scenario is evaluated for both current and f u t u r e use.Section. 5.4.1. page 5-8 Provide f u r t h e r e x p l a n a t i o n of why "the lack of d a t a r egarding seasonal variationshi ground water qual i ty is not considered a s ignif icant limitation."SegjloiLJj'g^pageJlli The discussion on page 5-10 states that "uncertainty exists in the degree ofcommunication between the alluvial and Garber-Well ington aqui f er s , The d a t a ui A p p e n d i x I suppor t s thef a c t of uncertainty as to the amount of i n f i l t r a t i o n , and it also s u p p o r t s the fa c t of uncer ta inty as to thedegree of communication between the l e a c l i a t e interval and the alluvial aquifer. Since this occurrence seems

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to be related to seasonal conditions, as the ground-water qual i ty is, is it reasonable to not consider theseissues in the evaluation of additional data needs?Sec t i on 5.5 page 5-12 Since the second round of sampling is wi th in 1 order of magni tude lower thanconcentrations associated with potent ial health risk, sediment samples in the North Pond area shall becollected, EPA request that the samples be kept on the list of addit ional data needs. The additional samplingdata should be incorporated into the ecological assessment. Also, EPA request that the f o l l ow ing items beadded to the list of addi t ional da ta needs.

1. Collect ion and analysis of u n f i l t e r e d groundwater wells. Thi s is needed to estimate exposureconcentrations.2. Collect ion and analysis of grouadwater f rom the pr iva t e ly owned wells located around the

l a n d f i l l . T h i s must be done to determine if contaminants have migrated to the pr iva t e lyowned wells.

Se<;tion_5.1 page 5-3. l ine 14-15 T h i s comment references the elevated contaminant levels north of the l a n d f i l lin the surface water and the associated sediment sample . P.2-121, line 24-25 and P.2-122,line 1-3,indicate s the source of contaminat ion is "sediment r u n o f f . " P.3-36, section 3.5.2.1, line 12-13, ind i ca t e sthat "seeps may account" for the elevated levels. P.3-49, section 3.8.5, line 9-13, indicates that surfacesoils have been p o t e n t i a l l y impacted by discharges from seeps. P.3-4G, section 3.6.2.2, line 24-26 and P.3-41,line 1-4, indicates that seeps or municipal refuse in that area could be the source of contamination. P.3-48,section 3.8.4, line 3, indicates p o t e n t i a l impacts from seeps originat ing within the l a n d f i l l . P.5-2, l ine 29-30and P.5-3, line 14-15, reference "seeps o r ig ina t ing wi th in the landfill "and" seeps t h a t occur on both sides ofth e l a n d f i l l .These references are in indication of not only a lack of consistency, but also of unnecessary repet i t ion.Rewrite to reduce the r e p e t i t i o n and el iminate the inconsistencies. The most important aspect is that mostof these references point to seeps as the source without any da ta to s uppor t the contention. It is j u s t as l ik e lythat the source is the municipal r e fu s e referred to on P.3-41, or separate dumping not related to cither. Theseeps should have been sampled when they were observed to ascertain if they were source.S e c t i o n 6.0 Several of the re f erence s are i n c o m p l e t e , e.g. Cannon 1983, Canrot 1986, Doll 1989, J o n g a n 1985,and Kai s c 1985.

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VOLUME IGeneral CommentsT a b l e s MosJ tables and text report parameter levels in parts per million; however, some tables (example 4-1to 4-7) report parameters in parts per bil l ion. Correct ah" parameter levels to report data in parts per million.

14 The 1144 elevation contour is drawn such that the Garber-Wellington water level is higher thanthe alluvial water level on 6/19/90. Rsdraw the contour.

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R E F E R E N C E S

Cassaret and Doull , 1980, "Toxicology" (Second Edit ion), Macmi l lau Publi shing Co., New York.Eisler, 1988, "Lead Hazards to F i s h , W i l d l i f e , and Invertebrates: A S y n o p t i c Review," R. Eisler, U.S.Fish and W i l d l i f e Biological Report 85 (1.14), Contaminant Hazard Reviews Report No.14. April1988.EPA, 1988, "Public H e a l t h Risk Evaluat ion Daiabase," personal c omput er so f tware package publ i shedSeptember 16, 1988 to updat e information in the " S u p e r f u u d Public H e a l t h Evaluation Manual".October 1986.EPA, I989a, "Risk Assessment Guidance for S u p e r f u n d , Vol. 1, H u m a n H e a l t h Evaluation Manual(Part A) Interim F i n a l , " EPA /540/1-89/002. December 1989.EPA, 1989b, "Ecological Assessment of Hazardous Waste Sites: A Fie ld and Laboratory Reference,"EPA/600/3-89/013 . March 1989.EPA, 1990, "Guidance for Data Useabih'ty in Risk Assessment" EPA/540/G-90/008. October 1990.G o l d e r Associates, 1989, "Mosley Road S a n i t a r y L a n d f i l l Remedial I n v e s t i g a t i o n / F e a s i b i l i t y S t u d y(Rl/FS) Work Plan. December 1989.

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[draft parallel baseline risk assessment for the … · 2018. 9. 8. · the variogram using curve...

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