unc-wrri -82-1 79 trihalomethane formation in water …

UNC-WRRI -82-1 79

TRIHALOMETHANE FORMATION I N WATER

TREATMENT PLANTS I N NORTH CAROL1 NA

P h i l i p C. Singer, James J. Barry 111, Glenn M. Palen, and Alan E. Scr ivner Department o f Environmental Sciences and Engineering

School o f Pub1 i c Heal th U n i v e r s i t y o f Nor th Carol i n a

Chapel H i l l , North Carol ina 27514

The work upon which t h i s p u b l i c a t i o n i s based was supported i n p a r t by funds provided by t h e O f f i c e o f Water Research and Technology, U. S. Department o f t he I n t e r i o r , Washington, D.C., through the Water Resources Research I n s t i t u t e o f The U n i v e r s i t y o f Nor th Carol ina as author ized by the Water Research and Development Ac t o f 1978.

P r o j e c t No. 6-1 26-NC

Agreement No. 14-34-0001 -9035, FY (1 979

A p r i l 1982

ACKNOW LEDGFIENTS

The authors would l i k e t o acknowledge the assis tance o f the superv isory and operat ions personnel assoc ia ted w i t h the var ious water u t i l i t i e s p a r t i c i p a t i n g i n t he survey, and the Water Resources Research I n s t i t u t e (WRRI) o f The U n i v e r s i t y o f Nor th Caro l ina f o r sponsoring t h i s research e f f o r t .

This research was c a r r i e d o u t i n the Department o f and Engineering o f the School o f Pub l ic Health, Univers Chapel H i l l . A t the t ime o f t h i s study, Flessrs. Barr.y,

Environmental Sciences i t y o f North Carol i n a a t Palen and Scr ivner were

graduate students i n t he Water ~ e s o u r c e s Engineering Program. Mr. Bar ry i s c u r r e n t l y a p r o j e c t engineer f o r t he Los Angel es County S a n i t a t i o n D i s t r i c t s , Carson, CA; M r . Palen and M r . Scr ivner a re engineers w i t h CH2M-Hill Consul t ing Engineers i n Ga inesv i l le , FL and C o r v a l l i s , OR, r e s p e c t i v e l y . Dr. Singer i s a Professor i n the Department o f Environmental Sciences and Engineering a t UFIC .

DTSCLAZ MER STATEMENT

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ABSTRACT

Analyses for t r i halomethanes in drinking water showed that t h i s c lass of contaminants i s formed during the course of water treatment in nine of the larger c i t i e s in North Carolina. Concentrations of these suspected carcino- gens frequently exceeded the establ i shed maximum contaminant level a t three of these locations.

Examination of several potenti a1 surrogate measures of t r i ha1 omethanes suggests tha t ul t rav io le t absorbance and total organic carbon are good indi - cators of t r ihal omethanes and the i r precursors. In addition, s t a t i s t i c a l analysis of data was used to identify seasonal variations, temperature e f fec ts , geographical trends, and other water qua1 i ty characteri s t i c s and treatment practices con t r i buti ng to the formation of t r i ha1 omethanes. The use of a standardized t r i ha1 omethane formation potenti a1 procedure proved to be particularly useful in this regard.

Chlorination and coagulation practices a t the Sweeney water treatment plant, in Wilmington, N C , were examined in an e f f o r t to reduce trihalomethane production. The point of i n i t i a l chlorine application was shifted to a point following sedimentation, reducing finished water THM concentrations substant ial ly . Similar resul ts were demonstrated, on a laboratory-scale, for Chapel Hill and Raleigh waters.

TABLE OF CONTENTS

LITERATURE REVIEW ....................................................... Previous Tr i halomethane Surveys ...................................

Discussion of Surveys ........................................... Methods fo r C o n t r o l l i n g THM Formation i n D r ink ing Water -----------

Removal o f THM Precursors by Coagulat ion ........................

Analys is o f Data and Discussion o f Resul ts ........................ S t a t i s t i c a l Techniques U t i l i z e d ................................. Surrogate Trihalomethane Measurements ........................... Changes i n THM and TOC Concentrat ions During the Course o f Water Treatment ................................................. Seasonal Va r ia t i ons and Temperature E f f e c t s ..................... Geographical Trends i n THM Formation ............................

LABORATORY-SCALE STUDIES OF TRIHALOMETHANE PRECURSOR REMOVAL ------------

Rale igh ....................................................... Wilmington ....................................................

Summary and Discussion of Resul ts .................................

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LIST OF FIGURES

Page

Hydrologic Features of North Carolina ............................ 26

Correlation Between Instantaneous THM Concentration in Finished Waters and TOC Concentration i n Raw Water ........................ 45

Nest t o East Distr ibution of THMs and TOC i n North Carolina Drinking \ later ................................................... Prel iminary Experimental Procedure f o r Eval uati ng the Effect of Coagulation on THM Formation .................................. Modi f i ed Experimental Procedure f o r Eval uati ng the Effect of Coagulation and Pre-oxi dation on THM Formati on ------------------- Flow Diagram f o r Wilmington Water Treatment Plant ---------------- Seasonal Variation in Raw Water Qua l i ty a t the Sweeney Water Plant ............................................................

J a r Test Procedure f o r Wilmington Coagulation Studies ------------ Effect of pH on Coagulation w i t h Alum (Sample 1 ) ----------------- Effect of pH on Coagulation with Alum (Sample 2 ) ----------------- Effect of Alum Dose on Water Quality (Sample 1 ) ------------------

LIST OF FIGURES (continued)

Page

19. Effect of Alum Dose on Water Qua l i ty (Sample 2 ) ---------------- 98

20. Effect of pH on Coagulation with Ferric Sulfa te (Sample 1 ) ----- 100

21. Effect of pH on Coagulation w i t h Ferr ic Sulfa te (Sample 2) ----- 101

22. Effect of Ferric Sulfa te Dose on Water Quaii ty (Sample 1 ) ------ 102

23. Effect of Ferric Sulfa te Dose on Water Qua l i ty (Sample 2 ) ------ 103

LIST OF TABLES Page

National Organics Reconnaissance Survey (NORS) .................... 7

National Organics Monitoring Survey (FiOMS) ........................ 9

THM Levels in East Texas Water Supplies ........................... 11

Survey of Tri halomethane Levels i n Kentucky Water Suppl i e s -------- 13

Case Study of Two North Carolina Water Supplies ------------------- 17

F a c i l i t i e s Par t ic ipat ing in THM Monitoring Survey ----------------- 2 4.

Sources of Water f o r F a c i l i t i e s in THM Survey ..................... 2 7

Capacity, Demand, and Detention Time Information f o r F a c i l i t i e s Surveyed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

!4orth Carol i na Tri ha1 omethane Survey Results: Selected Water Quality Parameters on Days of Sampling ............................ 38

Average TOC and THM Concentrations f o r Each of the F a c i l i t i e s Included in the North Carolina Survey ............................. 4 2

Surmary of Linear Regression Analyses ............................. 52

Seasonal Variations i n Average TOC and THM Concentrations --------- 55

Temperature Variations in Average TOC and THM Concentrations ------ 5 6

Raw Water Character is t ics f o r Preliminary Tests ------------------- 6 7

LIST OF TABLES (cont inued)

Page

Raw Water C h a r a c t e r i s t i c s f o r Modified T e s t s ------------------- Resu l t s of Coagulation and Permanganate Pre t rea tment of Chapel H i l l Raw Water .................................................

Resul t s o f Coagulation and Ozone Pre t rea tment of Chapel H i l l Raw Water ...................................................... Resu l t s of Coagulation and Ozone Pre t rea tment of Raleigh Johnson Raw ) la te r ......................................................

Resul t s of Coagulation and Permanganate Pre t rea tment o f Wilmington Raw Water ...........................................

Resul t s o f Coagulation and Ozone Pre t rea tment of Vi lmington Raw Nater ...................................................... Summary of Resul t s of Coagulation S t u d i e s ...................... Resul t s of Wilnington Sampling Program ......................... Resul t s o f Wilmington THM Analyses Performed by Independent Laboratory .....................................................

Water Qual i ty C h a r a c t e r i s t i c s o f Wilmington Water Used f o r J a r Tes t s ---------------- - ------- ..................................

SUMMARY AND CONCLUSIONS

On November 29, 1979, the U . S . Environmental Protection Agency established a Maximum Contaminant Level (MCL) of 0.10 mg/l for total t r ihalomethanes (TTHMs) in drinking water. In anticipation of th i s regulation, a two-year research project was in i t i a t ed i n September, 1978 to assess t r ihalomethane (THM) formation in North Carol ina drinking waters. Thirteen water treatment plants in nine of the major c i t i e s in North Carolina were sampled as par t of th is investigation. The c i t i e s included Asheville, Chapel Hil l , Charlotte, Durham, Gastonia, Greensboro, Raleigh, Wilmington, and Winston- Salem. Samples were collected a t each of the water treatment f a c i l i t i e s in these c i t i e s and analyzed f o r total organic carbon ( T O C ) , instantaneous and terminal (7-day) trihalomethanes, chlorine demand, and u l t rav io le t ( U V ) absorbance. Raw, se t t l ed , and finished water samples were taken. The data were analyzed by comparing the measured THM concentrations w i t h the 0.10 mg/l standard and with the organic carbon content and other physical and chemical water quality and treatment parameters in order to ascertain the existence of s ignif icant correlations between these parameters and THM formation. Each of the plants was sampled on a seasonal basis to allow for an examination of seasonal and temperature-related trends in THM formation.

The resul ts of the investigation showed tha t trihalomethanes were formed during treatment a t a l l locations investigated in th i s study. During the study period, the average concentration of TTHMs i n the finished water was found to be 72 pg/l, and the median concentration was 58 pg/l. For most of the treatment plants sampled, chloroform was the only THM species detected. No signif icant concentrations of THFls were detected in the raw water samples analyzed.

Both total organic carbon and seven-day chlorine demand of the raw water correlated well with the t r i halomethane formation potential of the raw water, and appear to be useful general indicators of the concentration of THMs i n finished water. Ul t rav io le t absorbance exhibited very strong correlations with t r i ha1 ome thane forma t i on potential and total organic carbon concentration i n raw water, as well as with instantaneous THM concen- t ra t ion in finished water. This suggests tha t UV absorbance could serve as a valuable surrogate for the measurement of THMs and TOC. In general, a1 1 of these correlations improved w i t h the elimination of data from those f a c i l i t i e s included in the survey which do not prechlorinate raw water.

Tri ha1 omethane concentrations increased during the course of treatment, with 50-70 percent of the concentrations in the finished water having been produced by the time the water passed through the se t t l i ng tanks. Coagulation and s e t t l ing, and f i 1 t ra t ion reduced terminal THM concentrations an average of 42 percent and 54 percent, respectively.

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Both seasonal and temperature v a r i a t i o n s i n THM format ion were observed. Instantaneous tr ihalomethane concentrat ions i n the f i n i s h e d water were found t o be lowest i n the w in te r months, w i t h h ighe r concentrat ions occur r ing i n the summer. This i s presumably the consequence o f slower r e a c t i o n k i n e t i c s a t the Tower w i n t e r temperatures as we1 1 as lower THM precursor concentrat ions i n the raw water dur ing the w i n t e r months. The h igher concentrat ions o f THMs i n the f i n i shed water du r ing the s u m r months appears t o be due t o bo th fas te r r e a c t i o n k i n e t i c s and the presence o f a g rea te r concent ra t ion o f precursors i n t h e raw water. The use o f a standardized te rmina l tri halomethane measurement, i n which pH and con tac t t ime are h e l d constant and excess c h l o r i n e i s provided, a1 lows comparisons among THM format ion p o t e n t i a l s o f the waters and al lows v a r i a t i o n s i n precursor content t o be separated from temperature, i .e. k i n e t i c , e f f e c t s .

A geographical d i s t r i b u t i o n o f THM format ion and raw water TOC was observed, w i t h lower concentrat ions occu r r i ng i n the western mountainous p a r t of t he s t a t e and increas ing toward the coasta l p l a i n s i n the east . Di f ferences i n the vegeta t ive content o f the watersheds and the accumulation o f humic ma te r ia l i n the surface waters as they f l o w toward the coast appear t o be responsib le f o r t h i s d i s t r i b u t i o n .

O f the t h i r t e e n p l a n t s analyzed, f o u r were found t o c o n s i s t e n t l y exceed the 100 pg/ l MCL f o r TTHMs i n the f i n i s h e d water. These f o u r p lan ts , Chapel H i l l , Raleigh-Baln (Southside), Raleigh-J~hnson (Norths ide) , and Wilmington are a l l l oca ted i n the eastern-most p o r t i o n o f North Carol ina. Wilmington, on t h e eas t coast of Nor th Carol ina, had the h ighest concentrat ions o f THMs i n the f i n i s h e d water among a l l the c i t i e s surveyed.

Durham, desp i te i t s h igh l e v e l s o f TOC and UV-absorbing substances and i t s h igh THMFP, had s i g n i f i c a n t l y lower concentrat ions o f THMs i n i t s f i n i shed water compared t o i t s neighboring Piedmont c i t i e s . This observat ion i s bel ieved t o be due t o the f a c t t h a t Durham does n o t p rech lo r ina te i t s raw water.

I n response t o these h igh THM l e v e l s and the observat ions made a t Durham, 1 aboratory experiments were conducted on raw waters from Chapel H i 11 , Raleigh, and Wilmington t o i n v e s t i g a t e the e f f e c t s o f coagu la t ion on the removal o f THM precursors, and the i n f l uence o f pretreatment ox idants on the e f fec t iveness o f coagulat ion. The cond i t i ons f o r measuring tr ihalomethane format ion p o t e n t i a l were standardized t o a i d i n comparisons between d i f f e r e n t experiments and t o i n d i c a t e r e l a t i v e amounts o f THM precursors present.

These 1 aboratory s tud ies showed t h a t coagulat ion w i t h a1 um f o l lowed by s e t t l i n g can s u b s t a n t i a l l y remove THM precursors i n a d d i t i o n t o o ther organics i n d r i n k i n g water. The THMFP was reduced an average o f 60%, and TOC was reduced by about 50% due t o coagu la t ion and s e t t l ing . UV absorbance and c h l o r i n e demand, o the r i n d i r e c t measures o f the nature and concent ra t ion o f organic substances i n the water, were reduced by 70% and 50%, respec t i ve l y . Accordingly, moving the p o i n t o f c h l o r i n a t i o n downstream o f s e t t l i n g should markedly reduce the format ion o f tr ihalomethanes a t the three t reatment p lan ts inves t iga ted.

Ox ida t i ve t reatment o f the raw water by ozone o r permanganate a t normal water t reatment p l a n t dosages reduced the concent ra t ion o f tri ha1 omthane precursors t o a s l i g h t degree. The nature o f t he organics was a l t e r e d by ox ida t ion , as i n d i c a t e d by changes i n UV absorbance. Pretreatment ox ida t i on , however, d i d n o t a f f e c t the subsequent behavior o f alum i n removing t r i h a l o - methane precursors.

I n accordance w i t h the r e s u l t s o f these l a b o r a t o r y j a r t e s t experiments, the p o t n t o f i n i t i a l c h l o r i n e a p p l i c a t i o n a t the Sweeney Water Treatment P l a n t i n Wilmington was s h i f t e d from the head o f the r a p i d mix tank t o a p o i n t f o l l ow ing sedimentat ion. This s h i f t r e s u l t e d i n a s i g n i f i c a n t decrease i n instantaneous THM concentrat ions i n the f i n i s h e d water from approximately 215 wg/1 t o about 90 ug / l . The concent ra t ion o f THM precursors was reduced by 50 t o 60 percent as a r e s u l t o f coagu la t ion and sedimentat ion p r i o r t o t he a d d i t i o n o f c h l o r i n e . I n l i g h t o f the r e l a t i v e success achieved a t the Wilmington p lan t , the remaining p lan ts i n Nor th Caro l ina which s t i l l have THM concentrat ions i n excess o f the MCL should consider s h i f t i n g t h e i r p o i n t o f i n i t i a l c h l o r i n e a p p l i c a t i o n from the r a p i d mix chamber t o a p o i n t f o l l ow ing sedimentat ion o r f i l t r a t i o n , prov ided adequate d i s i n f e c t i o n can be maintained.

INTRODUCTION

On November 29, 1979, the Environmental Protection Agency ( E P A ) amended the National Primary Drinking Water Regulations to include a f inal regulation for the control of trihalomethanes (THMs) in drinking water. This amendment establ ishes a Maximum Contaminant Level (MCL) of 0.10 mg/l and associated moni tor i ng and reporting requi rements for total t r i ha1 omethanes (TTHMs) that are introduced into drinking water during the course of water treatment through the reaction of natural ly-occurring organic substances and chlorine (Environmental Protection Agency, 1979). The regulation i s summarized in Table 1. This legis lat ion i s a part of EPA's overall strategy to reduce human exposure to hazardous organic chemicals. The Safe Drinking Water Act (PL 93-523) gives EPA the power to regulate contaminants tha t have the potential for adverse effects on human health, and to do so without defini- t ive proof of the harmful e f fec ts .

Background

I t has not been until the l a s t six or seven years tha t there has been any great in te res t in the study of chlorinated organic materials (including t r i halomethanes) in drinking water. I t i s 1 i kely that chlorinated organic compounds have always been formed during water treatment when chlorine i s used for disinfection, b u t only recently has the a r t of trace organic analysis advanced to the point where some of these compounds could be detected and rel iably quantified.

Rook (1974) in the Netherlands and Bellar, Lichtenberg, and Kroner (1974) in the United States were the f i r s t to demonstrate the presence of t r ihalomethanes in finished drinking water. Analysis of the raw water a t the same study locations showed these compounds to be e i ther absent or present a t very 1 ow concentrations, and the conclusion was drawn tha t the t r i halomethanes were formed when chlorine, used for disinfection, reacted with precursor substances to form chloroform and other halogenated organic compounds. A t the same time, a study of water quality in the lower Mississippi River (Environ- mental Protection Agency, 1974) indicated the presence of carcinogenic organic chemical s , and an epidemiological study of sel ected populations in New Or1 eans (Page and Harris, 1974) indicated a possible correlation between drinking water qua1 i t y and the incidence of cancer.

Publicity resulting from these studies hastened the passage of the Safe Drinking Water Act and led to additional studies surveying the nation's water supplies for organic contaminants (Syrnons e t a1 ., 1975; Environmental Pro- tection Agency, 1977). The surveys showed the occurrence of trihalomethanes in finished drinking water to be widespread and a d i rec t resu l t of the chlorination step in water treatment. In 1978, the EPA proposed a two-part regu- 1 ation to control t r i halomethanes and synthetic organic chemical s in drinking water (Environmental Protection A$?ency, 1978). Both parts of the proposed regulation were met with strong opposition fo r various reasons. The argu- ments against the regulation were founded on the contention that the epidemiological studies tha t had been conducted had fai led to establish a l ink between trihalomethanes and synthetic organic chemicals in drinking water and cancer in humans, and that the EPA had had to rely on extrapolation of

Table 1 Summary of TTHM Regulations

Fiaximum Contaminant Level ( M C L ) = 0.10 mg/l (100 micrograms per l i t e r ) Total Trihalomethanes

Appl icabi l i ty : Community water systems t ha t add d i s i n f ec t an t to the treatment process (ground and surface)

Effective: Systems >75,000: 2 years a f t e r promulgation Systems 13175,000: 4 years a f t e r promulgation Sys tems (1 0,000: S ta te d i sc re t ion

Monitoring requirements: Running annual average of a minimum of 4 samples per quar ter per p lant taken on same day. Systems using m u 1 t i p l e wells drawing raw water from a s ing le aquifer may, with S ta te approval, be considered one treatment p lant f o r determining the required number of samples.

Effective: Systems >75,000: 1 year a f t e r promulgation Systems 1 O,75,OOO: 3 years a f t e r promulgation Systems <10,000: S t a t e d i sc re t ion

Samples locat ions: 25% a t extreme of d i s t r i bu t i on system; 75% a t locations representa t ive of population d i s t r i bu t i on

Frequency :

For groundwater systems, reduced monitoring may be appropriate f o r c e r t a i n systems; S ta tes may reduce the requirements through considerat ion of appropr ia te data including demonstration by the system t h a t the maximum

, t o t a l t r i halomethane potent ia l (MTP) i s l e s s than 8.10 mg/l ; the minimum frequency would be one sample per year f o r MTP.

For groundwater systems not meeting the above MTP and f o r surface water systems, S ta tes may reduce the monitoring requirements i f a f t e r one year of data co l l ec t ion , TTHM leve l s a r e cons i s ten t ly below 0.10 rngll; the minimum frequency would be one sample per quar ter f o r TTHM.

The o r ig ina l frequency would be re ins ta ted i f the l eve l s exceed 0.10 mgll o r i f the treatment or source i s modified.

Reporting Requirements:

To s t a t e : Average of each quar te r ly ana lys i s , w i t h i n 30 days; un t i l S ta tes have adopted the regula t ions , reporting wil l be t o EPA unless S t a t e requests rece ip t of data from the public water systems.

Table 1 (con t . )

To Public and S t a t e : R u n n i n g annual average of each quar ter ly sample i f i t exceeds MCL a s prescribed by the public no t i f i c a t i on provisions.

Other Requi rements :

To ensure microbiological qual i t y : S t a t e approval of s i gn i f i c an t modifica- t ions i n the treatment process f o r the purpose of meeting the TTHM MCL.

Analytical requirements ; In accordance with speci f ied methods (purge and t r ap o r 1 iquid/ l iquid ex t rac t ion) conducted by c e r t i f i e d l abora to r ies .

Other Issues of I n t e r e s t : Guidance on a l t e rna t i ve d i s in fec tan t s

- Conduct monitoring when chlor ine dioxide i s used and residual oxidants should not exceed 0 .5 mg/l.

- The decision of using chloramines i s best made on a case-by- case basis by the S ta te .

- Standard p l a t e count should be a condition f o r S t a t e approval of systems where process modifications a r e contemplated.

Laboratory Avai 1 ab i l i ty ( in ter im c e r t i f i c a t i o n ) :

- To qual i fy f o r interim c e r t i f i c a t i o n . Laboratories wil l be requi red t o demonstrate thei r abi 1 i ty t o analyze the performance evaluation samples provided tothem by EPA's Environmental Monitoring and Support Laboratory (EMSL) t o within 20% of the " t r ue value" f o r each THM as well as the t o t a l .

- A qua l i ty assurance program will be es tabl ished t o ensure a l abora to ry ' s a b i l i t y t o perform qual i ty analyses.

resul ts from animal studies in i t s r isk assessment analysis. Furthermore, the second part of the proposed regulation, which prescribed the use of granular activated carbon ( G A C ) fo r the control of synthetic organic chemical s , caused additional controversy on the basis tha t GAC treatment for synthetic organic chemicals i s expensive, untried, and unproven from a practical view- poi n t (Pendygraf t, Schl egel , and Huston, 1979) .

After much debate, the E P A y in November 1979, issued i t s f inal rule on a maximum contaminant 1 eve1 for total trihalomethanes, which was summarized above. No action has been taken as yet on the second part of the i n i t i a l regulation with respect to synthetic organic chemicals in drinking water .

The t r i halomethane question i s particularly re1 evant to water suppl ies in the southeastern United States. The National Organics Reconnaissance Survey (NORS) conducted by EPA in 1975 showed a d i rec t correlation between the concentration of total trihalomethane species in finished water and the concentration of total organic carbon (TOC) in raw water (Symons e t a1 ., 1975). THM formation was also shown to be closely linked to the practice of prechlorination (Singer, Lawler and Babcock, 1976). I t has a1 so been demon- s t rated that humic substances, originating from natural vegetative decay processes, are the major precursors of chloroform and the other THM species (Stevens e t a l . , 1976; Babcock and Singer, 1979). The water supplies in the southeast are believed to be relat ively h i g h in humic content and in TOC, and prechl ori nation of these waters i s widely practiced. Consequently, water u t i l i t i e s in th i s region are prime candidates for high degrees of THM production. A sampling program a t the Durham and Chapel Hi l l , North Carolina water treatment plants conducted in 1976-77 showed average raw water TOC concentrations of 5.1 and 6.8 mg/l, respectively, and average chloroform concentrations in the finished water of 129 and 184 ~ g / l , respectively (Young and Singer, 1979). Compari son of these numbers with the NORS median concen- t ra t ions of 1.5 mg/l of TOC and 21 ug/l of chloroform in finished water and the 100 pg/l standard, demonstrated the urgency of the triahlomethane question to water u t i l i t i e s in North Carolina and to water supplies and water treatment practices i n the southeast, in general.

Accordingly, in anticipation of the THM regulation, a two-year research project was in i t i a t ed in September 1978 to assess THM formation in North Carolina drinking waters. The objectives of th is study were to :

a ) analyze raw and treated water quality a t the major water treatment f a c i l i t i e s in North Carolina with respect to organic carbon content, t r ea t - ment practices, and THM formation;

b ) analyze the data coll ected a t these faci l i t i e s by comparing THM concentrations with the 100 pg/l standard, organic carbon content, and other physical and chemical water qua1 i ty and treatment parameters in order to ascertain the existence of s ignif icant correlations between these parameters and THM formation;

c ) perform 1 aboratory t reatabi l i ty studies to investigate various means of reducing and controlling THM formation a t those f a c i l i t i e s which may have d i f f i cu l t i e s complying with the MCL; and

d) u t i l ize the resul ts of the bench-scale studies to make recornendations for plant-scale modifications that would allow these plants to comply with the regulation.

This report presents the resul ts of th i s study.

LITERATURE REVIEW

Previous Trihalomethane Surveys

Since 1974 and the discovery of trihalomethanes in finished drinking waters, there have been a number of surveys to determine the extent of formation of th i s contaminant in publ i c water supplies. These surveys include the National Organics Reconnaissance Survey (NORS) (Symons e t a1 . , 1975) ; the National Organics Monitoring Survey (NOMS) (Environmental Protection Agency, 1977); a survey by Glaze and Rawley (1979) of THM levels in selected East Texas water supplies; a survey by Minear (1 980) and co-workers of t r i halomethanes in Tennessee drinking waters; a survey by Zogorski, Allgeier, and Mull ins (1978) of THM levels in f i f teen Kentucky water u t i l i t i e s ; and a case study of two North Carolina publ i c water suppl ies by Young and Singer (1979). The procedures employed and the resul ts obtained in these s ix THM surveys provided the basis for the design of the North Carolina sampling program. Summaries of these surveys a re presented in Tables 2 through 7. In some tab1 es , additional correlations beyond those reported in the original publ i - cations were made by the authors. The information and comments in these summaries were selected because of the i r appl icabi l i ty to the current work and are not intended to be complete descriptions of these studies.

Discussion of Surveys:

All of these surveys had the same primary objective, i . e . t o determine the extent of formation of trihalomethanes (chloroform, bromodichloromethane, di brornochloromethane, and bromoform) in the finished water suppl ies of the water treatment fac i l i t i e s examined. As part of th i s objective, some attempt was usually made to identify the e f f ec t of water source and treatment processes on the formation of t r i halomethanes. From the resul ts of these surveys, i t i s obvious tha t t r i halomethanes a re ubiquitous in chlorinated drinking waters and are a d i rec t consequence of chlorination practice. In general, surface waters tend t o produce greater concentrations of THMs than ground water sources of supply. Some of these surveys a1 so indicate a seasonal variation in the production of THMs, with greater concentrations formed during the warmer summer months and the lower concentrations being generated during the winter. I t appears that the THM precursors react f a s t e r and to a greater degree a t warmer temperatures.

A secondary objective of these investigations was to examine various potantial surrogate measurements tha t might be used in a predictive manner to assess levels of THMs o r THM precursors in a sample of water without having to resort to tim-consuming and re1 at ively expensive gas chromatographic procedures. Through the use of these measurements, parameters influencing THM production could be identified. In general, those surrogate measures that show the most promise in th i s respect a re the total organic carbon concen- t ra t ion and the chlorine demand of the raw water. This i s n o t unexpected since THM formation involves both organic precursors and chlorine. The resul ts of these surveys indicate tha t both TOC and chlorine demand are good general indicators of THM formation potential b u t , since both of the para-

Table 2

National Organics Reconnaissance Survey (NORS) (Symons, e t a1 , 1975)

STUDY AREA

Nationwide, 80 c i t i e s , study population 36 mil l ion.

STUDY PERIOD/SAMPLE POINTSISAMPLE TYPES

January-April 1975/Raw, f inished water . / Iced.

THY SAMPLE HANDLING AND PRESERVATION

Transported on i ce and ref r igera ted unt i l analys is . No reducing agent added t o quench residual chlor ine .

G E N E R A L ORGANIC PARAMETERS INVESTIGATED

Non-volatile t o t a l organic caFbon ( N V T O C ) , u l t r a v i o l e t absorbance ( U V ) , emission f l uorescence scan ( EmFS) . r a ~ i d f l uorometric method ( R F M ) , carbon chloroform ex t r ac t ( C C E - m j : CONCENTRATION (finished water)

Raw Water

Locations Detected 46 Mean b+g/l) 0.19 Median (pgl l ) - - Range ( u g l l ) nf-1.2

nf = not found

NVTOC CONCENTRATION ( f i ni shed water)

Locations Detected 8 0 3.31 - -

Range (mg/l) (0.05-19.2 S E L E C T E D CORRELATIONS

Finished Water

80 67.7 28.2

~ 0 . 1 - 482

Dependent Independent Number of Correlat ion var iab le ~ a r i a b l e Observations Coeff ic ient TTHM-fin ( a ) NVTOC-raw ( b ) 82 0.75 . .

C12-DEMAND ' ( c ) 82 0.61 PRE C12 DOSE (d): 74 0.41 PRE C12 DOSE ( e ) 4 3 0.60

'mmxii NVTOC-raw ( f 0.98

NVTOC-raw P R E Cl DOSE ' 74 0.49

Table 2 (continued)

S E L E C T E D CORRELATIONS (continued ) ( a ) TTHM-fin: Total THM concentration in the finished water.

NVTOC-raw: NVTOC concentration of the raw water. C 1 2 DEMAND: Chlorine demand of water in treatment plant. P R E C 1 2 D O S E : Prechlorination dosage. Same as previous correlation except plants using activated carbon or lime-soda softening were excluded. Correlation between average TTHM-fin and NVTOC-raw grouped by 0.5 mg/l c e l l s .

Correlation between average TTHM-fi n and C1 DEMAND grouped by 1.0 mg/l c e l l s .

CHC13-fi n : Chloroform concentration in the finished water. UV-fin: U V absorbance of finished water. EmFS-fin: Emission fluorescence scan of finished water.

COMMENTS

Because of presence of suspended solids in raw water samples, some NVTOC data i s questionable, a n d U V , EmFS and RFM of raw water i s considered to be unrel iable.

Spearman rank correlation and log-log regression did n o t s ignif icant ly improve correlations between TTHMs and general organic parameters.

Higher THM concentrations occurred in those plants where (1 ) surface water was used as the source of the raw water supply, (2) raw water chlorination was practiced, and ( 3 ) greater than 0.4 mg/l of f ree chlorine residual in the finished water was maintained.

Lowest TTHM concentration occurred a t a f a c i l i t y using a ground water source and ozonation for disinfection.

+ Correlations by Singer, Lawler, and Babcock (1976)

++ Correlations by Symons (1976)

Table 3

National Organics Monitoring Survey (NOMS) (Environmental Protection Agency, 1977)

STUDY AREA

Nationwide, 113 c i t i e s

STUDY PERIOD/SNIPLE POI NTS/SAMPLE TYPES

Phase I : March-April 1976lFinished water (a ) / Iced . Phase 11: May-July 1976/Finished water/Quenched, unquenched,. Pnase 111: Nov. 1976-Jan. 1977/Finished water (b)/Quenched, unquenched.

( a ) Some raw water samples were taken f o r background information. ( b ) Dis t r ibut ion system samples taken a t f i v e f a c i l i t i e s .

THi4 SAMPLE HANDLING AND PRESERVATION

Iced ( I ) : Same as NORS, on i c e , no reducing agent added. Quenched ( Q ) : Reducing agent added a t time of sampling. Unquenched ( u Q ) : No reducing agent added, sample stored f o r 3-6 weeks a t 20-250C.

GENEWL ORGANIC PARAMETERS INVESTIGATED

NVTOC (Phases I , 11, 111), U V absorbance (11) , EmFS ( I , I I ) , CCE ( I , 11, 111) .

TTHM CONCENTRATION (f in ished water) Phase I Phase I1 Phase I11

Iced Quenched Un uenched Quenched Un uenched Locations Detected 18/18 2/113 Ikan ( u g / l ) 6 8 105 117 5 3 100

* 98/106

Pledi an (pg/l j 4 5 105 8 7 3 7 74 Range (-,dl) nf-457 2-309 nf-784 nf -295 nf -695

nf = not found NVTOC CONCENTRATION ( f i n i s hed water )

Phase I Phase I 1 Phase I11 Iced Quenched Unquenched Quonched Unquenched

Mean mg/l) ( c ) 2.1 2.3 2.1 2.4 2.4 Median (mg/l) ( d ) 1 .8 2.1 1.8 2.0 2 .O Range (mg/l) nf-9.3 0.35-4.05 nf-9.5 nf-10.0 nf-10.0

( c ) Mean of posi t ive r e s u l t s only. (d l Median of a l l r e s u l t s .

Tab1 e 3 (continued)

SIGNIFICANT CORRELATIONS

Dependent Independent Variable Variable

TTHM-f in (.I ) NVTOC-f i n (UQ) NVTOC-fin ( Q ) NVTOC-f in

TTHM-f i n ( Q ) NVTOC-f i n+ UV-f i n

Obser- vations

102 112 98

18 18

111

Phase I

I I 111

I I I I

I I

Correl a t i on Coefficient

0.55 0.70 0.60

COMNENTS

THM concentrations u p t o one order-of-magnitude lower were detected in water supplies using ground water sources rather than surface I

water sources. U V , ErnFS, and C C E did not correlate well with the concentrations of specif ic organic compounds. (However, these writers found s ignif icant correlations using the UV-absorbance data from the NOMS).

In Phase 111, f ive f a c i l i t i e s were studied for concentration of THlls in the i r dis t r ibut ion systems. These concentrations were generally found t o l i e between the quenched and unquenched concentrations.

+ Correl a t i ons by wri te rs .

Tab le 4

THM Leve l s i n E a s t Texas Water Suppl i e s (Glaze and Rawley, 1979)

STUDY AREA

Se lec ted Eas t Texas wate r supp l i es . Phase I i n v e s t i g a t e d 25 water s u p p l i e s ( 14 s u r f a c e water sources and 11 ground wate r sources) . Phase I 1 i n v o l v e d 12 su r f ace wate r sources and 1 ground wate r source. Pnase 111 focused on 5 f a c i l i t i e s w i t h su r f ace wate r sources,

STUDY PERIOD/SAMPLE POINTS/SAMPLE TYPES

Phase I A p r i l 1977 / Raw, f i n i s h e d water / Quenched ( Q ) Phase I 1 May-June 1977 / Raw, f i n i s h e d water / Quenched Phase 111 June-Ju ly 1977 / A f t e r d i f f e r e n t t rea tment / Quenched

processes, d i s t r i b u t i o n Termi na1 (T ) system

SAMPLE HANDLING AND PRESERVATION

Quenched: Buf fer -quench s o l u t i o n added a t t i m e o f sampl ing t o h a l t THM fo rma t i on and t o b r i n g pH t o l e v e l co r respond ing t o t h a t o f d i s t r i b u t i o n system. Samples s t o r e d on i c e and analyzed w i t h i n 48 hours o f c o l l e c t i o n .

Termina l : Quenched on -s i t e . Sample r e tu rned t o l a b o r a t o r y and pH a d j u s t e d t o 7.6-9.6, depending on f a c i l i t y . C h l o r i n a t e d w i t h a dose of 15 mg/ l , and s t o r e d i n t h e dark a t 260C f o r 5 days. Cond i t i ons were an a t t emp t t o s i m u l a t e c o n d i t i o n s i n t rea tment f a c i l i t y .

GENERAL ORGANIC PARAMETERS INVESTIGATED

T o t a l o rgan i c carbon c o n c e n t r a t i o n i n t h e raw wate r .

TTHM CONCENTRATIONS Phase I Phase I 1

Ground Surface Ground Sur face R a w F i n Raw F i n Raw F i n Raw F i n

Loca t i ons Detec ted ~77/1111/1414/140/11/17/12~ Mean ( ~ ~ 1 1 ) 1.4 47.9 1.0 339.2 o 399 1 .2 240.1 Range ( p g / l ) o - 1 .l- 0-1.9 130- --- --- 0-3.8 101 -

9.4 482.1 922 552

TOC CONCENTRATIONS

L o c a t i o n s Detec ted 1/11 na 14/14 na na na na n a Mean (rngl l ) 3.72 na 9.01 na na na na na Range (mg / l ) 0.67- na 2.9- na na na na na

9.0 15.8

na = n o t ana lyzed Mean va lues based on a l l ana lyzed l o c a t i o n s .

Table 4 (continued)

CORRELATIONS

Dependent Independent Number of Correlation Variable ' Variable Observations Coefficient

CHCl 3-f in TOC-raw ( a ) 14 0.586 ( b )

TTHM-f i n TOC-raw 14 ( c )

( a ) For Phase I surface water sources only. ( b ) Significant a t the 0.025 level . ( c ) Not s t a t i s t i c a l l y s ignif icant .

COMMENTS

Phase I surface water concentrations of THMs were thought to be higher than Phase I1 because of a period of unusually high runoff.

Phase I11 studies of f ive surface water treatment plants showed averape instantaneous concentrations of THMs in the finished water of about 200 p g/l , with a range of 100-275 u g / l . Average terminal THV concen- t ra t ions in the raw water were about 730 yg/ l , ranging from 450-990 p g / l . Reductions i n terminal THM concentration from raw t o finished water averaged 25 percent, ranging from 0-38 percent.

Removal of THM precursors from East Texas surface waters may n o t be achieved through the use of conventional treatment methods. Because of high THM concentrations formed from these waters, i t i s doubtful tha t the elimination or control of prechlorine would in i t s e l f achieve the MCL requirement for THMs.

Tab le 5

Survey o f T r iha lomethane L e v e l s i n Kentucky Water Sup 1 i e s ( Z o g o r s k i , A l l g e i e r , and M u l l i n s , 1978

STUDY AREA 7

F i f t e e n o f Ken tucky ' s l a r g e r w a t e r u t i l i t i e s . Four ground w a t e r and e l e v e n s u r f a c e w a t e r sources o f s u p p l y were i n v e s t i g a t e d .


March 1977-March 1 9 7 8 / F i n i shed WaterIQuenched

THM SAMPLE HANDLING AND PRESERVATION

A r e d u c i n g a g e n t was added t o samples t o quench r e s i d u a l c h l o r i n e . Samples were s t o r e d a t reduced tempera tu re and ana lyzed w i t h i n seven days of c o l l e c t i o n .

A THM P o t e n t i a l T e s t (THMPT) was d e s c r i b e d b u t n o t u t i l i z e d i n t h e f i e l d su rvey . F o r t h e THMPT t h e sample was a d j u s t e d t o pH 10.5-11.2, dosed w i t h 1 0 m g l l o f c h l o r i n e , i n c u b a t e d a t 30% f o r 3 days, and t h e n quenched and ana lyzed .

GENERAL ORGANIC PARAMETERS INVESTIGATED

Non-vol a t i l e t o t a l o r g a n i c carbon.

TTH:4 CONCENTRATIONS ( f i n i s h e d w a t e r s )

Ground Waters S u r f a c e Waters A11 Waters L o c a t i o n s D e t e c t e d 41 4 11/11 1 5/15 Mean ( u g / 1 ) 21.3 82.3 66.0 Range (;i g / l ) (1 5->35 50-1 40 (15-140

TOC CONCENTRATIONS ( f i n i s hed w a t e r s )

Ground Waters S u r f a c e Waters A11 Waters L o c a t i o n s D e t e c t e d 3 / 3 10 /10 1 3/ 1 3 Mean ( m g l l ) 2.4 4 .9 4.3 Range ( m g / l ) 2 .o-3 .O 1.7-7.5 1.7-7.5

CORRELATIONS

Dependent Independent Number o f C o r r e l a t i o n V a r i a b l e V a r i a b l e Observa t ions C o e f f i c i e n t

CHCl 3 - f i n ( a ) Temperature - - 0.893

TTHM-f i n C 1 2 Demand (b ) 13 0.67

TTHM-f i n NVTOC-f i nt 13 0.72 ( c )

( a ) P r e l i m i n a r y s t u d y i n v o l v i n g f i n i s h e d w a t e r f r o m t h e L o u i s v i l l e wa te r t r e a t m e n t p l a n t and tempera tu re o f Ohio R i v e r w a t e r .

( b ) C12 Demand = C12 dose minus C12 r e s i d u a l i n f i n i s h e d wa te r .

( c ) S i g n i f i c a n t a t t h e 0.01 l e v e l .

Table 6

Tennessee Trihalomethane Survey i in ear, 1980)

STUDY A R E A

Thir ty- three drinking water suppl ies , including the l a rge r c i t i e s of Tennessee, and representing 53 percent of the S t a t e ' s population. Ten ground water sources of supply and twenty-three surface water sources were involved.


Phase I Feb-April 1978 (wi n t e r ) a / ~ i n i s h e d Wa ter/Unquenched ( U Q ) Phase I1 May-June 1978 ( spr ing) /Finished WaterIQuenched ( Q ) , Unquenched Phase I11 Aug-Sept 1978 ( s u m e r ) /Finished Water/Quenched, Unquenched Phase IV Dec 1978-Jan 1979 ( fa1 1 )/Finished Water/Quenched, Unquenched

a ~ e a s o n s as speci f ied by invest igators

THM SAMPLE HANDLING AND PRESERVATION

Quenched : reducing agent added to el imi nate residual C1 2 , analyzed a f t e r 7 days.

Unquenched: no chemical addi t ions , analyzed a f t e r 7 days. ( I n Phase I , samples were analyzed a f t e r varying storage times, typ ica l ly g rea te r than 7 days . )

G E N E R A L ORGANIC PARAMETERS INVESTIGATED

NVTOC of raw water during the summer sampling period. Twenty-one of the 33 f a c i l i t i e s were sampled within a two-day period of time.

TTH?4 CONCENTRATION (f in ished water)

Winter Spring Summer Fa1 1 u Q AX Quq -- Q u Q

Mean (pg/1) 2 5 30 54 4 0 99 3 2 7 7 Median (pg/l ) 2 4 29 48 2 7 93 2 0 57 Range ( ~ g / l ) 0-83 0-102 6-123 1-118 2-265 0-145 1-242 Standard (pg / l ) 23 2 5 3 5 3 8 75 - 34 7 4

HVTOC C O N C E N T R A T I O N (raw water) Summer Mean (mg/l) 7-?

SIGNIFICANT CORRELATIONS

Dependent Independent Correl a t i on Level of Season Variable Variable Coefficient Significance

Summer TTHM-fin NVTOC-raw 0.758 ( b ) 0.0001

( b ) I f four outlying points a r e eliminated, the cor re la t ion coe f f i c i en t increases s i gn i f i c an t l y t o 0.91 2 .

Table 6 ( con t i nued )

SIGNIFICANT CORRELATIONS ( c o n t i nued)

Dependent Season V a r i a b l e

Win te r CHCL3 ( U Q ) TTHM (UQ)

Sp r i ng CHC13 (UQ)

Summer C H C I (UQ) TTHN (UQ) TTHM ( Q )

Independent V a r i a b l e

PH TREAT ( c ) PH TREAT

TURB ( d ) PRE CL2 ( c ) TURB PRE CL2 PRE CL PH TR&T PRECL2

RES CL2 ( f ) RES CL2

RES CL2 RES CL2 RES CL2 TURB RES CL2

C o r r e l a t i o n C o e f f i c i e n t

0.45 0.45

0.57 0.60 0.62 0.56 0.50 0.45 0.52

0.56 0.54 0.45 0.49

0.55 0.58 0.45 0.49 0.47

Level o f S i g n i f i c a n c e

0.0109 0.0115

0.0023 0.0008 0.0007 0.0018 0.0084 0.0152 0.0064

0.0011 0.0017 0.0148 0.0198

0.0018 0,001 1 0.0106 0.0142 0.0129

-

( c ) PH TREAT: F i n i shed wate r pH. ( e ) PRE CL2: P r e c h l o r i n e dose. -

( d ) TURB: T u r b i d i t y i n raw water ( f ) RES CL2: Res idual c h l o r i n e i n

( g ) TEMP: Temperature o f raw water . f i n i s h e d wate r .

Seasonal t r ends f o r b o t h quenched and unquenched average' THM con- c e n t r a t i o n s were observed, w i t h t h e summer y i e l d i n g t h e h i g h e s t average va lues and t h e w i n t e r t h e lowes t . On an i n d i v i d u a l p l a n t b a s i s , o n l y h a l f o f t h e f a c i l i t i e s f o l l o w e d t h i s t r e n d o f i n c r e a s i n g THM c o n c e n t r a t i o n f rom a l ow i n t h e w i n t e r , i n c r e a s i n g through t h e s p r i n g and s u m e r , w i t h a decrease i n t h e f a l l . Even i n these cases, t h e sumner THM l e v e l was n o t n e c e s s a r i l y t h e h i g h e s t .

Ch lo ro fo rm was t h e dominant THM spec ies produced, accoun t ing f o r about 80-95 percen t o f TTHMs on a we igh t b a s i s .

Surface sources produced t h e h i g h e s t THM concen t ra t i ons . Of these, r i v e r sources produced t h e h i g h e s t l e v e l s . Only seven o f t h e t h i r t y - t h r e e f a c i 1 i t i e s exceeded o r approached t h e 100 p g / l THM l e v e l on a year - round b a s i s . I n t h e summer, n e a r l y h a l f o f t h e f a c i l i t i e s had THM c o n c e n t r a t i o n s a t t h i s l e v e l o r above.

Table 7

Case Study of Two North Carolina Water Suppl f e s (Young and Singer , 1979)

STUDY AREA

Durham and Chapel Hi1 1, North Carol ina. The water treatment p lants f o r these c i t i e s a r e suppl ied by su r face sources.


July 1976-March 1977/Finished water/Quenched

T H M SAMPLING HANDLI NG AND PRESERVATION

Instantaneous chloroform samples were dosed w i t h a reducing agent a t the time of co l l ec t ion , and were s to red headspace-free a t reduced temperature u n t i l analyzed.

GENERAL ORGAN I C PARAMETERS INVEST1 G A T E D

Non-volatile t o t a l organic carbon (NVTOC), c o l o r

RESULTS O F DURHAM/CHAPEL HILL CASE STUDY

Average Concentrations and Ranges Chapel Hi l l Durham Durham July 76-Mar. 77 July-Dec. 1976 Jan.-Mar. 1977 Prechlor ina t ion Prechlorinat ion Pos t -chlor ina t ion

only only only

NVTOC (tng/l ) 6 .8 (4.2-12.1) 5.1 (3.6-8.7) 5.7 Pre C1 (mg/l) 6.5 (4.4-9.0) 5 .8 (4.9-7.4) 7

- - Post C 2 (mg/l ) - - - -- ---- 3.7 CHC13 ( d l ) 184(110-280) 129(90-190) 7 7

Note: In Jan . , 1977, Durham moved i t s poin t of ch lo r ine add i t ion from the rapid mix chambers t o a f t e r the sedimentation bas ins .

CORRELATIONS

Dependent Variable

Chloroform Chloroform Chloroform

NVTOC Chloroform Chlorine dose

Chloroform Chloroform Chloroform

Chlorine dose Chlorine dose

Chlorine dose Chlorine dose

D = Durham CH

Independent Variable

NVTOC NVTOC NVTOC

Color Color Color

Chlorine dose Chlorine dose Chlorine dose

Data S e t

D C . H .

D&C .H

C . H . C . H . C . H .

D C . H .

D&C.H.

NVTOC D NVTOC C . H .

Temperature D Temperature C . H .

= Chapel Hi l l

Corre la t ion Coef f i c i en t ( r )

0.50 0.39 0.54

0.05 0.44 0.56

0.44 0.12 0.29

Table 7 (continued)

COMMENTS

Study a1 so showed that chloroform concentration increased through various stages of treatment a f t e r i n i t i a l chlorine additions. NVTOC and residual chlorine concentrations decreased correspondingly.

Moving the point of chlorination a t the Durham plant from the rapid mix chamber t o a post-sett l ing location effected a 40 percent reduction in chloroform formation, with an associated 35 percent reduction in organic carbon and a 30 percent reduction in applied chlorine to meet target chlorine residuals for the distribution sys tern.

meters a re c o l l e c t i v e i n nature, they a re n o t 1 i k e l y t o serve as good p red i c to rs o f THM concentrat ions.

Another measurement t h a t shows some promise as a surrogate THM i n d i c a t o r i s UV-absorbance. I n t h e NORS (Symons .e t a l . , 1975), an at tempt was made t o measure the u l t r a v i o l e t absorbance of t he source water, b u t problems arose because o f i n t e r f e r i n g t u r b i d i t y i n the raw water samples. Thi s i n t e r f e r e n c e cou ld be e l im ina ted by f i l t e r i n g the sample p r i o r t o measurement as described by Dobbs, Wise, and Dean (1972) i n a d iscuss ion of UU-absorbance measurements i n wastewaters. This technique was consequently adopted i n the present s tudy w i t h g r e a t success (see subsequent chapters) .

The 1 ack o f c o r r e l a t i o n between THM concentrat ions and var ious parameters i n many o f these e a r l i e r s tud ies i s q u i t e 1 i k e l y due t o sample hand l ing and preserva t ion procedures. I n t he case o f unquenched samples as i n d i c a t o r s o f te rmina l tri halomethane formation, i t has been es tab l ished (T russe l l and Umphres, 1978) t h a t t he formation o f THMs cont inues i n the r e a c t i o n vessel u n t i l r es idua l c h l o r i n e i s completely d i ss ipa ted . Furthermore, the r e a c t i o n i s a f fec ted by pH, temperature, and l e n g t h o f t ime between sample c o l l e c t i o n and ana lys is . Therefore, unless t h e c h l o r i n a t i o n cond i t ions , pH, temperature, and r e a c t i o n t ime a re standardized f o r a1 1 samples, no meaningful comparisons among THM concentrat ions f o r unquenched samples can be made. Some o f t h e i n v e s t i g a t o r s i n the e a r l i e r surveys attempted t o s tandardize these con- d i t i o n s , b u t few o f them made prov is ions f o r the maintenance o f a c h l o r i n e res idua l throughout the r e a c t i o n per iod. I n cases where c h l o r i n a t i o n was o n l y a t a l e v e l t o s imu la te t h a t i n t he t reatment p lan t , i t i s l i k e l y t h a t t he c h l o r i n e was exhausted before the sample was analyzed. The r e s u l t i n g c o r r e l a t i o n s , us ing data from d i f f e r e n t waters and d i f f e r e n t t reatment con- d i t i o n s , a re n o t l i k e l y t o be very s i g n i f i c a n t .

I n t he case o f instantaneous THM ana lys is , most o f t he surveys employed a dech lor ina ted o r quenched sample t o measure THM concentrat ions a t t he moment of sampling. By e l i m i n a t i n g the res idua l ch lo r i ne , t he r e a c t i o n i s terminated. I n some cases, t he samples were s to red a t reduced temperatures w i thou t t he a d d i t i o n o f a dech lo r i na t i ng agent. This procedure would g i v e erroneous instantaneous THM measurements because, even though t h e r e a c t i o n i s slower a t lower temperatures, THM format ion s t i l l cont inues. Therefore, t h i s type o f sample (presumabl having d i f f e r i n g pH and c h l o r i n e res idua ls f o r d i f f e r e n t sample l o c a t i o n s 7 would have a l l the i nhe ren t problems of t h e non-standardized, unquenched sample descr ibed above.

Another apparent problem a r i s e s i n a number o f t he surveys w i t h regard t o data ana lys i s . Some c o r r e l a t i o n s a r e s u b s t a n t i a l l y improved by t a k i n g average values f o r t he dependent and independent va r i ab les . Th i s p r a c t i c e i s somewhat mis leading s ince the averaging process, by d e f i n i t i o n , would tend t o dampen the ac tua l v a r i a t i o n i n t he data. Stated another way, the co r re - l a t i o n c o e f f i c i e n t o f t he r e l a t i o n s h i p s us ing averaged values would improve, b u t t he s t a t i s t i c a l s i g n i f i c a n c e o f t h e r e l a t i o n s h i p , a l b e i t obscured, would a c t u a l l y remain unchanged,

As a f i n a l p o i n t regard ing the prev ious THM studies, i t should be noted t h a t one o f the e a r l i e r s tud ies (Young and Singer, 1979) i nvo l ved two t r e a t - ment p l a n t s t h a t were i nves t i ga ted as p a r t of t h i s c u r r e n t survey. During the e a r l i e r study, both o f these f a c i l i t i e s produced h igh concentrat ions o f chloroform. One o f the f a c i l i t i e s , i n Durham, Nor th Carol ina, purpor ted ly reduced i t s ch lo ro form product ion by 40 percent by moving the p o i n t of c h l o r i n a t i o n from the raw water t o t he s e t t l e d water. The m o d i f i c a t i o n was made du r ing January and mon i to r i ng cont inued on l y through March so there i s some quest ion as t o whether t h i s reduc t ion was due t o the t reatment m o d i f i - c a t i o n o r simply t o temperature e f f e c t s . The r e s u l t s o f the present work v e r i f y t h a t reduc t i on i n ch lorofom l e v e l s were, i n fac t , a r e s u l t o f t h e p l a n t mod i f i ca t i on .

Methods f o r C o n t r o l l i n g THM Formation i n D r ink ing Water

There a r e th ree bas ic methods f o r c o n t r o l 1 i n g THM product ion i n d r i n k i n g water:

a. removal of THMs a f t e r they have been formed;

b. use o f an a1 t e r n a t i v e d i s i n f e c t a n t which does n o t r e a c t w i t h organics t o form THMs; and

c. removal o f THM precursors p r i o r t o the a d d i t i o n o f ch lo r i ne .

Ac t i va ted carbon adsorp t ion and ae ra t i on are two methods f o r removing THMs a f t e r they have been formed. Fresh g ranu la r a c t i v a t e d carbon (GAC) i s an e f f e c t i v e adsorbent f o r removing THMs f rom d r i n k i n g water. However, l ong con tac t t imes are requ i red , breakthrough o f THMs o f t e n occurs w i t h i n a few weeks due t o competi t i o n w i t h o the r organics i n t h e water, and GAC i s expensive t o rep1 ace o r regenerate. These 1 i m i t a t i o n s make GAC imprac t i ca l t o use s p e c i f i c a l l y f o r t he removal o f THMs. A1 t e r n a t i v e l y , s ince THMs a r e v o l a t i l e , ae ra t i on can be used t o s t r i p them from so lu t i on , b u t a i r requ i re - ments a re h i g h and power cos ts can be p r o h i b i t i v e .

There are several o t h e r d i s i n f e c t a n t s t h a t can be s u b s t i t u t e d f o r ch lo r i ne . Chl oramines can be used t o ma in ta in res idua l d i s i n f e c t a n t l e v e l s i n d i s t r i b u t i o n systems, b u t chloramines cannot be used as a pr imary d i s i n - f e c t a n t . Ozone i s an e x c e l l e n t d i s i n f e c t a n t b u t i t i s unstable and cannot ma in ta in a res idua l through the d i s t r i b u t i o n system. Ozonation does n o t r e s u l t i n THM product ion, b u t ozone must be generated on-s i te, which makes i t expensive. Ch lor ine d iox ide i s s i m i l a r t o ozone i n t h a t i t must be generated on-s i t e and does n o t r e a c t w i t h organics t o form THMs. Ch lor ine d iox ide i s a s t rong d i s i n f e c t a n t and can prov ide a l o n g - l a s t i n g res idua l . However, i t i s expensive t o produce and requ i res storage o f a d d i t i o n a l chemicals (e.g., NaC102) a t the t reatment p l a n t . Ch lor ine i s the o n l y e f f e c t i v e d i s i n f e c t a n t t h a t i s p r e s e n t l y low i n c o s t and ab le t o ma in ta in acceptable res idua l d i s i n f e c t i n g power i n t he d i s t r i b u t i o n system. Hence, use o f an a1 t e r n a t e d i n s i n f e c t a n t t o c h l o r i n e does n o t appear t o be very p r a c t i c a l a t t h i s t ime.

Removal of THM precursors p r i o r t o the a d d i t i o n o f c h l q r i n e can be accompl i shed through adsorp t ion on a c t i v a t e d carbon, chemical ox ida t ion , o r coagulat ion. Whi le g ranu lar a c t i v a t e d carbon has been shown t o be an

effect ive adsorbent for humic substances (Snoeyink, McCreary, and Murin, 1977), GAC i s expensive and must be replaced or regenerated f a i r l y frequently. Powdered activated carbon has not been overly successful in removing THM precursors a t normal treatment plant doses (Zogorski, A1 lge ier , and Mu1 1 ins , 1978). In a s imilar manner, chemical oxidants such as ozone and permanganate, while moderately effect ive a t high oxidant concentrations (Glaze, e t a l , 1980; Singer, Eorchardt, and Col thurst , 1981 ) , are ineffective in control 1 ing THY formation a t conventional appl ication levels. Coagulation, on the other hand, has been demonstrated to be an effect ive method for removing THM precursors with 1 i t t l e modification in conventional coagulation practice.

Removal of THM Precursors by Coagulation:

Many researchers have studied the removal of col or-causi ng humic substances by coagulation. In the past, color was considered to be primarily an aesthet ic problem. Recently, however, with the 1 inkage between the production of THMs and the presence of humic substances which are in large part responsi b1 e fo r natural organic color in water, a resurgence of research in th i s f i e l d has taken place.

In 1965, Hall and Packham studied the removal of color by aluminum sul fa te and f e r r i c chloride. They concluded tha t the mechanisms responsible fo r removal of turbidi ty and color were different . The former was believed to be coagulated by e i the r charge neutralization or enmeshment in a metal hydroxide precipi ta te (such as A1 (OH)$, while the l a t t e r was be1 ieved to be removed by chemical precipitation. They found the optimal pH for color removal to be lower than tha t fo r turbidity removal ( l e s s than 5.0), and concluded tha t the removal mechanisms for aluminum sul fa te and f e r r i c chloride were the same.

, Black and Chri stman (1 963) investigated the removal of color-causing substances in six highly-colored surface waters from throughout the US using f e r r i c sulfate . They found a pH range of 3.5 - 3.8 to be optimal for color removal with f e r r i c su l fa te . In a t e s t conducted on one of the s ix waters examined, f e r r i c su l fa te was found t o be more e f f i c i en t fo r removing color than a1 um.

More recently, Edzwald, Haff and Boak (1977) studied the removal of peat- extracted humic acid with a1 um and with a1 um/polymer combinations. Optimal removals were obtained when alum was added followed by the addition of polymer. Various polymers with d i f fe rent charge densi t ies and molecular weights were investigated and found to be applicable fo r the removal of humic'acid. The des tabi 1 i zation mechanisms were identified as adsorption-charge neutral i zation by soluble, hydrolyzed aluminum species and in terpar t ic le bridging by the high molecular weight polymers.

Babcock and Singer (1979) reported s ignif icant reductions i n chloroform formatfon (up to 70%) fol lowing alum coagulation of solutions containing humic and fulvic acid extracts . Alum was found to selectively remove chloroform precursors from among the other organics contained in the extracts .

Kavanaugh (1978) and Young and Singer (1979) combined 1 aboratory-scale experiments with plant-scale modifications to reduce THM levels a t Contra

Costa County, Cal i fo rn ia and Durham, North Carol ina, respectively. In the Contra Costa study, alum and Fe(II1) coagulation were invest igated, with s imi la r r e su l t s . Young and Singer applied the r e su l t s of bench-scale alum coagulation s tud ies to the operation of the Durham water treatment plant . The point of i n i t i a l chlorine application was sh i f t ed from the rapid mix chamber t o a location a f t e r s e t t l i n g . As a r e s u l t , a 40% reduction in THM formation was noted.

Semmens and Field (1980) investigated the removal of THM precursors by a1 um coagulation and reported s jmilar r e su l t s as those of previous researchers. They noted t h a t the optimal conditions fo r organics removal and t u rb id i t y removal were di f f e r en t b u t found t h a t good organics removal usually accompani ed good tu rb id i ty removal. Alum dose and pH were found to be the control l ing factors f o r organics removal, w i t h pH playing a major role ; an optimal pH of 5.0 was noted. High alum doses were found to s ign i f ican t ly improve THM precursor removal . A 65% reduction i n THM precursors was noted with an a1 u m dose of 100 mg/l a t pH 5.0. UV absorbance, TOC and fluorescence were a l l found to co r r e l a t e we1 1 wi t h THM precursor concentration.

In a re la ted study, Scheuch and Edzwald (1981) investigated the use of a cat ionic polyelectrolyte and d i r e c t f i l t r a t i o n f o r removing THM precursors from highly-colored, low tu rb id i ty waters. Actual r i v e r water samples, as well as syn the t ic humic and fu lv i c acid solut ions , were t es ted . Direct f i l t r a t i o n of the humic acid solution resul ted in a color reduction of approximately 90% and a corresponding reduction of between 50 and 65% in the chloroform formation potential of the water. Lower removals were noted f o r f u lv i c acid solut ions; color was reduced by 50-85% and chloroform formation potential was reduced by 35-40%. A cationi c polyelect rolyte of high charge density and moderate molecular weight (Betz 1190) was used i n these experiments as a coagulant.

3. f4ORTH CAROLINA TRIHALOMETHANE SURVEY

Sampl ing Program and Procedures

Description of Facil i t i e s Surveyed:

The u t i l i t i e s selected for th is survey were chosen on the basis of popu- la t ion. The original EPA proposal for regulation of THMs was limited to those systems serving greater than 75,000 persons. For th i s reason, only those systems serving more than 75,000 consumers, and two s l ight ly smaller systems, Chapel Hi 11 and Wilmi ngton, were included in the monitoring program. Hence, nine of the larger c i t i e s in North Carolina, encompassing thirteen treatment plants were involved in the study. Table 8 i s a l i s t i n g of the f a c i l i t i e s participating in the program, along with a compilation of service population as estimated by Boney, Wiggins, and Rimer (1977). The nine u t i l i t i e s investigated serve a total population of l,Z8l,000, which represents about twenty-five percent of the S ta t e ' s total population.

As indicated by Figure 1, these population centers l i e mainly in the Piedmont Region of the State. Asheville, in the Blue Ridge Mountinas, and Wilmington, on the Atlantic coast, give good west to eas t dis t r ibut ion across the State. Figure 2 shows the major hydrologic features of North Carolina.

Background information pertaining to source of supply, capacity of fac i l i ty , water qual i ty character is t ics , and type of treatment was collected for each of the thirteen treatment plants participating in th i s study. The information was obtained from a variety of sources including operating records of the treatment plants, consul tation with personnel a t the plants, examination of blueprints and plans, and from pub1 ished sources (Boney, Wiggins, and Rimer, 1977; Mann, 1978; US Geological Survey, 1978).

Table 9 1 i s t s the water sources, the intake locations, and the drainage areas feeding the various water sources of the f a c i l i t i e s studied. Table 10 gives information on the safe yield of raw water source, plant capacity, water demand of service population, and treatment and clearwell storage time for each f a c i l i t y . Pertinent information on water quality character is t ics and on chemical dosages and residuals i s sumnarized i n Table 11, which shows average values and ranges for 1979. Only selected parameters a re 1 is ted i n t h i s table for raw and finished water qual i t y , and for coagulant and disin- fectant chemical dosages. Complete information fo r a l l parameters routinely measured and chemicals applied was collected but i s not presented here. Flow diagrams showing unit processes, vol umes of treatment uni ts , average hydraulic detention times, as well as points of chemical application are included as Appendix A.

As indicated by Table 9, a l l of the treatment plants selected for th i s survey have surface water sources of supply. Of the thir teen f a c i l i t i e s investigated, twelve employ conventional surface water treatment systems consisting of chemical additions, rapid mixing, flocculation, se t t l ing , f i l - t ra t ion , and clearwell storage. The lone exception, Ashevil l e , uses d i rec t f i l t r a t i o n which eliminates the sedimentation step. All but Durham add chlorine to the raw water for purposes of disinfection and fo r oxidation, and many add chlorine a t mu1 t i p l e points during treatment. Durham abandoned the

Table 8

F a c i l i t i e s P a r t i c i p a t i n g i n THM Monitoring Survey

Ci t y County Treatment F a c i l i t y Populat ion Served

Ashevill e Buncombe Black Mountain P lan t 120,000

Gas ton i a Gas ton Gastonia P l an t 75,000

Char1 o t t e Mecklenburg H o s k i n s P l a n t Vest P l an t

Wi ns ton Sal em Forsyth Nei 1 son P lan t Thomas P lan t

Greensboro Gui l ford Mi tche l 1 P l an t Townsend P lan t

Chapel Hi1 1 O r a n ~ e OWASA P lan t 50,000

Durham Durham Hi l l anda le P l an t 100,000

Raleigh Wake Johnson Fi 1 t e r P l an t 180,000 Bain F i l t e r P l an t

Wi lmi ngton New Hanover Sweeney P lan t 52,000 - -

Total Se rv i ce Populat ion 1,281,000

Table 9 +

Sources o f Water f o r Fac i l i t i e s i n THM Survey

Intake Location Upstream

Faci 1 i ty

Ashevil l e

Source o f Water Lat i tude, ~ r a i nage Area

Impoundment Longitude (sq. m i . )

North Fork Swannanoa River North Fork Reservoir

Gas t o n i a South Fork Catawba River Lake Rankine Long Creek

Charlotte, Hoskins Catawba River Mountain I s land Lake

Char lot te, Vest Ca tawba River Mountain Is land Lake

N v Winston Salem, Ne i l son Yadkin River

Winston Salem, Thomas

Greensboro, M i tche l 1

Greensboro, Townsend

Chapel H i l l

Du rham

Ral eigh, Johnson

Raleigh, Bain

W i lmington

Salem Creek Salem Lake Yadkin River

Bush Creek Lake Higgins Reedy Fork and Horsepen Creek Lake Brandt

Reedy Fork Creek Lake Townsend

Nevi1 l e , Price, Morgan Creek Un ivers i t y Lake

F l a t River Lake Michie

Neuse River Beaver Creek Beaver Dam

Walnut Creek L. Johnson, L. Raleigh S w i f t Creek L. Wheeler, h. Benson

Cape Fear River Toomer ' s Creek

+ Boney, Wiggins, and Rimer (1977) ; Mann (1978); US Geological Survey (1978).

Table 10

Capacity, Demand, and Detention Time In format i on f o r Fac i l i ti es Surveyed

Average Detention Time: Safe Y i e l d o f P lant Capacity Average Da i l y Maximum Da i l y Treatment and Clearwell

F a c i l i t y Source (mgd) (mgd Demand (mgd) Demand (mgd) Storage (h rs )

Ashevil l e

Chapel H i l l

Charlotte, Hoskins

Charlotte, Vest

Durham

Gastonia

Greensboro , M i tche l 1

Greensboro, Townsend

Raleigh, Bain

Raleigh, Johnson

Wilmington

Winston Salem Nei 1 son

Winston Salem Thomas

F a c i l i t y

Ashev i l l e

Chapel H i l l

Cha r lo t t e , Hoskins

Cha r lo t t e , Vest

Durham

Gastonia

Greensboro, Mi t che l l

Greensboro. Townsend

Raleigh, Bain

Raleigh, Johnson

Wilming ton

Winston Salem, Neil son

Winston Salem. Thomas

Mean Range

Mean Range

Mean Range

Mean Range

Table 11

Selec ted Water ~ u a l i t ~ C h a r a c t e r i s t i c s , Chemical Dosages and Res iduals (1979 Average va lues )

Water Qua l i t y Parameters Chemical Dosages and Res idua l s Raw Water Raw Water Raw Water Raw F i n i s e F i n i s e Water Pre-C Pos t C urn Carbon KMNO4

Flow Turb id i t y True Color Temperature Water Waterh C 1 2 $sPdual Dose Dose l2 g s e Dose Dose mgd -- (NTU) (CU) ( 3) pH pH (mgll) (mg/l) ( ~ 1 1 ) ' (mg/l) ( ~ d l ) (rng/l) - pp

Yes - - -

3.85 45.8 0-6.5 32-85.5

0.6 8.9 0.3-0.9 8-11

0.42 8.27 0.32--52 6.2-11.6

Mean 18.7 56 60 61 6.7 7 .1 1.7 - 4.3 29.1 - - Range 12.5-23.7 15-210 30-75 40-78 6.3-7.0 - - - 2.2-8.5 18-43 - -

Mean 16.0 12.8 - 6 1 7.8 7.3 0.79 3.22 - 19.9 - 0.27 Range 7.1-23.1 3-62 - 39-82 7.1-9.5 - - 1.9-5.7 - 19-20.8 - 0.25-0-31

Mean 11.2 26.9 - 63 7.9 7.2 - 2.27 3.58 32.0 - - Range 2.3-18.6 2-193 - 39-82 6.5-7.4 - - - - 13-57.9 - -

Mean 13.4 14.6 - 64 6.7 7.4 1 .96 0.45 4.09 1 8 - - Range 7.1-17.9 1.6-80 - 39-88 5.6-7.6 - - - 3-10.2 11-37 - -

Mean 6.14 39 92 64 6.5 7.5 1.43 7.5 0.48 30.9 5.0 - Range 1-13.7 10-125 25-200+ 41-86 6.1-7.0 - - 3.4-16.3 0-2.9 0-82 0-18.4 -

Mean 19.0 24.3 5 7 62 7.0 7.2 1.44 5.75 1.91 41.0 6.2 - Range 10.8-26.3 5-75 20-140 39-84 6.7-7.4 - - 3.4-14.3 0.55-5.3 25.7-65.6 3-9 -

Mean 9.3 33 95 64 6.5 7.2 1 .9 6.5 0.87 3 3 1.7* - Range 5.4-12.0 5-150 37-236 43-91 6.1-6.9 - - 3 .l-13 .O 0.1-2.9 0-54 0-14.8 - Mean 14.8 51.2 - 59.5 7.0 7.5 1.47 2.28 0.98 14.9 - - Range 3.3-24.7 6.5-400 - 33-83 6.2-7.8 - - 0.94-5.9 0.33-1.8 2-48.3 - -

Mean 18.6 35 - 6 1 6.6 7.3 1.23 7.88 1 .06 19 .5 - - Range 12.5-24.1 5-170 - 36-82 5.9-7.5 - - 0.77-5.2 0.2-2.4 9.5-34.1 - -

Average Mean 15 .1 26 4 6 6 1 6.9 7.6 1.45 3.40 2.01 25.1 2.6 0.47

practice of prechlorination in 1977 in favor of a single chlorine addition a f t e r sedimentation in order to reduce THM levels. Two plants add chlorine to the source water a t raw water pumping s tat ions, a practice which a1 lows for longer chlorine contact time and the potential for production of THMs prior to the time the water enters the treatment plant. This i s standard practice a t the Greensboro-Mi tchell plant, and was an occasional practice, since discontinued, a t the Wilmington f a c i l i t y . Activated carbon i s consi s- tently used a t four of the f a c i l i t i e s and potassium permanganate a t only two, primarily for t a s t e and odor control . Pre-chlorine and pos t-chlorine dosages a t a1 1 of the fac i l i t i e s in 1979 averaged 3.40 mg/l and 2.01 mg/l , respec* t ively, with an average residual chlorine concentration in the finished water of 1.5 mg/l. All of the plants except for Asheville use alum for coagu- la t ion , and many use polymers as coagulant and f i l t e r a ids .

Based upon the resul ts of NORS (Symons, 1975), t h i s combination of surface water sources, extensive prechl ori nation practices, and relat ively high chlorine residuals in the finished waters makes these f a c i l i t i e s prime candidates for high levels of THM production.

Sampl ing Program:

During the survey, each of the treatment plants was sampled on a seasonal basis. Four or more samples were collected from most plants to allow f o r an examination of any seasonal or temperature-related trends in THM forma t i on. Some early THM resul ts were discarded due to their lack of r e l i a b i l i t y ; however, additional sampli ng v i s i t s were made l a t e r in the survey to insure an adequate seasonal dis t r ibut ion of samples.

During each sampling v i s i t , samples were collected for the analysis of TOC, instantaneous and terminal (7-day) THMs (see be1 ow), 7-day chlorine demand, and U V absorbance. TOC and THM samples were taken a t three locations in each plant (raw, se t t led , and finished waters). UV absorbance and 7-day chlorine demand were measured on raw water samples only. Most samples were taken from laboratory sampling taps provided a t the treatment plants. How- ever, in some cases where taps were not available, samples were taken from the treatment basins themselves. Following the i r collection, the samples were returned to Chapel Hi1 1 , where they were analyzed in the laboratories of the Department of Environmental Sciences and Engineering a t the University of North Carol ina for the parameters described above. No samples were taken from the dis t r ibut ion system of any of the c i t i e s included i n the survey.

In addi t i on, i nforma t i on was col 1 ected from plant records, and/or personnel describing the operation of the plant, raw water qua1 i ty , and chemical dosages appl i ed on the day of sampl i ng . These data included: raw water color and temperature; raw, se t t l ed , and finished water turbidi ty , pH and chlorine residual; treated water flow; and the concentration and location of any chemical additions being made on tha t day in the plant.

Sampling and Handling Procedures:

A1 1 gl assware used in sampl i ng and analytical determinations was made chlorine demand-free (CDF) by soaking, not less than 12 hours prior to use, in a strong chlorine solution where the concentration was a t l e a s t 100 mg/l .

The glassware was then wgll -rinsed with chlorine demand-free water (CDFW) and placed in an oven a t 105 C , usually for several hours. Dist i l led, deionized, carbon-fil tered water was made chlorine demand-free by adding 3-5 mg/l of chlorine and holding fo r a period of two days; the water was dechlorinated by exposure to u l t rav io le t l i g h t fo r a period of one and one-half hours. Since CDFW was used in large quantit ies for a l l analytical work as we1 1 as for cleaning glassware, i t was made and stored in five-gallon glass carboys f i t t e d with H$04 a i r traps to prevent contamination during storage.

Instantaneous trihalomethane concentration (INST) refers to the concen- t ra t ion of THMs in the water a t the moment of sampling. This type of sample was collected in 60 ml ground-glass stoppered bottles to which approximately 10 mg of sodium su l f i t e had been added to quench any residual chlorine in the water. The su l f i t e crystals were added in amounts well in excess of that required to reduce a l l residual chlorine in order to terminate THM production. The bottles were carefully f i l l e d , minimizing turbulence, and seal ed headspace-free. Parafi lm was pl aced over the stopper to prevent loosening during transport. The samples were stored a t room temperature, in the dark, and analyzed within 48 hours of collection.

Termi nal t r i ha1 omethane concentration (TERM), i n thi s study, refers to the concentration of THMs tha t i s produced from a given sample in seven days, under conditions of controlled pH, temperature, and i n the presence of an excess amount of chlorine added to insure the existence of a residual a f t e r seven days. The terminal THM concentration, as described herein, i s a measure of THM precursor material in the water. This procedure d i f fe rs from the unquenched samples used by several other investigators in tha t an excess amount of chlorine i s provided and a l l chlorination conditions, for a l l samples, are uniform. The use of th i s standardized chlorination procedure made comparisons of waters from different sources possible. By sub- tracting the INST THM concentration from the TERM THM concentration, the t r i - halomethane formation potential (THMFP) of the water, i .e. the residual concentration of THM precursors, a t the point of sampling could be calculated.

rV-

Samples for TERM THM analysis were collected in 60 ml bottles identical to those used for the INST THM samples. A phosphate buffer solution was prepared such tha t a 1 ml addition would hold the pH a t a constant level of 6.7. A stock solution of sodium hypochlorite was prepared such tha t a 1 ml addition to the 60 ml sample bot t le would yield a pre-determined amount of f ree residual chlorine, usually between 15 and 20 mg/l . The stock chlorine solution was standardized prior to the time of each sampling by iodimetric t i t ra t ion using 0.025N sodium thiosul f a t e t i t r an t which was standardized using potassium biniodate (Standard Methods, 1976). After the addition of the phosphate buffer and the chlorine, a sample of the water was slowly added. The bot t le was capped and the contents mixed thoroughly. The chlorinated sample was sealed and stored headspace-free for seven days, in the dark, a t room temperature. A t the end of the reaction period, residual chlorine was quenched and THMs measured within 12 hours,

Samples for total organic carbon were collected, in most cases, in 60 ml Pierce bottles with rubber-lined Teflon septa and aluminum crimped-top seals .

On occasion, glass-stoppered bottles were used. To inhib i t biological degra- dation of the organic carbon, the pH of the sample was decreased to about 3 with a 1 m l addition of 0.5N phosphoric acid solution. These samples were sealed and stored under refrigeration until analysis, which was usually conducted within ten days of sample collection.

In addition to THM and TOC samples, samples of the raw water were taken a t each f a c i l i t y for measurement of UV absorbance, and residual chlorine a f t e r the seven-day storage period. The residual chlorine samples were prepared in the same way as the terminal THM samples, and the UV absorbance samples were handled in the same fashion as the TOC samples. U V measurements were made within 24 hours of sample collection.

Analytical Procedures:

THMs were measured with a Tracor MT-220 gas chromatograph (GC) and a halogen-specific Tracor 700 Hall Electrolytic Conductivity Detector. Sample concentration was accomplished by the purge and t rap procedure developed by Be1 1 a r and Li chtenberg (1974; Environmental Protection Agency, 1979) . The aqueous sample was f i r s t extracted by ine r t nitrogen gas which was bubbled through the sample. Volatile organics were trapped in a s ta in less steel column f i l l e d with Tenax 60/80 mesh adsorbent. The purge time for th i s s tep was 11 minutes a t a gas flow ra te of 20 ml/min. After the concentration step, the t rap was placed in ser ies a t the head of the GC column and the contents were thermally desorbed from the sorbent material to the GC column packed with Chromosorb lo&. Nitrogen gas, flowing a t 20 ml/min., a t an i n l e t temperature of 125 C , was used for t h i s three-minute t ransfer . After desorp- tion to the G C column, separation was then carried ou& by temperature program- ming, heating the column from room temperature to 190 @ and holding a t t h i s temperature until a l l THM species were detected and peaks recorded on a chart recorder. The THMs were detected by pyrolysis a t 850 '~ in a hydrogen atmosphere in which the organic halides were converted to HC1 which was subsequently dissolved in methanol and detected as a change in conductivity. Total time requirements for concentration and detection of the THMs was 20 to 30 minutes per sample, depending on the THM species present in the sample.

Quan t i tation of the THM concentrations was accompl i shed by comparison of the peak heights to a standard curve prepared by the analysis of known con-' centrations of chloroform. The standards were prepared, on the day of analy- s i s , by the dilution of Aldrich Gold Label Chloroform i n HPLC-grade methanol, and making ser ia l dilutions of th i s stock in d i s t i l l e d , deionized, carbon- f i l t e red water to obtain the desired concentration. Over the range of chloroform concentrations encountered in th i s study, the detector response was found to be 1 inear. Injection reproducibility fo r a single sample was usually on the order of 5-10 percent. The 1 ine generated from th is procedure usually had a small negative intercept which indicated a specif ic detection l imi t a t a par t icular attenuation. Other THM species besides chloroform were not quantified because they occurred in only a few instances and then only in trace amounts. Chloroform was the primary THM species detected, with bromodichloromethane occurring infrequently. Dibromochlorornethane and bromoform were not detected a t a l l during th i s study. Therefore, the concentration of chl oroform was taken t o represent the total t r i ha1 omethane (TTHM) concentration.

T o t a l o rgan i c carbon was determined us ing a Dohrmann 52-S Carbon Analyzer o u t f i t t e d w i t h a PR-1 u l t r a - l o w l e v e l i n l e t which a l l ows f o r u g / l s e n s i t i v i t y . The method employs u l t r av i o l e t - p romo ted chemical o x i d a t i o n o f o rgan ic carbon t o carbon d i o x i d e by p e r s u l f a t e , convers ion o f t h e CO, t o methane, and flame i o n i z a t i o n d e t e c t i o n of t h e r e s u l t a n t methane. Ten ml water samples were a c i d i f i e d w i t h phosphor ic a c i d t o b r i n g t h e pH t o about 2 t o conve r t i n o r g a n i c carbon t o CO . The sample was d i l u t ed t o 50 ml , and 1 ml o f a 5 pe rcen t p e r s u l f a t e soPut ion was added. I n t h e f i r s t cyc le , he l ium purges t h e sample, t r a n s f e r r i n g b o t h CO f rom i n o r g a n i c carbon sources and purgeable o rgan i c carbon (POC) t o a CO sc?ubber ( 1 i th ium hydrox ide) . The Cop i s removed and t h e POC proceeds th60ugh t h e n i c k e l c a t a l y s t r e d u c t i o n system where i t i s conver ted t o methane and measured by a f lame i o n i z a t i o n d e t e c t o r (FID) . A d i g i t a l POC read ing i s then taken f rom t h e i n t e g r a t o r . I n t h e second cyc le , he l ium t r a n s f e r s t he 1 i q u i d sample through a q u a r t z r e a c t i o n c o i l where t h e p e r s u l f a t e and UV i r r a d i a t i o n o x i d i z e a l l remain ing o rgan ics t o CO . The sample i s purged o f t h e CO which i s then t r a n s f e r r e d t o t h e r e d u c t i g n zone and t h e d e t e c t o r . Again, an i n t e g r a t e d d i g i t a l read ing f o r TOC i s d i sp l ayed which i nc l udes t h e p r e v i o u s l y - d i sp l ayed POC v a l ue. T y p i c a l l y , t he POC was l e s s than one pe rcen t of t h e TOC.

A s tandard curve was generated f o r each s e t o f analyses by t h e prepa- r a t i o n and measurement o f known standards o f potassium hydrogen p h t h a l a t e (KHP) d i s s o l v e d i n d i s t i l l e d , de ion i zed wate r . Over t h e range o f 0-18 mg/l TOC, the response was found t o be l i n e a r . Sample measurements were very r e p r o d u c i b l e and accura te t o about 0.1 mg/ l . T o t a l c y c l e t ime pe r sample was about 8.5 minutes.

Some TOC measurements were made on a Beckman Model 915A Carbon Analyzer . D i r e c t aqueous i n j e c t i o n o f m i c r o l i t e r amounts o f sample t h a t had been a c i d i f i e d and purged e x t e r n a l l y t o remove i n o r g a n i c carbon were made i n t o t h e Ana lyzer . Use o f t h i s i ns t rumen t was d i scon t i nued i n f a v o r o f t h e Dohrmann ana lyzer because o f t h e need f o r l owe r d e t e c t i o n l i m i t s r e q u i r e d f o r some samples .

I t should be noted t h a t t h e r e was some evidence t h a t t h e Beckman i n s t r u - ment tended t o underest imate t h e amount o f TOC i n raw wate r samples because of incomple te convers ion o f some p a r t i c u l a t e o r ma romol ecu l a r o rgan i c carbon 6 t o CO , desp i t e t h e h i g h o x i d a t i o n temperature (950 C) used i n t he oven. ~ d m i t g e d l y, t h e a c i d-persu l f a t e , UV-catalyzed o x i d a t i o n process employed by t h e Dorhmann procedure i s n o t as v igorous as t h e h igh- temperature o x i d a t i o n and, there fo re , some o f t h e o rgan i c m a t t e r i n t h e raw wate r may n o t be t o t a l l y conver ted t o CO and u l t i m a t e l y t o methane by t h i s procedure e i t h e r . Hence, o rgan i c carbon 'measurements i n the raw wate r samples may be somewhat low.

Residual c h l o r i n e was measured us ing t h e s tandard ized N,N-diethyl-p- phenyl enediamine (DPD) procedure (Standard Methods, 1976) us ing a f e r r o u s ammonium s u l f a t e (FAS) t i t r a n t and a DPD i n d i c a t o r . The FAS t i t r a n t was s tandard ized w i t h s tandard potassium dichromate us ing a f e r r o i n i n d i c a t o r . The seven-day c h l o r i n e demand o f t h e raw wate r was c a l c u l a t e d by s u b t r a c t i o n o f t h e r e s i d u a l c h l o r i n e a f t e r seven days f rom t h e known amount o f a p p l i e d c h l o r i n e .

UV absorbance was measured on a Varian Techtronic Model 635 Spectro- photometer. To avo id i n te r fe rences o f p a r t i c u l a t e ma te r i a l i n the raw water sample, the sample was f i l t e r e d through a 0.45 vm c e l l u l o s e aceta te membrane f i l t e r . An u l t r a v i o l e t 1 i g h t source a t a wavelength o f 254 nm was used f o r the measurement. Both the blank and sample were he ld i n 1 cm quar tz g lass c e l l s .

Residual pH o f the c h l o r i n a t e d samples a f t e r seven days was measured on a F isher Accumet Model 230A pH meter us ing standard b u f f e r s f o r c a l i b r a t i o n .

Resul t s

The complete data s e t f o r the North Carol ina THM survey i s 1 i s t e d i n Tables 12 and 13. A l l TOC and THM data a re conta ined i n Table 12, w h i l e Table 13 i s a l i s t i n g o f data desc r ib ing the raw water c h a r a c t e r i s t i c s and c h l o r i n e dosages a t each of the p lan ts a t the t ime o f sampling. Most o f t he p l a n t s have e i t h e r 5 o r 6 data e n t r i e s , represent ing t h e e n t i r e sampling per iod. The W i lmington-Sweeney p l a n t was sampled more f r e q u e n t l y than the o the r p l a n t s over a sho r te r pe r iod o f t ime i n view o f t h e h igh THM l e v e l s and the m o d i f i c a t i o n i n p l a n t operat ions (see Chapter 5 ) .

Instantaneous THM l e v e l s i n the f i n i shed water, as shown i n Table 12, ranged from 9 t o 257 vg / l f o r t he A s h e v i l l e and Wilmington p lan ts , respec- t i ve l y . Instantaneous THM concentrat ions i n the raw water were t y p i c a l l y below the l i m i t o f detect ion, u s u a l l y l e s s than 5 v g / l . I n a few instances, h igher l e v e l s were recorded f o r the Greensboro-Mitchell and Wilmington-Sweeney p l a n t s . These corresponded t o samples c o l l e c t e d a f t e r c h l o r i n e was added a t raw water pumpi ng s ta t i ons , upstream o f t h e t reatment p l a n t s . When u n c h l o r i - nated samples o f raw water were taken d i r e c t l y from the source, the i ns tan - taneous THM l e v e l s were found t o be below the l e v e l o f de tec t i on .

Raw water te rmina l THM concentrat ions (seven-day THM forma t i o n p o t e n t i a1 a t pH = 6.7 i n t he presence s f excess c h l o r i n e ) ranged from 61 t o 793 u g / l . F in ished water te rmina l THM l e v e l s were p r e d i c t a b l y lower and ranged f rom 40 t o 427 p g / l .

Raw water t o t a l organic carbon (TOC) concentrat ions ranged from 0.7 t o 10.8 mg/l . Raw water UV absorbance v a r i e d from 0.009 t o 0.385.

I t should be noted again, t h a t a l l o f t h e THM, TOC, UV absorbance, and 7-day c h l o r i n e demand measurements l i s t e d i n Tables 12 and 13 were made by t h i s research team. The remaining data were taken from var ious t reatment p l a n t records. Because the r e s u l t s of t h i s research team were conducted un i fo rm ly and were subjected t o v e r i f i c a t i o n by var ious qua1 i ty assurance procedures, these r e s u l t s a re repor ted w i t h g reater c e r t a i n t y than those obta ined from t h e d i f f e r e n t t reatment p l a n t records.

F igure 3 i s a frequency d i s t r i b u t i o n diagram o f a l l instantaneous THM data f o r f i n i s h e d water samples c o l l e c t e d du r ing the survey. When p l o t t e d on a log-probabi 1 i t y coord ina te scale, a 1 i near re1 a t i o n s h i p r e s u l t s r e f l e c t i n g a geometr ical ly-normal d i s t r i b u t i o n o f the data. As i n d i c a t e d by t h e graph, the median concent ra t ion o f THMs i n the f i n i s h e d waters i s approximate ly 58

Table 12

NORTH CAROLINA TRIHALOMETIIANE SURVEY RESULTS: TOC AND THM CONCENTRATIONS

Date ------ TOC (mg/l) ------ --- INST THM (pg/l) ---- --- TERM THM (pg/l) ---- Treatment Facility Sampled - Raw Settled Finished Raw Settled F i n i s h e d Raw Settled F i n i s h e d - -- -

Asheville 6/9/79 0.7 0.8 0.7 - - 13 - - - 3/4/80 0.7 0.9 0.9 < 1 6 9 6 1 56 5 6

Chapel Hill

Charlotte-Hoskins 3/9/79 2.4 1.7 6/27/79 1.4 1.7 10/2/79 3.8 3.6 1/9/80 1.7 1.3 4/16/80 1.5 1.0 8/15/80 1.8 1.8

Charlotte-Vest 3/9/79 2.2 1.2 6/27/79 1.5 1.1 10/2/79 3.8 3.1 1/9/80 1.6 1.2 4/16/80 1.4 1.0 8/15/80 1.8 1.7

Durham-Hillandale 1/23/79 6.8 4 -4 4.0 - - 7/30/79 6.5 4.4 3.2 < 2 8 11/6/79 . 7.1 4.5 3.5 < 2 11 11/30/80 8.1 3.4 3.0 < 2 8 4/29/80 6.1 3.3 3.0 <4 13

Table 12 (continued)

Treatment ~acility

Gastonia

Greensboro-Mitchell

Greensboro- Townsend

Raleigh-Bain

Raleigh-Johnson

Sampled

3/9/79 6/27/79 10/27/79 1/9/80 4/16/80

3/22/79 6/8/79 9/26/79 1/2 3/80 4/9/80 9/4/80

3/22/79 6/8/79 9/26/79 1/23/80 4/9/80 9/4/80

2/14/79 7/2 5/79 9/12/79 2/6/80 4/29/80

2/14/79 7/25/79 9/12/79 2/6/80 4/29/80

Raw Settled Finished

--- INST THM fug/l) ---- Settled

- - 4 1 10 3 1

- - 4 6 4 4 4 2 12

- - 2 7 4 1 17 3 0

- 97 132 58 62

- 30 74 2 9 56

Finished

- - 52 17 3 1

- 4 1 92 54 5 4 2 1

- 2 7 3 2 4 0 2 3 38

- 11 3 172 79 117

- 9 0 128 62 8 1

--- TERM THM (pg/l) ---- Raw -

- - 253 132 230

- - 3 56 2 12 303 -

- - 298 230 185 -

139 349 4 18 233 329

176 373 770 303 409

Settled

- - 128 9 7 127

- - 215 13 3 177 - - - 204 160 164 -

8 2 249 402 171 241

123 183 44 5 17 5 257

Finished

- - 117 70 106

- - 219 147 172 148

- - 210 159 169

Treatment Facility

Wilmington-Sweeney

Winston-Salem- Neilson

Winston-Salem- Thomas

Table 12 (continued)

Date ------ TOC (mg/l) ------ --- I N S T THM (~g/l) ---- --- TERM TIfM (pg/l) ---- Sampled Raw -

10/23/79 8.9

Settled

6.0 4.7 4.9 5.1 4.0 3.8 2.9 3.1

5.2 1.0 1.5 2.0 1.5 1.5

1.7 2.0 1.6 2.3 1.9 1.3

Finished

5.4 4.2 3.5 3.8 4.1 3.6 2.9 3.0

0.7 0.8 1.0 2.3 0.9 1.3

1.6 1.3 1.5 1.8 1.6 1.7

Settled

110 84 138 185

< 7 <6

< 14 < 3

- - 38 2 8 2 4 3 1

- - 3 9 18 34 34

Finished

152 111 2 57 215 9 0 176 9 4 9 1

- - 5 0 4 0 7 1 38

- -

4 9 2 8 62 4 9

Raw Settled

352 251 530 501 271 262 205 182

- - 126 158 99

-

- - 160 14 5 178 -

F i n i s h e d

T a b l e 1 3

NORTH CAROLINA TRIHALOMETHANE SURVEY RESULTS: SELECTED WATER QUALITY PARAMETERS ON DAYS OF SAMPLING

Raw Water 7-day

CL Demand ?mg/l)

Raw Water Turbid it y

( NTU

0.4 0.5

21.0 10.0 8.0 27.9 18.0 17.2

24.0 8.0 5.2 3.4 6.9 4.2

22.0 6.3 4.6 3.2 9.5 3.9

95.0 20.0 24 -0 50.0 24.0

60.0 24.0 10.0 7.0 11.0

C1 Demand b

2 (mg/l)

Sample Treatment Facility Date

Raw Water W Absorbance

Raw Water Color !CU)

Asheville

Chapel Hill 12/13/78 8/7/79 10/21/79 1/30/80 4/29/80 6/6/80

Charlotte-Hoskins

Charlotte-Vest

Durham-Hillandale

Gastonia

Greensboro-Mitchell

~reensboro-Townsend

Raleigh-Bain

Raleigh-Johnson

Winston Salem-Neilson

Winston Salem-Thomas

Table 13 (cont inued)

a ~ r e - ~ 1 2 refers to chlorine additions prior to sedimentation; post-C12 refers to chlorine additions after Settling

b ~ 1 2 Demand = (Pre-C12 Dose + Post-Cl2 Dose) - (Finished water C12 Residual)

-

- - - - - - - - - - - - -

Median Concentration 58 f i g / l -

-

I I I I I I I I I I I I I I I I I I I I

2 5 . 10 15 20 30 40 50 60 70 80 85 90 95 98

PERCENT OF OBSERVATIONS LESS THAN OR EQUAL TO GIVEN CONCENTRATION

Figure 3. Frequency Distr ibut ion Plot of l nstantaneous THM Data for Finished Water Samples.

1 This i s somewhat lower than the mean concentration of 72 pg/l , and i s much higher than the NORS median concentration of 28 pg/l (Symons e t a1 ., 1975) and the NOMS median concentration of 37 pg/l (Environmental Protection Agency, 1977). This i s a reflection of the high humic content of these water sources and the prechlorination practices employed in th i s region in comparison to those across the nation as a whole.

Table 14 presents the average raw water TOCs, finished water instantaneous THMsy and raw water terminal THMs for each of the f a c i l i t i e s sampled. Of the thirteen treatment plants involved in th is study, four had average THM concentrations in the finished water close to , or in excess of the 100 ug/l MCL on a year-round basis. These were the Chapel Hil l , Raleigh Bain, Raleigh Johnson, and Wilmington treatment f a c i l i t i e s . These plants are located in the eastern portion of the study area, with Chapel Hill and Raleigh lying in the eastern-most part of the Piedmont Region, and Wilmington located on the Atlantic coast. In general, these f a c i l i t i e s also had UV absorbances and seven-day chlorine demands for the raw waters, prechlorination dosages, and chlorine demands during treatment that were higher than the average values of a1 1 the plants surveyed. Further consideration of correlations between THM production and raw water qua1 i ty and treatment, and factors contri buti ng t o THM formation are presented in the next sect ian.

Two plants altered the i r prechlorination practices during the l a t t e r part of the survey in an e f fo r t to lower THM production (see Table 13). The basis for th i s change was the substantial reduction in THM production observed a t the Durham water treatment plant following the i r elimination of prechl ori nati on (Young and Singer, 1979) . Chapel Hi 11 decreased i t s prechlorine dose on November 1, 1979. As a resu l t , THM levels appeared to drop s1 ightly. Wi lmington el iminated prechlorination a1 together on June 2, 1980. This change resulted in a s ignif icant drop in THM levels during the summer months (see Table 12). Details of the Wilmington modification are presented in Chapter 5.

Analysis of Data and Discussion of Results

S ta t i s t i ca l ,Techniques Utilized:

A primary objective of th i s study was to assess the formation of t r i - halomethanes in North Carolina drinking waters. This assessment included the examination of various factors tha t contribute to the formation of THMs in these water supplies. To quantify and validate the observations that came from th i s investigation, i t was necessary to rely on s t a t i s t i c a l concepts and techniques. Most of the s t a t i s t i c a l analysis took the form of simple descr ipt ive s t a t i s t i c s and univariate models, although some multivariate models were examined.

Data analysis was primarily through the use of a group of computer pro- grams collectively called the S ta t i s t ica l Analysis System (SAS) (Helwig, 1978; He1 wi g and Counci 1 , 1979). The General Linear Model ( G L M ) procedure was used for the regression analyses. Most of the models t h a t were formu- 1 ated were 1 i near with a single i ndependent variable; however, some mu1 tip1 e

Table 14

AVERAGE TOC AND THM CONCENTRATIONS FOR EACH OF THE FACILITIES

INCLUDED IN THE NORTH CAROLINA SURVEY*

Finished Water Raw Water Raw Water TOC INST THM TERM THM

Tredtment Facility -. mg/l ~.rg/l WJ/1

Asheville 0.7 11 61

Chapel Hill 6.6 105 400

Charlotte-Hoskins

Charlotte-Vest

Durham

Gastonia

Greensboro-Mitchell

Greensboro-Townsend

Raleigh-Bain

Raleigh-Johnson 6.4

~ilmington 7.7

Winston-Salem-Neilson 4.0

Winston-Salem-Thomas 4.8

*Each entry in this table, with the exception of Asheville, represents-an average of at least three, and usually four, separate samples, collected at different times of the year, to avoid seasonal bias. In the case of Wilmington, a large portion of the samples were collected during the spring and summer months in order to evaluate the impact of Wilmington's decision to discontinue prechlorination on June 2, 1980.

l i n e a r regressions were a l so evaluated. I n add i t i on , l o g t ransformat ions o f the independent va r i ab les were used i n the t e s t i n g o f some o f t he models. I n t h i s repo r t , o n l y the r e s u l t s o f t he simple l i n e a r regressions a re presented.

I n general, t he b e s t - f i t t i n g model was determined by the l e a s t squares approach. The goodness o f f i t was eveluatedon the bas is o f t he P e a r ~ o n c o r r e l a t i o n c o e f f i c i e n t , r, o r the mu1 t i p l e c o r r e l a t i o n c o e f f i c i e n t , r , and the F - s t a t i s t i c . A b r i e f d e s c r i p t i o n o f these terms fo l l ows .

2 The general i z e d c o r r e l a t i o n c o e f f i c i e n t , r , i s a measure o f how much v a r i a t i o n i n t he dependent v a r i a b l e can be accounted f o r by the proposed model. I t i s t he r a t i o o f t h e sum o f squares f o r the model d i v i d e d by t h e sum o f squares f o r the co r rec ted t o t a l , i .e . , t he r a t i o o f t he expla ined v a r i $ t i o n d i v i d e d by the t o t a l v a r i a t i o n . I n general, I h e l a r g e r the value o f r , t h e b e t t e r the f i t o f t he model . The value o f r ranges from 0 t o 1, and i s de f ined f o r regressions i n v o l v i n g any number o f independent va r i ab les .

The Pearson c o r r e l a t i o n c o e f f i c i e n t , r , i s o n l y de f ined i n cases i n which the re i s one dependent v a r i a b l e and one independent variablle, and when a l i q e a r c o r r e l a t i o n i s proposed. I n t h i s case, r i s s imply the square r o o t o f r , w i t h i t s s ign determined by the s lope of the l i n e . The c o e f f i c i e n t r takes on values from -1 t o +1, w i t h values c lose r t o e i t h e r extreme ( - 1 o r +1) i ndi c a t i ng s t ronger c o r r e l a ti ons .

The F d i s t r i b u t i o n i s used t o measure the s t a t i s t i c a l s i g n i f i c a n c e of a regression. The s t a t i s t i c a l s i g n i f i c a n c e i nd i ca tes the p r o b a b i l i t y t h a t a g iven c o r r e l a t i o n cou ld have happened by chance. For example, a c o r r e l a t i o n t h a t i s s t a t i s t i c a l l y s i g n i f i c a n t beyond the a = 0.01 l e v e l i n d i c a t e s a con- d i t i o n i n which t h e r e l a t i o n s h i p under i n v e s t i g a t i o n cou ld have occurred by chance o n l y one percent o f t he t ime o r l ess . For s c i e n t i f i c analyses, the a = 0.01 l e v e l i s u s u a l l y taken t o be t h e minimum l e v e l o f s t a t i s t i c a l s i g - n i f i cance i n o rder t o v e r i f y t he va l i d i ty o f a proposed model . However, i n many d i s c i p l ines, f o r example the soc ia l sciences, h igher a-values are acceptable. The F - s t a t i s t i c can be c a l c u l a t e d by the equat ion

F - - r2 /a a, n-a-1 2 ( 1 - r ) / (n-a-1)

where a i s t he number o f independent va r i ab les i n the proposed model o r the numbero f degrees o f freedom o f the numerator, n i s the number o f observa- t i ons , and n-a-1 i s t he number o f degrees o f freedom o f the denominator. A f t e r t h i s va lue i s ca lcu la ted , i t i s compared t o values o f t he F d i s t r i - b u t i o n i n s t a t i s t i c a l t ab les (Helwig, 1978; Helwig and Counci l , 1979). If the c a l c u l a t e d value i s g rea te r than the tabu la ted value f o r Fa , n-a-1, a then the regress ion i s s a i d t o be s t a t i s t i c a l l y s i g n i f i c a n t a t the a - l eve l . Therefore, the F - s t a t i s t i c i s a more meaningful s t a t i s t i c a l parameter than the general i zed o r 1 i near c o r r e l a t i o n c o e f f i c i e n t s because i t takes i n t o account the number o f observat ions i nvo l ved i n the regre6sion.

For example, a regression of three data points might r e su l t i n an r 2 value close to unity; however, the F-s ta t i s t ic would take into consideration the small number of observations and indicate that the correlation was not s t a t i s t i c a l l y s ignif icant . In many of the models that will be presented in th i s chapter, > 0.0001, i . e . the correlations are s ignif icant beyond the 0.01 percent l e v a .

Other mi scel laneous s t a t i s t i c a l descriptors include the standard devi - ation and the coeff ic ient of variation. The standard deviation i s the square root of the average of squared deviations from the mean of the independent variable. The coefficient of variation i s equal to the standard deviation of the dependent variable, divided by the mean, mu1 tip1 ied by 100. The coefficient of variation i s often preferred as a measure of var iab i l i ty because i t i s dimensionless.

Surrogate Tri ha1 omethane Measurements:

A number of potential indicators of THM formation were investigated. The intention of these investigations was to eval uate possi bl e surrogates for trihalomethanes as well as to identify the various factors contributing to THM formation. The advantage of the use of surrogates i s tha t time-consuming, costly, specif ic THM analyses might be replaced in some circumstances by re1 at ively simp1 e , easi ly measurable, non-specific indicators. Since non- specific analyses are col lect ive in nature and respond to a larger number of impurities in water, they most l ike ly could not be used to meet specif ic monitoring requirements, However, they could be very useful in day-to-day water quality evaluation and process control.

Other researchers (Symons e t a1 . , 1975; Envi ronmental Protection Agency, 1977; Glaze and Rawley, 1979; Minear, 1980) have shown tha t total organic carbon (TOC) i s a reasonable indicator of THM precursors in raw drinking water. A correlation between instantaneous THM concentrations in finished water ( INSTF) and TOC concentrations in raw water (TOCR) for a1 1 the data from the North Carolina survey i s shown i n Figure 4 and support t h i s finding. The resulting l inear relationship has a correlation coeff ic ient of 0.65 and i s s t a t i s t i c a l l y s ignif icant beyond the 0.0001 1 eve1 . The correlation yields a relat ively good f i t considering tha t data from thirteen d i f fe rent treatment plants, using different sources of water, and samples collected a t d i f fe rent times of the year a re used in the relationship. In a l l , 56 data samples were included in the analysis. The circled points a re data from the Durham water treatment plant, which does not prechlori nate, and the Wilmington plant a f t e r prechlorination was discontinued on June 6, 1980. When these eight points are el imi nated from the regression analysis, the correlation coeff ic ient i s s ignif icant ly increased to 0.70. Furthermore, i f obvious out1 i e r s are el iminated, the correlation becomes even be t te r . In this analysis, however, no attempt has been made to eliminate data solely for the purpose of improving the f i t of a proposed model, and unexpl ai ned outlying points have been incl u - ded in a l l correlations. The correlation shown by Figure 4 between INSTF and TOCR compares favorably to those resulting from the NORS (Symons e t a1 . , l975), NOMS (Environmental Protection Agency, l977), East Texas (Glaze and Rawley, 1979), and Tennessee (Minear, 1980) studies performed by other investigators, where relationships between the same variables resulted in

INISHED WATER INSTANTANEOUS .THM CONCENTRATION ( y g / I)

correlation coefficients of 0.74, 0.72, 0.59, and 0.76, respectively. However, many of these other surveys do not include data collected over the ent i re year.

A simi 1 a r correlation between terminal THM concentration in raw water (TERMR) and TOC concentration in raw water (TOCR) i s shown in Figure 5. The data resu l t in an even better correlation, again s ignif icant beyond the 0.0001 level , with a Pearson correlation coeff ic ient of 0.84. As expected, the f i t of the l inear model for the TERMR parameter i s better t h a n tha t involving the INSTF parameter, with less deviation from the regression l ine . The standard deviation for the terminal THM regression was only 30.9 as compared to 64.7 and 70.3 for the two instantaneous THM regressions discussed above. Even though the data are from a l l treatment plants and a1 1 sampling periods, the standardized chlorination procedure and contact conditions associated with the TERM THM measurement places the samples on a common base. This type of analysis negates the e f fec t of uncontrolled variables such as temperature, chlorine dose, pH, and reaction time tha t are inherent in the instantaneous THM analysis. Other investigators have also used some form of a terminal THM measurement, b u t the factors which were controlled were not always handled in the same way. To allow for meaningful comparisons of the amounts of THM precursors present in waters from various sources, consideration should be given to making the terminal THM measurement a standardized procedure. Since raw water terminal THM concentration i s equivalent to raw water THM formation potential (THMFP) for a l l the waters tested during th i s survey, t h i s strong correlation indicates tha t raw water TOC i s a good indicator of the THM precursor content of the water.

Another quantitative surrogate parameter evaluated was ul traviol e t absorbance a t a wavelength of 254 nm. Only samples of raw water were analyzed for UV-absorbance. The samples were f i l t e red prior to the measurement in order to remove potentially interfering suspended sol ids. I t has been shown (01 iver and Lawrence, 1979; Zogorski , A1 1 geier, and Mu1 1 ins, 1978) tha t f i l t r a t i o n of raw water samples through a 0.45-micron f i l t e r reduces haloform formation 1 eve1 s by only small amounts; therefore, f i l t ra t ion of the samples was not expected to a l t e r the THM formation potential of the waters under investigation to any s ignif icant degree.

Correlations between TOC i n the raw water, TERM THM in the raw water, and INST THM i n the finished water and the UV-absorbance of the raw water a re presented in Figures 6, 7, and 8 , respectively. All data were included in the analysis. All of these correlations a re s ignif icant beyond the 0.0001 level and exhi b i t very strong 1 inear relationships with correlation coeffi - cients ranging from 0.74 for the instantaneous THM correlation, to 0.93 fo r the terminal THM model, as shown. In f ac t , when the Durham data and Wi lmington data taken a f t e r the plant eliminated prechlori nation were excluded from the analysis for the instantaneous THM correlation with UV absorbance, the correlation coeff ic ient increased to 0.84. A t t h i s level of significance and goodness of f i t , i t i s possible to consider UV-absorbance as a predictive surrogate for each of these parameters. This i s qui te encouraging since the analysis takes only minutes to perform, with equipment no more elaborate than a spectrophotometer with an u l t rav io le t l i g h t source. I t should be noted tha t the correlations involve a l l data from a l l sampling periods, spanning f a i r l y wide ranges of TOCR (0.7-10.8 mg/l ) , T E R M R ( ~ ~ ~ - 7 9 3 ug / l ) , and INSTF (9-259 pg/ l ) .

RAW WATER TOC CONCENTRATION (mg/ l )

FINISHED WATER INSTANTANEOUS THM CONCENTRATION (yg/ I)

Regressions relat ing TOC and THM concentrations to other parameters, such as 7-day chlorine demand, color, and turbidity were also investigated . A signif icant correl ation was observed between the 7-day chlorine demand of the raw water and terminal THM concentration of the raw water. The correlation coefficient was 0.90 and the level of significance was 0,0001. This i s not surprising in l i gh t of the prominent role of chlorine in the terminal THM t e s t and the uniform conditions of pH, temperature , and contact time under which the 7-day chlorine demand and terminal THM samples were analyzed.

Raw water color was found to correlate well with both raw water U V absorbance ( r = 0.90) and f i ni shed water i ns tantaneous THM concentration ( r = 0.70). The l a t t e r correlation was s ignif icant ly improved ( r = 0.77) when the data from the plants not practicing prechlorination were excluded. The correlation between U V absorbance and color of the raw water i s particularly strong, as would be expected, based on the UV-absorbing character is t ics of humic material which i s the main contributor to organic color in water.

Regressions involving turbidity in the raw water did not resu l t in s t a t i s t i c a l l y s ignif icant correlations, implying tha t the THM precursors are not uniformly associated with particulate matter.

Table 15 i s a summary of the correlations involving a l l of the surrogate measurements investigated for THMs and TOC. Included are the associated s t a t i s t i c a l information for each relationship.

Changes in THM and TOC Concentrations During the Course of Water Treatment:

The average concentrations of TOC, INST THM, and TERM THM for a l l raw, se t t l ed , and finished water samples, utilizing a l l of the data collected, are presented in Table 16. The corresponding percent reductions in TOC and TERM THM concentrations through treatment are also shown. A progressive production of THMs through treatment i s indicated. In general, the instantaneous THM concentration in the raw water i s very low, and the concentration in the se t t led water i s , on the average, 57 percent of tha t in the finished water. The increase i n the t r i halomethane concentration during treatment i s due to the increase in chlorine contact time as treatment progresses. In addition to th is increase in INST THM concentration through treatment, a s ignif icant reduction in TOC and TERM THM concentration i s noted. On the average, coagulation and sedimentation i s effective in removing 38 percent of the TOC and 42 percent of the THMFP in the raw water, with an additional 9-12 percent removal through the remai ni ng treatment processes ( i . e . , f i l - t r a t i o n ) .

The imp1 ications of these reductions in THMFP as a resu l t of coagulation, sed imenta t i~n~and f i l tration,from the standpoint of prechlorination practices are obvious. If the point of application of chlorine i s shifted to a post- sedimentation or post-fi 1 t ra t ion location, s ignif icant reductions in THM formation can be anticipated. Such studies are discussed in the next two chapters and have already been demonstrated on a plant-scale a t Durham (Young and Singer, 1979).

Table 1 5

Summary of - L inea r Regress ion Analyses

Dependent V a r i a b l e

Independent V a r i a b l e

INSTF

INSTF

TE RMR

TOCR

TERMR

INSTF

INSTF

INSTF

TE RMR

TERNR

INSTF

INSTF

WR

TOCR

TOCR

TERMR

INSTF

INSTF

UVR

Bef i n i t i o n s

TOCR

TOCR

TOCR

WR

WR

UVR

UVR

CL27DD

CL27DD

COLR

COLR

COLR

COLR

COLR

TURBR

TURBR

TURBR

TURBR

TURBR

S lope - 13.74

15.33

64.63

29.05

2105.7

505.8

578.0

6.21

36.77

3.69

1.11

1.22

2.49

0.04

0.03

1.83

0.27

0.33

1 .43

I n t e r c e p t

C o r r e l a t i o n C o e f f i c i e n t

( r ) Level of

S i g n i f i c a n c e

INSTF = Finished Water I n s t a n t a n e o u s THM Concent ra t ion (lJg/l)

TOCR = Raw Water TOC Concen t r a t i on (mg/l)

CL27DD = Raw Water 7-Day Ch lo r ine Demand (mg/l)

TllRllR = R a w Water T u r b i d i t y (NTU)

C o e f f i c i e n t of V a r i a t i o n

No. of Obse rva t i ons

TERMR = Raw Water Terminal THM Concen t r a t i on ( u g / l )

WR = Raw Water UV Absorbance

COLR = Raw Water Color (CU)

Date Base

a l l d a t a

o n l y p l a n t s t h a t p r e c h l o r i n a t e

a l l d a t a

a l l d a t a

a l l d a t a

a l l d a t a . on ly p l a n t s t h a t p r e c h l o r i n a t e

a l l d a t a

a l l d a t a

a l l d a t a

a11 d a t a


a l l d a t a

a l l d a t a

a l l d a t a

a l l d a t a

a l l d a t a


a l l d a t a

Table 16

Average Concentrat ions o f TOC and THMS a t Var ious P o i n t s

i n t h e Treatment P lan t s . ( A l l da ta a re i nc l uded ) .

Raw S e t t l e d F in i shed Water Water Water

4.7 2.9 2.5

I n s t . THM ( p g / l ) 7.0 4 1 7 2

Term. THM ( v g / l ) 324 188 148

7; Reduct ion i n TOC - - - 38 47

% Reduct ion i n Term. THM --- 4 2 54

In the previous discussion of surrogate parameters, i t was shown that TOC concentration in the raw water i s a legitimate indicator of the THM precursor content. For example, the THM formation potential in the raw water (THMFP = TERM - INST) correl a tes very strongly wi t h TOC concentrations in the raw water, with a correlation coefficient of 0.84. However, THMFP was found to be l e s s strongly correlated with residual TOC in the various treated waters. Decreased correl ation coeffi c ients , 1 eve1 s of significance, and slopes of the regression l ines for the se t t led and finished water samples when compared to these parameters for the raw water samples indicate tha t coagulation, s e t t l ing , and f i l t ra t ion remove the consti tuents compri sing the TOC and THM precursors to a different degree and in a non-uniform fashion for d i f fe rent waters. Accordingly, TOC cannot be used as a surrogate for THM formation potential a f t e r the raw water has undergone treatment.

Seasonal Variations and Temperature Effects:

The North Carolina THM data were also examined for the presence of any seasonal or temperature trends. Tables 17 and 18 group average TOC and THM concentrations by season and temperature range, respectively. With respect to temperature, the data were grouped into four temperature ranges in order to allow approximately the same number of observations in each group.

The instantaneous THM concentrations in the finished waters are clear ly lower in the winter months than in any of the other seasons (see Table 17). The highest concentrations were observed in the summer months. The lower instantaneous THM concentrations in the winter are probably due t o lower temperatures and correspondingly slower kinetics of the THM formation reaction, as well as to lower THM precursor concentrations as reflected by the terminal THM values for the raw waters (see Table 17) . Correspondingly, the higher instantaneous THM concentrations in the finished waters during the summer months can be at t r ibuted to both fas te r reaction kinetics a t the higher summer temperatures and to the presence of a greater concentration of THM precursors in the raw waters. Raw water terminal concentrations (equivalent to THM formation potential) were highest in the spring and summer months, presumably due to enhanced leaching of organic material from decaying vegeta t ive matter a t the warm water temperatures.

Table 18 shows, however, tha t temperature i s not the only factor respon- s ib le for these seasonal differences. instantaneous THM concentrations in &he finished water were higher in the 60-75 F range than for waters with T > 75 F. Again, t h i s i s a t t r ibuted to the higher THM formation potential (terminal THM concentration) of the raw waters a t these intermediate temperatures.

Regression analyses for INST THM concentration in the finished water and TERM THM concentration in the raw water as a function of TOC concentration in the raw water were performed for the data from each of the four seasons and the four d i f fe rent temperature ranges. The resul ts of these regression analyses a re shown in Table 19. In general, the seasonal and temperature groupings improved the correlations between the dependent variables of INST THM in the finished water and TERM THM in the raw water, and the independent variable of TOC in the raw water. The improved correlation coefficients when the variables were grouped according to season or temperature indicate t h a t a s ignif icant amount of the sca t t e r in the correlations involving the

Table 17

SEASONAL VARIATIONS IN AVERAGE TOC AND THM CONCENTRATIONS

Sampling Season Point

TOC No. of !mg/l) Observations

Inst. THM No. of Cll~/l) Observations

Term. THM No. of llJg/l) Observations

Spring raw* settled finished

Summer raw* settled finished

Fall raw* settled finished

Winter raw* settled finished

*Corresponds to raw water taken prior to any chlorine addition.

Tab le 18

TEMPERATURE VARIATIONS IN AVERAGE TOC AND THM CONCENTRATIONS

No. of Observations

Term. THM No. of Sampling Point

No. of Inst. THM Observations hd1)-

Temperature (OF)

TOC (mg/l)

4.2 2.8 2.5

4.0 2.4 1.9

(lJg/l) Observations

raw* settled finished




*Corresponds to raw water taken. prior to any chlorine addition.

INSTF INSTF INSTF INSTF

TERMR TERMR TERMR TERMR

INSTF INSTF INSTF INSTF

Table 19

Cor re l a t ions I l l u s t r a t i n g Seasonal and Temperature E f f e c t s on THM Formation

Dependent Independent Var iab le Var iab le Slope

TOCR TOCR TOCR TOCR

TOCR TOCR TOCR TOCR

TOCR TOCR TOCR TOCR

TERMR TOCR TERMR TOCR TERMR TOCR TERMR TOCR

INSTF TOCR

TE RMR TOCR

Cor re l a t ion Coef f i c i en t Level of C o e f f i c i e n t No. of

I n t e r c e p t (r) Sign i f i cance of Var i a t ion Observat ions Date Base

sp r ing Excluding p l a n t s summer where p rech lo r i - f a l l na t ion is n o t w in te r p rac t i ced

sp r ing summer A l l d a t a f a l l w in t e r

T545.0 Excluding 45.0<T160.0 p l a n t s where 60.0<T<75.0 prechlor ina- T>75.0 t i o n i s n o t

p rac t i ced . ~ 1 4 5 . 0

Excluding p l a n t s where p r e c h l o r i n a t ion i s n o t p rac t i ced

A l l d a t a

e n t i r e data s e t a re due t o v a r i a t i o n s i n t he temperature and the precursor con ten t o f t he water which v a r i e s accord ing t o season. The decreased 1 eve1 o f s i g n i f i c a n c e f o r t he grouped c o r r e l a t i o n s compared t o t h a t f o r t h e e n t i r e data s e t i s a r e f l e c t i o n o f t h e smal le r number o f observat ions associated w i t h t h e grouped c o r r e l a t i o n s .

Geographical Trends i n TtIM Formation:

A d e f i n i t e geographical t r end was observed i n t he data, i n d i c a t i n g i nc reas ing THM and TOC concent ra t ions from west t o eas t across t h e s t a t e . A h is togram of average THM concent ra t ions (see F igure 9), by l o c a t i o n , con- s t r u c t e d f rom t h e r e s u l t s presented p rev ious l y i n Table 14, c l e a r l y shows t h a t bo th INST THM and TERM THM l e v e l s , as w e l l as THMFP, inc rease i n va lue f rom very low concent ra t ions i n the mountains ( A s h e v i l l e ) , t o h igher values through t h e Piedmont, reaching maximum l e v e l s a t t he A t l a n t i c coas t a t Wilmington. Th i s may be due t o t he na ture o f t he vege ta t i on i n t h e d i f f e r e n t watersheds, o r t o the accumulat ion o f humic m a t e r i a l s i n t he sur face waters as they f l o w toward the coast . Corresponding increases were a l s o noted f o r UV-absorbance and c h l o r i n e demand o f t he raw waters.

F igure 10 shows a p l o t o f THM and TOC concent ra t ions f o r the var ious l o c a t i o n s f o r the A p r i l 1980 sample round. Again, t h e west t o eas t inc rease i n concent ra t ions i s s t r i k i n g l y ill us t ra ted . An apparent except ion t o t h i s t r end i s i n d i c a t e d by t h e Durham fac i1 i t . y . Despi te having n e x t t o t h e h ighes t THM format ion p o t e n t i a l o f t he c i t i e s sampled, and r e l a t i v e l y h igh TOC concentrat ions, t he instantaneous THM concen t ra t i on i n t he f i n i s h e d water a t Durham i s about h a l f t h a t of i t s ne ighbor ing t reatment p l a n t s . Durham te rmi - nated i t s p r e c h l o r i n a t i o n p r a c t i c e i n 1977 i n an a t tempt t o reduce THM pro- duc t ion , o p t i n g t o add c h l o r i n e o n l y a f t e r sedimentat ion. The m o d i f i c a t i o n appears t o have r e s u l t e d i n t h e des i red e f f e c t . P r i o r t o t he change i n t h e p o i n t of a p p l i c a t i o n o f ch lo r i ne , Durham's THM concent ra t ions (Young and Singer, 1979) were comparable t o those o f i t s ne ighbor ing f a c i l i t i e s .

AVERAGE THM CONCENTRATION ( p g / l )

Asheville

IU r or>

skins, Vest (Average)

Greensboro Townsend

w

Raleigh Johnson

4 03

4. LABORATORY-SCALE STUDIES OF TRIHALOMETHANE PRECURSOR REMOVAL

The resu l t s presented in Chapter 3 indicate that three of the c i t i e s i n North Carolina which were sampled had average instantaneous THM concentrations in the finished water in excess of the 100 pg/l MCL. Table 14 shows tha t Chapel Hil l , Raleigh, and Wilmington would have d i f f icu l ty in meeting the THM regula- t ion. Prechlorination doses a t these plants ( the addition of chlorine to the raw water prior to coagulation and se t t l i ng ) were the highest among the t r ea t - ment plants surveyed (see Table 1 2 ) . Hence, for the second phase of th i s project, laboratory studies were conducted on raw waters from Chapel Hi l l , Raleigh, and Wilmington to determine the e f fec t of treatment modifications on the formation of t r i halomethanes. The modifications involved the appl ication of coagulation and se t t l ing prior to chlorine addition, as was demonstrated previously by Young and Singer (1979) on Durham water. In addition, since some of these f a c i l i t i e s rely on prechlorination for iron and manganese oxida- t ion and t a s t e and odor control, an evaluation was a l so made of the impact of ozone and permanganate addition, as a1 ternative pretreatment oxidants to chlorine, on subsequent coagulation.

Experimental Procedures

Raw water was collected a t the Chapel Hil l , Raleigh, and Wilmington t r e a t - ment plants on the same day tha t sampling was carried out fo r the f i e l d survey. The raw water taps in the chemistry laboratories a t each plant served as sampling points. (No chemicals had been added t o the water prior to the point of sample col lect ion.) Five gallons of raw water was collected in a p las t ic carboy, and was stored in the dark for no longer than one week in order t o minimize changes in water quality.

Two se t s of experiments were performed. The f i r s t s e t served as a preliminary investigation to observe the e f fec t of coagulation with alum and subsequent se t t l ing on instantaneous THM formation a t detention times parallel to those within the treatment plants. The second s e t of experiments consisted of a more controlled evaluation of precursor removal by coagulation with alum, and the e f fec t of oxidation on the coagulation of precursors.

A standardized THMFP ( t r i ha1 omethane formation potential ) procedure was used in order to quantify the amount of precursor material present in the water a f t e r various types of treatment. This procedure was identical t o tha t used in the North Carolina THM survey discussed in Chapter 3. Water samples were buffered a t pH 6.7 with phosphate s a l t s and dosed with excess chlorine in order to insure a residual throughout the reaction period. A contact time of 7 days was chosen in order to allow THM formation to approach completion. The samples were stored in the dark, headspace-free, a t room temperature, during the contact period. The THMFP analysis was not intended to simulate conditions in a treatment plant or in a dis t r ibut ion system b u t instead was intended to provide uniform chlorination conditions for purposes of comparison among different sampl es. Seven-day chlorine demand was a1 so measured (under the same conditions as the THMFP procedure) to r e f l ec t the quantity of chl ori ne-dmandi ng material in the water.

Other measurements were made of the TOC concentration, UV absorbance ( a t 254 n m ) , and turbidi ty of the various water samples. TOC and UV absorbance were used as potential surrogates for precursor material as discussed in Chapter 3 . Turbidity measurements were made to evaluate the effectiveness of coagulation in removing suspended part ic les .

Glass-stoppered bot t les (60 ml s ) were used for collection of THMFP and chlorine demand samples. TOC samples were collected in Pierce glass v ia l s with Teflon septa. Wheaton 150 ml glass-stoppered bottles were used for collection of UV absorbance and turbidi ty samples. All glassware was made chlorine demand-free by soaking in a concentrated chlorine solution for a period of a t l eas t 24 hours and then rinsing with chlorine demand-free water.

Chlorine demand-free water was prepared by contacting 5 gallons of water with 3 mg/l chlorine for 48 hours. UV 1 ight was then used to dechlorinate the water. Five-gallon glass carboys were used to s tore the chlorine demand- free water .

Prel lmi nary Experimental Procedure:

The purpose of the f i r s t s e t of experiments was to show the ef fec t of alum pretreatment on instantaneous THM formation. These experiments were designed to approximate conditions through se t t l i ng within each treatment plant. Figure 11 shows the experimental setup.

Chlorine doses applied to the raw water were equivalent to the average daily amount of total chlorine added in the treatment plant, based on plant records. One chlorinated raw water sample was held for a detention time equal to the average detention time within the en t i r e plant ( t ) . The second raw water sample was held for a period of time equal to the reAaining detention time within the plant a f t e r s e t t l i ng ( t 2 ) All samples were buffered a t pH 6.7 with a phosphate buffer.

Alum doses for coagulation were based on plant records for the day of sampling. Since lime or caustic was added along with alum to the rapid mix chambers a t the treatment plant, the pH of the laboratory samples was raised with NaOH i f i t dropped below 5.5 during the one-minute of rapid mix a f t e r the addition of alum. The 'samples were flocculated for 20 minutes a t 30 rpm on a conventional j a r t e s t machine, followed by 60 minutes of se t t l i ng . Aliquots of the se t t led water were taken for TOC analysis, a f t e r which chlorine and the phosphate buffer were added to the remaining set t led water. The samples were then stored headspace-free, for a period of time equal to the detention time within the plant a f t e r s e t t l i ng ( t 2 ) Detention times were based on average plant flows.

Three different concentrations of chlorine (3, 4 , and 5 mg/l) were added to the se t t led water. The intent was t o ensure that a f ree residual chlorine concentration of 1 to 2 mg/l C12 would be maintained. A t the end of the specified detention time for a1 1 samples, residual chlorine was measured using the DPD procedure (Standard Methods, 1976) and the remainder of the sample was quenched with excess sodium sul f i t e t o reduce chlorine to chloride. The samples were then re-sealed headspace-free, and stored for subsequent THM analysis. THM was measured on a Tracor MT 220 Gas Chromatograph with a

Chlorine + Buffer

THM t 2

THM

Alum Coagulation

Chlorine

Buffer

t2 4- THM

Note: t l = Detention time through the entire plant. t 2= Remaining detention time within plant after settling.

l uati n g Figure 11. Pre l imina the Effect

r y Experimental Procedure for Eva of Coagulation on THM Formation.

Hal 1 Elect rolyt ic Conductivity detector using the purge and t r ap procedure (Be l la r and Lichtenberg,l974). The TOC analysis was performed on a Dohrmann DC-54 Ultra Low Organics module. Details of these procedures have been discussed e a r l i e r i n Chapter 3 .

This preliminary experimental procedure was applied t o Wilmington and Raleigh Bain waters with tl equal t o 30 hours and t equal t o 24 hours fo r Wilrnington, and t l equal t o 48 hours and t 2 equal t6 38 hours f o r the Raleigh Bain plant . The major drawback of t h i s approach was t h a t r e s u l t s did not give a t r ue representation of the e f f ec t of coagulation on precursor removal. The chlorine contact conditions were not standardized and contact times were n o t long enough f o r the THM react iontoapproach completion. Accordingly, the experimental procedure was modified t o make use of the standardized THMFP procedure in place of the instantaneous THM measurements.

Modified Experimental Procedure:

The purpose of the second s e t of experiments was t o show the e f f e c t of coagulation and s e t t l i n g on the removal of THM precursors, and the influence of pretreatment with oxidants on the effect iveness of coagulation. All t e s t s were conducted on a laboratory scale using a conventional j a r t e s t apparatus.

Figure 12 shows a flow diagram of the overall experimental procedure. Samples of raw water were collected f o r the measurement of TOC concentration, THMFP, chlor ine demand, U V absorbance, and tu rb id i ty . The samples col l ected fo r TOC analysis were t rea ted with phosphoric acid t o decrease the pH t o approximately 2 in order t o i nh ib i t biological a c t i v i t y , and stored i n a re f r igera to r pr ior t o subsequent analysis . Chlorine demand and THMFP samples were t reated w i t h a known amount of chlorine (15-23 mg/l) and phosphate buffer (pH 6 .7) , sealed headspace-free, and stored in the dark f o r 7 days a t room temperature. A t the end of the storage period, residual chlorine was measured i n one s e t of samples using the D P D procedure (Standard Methods, 1976). The residual chlorine in a paral le l s e t of samples was quenched with excess s u l f i t e t o stop THM production. These THMFP samples were then re-sealed headspace- f r ee , and stored u n t i l subsequent THM analysis . The samples were analyzed for THPls within 2 days a f t e r the chlorine was quenched.

Para1 1 el samples ' of the raw water were coagul ated w i t h a1 um. A1 urn doses were based on plant data f o r the day of sampling and no attempt was made to optimize coagulation. Additions of alum were made while the samples were rapidly mixed on a magnetic s t i r r e r . The pH was monitored, and NaOH was added, in a few t e s t s , t o keep the pH above 5.5.

After alum was added, the samples were rapidly mixed f o r 1 minute and then t ransferred to the j a r t e s t machine where they were slowly mixed f o r 30 minutes a t 40 rpm. After 60 minutes of s e t t l i n g , samples of the s e t t l e d water were taken f o r the measurement of TOC concentration, THMFP, tu rb id i ty , UV absorbance, and chlorine demand, a s described above.

A t h i rd s e t of raw water samples was oxidized w i t h ozone or permanganate. For permanganate, doses of 1, 2, and 3 mg/l KMn04 were applied t o a s e r i e s o f samples of raw water. Permanganate was added from a concentrated stock solut ion of approximately 1000 mg/l I(Mn04 tha t had been standardized by

amperometric t i t r a t i o n w i t h pheny la rs ine ox ide (PAO) as the t i t r a n t . A f t e r t he a d d i t i o n o f permanganate, each sample was s low ly mixed on a j a r t e s t machine a t 40 rpm f o r a con tac t pe r i od o f 2 hours t o i n s u r e complete r e a c t i o n o f t he permanganate. A t t he end o f t h e r e a c t i o n period, a l i q u o t s o f t he o x i d i z e d water were analyzed f o r r e s i d u a l permanganate by amperometric ti t r a t i o n t o show t h a t t he permanganate was complete ly consumed.

For t he ozone s tud ies , concentrated ozone s o l u t i o n s (approx imate ly 40 mg/l 03) were prepared i n a con tac t r e a c t o r us ing a Union Carbide LG-2-L1 ozone generator w i t h oxygen as the feed gas. D i l u t e s u l f u r i c a c i d s o l u t i o n s w i t h a pH of about 4 were ozonated i n t h e r e a c t o r t o produce the des i red ozone s tock s o l u t i o n s . A pH of 4 was se lec ted t o min imize ozone decomposit ion. Dissolved ozone concent ra t ions i n t he s tock s o l u t i o n s were measured i o d i m e t r i c a l l y , us ing standard Na2S203 as the t i t r a n t . S p e c i f i e d volumes (50, 109, and 200 m l s ) o f t he ozone s tock s o l u t i o n were added t o a s e t o f 2 - l i t e r beakers con ta in ing raw water. Add i t i ons of t he ozone stock s o l u t i o n d i l u t e d t h e raw water samples by as much as 10%. Concentrat ions o f t he a p p l i e d ozone were c a l c u l a t e d based on the e x t e n t of d i l u t i o n o f the s tandard ized ozone s tock s o l u t i o n . The pH was ad jus ted t o 6.5 w i t h NaOH and t h e s o l u t i o n s were immediately t r a n s f e r r e d t o a 2 - l i t e r reagent b o t t l e and stoppered headspace-free t o prevent l o s s o f ozone. ( I n t h e f i r s t ozone experiment on Rale igh raw water, the pH was n o t c o n t r o l l e d and ranged from 6.0 t o 6.5.) The s o l u t i o n s were mixed and a l lowed t o r e a c t f o r 45 minutes. ( I n the experiments on Raleigh and Wilmington raw waters, t he r e a c t i o n was c a r r i e d o u t i n an open beaker, w i t h o u t s t i r r i n g . ) Residual ozone was measured by t h e i n d i g o procedure (Bader and Hoigne, 1981 ) t o ensure t h a t ozone was complete ly consumed a t t he end o f t he r e a c t i o n p e r i od .

A f t e r t he ozone o r permanganate reac t i ons were complete, a1 i q u o t s o f the ox id i zed samples were taken f o r t h e measurement o f TOC, THMFP, c h l o r i n e demand, UV absorbance, and t u r b i d i t y . Ch lo r i na t i ons were c a r r i e d o u t i n a standard manner, as descr ibed above. The ox id i zed waters were then coagulated w i t h alum and s e t t l e d , us ing t h e standard j a r t e s t procedure p r e v i o u s l y descr ibed and samples were taken again f o r ana l ys i s o f TOC, THMFP, c h l o r i n e demand, UV absorbance, and t u r b i d i t y . All a n a l y t i c a l procedures were t h e same as those descr ibed p r e v i o u s l y i n Chapter 3.

Experimental Resul t s

Pre l im ina ry Experiments:

The c h a r a c t e r i s t i c s o f t he raw waters used i n t h e two p r e l i m i n a r y experiments a r e shown i n Tab1 e 20. T u r b i d i t y measurements were re1 a t i v e l y low b u t concent ra t ions o f TOC and THMFP were h igh. Ch lo r i ne demand measurements were made o n l y on t h e Wilmington sample.

The o b j e c t i v e o f t he p r e l i m i n a r y experiments was t o show t h e e f f e c t o f coagu la t i on on the fo rma t i on o f instantaneous THMs w i t h i n a t rea tment p l a n t . Table 21 shows the r e s u l t s o f both t e s t s . The r e s u l t s i n d i c a t e t h a t alum coagu la t i on and s e t t l i n g reduces instantaneous THM format ion s u b s t a n t i a l l y . I n t h e Rale igh experiment, alum coagu la t i on and s e t t l i n g reduced t h e 38-hr THM fo rma t i on by more than 50%. TOC was n o t measured i n t h i s experiment so a comparison between TOC removal and THM reduc t i on cou ld n o t be made. I n t he Wi lmington experiment, coagu la t i on w i t h alum f o l lowed by s e t t l i n g reduced t h e 24-hr THM format ion by about 40-50%. TOC, however, was reduced by o n l y 15%.

Table 21

Results of Preliminary Experiments on Raleigh Bain and Wilmington Raw Waters

Sampl e

Reaction Time C12 Dose* THM # TOC Cl Residual Raleigh Bain ( hours) (m!?/l) (!dl (mg/1) ( W / l >

Raw Water Control 1 48 Raw Water Control 2 38 Se t t l ed Water 38 Se t t l ed Water 38 Se t t l ed Water 38

Raw Water Control 1 30 8.1 236 7.1 0.9 Raw Water Control 2 24 8.1 202 7.1 1.4 Se t t l ed Water 24 5.8 124 6.0 1 .4 Se t t l ed Water 24 4.6 107 6.0 0.9 Se t t l ed Water 24 3.5 1 09 6.0 0

* The chlor ine stock solut ion f o r the Raleigh t e s t was not standardized properly; hence the doses a r e only approximate and somewhat questionable i n view of the high res iduals .

# The tri halomethane react ion was carr ied out i n pH 6.7 phosphate-buffered solut ion.

Comparison of the THM concentrations in the two controls with different reaction times indicates tha t the THM reaction was not complete a t the end of the 24- and 38-hour reaction periods. Hence, the modif i ed experimental

I procedure was used for the remainder of the laboratory experiments to more quantitatively i l l ustrate the effects of coagulation on THM precursor removal .

Modified Experiments:

The raw water quality of the samples examined in the modified experiments i s shown in Table 22. The waters were characterized, in general, by relat ively low turb id i t ies , high concentrations of TOC, and high THMFPs.

Chapel Hill

Two experiments were performed on Chapel Hill raw water. The resul ts of these experiments a re shown in Tables 23 and 24. The f i r s t experiment, in addition to evaluating the effectiveness of coagulation, involved the use of permanganate as a pretreatment oxidant. The second experiment used ozone.

The resu l t s show tha t coagulation with alum and se t t l i ng , alone, effected a substantial reduction in each of the parameters measured. THMFP was reduced by more than 50% in both experiments, from 288 to 108 pg/l in the f i r s t experiment (see Table 23), and from 294 to 146 ug/l in the second experiment (see Table 24). I n both experiments, the TOC concentration was reduced to about 2.0 mg/l by coagulation and se t t l ing , and UV absorbance was reduced by approximately 70%. Pretreatment with alum also s ignif icant ly lowered the turbidi ty , as expected, and the 7-day chlorine demand was reduced to a level one-half to one-third tha t of the raw water demand.

The ef fec ts of oxidation alone are less s ignif icant than for coagulation and se t t l i ng . THMFP was essent ial ly unchanged for a l l three doses of perman- qanate b u t when ozone was used as the oxidant, THMFP decreased somewhat as the oxidant dose increased. However,since the two experiments were on different waters, the resul t s are not direct ly comparable. Dil ution effects resulting from the addition of the ozone stock solution could account for u p to approximately 10% of the observed decrease i n THMFP in the ozonated samples. The THMFP decrease, how eve^, i s as high as 20%.

Ozone and permanganate had d i f fe rent e f fec ts on TOC. The low dose of ozone (see Table 24) had no impact on TOC while the higher ozone dose decreased TOC s l ightly. The TOC concentrations in the samples treated with permanganate, however, appear to be higher for a l l doses of permanganate. These apparent increases in measured TOC may be at t r ibuted to shortcomings in the TOC analytical procedure. I t i s conceivable that not a l l of the organics present in the orlginal water sample were converted to C02 in the carbon analyzer. Some of the larger , macromolecular or par t iculate organic carbon may have been more diff lcul t to oxidize. Hence, the measured raw water TOC values could be low due to incomplete oxidation of some of the organic material. After oxidation, some of th i s organic material may have been altered to a form which was more easi ly oxidized in the TOC analyzer and therefore became measurable as TOC. Since no organic carbon was added to the water when permanganate was applied and since the TOC observations are no t consistent with the U V absorbance and chlorine demand resu l t s , the apparent increase in TOC due t o the application of permanganate must be an analytical a r t i f a c t .

Table 22

Samp 1 e

Chapel H i l l

Chapel H i l l

Raleigh- Johnson

u o Wilmington

Wilmington

Raw Water Charac te r i s t i cs f o r Modi f ied Tests

Date Date o f Raw Water T u r b i d i t y TOC UV Col l e c t e d Experiment Source (NTU) (mg/ 1 ) Absorbance

1 /30/80 2/05/80 Un ive rs i t y 15 6.1 0.170 Lake

3/95/80 3/07/80 U n i v e r s i t y 6.1 3.4 0.116 Lake

2/06/80 21 1 4/80 Neuse River 15 6.6 0.160

211 3/80 211 6/80 Cape Fear 15 6.7 0.190 River

211 3/80 211 9/80 Cape Fear 14 5.9 0.190 River

Table 23

Results of Coagulation and Permanganate Pretreatment of Chapel Hill Raw Mater

Chlorine Demand* (mg/l)

l m g l l KMn04 + 119

50 mg/l Alum

2 mg/l KMn04 + 121

50 mg/l Alum

3 mg/l KMn04 + 112

Turbidity (NTU)

15

2 .5

15

50 mg/l Alum

Treatment

none

50 mg/l Alum

1 mg/l KMn04

* Applied chlorine dose = 15.3 mg/l

TOC (mg/l)

6 . 1

2 .3

6 . 6

THMFP* b d l )

288

108

282

UV Absorbance

0.170

0.054

0.140

Table 24

Resul ts o f Coagulation and Ozone P re t r ea tmen t o f Chapel Hill Raw Water

THMFP* Treatment

none 1 294

30 mgll Alum 146

1.1 mg/l O3

0.72 mgll O3 + 30 mg/l Alum

1.1 mgll O3 + 30 mg/l Alum 1 145

I UV Turbidity Chlorine* (mg/l) Absorbance (NTU) Demand (mg/l)

* Applied c h l o r i n e dose = 19.8 mg/l

The o t h e r parameters measured were a l so a f f e c t e d t o some degree by ox ida t i on . UV absorbance decreased w i t h i n c r e a s i ng ox idan t dose f o r bo th ozone and permanganate, i n d i c a t i n g t h a t the na ture o f the organics was a1 t e r e d by 0x4 da t i o n . T u r b i d i t y decreased s l i g h t l y i n both cases and, s i nce ozone and permanganate a re ox idants, the c h l o r i n e demand of the samples a1 so decreased w i t h i ncreas i n g o x i dan t dose.

The r e s u l t s o f the combined t reatment show t h a t o x i d a t i o n had o n l y a minor impact on the e f f ec t i veness o f coagulat ion. THMFP values us ing both ox idants f o l l owed by coagu la t ion were e s s e n t i a l l y the same when compared t o the samples t h a t were t r e a t e d by alum alone, a1 though the permanganate- t r e a t e d samples showed a s l i g h t inc rease i n THMFP compared t o the samples t h a t were o n l y coagulated. The samples t h a t were o x i d i z e d w i t h permanganate p r i o r t o coagu la t i on showed a s i g n i f i c a n t inc rease i n res idua l TOC conipared t o t he samples t h a t were o n l y coagulated. Th is apparent inc rease c o u l d have been due t o t he a n a l y t i c a l l i m i t a t i o n s discussed above o r t o a l t e r a t i o n o f t he organ ic m a t e r i a l by the ox idant . It may be theo r i zed t h a t the ox idants conver t the organics t o a smal ler , more po la r , and more so lub le formythereby making the r e s i d u a l TOC more d i f f i c u l t t o coagulate. Since the c h l o r i n e demand was s l i g h t l y h ighe r f o r samples t h a t had been o x i d i z e d w i t h permanganate and then coagulated compared t o samples t h a t were o n l y t r e a t e d w i t h alum, the apparent inc rease i n res idua l TOC may, i n f a c t , be r e a l . Removals o f UV-absorbing m a t e r i a l and t u r b i d i t y by coagu la t ion and s e t t l i n g were una f fec ted by o x i d a t i o n w i t h e i t h e r ozone o r permanganate.

Rale igh

Raw water f o r t h i s experiment was taken from the Rale igh Johnson t r e a t - ment p l a n t . Ozone was used as the pre t rea tment ox idan t and-the r e s u l t s o f the experiment a re summarized i n Table 2 5 .

Coagulat ion and s e t t l i n g had the same e f f e c t on Rale igh water as on Chapel H i l l water i n t h a t the concentrat ions o f each o f the parameters measured were reduced s u b s t a n t i a l l y . The removal o f o rgan ic m a t e r i a l by coagu la t ion and s e t t l i n g a lone was apprec iable, as shown by reduc t ions i n THMFP o f 57%, TOC 52%, UV absorbance 75%: and c h l o r i n e demand 50%. T u r b i d i t y i n t he raw water was a l s o removed e f f e c t i v e l y , as expected, by coagu la t ion and s e t t l ing .

Ox ida t ion by ozone had a measurable impact on a l l parameters. The THMFP was lowered as a r e s u l t o f o x i d a t i o n o f precursors, b u t n o t t o the e x t e n t t h a t r e s u l t e d f rom coagu la t i on and s e t t l i n g . The decrease i n THMFP was g rea te r w i t h i nc reas ing doses o f ozone. Wi th the except ion o f t he 8.1 mg/l value, smal l reduc t ions i n t he TOC concent ra t ion were observed as a r e s u l t o f ozonat ion. Ozone a l s o a1 t e r e d the n a t u r e o f the organics i n the water as seen by the s i g n i f i c a n t reduc t i on i n UV absorbance. T u r b i d i t y was o n l y s l i g h t l y reduced w i t h i nc reas ing doses o f ozone, b u t d i l u t i o n resu l t i n g f rom the a d d i t i o n o f the ozone s o l u t i o n may have been respons ib le f o r t h i s observed decrease. A1 though ozone i s a s t r o n g ox idant , o n l y minor reduc t ions i n the c h l o r i n e demand were observed w i t h i nc reas ing ozone dose.

The e f f e c t o f ozone pre t rea tment on coagu la t i on was v i r t u a l l y the same as the resu l t s f rom Chapel H i 11 . THMFP values were essen t i a l l y unchanged compared t o t h e va lue ob ta ined w i t h coagu la t ion alone, regard less o f the

Treatment

Table 25

Resu l t s o f Coagulation and Ozone Pre t rea tment o f Ra l e igh Johnson Raw Water

none

40 mg/l Alum

1.3 mg/l O3

2.5 mg/l O3

4.4 mgll O3

40 mg/l Alum

2.5 mgll O3 + 40 mg/l Alum

4.4 mg/l O3 + 40 mg/l Alum

uv Absorbance

0.160

Turbidity (NTU)

Chlorine* Demand (mg/l)


ozone dose. Residual TOC increased a t the highe -ose o f ozon e compared t o the r e s u l t a n t TOC from coagu la t ion alone. he reduc t i on i n UV absorbance a f t e r coagu la t i on was enhanced s l i g h t l y as a r e s u l t o f the ozone pret reatment . T u r b i d i t y values f o r samples t h a t had been ox id i zed w i t h ozone p r i o r t o coagu la t ion were s l i g h t l y lower than the t u r b i d i t y o f t h e sample which had o n l y been coagulated and s e t t l e d . There was v i r t u a l l y no change i n the c h l o r i n e demand of the coagulated water as a r e s u l t o f ozone pret reatment .

Wilmington

Two t e s t s were performed on Wilmington raw water. Both t e s t s were conducted on t h e same raw water t o p rov ide an o p p o r t u n i t y f o r comparison between ox idants . S l i g h t reduc t ions i n THMFP, TOC, and c h l o r i n e demand were observed over the three-day storage p e r i o d between the two tes ts , p o s s i b l y due t o b i o l o g i c a l a c t i v i t y . The resu l t s o f the two experiments a r e presented i n Tables 26 and 27,

I n both t es t s , coagu la t ion reduced t h e concent ra t ions o f each o f the parameters measured by a t l e a s t 50%. THMFP values were reduced t o approx i - mate ly 130 vg / l i n both experiments, corresponding t o a 66% removal o f THM precursors due t o coagu la t i on and s e t t l i n g alone. Reductions i n t he TOC concent ra t ions o f t he samples were subs tan t i a l , b u t n o t as g rea t as the reduc t ions i n THMFP. Tn bo th tes t s , the TOC concent ra t ion was reduced t o approx imate ly 3 mg/l , correspondi ng t o an average reduc t i on o f 50%. Coagu- 1 a t i o n w i t h a1 um f o l 1 owed by s e t t l i n g removed 80% o f t he UV-absorbing m a t e r i a l i n both experiments. T u r b i d i t y was a l s o reduced s i g n i f i c a n t l y by coagu la t i on and s e t t l i n g , as expected. The e f f e c t s o f coagu la t i on and s e t t l i n g on the 7-day c h l o r i n e demand appear t o be d i f f e r e n t f o r t h e two runs. However, the va lue of 4.8 mg/l i n Table 26 i s be l i eved t o be erroneous i n view o f the resu l t s w i t h permanganate and alum together as shown i n t h e bottom p a r t o f the tab le . I t would appear, there fo re , t h a t coagu la t i on and s e t t l i n g reduced the c h l o r i n e demand by approx imate ly 50%.

Ox ida t i on by ozone and permanganate gave very s i m i l a r r e s u l t s . Both t e s t s showed decreasing THMFPs w i t h i nc reas ing doses o f ox idant , w i t h a 20% decrease a t the maximum doses app l ied . T u r b i d i t y was o n l y s l i g h t l y reduced by both ox idants . S i m i l a r l y , o n l y a minor decrease was seen i n the 7-day c h l o r i n e demand data, desp i t e the apprec iab le amounts o f t he pre t rea tment ox idan ts app l ied .

I n the case o f TOC, o x i d a t i o n by both permanganate and ozone a t low doses appears t o have increased the TOC concen t ra t i on compared t o t he raw water TOC. This unusual observa t ion may be a t t r i b u t a b l e t o a n a l y t i c a l d i f f i c u l t i e s associated w i t h the measurement o f TOC i n t he raw water, as d iscussed above. A t h i ghe r doses o f ox idant , however, t he concent ra t ion o f TOC decreased i n samples o x i d i z e d w i t h ozone, w h i l e t he concen t ra t i on o f TOC i n the permanganate-treated samples remained g rea te r t h a t t he concen- t r a t i o n s i n the raw water.

D i f f e r e n t t rends were a l s o noted i n the UV absorbance r e s u l t s . The samples t r e a t e d w i t h permanganate showed a s l i g h t inc rease i n UV absorbance, w h i l e t he UV-absorbance o f the samples t r e a t e d w i t h ozone decreased w i t h i nc reas ing ozone dosage.

Table 26

Resul ts o f Coaqul a t i o n and Permanganate P re t r ea tmen t of W i lmi ngton Raw Water

Treatment

none

30 mg/l Alum

1 mg/l KMn04 + 30 mg/l Alum

2 mg/l KMn04 + 30 mg/ 1 Alum

3 mg/l KMn04 + 30 mg/l Alum


THMFP* ( p g / l )

376

123 I

343

320

308

123

134

134

Turbidity 0J"w

14

1.9

12

12

11

2.0

3.0

1.2

Chlorine* Demand (mg/l)

13.4

4.8

11.9

12.4

11.8

6.9

6.8

8 .1

. TOC (mg/l)

5.9

3.0

7.0

7 . 1

6.5

3.3

3.3

3.7

UV Absorbance

0.190

0.037

0.216

0.196

0.220

0.035

0.045

0.037

F I m m . . . u m m d d d

u m u d d d

o o a 03 a 0 d d d

Oxidation eri t h permanganate o r ozone had very 1 i t t l e impact on the effect iveness of coagulation. THMFP measurements on samples t h a t were oxidized by ozone o r permanganate and then coagulated were the same as those fo r samples tha t were t reated w i t h alum alone. Samples t ha t were oxidized, coagulated, and s e t t l e d had higher concentrations of residual TOC than samples t h a t were only coagulated and s e t t l e d . The increase in TOC was paral le led by a s imi la r increase in chlorine demand, although the changes in the l a t t e r were more e r r a t i c . Pre-oxidation had almost no e f f e c t on coagulation of tu rb id i ty and UV-absorbing material . Summary and Discussion of Results

The r e su l t s of a l l the experiments grouped together show tha t coagulation with alum followed by s e t t l i n g provides an e f fec t ive method f o r removing TOC and THM precursors from drinking water. Table 28 summarizes the r e su l t s of the coagulation experiments using the modified procedure. The THMFP was reduced by an average of 61%, indicating t h a t coagulation removes a substant ia l portion of THM precursors. In a l l cases, the reduction in THMFP was g rea te r than the reduction in TOC, a1 though the TOC reductions were appreciable. The TOC concentrations in the untreated raw water a r e questionable, however, due t o trends seen a f t e r oxidation of the raw water. As was discussed above, TOC concentrations increased a f t e r oxidation when there was no apparent source of contamination, indicating t h a t the measured TOC concentrations of the raw water may be low. Hence, the percent reduc- t ions i n TOC may ac tua l ly be greater than those reported in Table 28.

Table 28 a l so shows t h a t o ther indicators of the organic content and THMFP of the waters were s ign i f ican t ly reduced due to coagulation and s e t t l i n g . U V absorbance was reduced by an average of 76%, indicat ing t h a t UV-absorbing substances a l so appear t o be more amenable t o coagulation than other organics included i n the TOC measurement. The organic content as re f lec ted by the 7-day chlorine demand was a l so subs tan t ia l ly reduced by coagulation.

Oxidation alone, using ozone o r permanganate a t normal treatment plant doses, reduced the THMFP to some degree b u t not to as g rea t an ex ten t as coagulation. The impac.t of oxidation on coagulation and s e t t l i n g was re la - t i ve ly minor, although oxidation did a1 t e r the nature of the dissolved organics. TOC was the only parameter t h a t was s i gn i f i c an t l y affected by oxidation pr io r t o coagulation. However, despi te the increase i n TOC, oxidative pretreatment did not enhance THM formation.

Accordingly, i f THM l eve l s a t a given water p lant are found to be excessive and plant operations need to be modified in order to bring the water in to compl iance with the MCL f o r TTHMs, i t would appear t h a t the removal of THM precursors by coagulation pr io r t o the addit ion of chlorine would be a des i rable , i n i t i a l modification to implement before other, more cos t ly process modifications a r e considered. In s i tua t ions where iron and manganese or t a s t e and odor problems a re encountered, ozone o r permanganate could be used t o overcome these problem without in te r fe r ing with subsequent THM removal by coagulation. In a l l cases, however, adequate dis infect ion must be assured.

QI e d LO12

5. PLANT-SCALE STUDY OF TRIHALOMETHANE CONTROL

Towards the end of the Morth Carolina THM monitoring survey discussed in Chapter 3 , and in view of the resul ts of the laboratory-scale studies of THM precursor removal discussed in Chapter 4, i t was decided to investigate THM control on a plant-scale. The Sweeney Hater Treatment Plant, in Wilrnington, NC, was chosen for th i s purpose since Wilmington was found to have the highest finished water instantaneous THM concentrations among a l l the c i t i e s surveyed. I t was theorized t h a t any method which would bring Wilmington into compliance with the MCL would also be successful a t other plants in the s t a t e with finished water instantaneous THM concentrations in excess of the MCL. Additionally, Wilmington was chosen for further study because of the versati l i ty of the Sweeney water plant with respect to the number of potential points for chlorine application.

I t should be pointed out that compl iance with the THM regulation i s based upon a moving average THM concentration computed from samples taken quarterly a t f ive locations in the dis t r ibut ion system. Since a fu l l year of sampling was not conducted a t Wilmington, and since no samples were collected from the dis t r ibut ion system, S t i s not possible to s t a t e unequivocably whether or n o t Wilmington i s in compliance with the regulation, or the extent to which the MCL i s exceeded.

Description of the Sweeney Water Treatment Plant

The c i ty of Wilmington i s located in New Hanover County, in the southeastern portion of North Carolina. I t has a population of between 50,000 and 60,000 and an average water use of approximately 10 to 11 rngd. This includes water used for industrial as well as municipal applications.

Wilmington's potable water source i s the Cape Fear River, a t King's Bluff, approximately 26 miles upstream of the c i t y of Wilmington. The Cape Fear passes through the southeastern portion of Morth Carolina and has a drainage area of approximately 5220 square miles a t the King's Bluff location (U.S. Geological Survey, 1978). Downstream of King's Bluff, the Cape Fear i s subject to the influx of saltwater which makes i t i~nsui table as a source of fresh water. The maximum a1 lowabl e d ra f t for the Cape Fear River a t the King's Bluff pumping s ta t ion has been estimated to be about 180 mgd (U. S. Geological Survey, l978), well in excess of the needs of the c i t y of Wilming- t o n .

A t King's Bluff, water i s withdrawn d i rec t ly from the Cape Fear River and pumped through a large transmission main to the Sweeney plant, located withln the c i ty l imits of Wilmington. The approximate travel time for water from the King's Bluff pumping s tat ion to the Sweeney plant i s 9 hours, based on an average flow of 10 mgd. The raw water pumps a t King's Bluff have a capacity of 12 mgd. Screenfng, to protect the raw water pumps, i s the only form of treatment a t King's Bluff. Originally, the pump s ta t ion was designed to provide for chlorination a t King's Bluff in order t o control nuisance growths in the transmission main. However, t h i s practice was deemed unnecessary and was discontinued several years ago.

The Sweeney water plant t r ea t s a l l of the water which i s pumped from King's E l uff. I t has a capacity of 12 mgd and i s a conventional surface water treatment plant. A schematic of the plant i s provided in Figure 13 which a1 so shows the various points where chemicals can be added and samples can be taken. The Sweeney plant i s unusual in tha t i t i s possible t o add chlorine a t f ive d i f fe rent locations. I t would seem a good idea to incorporate th i s type of design f l ex ib i l i t y into a l l new plants of th i s s ize in l i gh t of the growing concern over the health e f fec ts of various chlorinated organic compounds in drinking water.

Water entering the Sweeney plant i s f i r s t passed through two rapid mix chambers which have a combined volume of about 7500 f t 3 . Here, alum and caustic (or 1 ime) are added to provide coagulation and to control the pH of the incoming water, respectively. Powdered activated carbon can a1 so be added a t th i s point when tas te and odor problems ar i se . Up until June 2 , 1980, chlorine was added a t the head of the f i r s t rapid mix chamber.

Following rapid mixing, the water passes through a flocculator with a detention time of about 35 minutes (based on a flow of 10 rngd) and into one of 1 2 sedimentation tanks. The combined sedimentation tank volume i s about 2.63 mg, allowing a 6.3-hour detention period for se t t l i ng . Following sedimentation, the water i s chlorinated and f i l t e red . After f i l t r a t i o n , the water can be chlorinated again, and fluoride i s added. Caustic i s also added a t t h i s point to ra i se the pHy and phosphate i s added for corrosion control.

After these chemicals have been added, the water flows into a 17-mg clearwell where i t i s stored for approximately 41 hours (on a 10 mgd flow basis) before i t i s pumped into the dis t r ibut ion system. This long detention time in the clearwell allows more than adequate chlorine contact time for disinfection purposes. A t the pump suction well, more chlorine can be added t o insure the presence of an adequate chlorine residual in the dis t r ibut ion system.

Six sampling points from which grab samples can be taken are also Identified i n Figure 13. Sample point 1 i s located a t the King's Bluff pump s ta t ion . A water sample was taken from t h i s location on only one occasion (2/13/8O), during a brief period in which chlorine was added a t the pump s ta t ion on a t r i a l basis. On that occasion, a sample was collected from the discharge side of the raw water pump, prior to the addition of chlorine. Points 2, 3, and 6 were routinely sampled and designated raw, se t t l ed , and finished water samples, respectively. As indicated in the figure, sample 2 was taken prior to the addition of any chemicals a t the Sweeney plant. On the f i r s t Wilmington v i s i t (10/23/79), a sample was also taken from point 5. Water samples corresponding to points 2 through 6 were a l l taken from sampl i ng taps in the 1 aboratory a t the Sweeney plant. These taps were allowed t o run continuously t o insure the ava i lab i l i ty of a representative sampl e .

Raw Water Characteri s t i c s

The qua1 i t y of water treated a t the Sweene !y plant varies throughout the year, depending on such factors as temperature, r a in fa l l , and the growth and decay of vegetative matter in the drainage area. For example, turbidity i s direct ly affected by rainfal l intensity and duration. Taste and odor and color are governed by the yearly cycle of vegetative growth. Chemical requirements a t the treatment plant are , therefore, dependent on these seasonal variations.

Monthly average values for selected water quality parameters and chemical dosages ( e .g . raw water temperature, raw water turbidity, chlorine demand, total chlorine applied, and required alum dose) for the Sweeney water plant are outltned in Figure 14 for a two-year period, from July 1978 to July 1983. These data represent monthly average values which were taken from plant records. From th is figure, i t i s evident tha t each of the water quality parameters vary throughout the year.

Raw water temperature i s highest between July and September and i s lowest in January and February. Both chlorine demand and total applied chlorine closely follow the temperature variation. During the hot summer months of the year, the ra te of chlorine react ivi ty i s increased, making i t possible fo r reactions in the plant t o take place f a s t e r , thereby requiring the addition of more chlorine to achieve the desired chlorine residual. Also, during t h i s time of the year, sunlight intensi ty i s highest. Since the flocculation and sedimentation tanks a t the Sweeney plant a re open, the destruction of chlorine by sunlight would also be expected to be highest during t h i s time of the year.

Chlorine demand and the required chlorine dose are a1 so s ignif icant ly infl uenced by the presence of chlorine-demandi ng substances, such as iron and manganese, organic material, and various other reducing agents. However, t h i s relationship i s d i f f i c u l t to express in terms of any water quality parameter which i s routinely measured a t the plant.

Variations were also observed in raw water turbidity, total alum dose, and raw water color. In general, however, these variations did not exhibit the seasonal pattern wtiich was noted for raw water temperature, chlorine demand, and total chlorine dose. This i s most l ike ly because turbidi ty , alum dose, and color a re a l so dependent on such factors as rainfal l and runoff which are not necessarily seasonally-dependent.

During the North Carolina THM survey, the highest THM production was ncted in a l l the plants during the warm, sumer months (see Chapter 3 ) . In Wi lmington, temperature, chlorine demand, and total chlorine dose were a1 1 found t o be highest in the summer, indicating a high potential fo r THM production a t t h i s time of the year. As a resu l t , t h i s season was considered to be the c r i t i c a l time with respect to THM production and was selected to be the optimal time for making plant-scale modifications to control THM production.

RAW WATER

TEMPERATURE

TOTA L

RAW

TOTAL ALUM DOSE (mg/l)

RAW WATER

TURBID1 TY (NTU)

J A S O N D J F M A M J J A S O N D J F M A M J J

DATE

Figure 14. Seasonal Variation in Raw Water Quality at the Sweeney Water Plant.

Monitoring Survey and Modifications of Prechlorination Practice a t the Sweeney Plant

The Wilmington monitoring survey was conducted over an 11-month period, during w h i c h time a to ta l of e igh t samples were col lected. The Sweeney plant was f i r s t sampled on October 23, 1979. The remaining samples were taken between February 13, 1980 and September 30, 1980, on approximately a monthly basis . On June 2, 1980, the point of i n i t i a l chlorine application was sh i f t ed from the rapid mix chamber t o a point downstream of the sedimentation basins ,pr ior t o f i l t r a t i o n ( see Figure 13) . The decision t o make t h i s change was based on the THM reductions observed in Durham following a change in the1 r point of chlorine application (Young and Singer, 1979) and on the r e su l t s reported in Chapter 4 .

The r e su l t s of the Wilmington THM survey are presented i n Table 29. Both THM and TOC data a r e included. As indicated, the point of i n i t i a l chlorine appl ica t ion was sh i f t ed on June 2, 1980, from the rapid mix chamber to a polnt between sedimentation and f i l t r a t i o n .

On February 13, 1980, raw water samples were taken from the King's Bluff pumping s t a t i on and the raw water tap in the Sweeney laboratory which samples the raw water entering the plant . During t h i s period, prechlorination a t the King's Bluff location was practiced on a t r i a l bas is f o r a sho r t period of time. As a r e s u l t , i t was necessary t o sample the King's Bluff location, a t a point p r io r t o the addit ion of chlorine, t o get a t r ue raw water sample. The instantaneous THM concentration in the King ' s Bl uff sample was found to be below the l i m i t of detection of the G C . However, the raw water enter ing the Sweeney p lan t on February 13, 1980 was found t o have an instantaneous THM concentration of 103 ug/l. T h i s high THM concentration was a t t r i bu t ed to the long chlorine contact time (approximately 9 hours) in the transmission main between King's Bluff and the Sweeney plant . Fol lowing t h i s observation, the pract ice of prechlorination a t the King's Bluff locat ion was discontinued.

In order to assess the impact of the change in the point of i n i t i a l chlorine appl icat ion, samples were col lected and analyzed on May 27, 1980 and June 6, 1980, j u s t . p r i o r t o and immediately a f t e r the June 2 change. This sho r t period was chosen t o minimize any changes i n water qua l i ty o r temperature on THM formation. As a r e s u l t of the modification, a s i gn i f i c an t reduction i n f inished water instantaneous THM concentration was noted, from 215 t o 90 vg/ l . The percent reduction i n f inished water instantaneous THMs was much grea te r than the corresponding reduction i n THM precursor content (terminal THM) f o r the two samples. On two subsequent sampling v i s i t s , August 12, 1980 and September 30, 1980, the instantaneous THM concentrations i n the f inished water were found t o be approximately the same as on June 6, 1980, despite the high temperatures and high THM precursor content noted f o r the corresponding raw water samples. This documents the posi t ive e f f e c t of the treatment modification. However, the f in ished water instantaneous THM concentration f o r the sample taken on July 14, 1980 was found t o be considerably higher (176 vs. approximately 90 vg/ l ) than f o r the o ther three samples taken a f t e r the modification was made, despite the f a c t t ha t the precursor content of the s e t t l e d water was about the same. The reason fo r t h i s s ing le discrepancy i s not known.

Date Sampled

Location of Sample

raw s e t t l e d f i n i s h e d

King's Bluff raw s e t t l e d f i n i s h e d

raw s e t t l e d f i n i s h e d

raw s e t t l ed f i n i s h e d

Table 29

Resul t s o f Wilmington Sampling Program

POINT OF CHLORINE APPLICATION SHIFTED

raw 8 .5 ND s e t t l e d 4 .O 1.1 D f i n i s h e d 4.1 93.0

raw 7 -0 IJ D s e t t l e d 3 -8 ND f i n i s h e d 3.6 176

Raw Water

Temperature ( OC)

A1 though sampling was stopped i n September, i t i s be1 ieved, based on the seasonal and temperature e f f e c t s observed i n connect ion w i t h the Nor th Carol i na THM survey discussed i n Chapter 3, t h a t f i n i s h e d water instantaneous THM l e v e l s i n the Sweeney p l a n t would decrease i n t h e co lde r months. Hence, t h e r e s u l t s presented i n Table 29 cover the most c r i t i c a l p e r i o d of t he year and subs tan t i a te t h e impact o f t he m o d i f i c a t i o n i n a s s i s t i n g Wilmington t o comply w i t h t h e THM standard.

On two occasions, March 10, 1980 and August 6, 1980, p a r a l l e l samples were c o l l e c t e d by personnel a t the Sweeney p l a n t f o r ou ts ide ana lys i s by an independent l abo ra to ry . These r e s u l t s a re presented i n Table 30 and were found t o be cons i s ten t w i t h the f ind ings o f t h i s study. I n a d d i t i o n t o the two i n - p l a n t samples, the ou ts ide l a b o r a t o r y a l s o analyzed samples from two p o i n t s w i t h i n the d i s t r i b u t i o n system, a t C i t y Hal 1, approximately the mid- p o i n t o f the d i s t r i b u t i o n system, and Echo Farms, the most d i s t a n t p o i n t i n the d i s t r i b u t i o n system. The resu l t s show t h a t THM product ion cont inued i n t h e d i s t r i b u t i o n system, w i t h instantaneous THM concentrat ions o f 158 and 180 pg/ l noted a t Echo Farms on March 10, 1980 and August 6, 1980, respec t i ve l y . I n terms o f t he THM regu la t i on , which requ i res THM mon i to r i ng w i t h i n the d i s tri b u t i o n sys tem, these f i n d i n g s a re s i g n i f i c a n t , i n d i c a t i n g t h a t Wi lmington 's THM problems were n o t complete ly so lved by s h i f t i n g the p o i n t o f i n i t i a l c h l o r i n e appl i c a t i o n .

P r i o r t o moving t h e p o i n t o f i n i t i a l c h l o r i n e app l i ca t i on , some concern was expressed as t o whether adequate d i s i n f e c t i o n cou ld be prov ided a t the Sweeney p l a n t i f c h l o r i n e a d d i t i o n was postponed u n t i l a f t e r the sedimen- t a t i o n stage o f treatment. I n o rder t o i n s u r e adequate d i s i n f e c t i o n , an expanded m i c r o b i o l o g i c a l mon i to r i ng program was i n i t i a t e d by Sweeney water p l a n t personnel approximate ly one month be fore the change was made. The b i o l o g i c a l qua1 i ty o f the water del i v e r e d t o the consumer was considered t o be o f paramount importance du r ing t h i s per iod. It was agreed t h a t t h e i n i t i a l c h l o r i n e con tac t p o i n t would be moved back t o the r a p i d mix chamber a t t he f i r s t s igns o f u n s a t i s f a c t o r y d i s i n f e c t i o n . For the Sweeney water p lan t , t he a v a i l a b l e c h l o r i n e con tac t t ime i n the 17 mg c l e a r w e l l proved t o be more than adequate f o r good d i s i n f e c t i o n . However, i n another t r e a t - ment p l a n t w i t h l ess c l e a r w e l l detent ion, t h i s would n o t necessa r i l y be the case.

P o t e n t i a l problems o f nuisance a1 gal growths i n the sedimentat ion tanks r e s u l t i n g f rom moving the p o i n t o f c h l o r i n e a d d i t i o n were a l s o considered before the change was made. Tn t h e Sweeney p lan t , t h i s d i d n o t prove t o be a problem.

Add i t i ona l Studies

Fo l lowing the change i n t h e p o i n t o f i n i t i a l c h l o r i n e a p p l i c a t i o n a t the Sweeney water p lan t , t r ihalomethane l e v e l s were s t i l l found t o be i n excess o f the MCL,especially i n the d i s t r i b u t i o n system. I n an e f f o r t t o reduce

THM p roduc t i on even f u r t h e r , a se r i es o f j a r t e s t experiments were conducted t o determine i f the coagu la t ion process cou ld be improved w i t h respect t o the removal o f THM precursors. Th i s was considered t o be the most l o g i c a l cons idera t ion i n f u r t h e r reducing THM product ion a t the Sweeney p l a n t .

Procedures:

J a r t e s t experiments were conducted on two se t s of raw water samples from Wilmington, coll ected on 7/14/80 and 9130180. These samples were coll ected in 5-gal lon p las t ic containers, returned to Chapel Hi 11, and stored in the dark a t room temperature until the experiments could be performed. The period of time between sample collection and the complete s e t of j a r t e s t s was between one and two weeks for both samples. Alum, f e r r i c su l fa te , and a n alum/polymer combination were evaluated fo r the i r effectiveness in removing THM precursors.

Jar t e s t s to determine the optimal pH for coagulation were run f i r s t . A sub-optimal coagulant dose, as determined from Sweeney plant records and the published l i t e ra tu re , was used for both alum and f e r r i c sulfate . The optimal pH determined from these experiments was then used in additional jar t e s t s to determine the optimal doses for the two coagulants and for the alum/polymer combination.

A similar ja r t e s t procedure, as out1 ined in Figure 15, was used for a l l of the investigations. Raw and se t t led water turbidity, TOC, terriinal THM, U V absorbance (254 nm), and 7-day chlorine demand were measured t o evaluate the effectiveness of each of the coagulants.

All samples were f i r s t rapid-mixed on a magnetic s t i r r e r . Rapid-mix times and chemical addition procedures were a1 tered s l ightly for different ja r t e s t s , depending on whether coagulant dose or pH was the variable of in te res t . In the f i r s t s e t of experiments fo r optimizing the pH of coagu- la t ion , a pH range of 4-7 was investigated fo r alum and a pH range of 3-6 was examined for f e r r i c sulfate . These ranges were based on previous reports by Black e t a1 . (1963), Babcock and Singer (1979), Edzwald, Haff, and Boak (1977), and others. For a l l pH optimization experiments, a s ingle coagulant dose, considered to be below the optimal dose, was used. In the second s e t of pH optimization experiments, a wider pH range (3-8) was investigated for both coagulants.

The optimal pH of each coagulant was then used fo r a l l of the remaining coagulation experiments. Alum and f e r r i c su l fa te concentrations of 0, 10, 20, 30, 40, 50 and 100 mg/l were investigated. These coagulants were added while the samples were undergoing rapid mixing. Care was taken to maintain the pH of the sample a t the optimal level while the coagulant was being added.

For the alum-polymer experiments, the desired alum dose was added to the sample and the sample was rapid-mixed for a period of two minutes. The polymer was then added to the sample and mixed fo r another 30 seconds t o allow for i t to disperse. The optimal alum dose, and a sub-optimal alum dose in combination with f ive polymer doses, were employed. The polymer doses ranged from 0 to 1.0 mg/l in the f i r s t s e t of experiments and 0 to 0.5 mg/l in the second s e t of experiments. Betz 1160, a cationic polymer with a molecular weight of 30,000, was used in these experiments.

I\ control, with zero mg/l of coagulant, was run fo r each of the raw water samples tested. The control was subjected to the same mixing and s e t t l i ng conditions as the other samples.

Raw Water

Measure: TOC, turbidity, UV absorbance (254 nm), temperature, pH, terminal THM, 7-day ch l o r i ne demand. - Adjust pH of raw water to desired level.

Rapid m ix sample fo r 2 min. wh i le adding a l um o r f e r r i c sulfate, ma in ta in ing pH at i t s pre-set level. (For alum-polymer experiments, rapid m i x sample a n addit ional 30 sec. wh i le adding polymer.

r--- Flocculate 30 min. @ 40 rpm on j a r test machine.

1- Settle 60 min.

t- Measure turbidi ty, pH, UV absorbance, and TOC of settled water.

1- Add 1.0 m l phosphate bu f fe r (pH = 6.7).

Add 1.0 m l of standardized ch lo r ine stock so lu t ion to provide a n i n i t i a l ch l o r i ne concentrat ion of approximately 20 mgll.

Store samples for 7 days at room temperature in t h e da r k.

t- Measure residual CI2 after 7 days.

Quench residual C12 w i th sodium sulf i te.

Measure THMs produced after 7 days.

Figure 15. Ja r Test Procedure For Wi lmington Coagulation Studies.

In a l l of the ja r t e s t experiments, a sample volume of 500 ml was used. A1 1 pH adjustments were made with e i ther 2 x 10-2 M Na2C03 or 10-1 M H2SO4 solutions. Fresh alum stock solutions and Betz 1160 solutions were prepared for each s e t of j a r t e s t experiments using chlorine-demand-free water. All f e r r i c su l fa te stock solutions were made in 10-1 M H2SO4 to minimize Fe(II1) hydrolysi s during preparation.

Following the rapid mix and chemical addition steps, the samples were flocculated for 30 minutes a t 40 rpm on a Phipps and Bird ja r t e s t apparatus. No e f f o r t was made t o investigate the effects of different mixing intensi t ies on the j a r t e s t resul t s ; the same mixing in tens i t ies were used throughout th i s study. Following flocculation, the samples were allowed to s e t t l e fo r 60 minutes. After s e t t l ing, supernatant samples were withdrawn for the analysis of the various parameters indicated above.

A1 1 TOC, terminal THM, and 7-day chlorine demand samples were taken and analyzed in accordance with the procedures out1 ined in Chapter 3. The pH of the sample was measured immediately upon completion of each experiment using a Fisher Accumet Model 230A pH meter, standardized with Fisher pH buffers a t two pH values. Turbidity was measured on a Hach Model 18900 Ratio Turbidlmeter. For the UV absorbance measurements, the pH ~f a l l samples was adjusted to 6.7 with 10-2 M phosphate buffer in order to negate the e f fec ts of pH on the UV absorbance measurement. Following pH adjustment, samples were immedfately f i l t e red and analyzed on a Varian Techtronic Model 635 Spectrophotometer. For the treated water samples, 5 cm quartz ce l l s were used for measuring UV absorbance in order t o increase the sens i t iv i ty of the measurement, while 1 cm ce l l s were used for the raw water samples. All of the measured values were subsequently adjusted for a 1 cm l igh t path, and the absorbance values reported in the resu l t s below apply to a 1 cm 1 ight path. A1 1 absorbance measurements were made a t 254 nm.

Because of the length of time required for TOC and THM analysis, only those samples corresponding to the optimal doses for reducing UV absorbance and turbidity were analyzed for residual TOC and terminal THM.

Resul t s and Discussion:

The resul ts of the two s e t s of ja r t e s t experiments conducted on Wilming- ton water a r e presented i n Figures 16 through 24. Of the water quality parameters measured, TOC, terminal THM, UV absorbance, and turbidi ty a re graphed to enable comparison among the resul ts. The seven-day chlorine demand data were found to correlate f a i r l y well w i t h TOC, terminal THM, and UV absorbance. However, the values were much more variable.

The water qua1 i ty character is t ics of the two waters examined were quite different , a s indicated in Table 31. The THM precursor content of the raw water collected on 7/14/80 was considerably higher than t h a t of the water collected on 9/30/80. Likewise, the turbidi ty of the former was almost twice tha t of the l a t t e r . The other water quality parameters varied in a similar fashion.

Alum Coagulation Results

The optimal pH for alum coagulation, based on the f ive parameters investigated, was found to 1 i e within the range of 5 to 6 for both of the water samples tested (see Figures 16 and 17) . Turbidity and the various organic parameters were both minimized in t h i s pH range, suggesting a possible simi- l a r i t y in the hydrolyzed Al(1II) species responsible for the coagulation of THM precursor compounds and col loidal material making u p the turbidity .

Similar optimal pH values have been reported by other investigators for alum coagulation of color-causing substances, humic materials, and THM precursors. Babcock and Singer (1979) found tha t color and TOC removals were best a t pH values below 5.5 when coagulating humic substances with alum. Likewise, Black and Willems (1961) reported an optimal pH range of 5 .2 to 5.7 for the coagulation of color-causing substances by a1 um. Hal 1 and Packham (1 965) found the coagulation of humic substances to be optimal in the pH range of 5 t o 6. Semmens and Field (1980) found a pH of approximately 5.0 to be optimal for the removal of both organic substances, as measured by UV absorbance and TOC, and turbidi ty . However, they noted that organics were not removed as effect ively a t higher pH values. The authors concluded tha t the mechanisms responsible fo r the removal of organic material were different a t different pH values.

In addition t o correlating we1 1 with the previously-reported optimal pH ranges in the 1 i tera ture, the optimal pH range determined in these experi - ments was found to be very close to the actual pH values of the se t t led water a t the Sweeney plant on 7/14/80 and 9/30/80. In view of th i s s imilar i ty , i t seems unl ikely that any s ignif icant improvement in the removal of THM precursors can be real ized by a1 tering the pH of coagulation a t the Sweeney plant.

The optimal alum dose for the f i r s t raw water sample was found to be about 20 mg/l for turbidity removal and 30 mg/l for THMFP and TOC removal (see Figure 18). With a 30 mg/l alum dose, the terminal THM was reduced 62%, from 606 to 228 pg/l. A t higher alum doses, 1 i t t l e additional removal of THM precursors was achieved. UV absorbance and TOC followed a similar pattern and were reduced 76% and 51%, respectively, following treatment with 30 mg/l alum. Turbidity was reduced from 13.6 t o 0.4 NTU w i t h an alum dose of 20 mg/l .

The optimal dose of alum for the second raw water sample was not as c lear ly defined (see Figure 19). An optimum of 20 mg/l was noted for turbidi ty removal and 30 mg/l appeared to be the optimal dose for TOC removal . No clearcut optimum was noted fo r the removal of THMFP. Despite the lower turbidi ty and THM precursor content of thissample, the same alum dose was required as for the f i r s t sample. A substantially lower percent reduction in terminal THM a t a 30 mg/l alum dose was noted for the l a t t e r sample (a reduction of 38% in the terminal THM concentration versus a 62% reduction for the f i r s t sample). Part of th is discrepancy can be explained by the uncertainty in the terminal THM measurements fo r t h i s experiment which were more variable than in previous experiments. However, the majority of the difference i s be1 ieved to be due to the nature of the organics in the raw water. Reductions in TOC and UV absorbance were also lower for the second sampl e .

h

E Terminal THM =6O6 ,ug/l C

UV Absorbance = 0 . 2 6 6 0.300 * In CU 0.250 -

Terminal THM

- Alum Dose = 20 mg/l j 0.050

I 1 I I I I I I I I I 1 0.000 - RAW WATER - - Turbidity = 13.7 NTU - - TOC =7.0 mg/l - - - -

4.0 4.5 5.0 5.5 6.0 6.5 7.0

pH OF COAGULATION

F igu re 16. Effect of pH o n Coagu la t ion w i t h A l u m (Sample 1).

- RAW WATER - - Terminal THM = 389 ~ g / l - - UV Absorbance = 0.173 -

Terminal

Absorbance

- - Alum Dose = 20 mg/ l -

I I I I I I I I I I I -

I

- RAW WATER Turbidity = 7.9 NTU

T O C = 4.5 mg/ l

pH OF COAGULATION

Figure 17. Effect of pH on Coagulation wi th A l u m (Sample 2).

h RAW WATER 7 600 Terminal THM = 606 ~ g / l U, U V Absorbance =0.266

3 500

- - 0 I I I I I I I I I I I I - RAW WATER - - Turbidity = 13.7 N T U - - TOC = 7 . 0 mg/ l -

25 - - - -

20 - 7

ALUM DOSE (mg/l)

Figure 18. Effect of A l u m Dose on Water Quality (Sample 1).

RAW WATER Terminal THM = 3 8 9 y g / l

UV Absorbance = 0.173 0.300 500

I I I I I I I 1 I I I

- RAW WATER Turbidity = 7.9 N T U

TOC = 4.5 mg/ l $ 6.0

t \ Turbidity

ALUM DOSE (mg/ l )

F igu re 19. Effect of Alum Dose on Water Q u a l i t y (Sample 2).

On 7/14/80 and 9/30/80, the actual alum additions of 32 and 19 mg/l a t the Sweeney plant resulted in 57% and 47% reductions in terminal THM levels , respectively (see Table 24, ea r l i e r in th i s chapter). In l i gh t of the s imilar i ty between actual THMFP removals a t the Sweeney plant and the resu l t s of these j a r t e s t s , i t seems unl i kely that much additional improvement can be made a t the Sweeney plant w i t h regard to the coagulation of THM precursors in the water by alum. On both occasions, the reductions in THMFP a t Wilmington, on a plant-scale, were equal to or greater than the optimal remova 1 s i ndi ca ted by the ja r t e s t s .

Ferric Sulfate Coagulation Results

An optimal pH range of between 3.5 and 5.5 was determined for coagulation with f e r r i c su l fa te , based on the f ive parameters analyzed (see Figures 20 and 21). In general, the data corresponding to the f e r r i c su l fa te experiments were found to be somewhat more variable, showing s l ight ly l e s s d is t inc t ive trends.

The optimal pH range determined in these experiments correlates well with previous resu l t s reported in the l i t e ra tu re by other investigators. Black e t a1 . (1963) reported an optimal pH of 3.4 to 3.9 for the removal of color from six highly-colored surface waters using f e r r i c su l fa te . Simil a r resul t s were obtained by Hal 1 and Packham (1965) for the i r coagulation studies of humic and fulvic acid with f e r r i c chloride.

The optimal f e r r i c sulfate dose fo r THMFP removal was found to be about 30 mg/l f o r the f i r s t water sample (see Figure 22) and 20 mg/l fo r the second water sample (see Figure 23). Optimal turbidi ty removal was achieved with 20 mg/l of f e r r i c sulfate for both of the waters. Terminal THMs were reduced 64% (from 606 to approximately 220 ug/l) fo r the f i r s t water and 52% (from 389 to 187 pg/l) for the second water under optimal conditions, ref lect ing s l ight ly greater THM precursor removals with f e r r i c su l fa te than with alum. THMFP reductions wi t h f e r r i c sulfate were s l ightly greater than those noted in the Sweeney water plant on 7/14/80 and 9/30/80 (see Table 29). TOC was reduced 61% fo r the f i r s t water (from 7.0 to approximately 2.8 mg/l ) and 45% fo r the second water (from 4.5 to 2.5 mg/l) under optimal conditions. UV absorbance was reduced 75% (from 0.265 to 0.067) and 64% (from 0.173 to 0 .O63) under optimal conditions fo r the f i r s t and second waters, respectively.

A1 um-Pol ymer Coagul ation Resul t s

Betz 1160 additions were found to have 1 i t t l e impact on the removal of THM precursors fo r the two waters tes ted, under the mixing conditions of the ja r t e s t s . In a l l cases, the terminal THM reductions fo r samples treated with alum and Betz 1160 were similar to the corresponding reductions observed with alum alone. These resu l t s were somewhat unexpected in view of the previous findings of Edzwald, Haff and Boak (1977) and James (1980). Edzwald, Haff and Boak (1977) noted s ignif icant improvements in humic acid removals when 0.5 mg/l of Betz 1160 was added i n conjunction with alum compared with the removals noted fo r alum alone. James (1980) noted a 79% reduction in TOC when alum and Betz 1160 were used in combination compared with a 32% reduction in TOC when alum was used alone. For the Wilmington waters tes ted, however, only turbidi ty removal from the f i r s t water sample a t the lower alum dose was

- Ferric Sulfate -

- 0.300 Dose = 20 mg/ l - 0.200

1- 0.100

n

600 0 -

- 0 I I I I I I I I I I I I

- RAW WATER - - Turbidity = 13.7 NTU - - TOC = 7.0 mg/l

25 -

20

15 - - 10 - -

- RAW WATER - - Terminal THM = 606 ,ug/l -

UV Absorbance = 0 .266 C

5 - - Turbidity - 1.0

e- - - 0 1 - I I I - 1 I I I -nn

pH O F COAGULATION

Figure 20. Effect of pH on Coagulation wi th Fer r i c Sulfate (Sample 1).

RAW WATER Terminal T H M =389 y g / l UV Absorbance =0.173

Terminal THM

uv Absorbance

0

50 t Ferric Sulfate Dose = , 2 0 mg/ l >

RAW WATER Turbidity =7.9 N T U

TOC = 4.5 mg / I 6.0

pH OF COAGULATION

F i g u r e 21. Effect of pH o n Coagu la t ion with F e r r i c Su l fa te (Sample 2).

I- ,

h

RAW WATER E C

Terminal THM = 6 0 6 y g / l 0.300 * UV Absorbance = 0 .266

LC> 500 0.250 2

> 0.000 =

RAW WATER 7.0 Turbidity =13.7 NTU

TOC = 7.0 mg /I 25

6.0

Turbidity

0 -1/ 1.0 1 A A

7 y 7 " - 0 0 20 40 60 80 100

FERRIC SULFATE DOSE (mg/l)

Figure 22. Effect of ~ e r r i c Sulfate Dose on Water Qual i ty (Sample 1).

h

n E 600 Terminal THM = 389 )g/l C

0, 0.600 *

U V Absorbance = 0 .173 ' 500 In

w 0.500

UL

W U V Absorbance 0.100 el I- \

RAW WATER -I Turbidity = 7.9 N T U

TOC = 4.5 mg/ l

2 - Turbidity - 1.0 - 0 - 0 1 I I ? I I I I V I I 0.0

FERRIC SULFATE DOSE (mg/l)

Figure 23. Effect of Ferric Sulfate Dose on Water Quality (Sample 2).

aided by the use of the polymer (see Figures 24, 25, and 26). In 1 ight of the negligible e f fec t of the polymer additions noted i n these experiments, i t seems unlikely that a cationic polymeric coagulant aid could play a major role in treatment a t the Sweeney plant.

I t i s conceivable t h a t an anionic or nonionic polymer might produce d i f fe rent resu l t s than the cationic, Betz 1160 polymer used here. This possibi l i ty remains to be investigated, a1 though the 1 ikelihood of such a n improvement seems doubtful based on the work of Edzwald, Haff and Boak (1977) which showed the cationic polymer to be the most appropriate for removing the negatively-charged precursor molecules.

Implications of and Considerations fo r Further Investigation:

In 1 ight of the s imi lar i ty between optimal THM precursor removal s observed in the ja r t e s t s and actual treatment plant performance, i t seems unlikely tha t alum coagulation can be improved to allow a fur ther reduction i n THM formation a t the Sweeney plant. The use of a combination of alum and Betz 1160 polymer can also be ruled out as a means of s ignif icant ly reducing THM precursor levels. While other alum-polymer combinations might be investigated, i t i s doubtful t ha t the corresponding reductions in THM precursor concentrations would be suf f ic ien t to lower TTHMs in the dis t r ibut ion system to levels below the MCL.

Ferric su l fa te was found to give s l ight ly bet ter resu l t s than the observed plant-scale resu l t s with alum. However, In view of the additional THM formation noted in the Wilmington dis t r ibut ion system (see Table 301, i t appears unlikely that the reduction associated with the use of f e r r i c su l fa te would be of suff ic ient magnitude to insure compl iance with the MCL.

Hence, i t can be concluded tha t fur ther optimization of coagulation, or a change in coagulants a t the Sweeney plant, i s not jus t i f ied . Accordingly, other means of THM control need to be considered.

Several options remain to be investigated which could bring Wilmington into compl iance with the MCL for THMs. Understandably, these remaining options are more expensive than the approaches which have been t r i ed thus f a r .

One approach which has yet t o be investigated involves the application of ammonia to the chlorinated water leaving the clearwell, before i t enters the dis t r ibut ion system. In t h i s way, any remaining f ree chlorine would be converted to combined chlorine (chloramines) , thereby arrest ing the THM formation reaction (Stevens, e t a1 ., 1976). If t h i s approach was adopted, THM production in the Wilmington dis t r ibut ion system could be dras t ica l ly reduced. A t the present time, adequate detention time i s available in the plant clearwell to a1 low sat isfactory primary disinfection with f ree chlorine. Ammonia would be added only t o a s s i s t in residual protection. The THM monitoring resu l t s fo r Wilmington, presented ea r l i e r in t h i s chapter, have verif ied tha t finished water THM concentrations leaving the plant a re below 100 pg/l under most conditions as a r e su l t of moving the point of chlorine addition t o a f t e r sedimentation. Only in the dis t r ibut ion system do THM concentrations increase above the MCL. I t , therefore, seems l ike ly tha t a reduction in THM production in the Wilmington dis t r ibut ion system, by t ie ing u p the free chlorine as chloramines, could maintain overall THM production below the 100 pg/l l imi t .

- RAW WATER - - Terminal THM = 6 0 6 y g / l - - UV Absorbance = 0 . 2 6 6 ' -

Terminal THM

n 0

- UV Absorbance - -

Alum Dose = 2 0 mg/ l - pH = 5.5

RAW WATER Turbidity = 13.7 N T U 6.0

TOC = 7 .0 mg/l 5.0

4.0

6 3.0

Turbidity - 1.0

0 0.0 0.01

0.0 0.05 0.5 1.0

POLYMER DOSE (mg/l)

Figure 24. Effect of Alum and Polymer Combination on Water Quality (Sample 1).

n

E Terminal THM = 606 ,ug/l 0.300 q- c

UV Absorbance = 0 . 2 6 6 10 500 0.250

Terminal THM

0

300 n - -

UV Absorbance v - -

QlOO

100 2ool =

Alum Dose = 30 mg/l pH = 5.5 0.0 5 0

I I 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1

RAW WATER 0.000 -

Turbidity = 13.7 NTU TOC = 7.0 mg/l

TOC 15 U "

k Turbidity

POLYMER DOSE (mg/l)

Figure 25. Effect of A lum and Polymer Combination on Water Quality (Sample 1).

RAW WATER Terminal THM = 389 y g / l

UV Absorbance = 0.173

Alum Dose = 2 0 mg/ l pH = 5.5

300 Terminal

THM 0

200 0

UV Absorbance 100 0

d

0.000 R A W WATER

Turbidity = 7.9 NTU TOC = 4.5 mg / l

6.0

2.5 5.0

2 .o

0.5 L, . Turbidity 3 1.0 w

POLYMER DOSE (mg/l)

Figure 26. Effect of A l u m a n d Polymer Combinat ion o n Water Qua l i t y (Sample 2).

The use of chlormaines for residual protection in the dis t r ibut ion system i s probably the most economical of the remaining options available for the Sweeney plant. A t the present time, a f ree chlorine residual of between 2.0 and 2.5 mg/l i s maintained i n the water leaving the clearwell. Assuming enough ammonia was added to the clearwell eff luent to convert the available chlori ne to chloramines ( t h i s would require approximately 0.5 mg/l ammonia), the cost of using chloramines in the dis t r ibut ion system would be approximately $2010/year, based on an ammonia cost of 12$/1b (Clark, 1979) and a flow of 11 mgd. In making th is estimate, no consideration has been given to the cost of storage f a c i l i t i e s or feeding equipment for the ammonia; however, these costs are not expected to be prohibitive.

A second option which merits consideration a t the Sweeney plant is the addition of powdered activated carbon (PAC) as an adsorbent for THM precursor removal . Reports by Symons (1 978) and Anderson e t a1 . (1 980) have shown tha t PAC doses of 20-25 mg/l can r e su l t in removals of THM precursors of up t o 55% depending upon the type of carbon and the nature of the water in question. Anderson e t a l . (1980) found tha t doses as low as 7.0 mg/l were able to remove u p to 25% of the THM precursors. Since the Sweeney plant currently has the capabili ty fo r addition of powdered activated carbon to the rapid mix tank, i t would be relat ively simple to conduct bench-scale and plant-scale experiments with several different brands of PAC t o determine the i r re lat ive impact on THM precursor removal. I t should be noted, however, that i t i s not c lear t h a t the addition of PAC in conjunction with coagulation would r e su l t in a s ignif icant decrease in THM precursors above the removals associated with the use of coagulation alone. I t i s possible tha t the precursor compounds removed by the addition of PAC a re the same compounds which are removed effect ively by coagulation.

Assuming tha t similar resu l t s to those presented by Anderson e t a1 . (1980) could be obtained, requiring a carbon dose of approximately 25 mg/l, the cos t of PAC treatment would be about $690/day, or $252,00O/year. This estimate i s based on a PAC uni t cos t of $30/100 Ib, the present cost paid by the Sweeney water plant. I t i s I i kely tha t a lower dose of PAC could be used during the winter months o f the year, when THM problems are l e s s severe. However, specif ic t e s t s would have to be conducted on Wilmington water to substantiate t h i s assumption. Clearly, the costs associated with the use of PAC a re appreciably higher than those associated with the use of chloramines for dis t r ibut ion system protection. Specific t e s t s would be required a t the Wilmington plant before a more precise cost figure could be obtained.

I t should be noted tha t w i t h the present THM regulation (Environmental Protection Agency, 1979),compl iance i s based on a moving average THM concentration calculated from quarterly samples taken a t f ive sampl ing locations in the dis t r ibut ion system. Since a fu l l year of sampling has not been completed a t Wilmington, i t i s not possible to say unequivocably whether or not the plant i s in compliance with the MCL, o r the extent to which the MCL i s exceeded.

In summary, i t appears tha t several possible options fo r reducing THM production remain to be investigated a t Wilmington. The use of chloramines f o r dis t r ibut ion system disinfection appears to be the most promising and should, therefore, be the f i r s t option investigated. Anothen modification

which could be made a t the Sweeney p l a n t i s t o f u r t h e r s h i f t the p o i n t o f i n i t i a l ch l o r i ne appl i c a t i o n from a p o i n t fo l l ow ing sedimentation t o a p o i n t f o l l ow ing f i l t r a t i o n , These opt ions would requ i re minimal changes i n p l an t operat ion and would be inexpensive, However, both o f these opt ions would requ i re careful moni tor ing o f co l i f o rm counts w i t h i n the p l a n t and i n the d i s t r i b u t i o n system t o insure adequate p ro tec t ion o f the water. A t h i r d a1 t e rna t i ve ava i lab le t o Wilmington i s t o experiment w i t h the add i t i on o f powdered ac t i va ted carbon dur ing the r a p i d mix stage o f treatment. Other options, e.g. the use o f a l t e rna te oxidants, such as ozone o r ch lo r ine d iox ide and the use o f granular ac t i va ted carbon (GAC) columns, are a lso ava i lab le t o Wilmington. However, on an economic basis, i t appears u n l i k e l y t h a t these opt ions would be as cos t -e f fec t i ve as the opt ions a1 ready discussed.

It i s worth r e - s t a t i ng t h a t the seve r i t y o f the THM problem a t Wilmington s t i l l remains t o be ascerta ined more completely, f o l lowing the completion of a year-round sampling program. The r e s u l t s o f t h i s survey w i l l have a d i r e c t bearing on t he se lec t ion o f f u t u re approaches f o r treatment modif i c a t i o n . Also, i t should be noted t h a t the lower Cape Fear River has been l abe l l ed as a "vulnerable water source" by the EPA because o f the possib le presence o f hazardous organics o f i n d u s t r i a l o r i g i n . I f t h i s i s the case, Wilmington may have no choice bu t t o provide GAC o r some other a l t e r n a t i v e treatment f o r removal of these organics i n the fu ture , depending upon forthcoming EPA regu la t ions. An t i c i pa t i on o f the impact o f these regu la t ions should be considered i n making any major modi f ica t ions.

References

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APHA, Standard Methods f o r the Examination of Water and Wastewater, 14th ed i t ion , American Public Health Association, Washington, u.c., lY/b.

Babcock, D. B . and Singer, P. C . , "Chlorination and Coagulation of Humic and Fulvic Acids," Journal of the American Water Works Association, Vol. 71, pp. 149-1 53, March 1979.

Bader, H . and J . Hoigne, "Determination of Ozone in Water by the Indigo Method," Water Research, Vol . 15, pp. 449-456, 1981.

Bel lar , T. A. and Lichtenberg, J . Jay "Determining Volati le Organics a t Micro- gram-per-Li t r e Level s by Gas Chromatography," Journal American Water Norks Association, pp. 739-744, Dec 1974.

Bellar , T . A,, Lichtenberg, J . J . , and Kroner, R . C . , "The Occurrence of Organohal ides in Chlorinated Drinking Waters, '' Journal American Water Works Association, Vol. 66, p p . 703-706, Dec 1974.

Black, A . P. and Christman, R . F . , "Character is t ics of Colored Surface Waters," Journal of the American Water Works Association, Vol . 55, pp. 753-771, June 1963.

Black, A. P . and Christman, R. F., "Chemical Character is t ics of Fulvic Acids," Journal of the American Water Works Association, Vol. 55, pp. 897-913, July 1963.

Black, A . P . , Singley, J . E . , Whittle, G . P . , and Maulding, J . W . , "Stoichiometry of the Coagulation of Col or-Causing Organic Compounds with Ferr ic Su l fa te , " Journal of the American Water Works Association, Vol . 55, pp. 1347-1 367, Oct 1963.

Black, A. P . and Willems, D. G . , "Electrophoretic Studies of Coagulation f o r Removal of Organic Color," Journal of the American \ later Narks Association, Vol . 53, p p . 589-604, Yay 1961.

Boney, Wiggins, Rimer and Associates, "A Survey of the Municipal Water Suppl i e s of North Carolina, Vol . 1-13, Departvent of Human Resources, Division of Heal t 9 Services, Sanitary Engineering Section, Water Supply Branch, S t a t e of North Carol ina, 1977.

Clark, J . C . , J r . , "Econonlic Aspects of Tri ha1 omethane Control, " Paper presented a t a seminar f o r the Control of Organic Chemical Contaminants in Drinking Water, Jan 1979.

Dobbsy R . A . , Wise, R . H . , and Dean, R . B . , "The Use of Ul tra-Violet Absorbance f o r Monitoring the Total Organic Carbon Content of Water and Wastewater," biater Research, Vol. 6 , pp. 1173-1180, Oct 1972.

Edzwald, J.K., Haff, J . 5 . 3 and Boak, J , W,, "Polymer Coagulation of Hunic Acid Waters," Journal of the Environrnental Engineering Division, ASCE, Vol . 103, pp. 989-1 QCll, Dec 1977.

Env i ronmental Protection Agency, "Analytical Report, New Or1 eans Area Clater Supply Study," Region VI, Dallas, Texas, 1974.

Environmental Protection Agency, "Interim Primary Drinking Water Regulations: Control of Organic Chemical Contaminants in Drinking Water," Federal Register , Vo1. 43, No. 28, pp . 5756-5780, Feb. 9, 1978.

Environmental Protection Agency, "National Interim Primary 3rinking Water Regulations: Control of Trihalomethanes in Drinking Water; Final Rule," Federal Register, Vol . 44, No. 231, pp. 63624-68707, Nov. 29, 1979.

Environmental Protection Agency, "The Analysis of Tri ha1 omethanes i n Finished ka te r by the Purge and Trap Method," Method 501 . I , Environmental Monitoring and Support Laboratory, U.S. EPA, Cincinnati , Ohio, Yov. 6 , 1979.

Environmental Protection Agency, "The National Organics Monitoring Survey ,I' Technical Support Division, Office of Water Supply, U.S. EPA, 1977.

Glaze, W. H . and Rawley, R . , "A Prel iminary Survey of Trihalomethane Levels i n Selected East Texas Water Supplies," Journal American Water GIorks Association, Vol. 71, No. 9, pp. 509-515, Sept 1979.

Glaze, CJ. H . , e t a1 . , Oxidation of Water Supply Refractory Species by Ozone w i t h Ul t ra-Viole t Radiation, EPA 600/2-80-110, U.S. Environmental Protection Agency, Cincinnati , ~ h i o , 1980.'

Hal 1 , E . S. and Packham, R . F., "Coagulation of Organic Color w i t h Hydrolyzing Coagulants, " Journal of the American Water Norks Association, Vol . 57, pp. 11 49-1 167, Sept 1965.

Helwig, J . T., SAS Introductory Guide, SAS I n s t i t u t e , Inc., Raleigh, NC, 1978.

Helwig, J . T . and Council, K . A . , Editors, SAS User's Guide, 1979 Edition, SAS I n s t i t u t e , Inc., Raleigh, NC, 1979.

James, C . R . , "Selection of Coagulants i n Water Treatment: Considerations of Sludge Disposal," Report submitted i n pa r t i a l f u l f i l lmen t of the requirements f o r the degree of Master of Science i n Environmental Engineering, University of North Carolina, Chapel H i l l , IVC, 1980.

Kavanaugh, M. C . , "Modified Coagulation f o r Improved Removal of Tri halomethane Precursors," Journal of the American Nater Works Association, Vol. 70, pp. 61 3-621, Nov 1978.

Lonsdale, R . E . , "Atlas of North Carolina," University of North Carolina, Chapel Hi1 1, NC, 1967.

Hann, L . T . , J r . , "Pub1 i c Water Suppl l e s of North Carolina," Water Resources Invest igat ions 78-1 6, U . S. Geological Survey, Raleigh, NC, Apr 1978.

11 1

Mi near, R . A , , ' tProduction, Fate and Removal of Tri halomethanes in Municipal grinking Water Systems," Report No. 18, Tennessee Water Resources Research Center, The University of Tennessee, Apr 1980.

Oliver, B. G, and Lawrence, J , , "Haloforms i n Drinking Water: A Study of Precursors and Precursor Removal," Journal of the American Water Works Association, Vol . 71, pp. 161 -163, Mar 1973

Page, T . and Harris , R . F . , "Imp1 ica t ions of Cancer-Causing Substances in Mississippi River Water," Environmental Defense Fund Report, Washington, D . C . , Nov 6, 1974.

Pendygraft, G . W . , Schlegel, F. E . , and Huston, M. J . , "Organics in Drinking !later: A Heal t h Perspective," Journal of the American Water Works Association, V Q ~ . 71, pp. 118-1 26, Mar 1979.

Rook, J . J . , "Formation of Haloforms During Clilorination of Natural Waters," Journal of Water Treatment and Examination, Vol. 23, pp. 234-243, 1974.

Sciieucii, L . E. and Edzwal d, J . I(. , "Removi ng Col or and Ckl oroform Precursors from Low Turbidity Waters by Direct F i l t r a t i on , " Journal of the Anerican Mater 'dlsrks Association, Vol. 73, 810. 9 , pp. 497-502, Sept 1981.

Semmens, M. J . and Field, T . J . , "Coagulation: Experiments in Organics Removal ," Journal of the American Water Works Association, Vol . 72, pp. 476-483, Aug 1989.

Singer, P . C . , Law1 e r , D. F . , and Babcock, D. B., "Notes and Comients on the National Organics Reconnaissance Survey," Journal of the American Water Works Association, Vo. 68, 3 . , p. 452, Aug 1976.

Singer, P . C. , Borchardt, J . H . , and Colthurst , J . M . , "The Effects of Permanganate Pretreatment on Trihalomethane Formation in Drinking Water," ~ o u r n a l of the American Water Works Association, Vol . 72, pp. 573-78, Oct 1980.

Snoeyink, V. L . , McCreary, J . J . , and Murin, C. J . , Activated Carbon Adsorption of Trace Organic Compounds, EPA-60012-77-223, US EPA, Cincinnati, Ohio, 1977.

Stevens, A . A * , Slocum, C. J . , Seeger, D. R e , and Robeck, G . G . , "Chlorination of Organics i n Drinking Water," Journal of the American Water Works Association, Vol . 68, pp . 615-620, llov 1976.

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Symons, J . M., Bellar , T . A . , Carswell, J , K , , DeMarco, J , , Kropp, K . L . , Robeck, G , G , , Seeger, D. R . 3 Slocum, C . J . , Smith , B. L . , and Stevens, A.A . , "National Organics Reconnaissance Survey f o r Halogenated Organics," Journal of t h e Arqerican Nater Works Association, Vol . 67, No. 11, pp, 634- 647, Nov 1975.

,esearch labor at or.^, Off i c e of Research - and Development, US Environmental Protectton Agency, Washington, D . C. , Jan 1978.

Trusse l l , R. R. and Umphres, M . D . , "The Formation of Trihalomethanes," Journal of the American 'dater Works Association, Vol. 70, No. 11, pp. 604- 612, Nov 1978.

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I Young, J . S., J r . and Singer, P . C . , "Chloroform Formation i n Public Water Suppl i e s : A Case Study," Journal of the American Water Works Association, Vol. 71, No. 2, pp. 87-95, Feb 1979.

Zogorski, J . S., Al lgeier , G . D. and Mullins, R . L , J r . , "Removal of Chloroform from Dri n k i ng Water, " Research Report No. 11 1 , Uni vers i t y of Kentucky, Water Resources Research I n s t i t u t e , Lexi ngton, Kentucky, June 1978.

(Safe y i e ld 28-30 MGD)

Raw Water Sampl e

X

Pre-Fi 1 tered Sample

Fi 1 tered sampl e

Cl earwell ( 5 m9)

+ Clearwell Sample

F1 uori de Caustic b Phosphate f b Finished Sample

Cl as of 3/79 v

Total detention time is about 6.5 hours a t average flow of 22 MGD.

Figure A-1 . Flow Diagram of Asheville Water Treatment Plant .

c1 2 A1 um Caust ic KMn04 Po 1 yme r

U n i v e r s i t y Lake

Raw Water Sampl e

S e t t l e d Sample

Caust ic

C12

(0.181 MG Clear Water Conduit)

Phosphate F l uor ide

F i 1 t e red Sampl e

) Fin ished Sample

D i s t r i b u t i o n

To ta l de ten t i on t ime i s about 12 hours a t average f l o w o f 5 MGD.

F igure A-2. Flow Diagram o f Chapel H i l l Water Treatment P lan t .

116

Holding Reservoirs (100 MG) I I-+ Raw Water Sample

A1 u m Carbon - Flash M i x 1 (0.067 M G )

S e t t l ing Basins ( 4 M G ) n

+ -

I-+ Set t l ed Sampl e

Flocculation

I

Fil t e r s n

(0 .5 MG)

IT- Finished Sample

C1 i b L ime

Total detention time a t average flow of 22 MGD i s approximately 25 hours.

F i 1 tered Sample

Figure A-3. Flow Diagram of Char1 otte-Hoskins Water Treatment Plant .

117

Fl uori de 'I

Cl earwell (18 M G )

o old in^ Reservoir (100 MG) 4 + Raw Water Sampl e

Se t t l ing Basins ( 4 MG) 17

*

1-b Se t t l ed Sample

c12 A1 um b Carbon

Fi1 t e r s a C12 Fi 1 tered Sample Lime Fl uoride

Flash Mix

' (12 MG) Cl earwell ) Finished Sample

(0.050 M G )

Total detention time a t average flow of 22 MGD i s about 18.5 hours.

Figure A-4. Flow Diagram of Charlotte-Vest Water Treatment Plant .

I Raw Water Sampl e

-

Reservoir

Rapid M i x I

(45 M G )

(0.288 MG)

I

* Fl occul ator

Set t l ing Basins ( 2 M a F i l t e r Aid

Caustic F1 uori de Phosphate

( 3 MG)

Settled Sample

Fi l te rs

Filtered Sample

*

Total detention time i s 9 hours a t average flow of 19 MGD.

Clearwell

* b 'I

Figure A-5. Flow Diagram of Durham Water Treatment Plant.

(4.5 MG)

Additional Storage

-

4 Pumps

b

* ' Finished Sample 'I

Distribution Distribution

Rankine Lake I( ( a o o M ~ )

KMn04 Raw Water Sample

A1 um F lash Mix

S e t t l i n g Bas ins u 1(3327 MGi

*

S e t t l e d Sample

F i 1 t e r s

F l occu l a t o r

Caus t i c F i 1 t e r e d Sample Phosphate

(0.125 MG)

(5.850 MG)

1 F i n i s h e d Sample

T o t a l d e t e n t i o n t ime i s approx imate ly 14 hours a t average f l o w o f 16 MGD.

F i g u r e A-6. Flow Diagram o f Gaston ia Water Treatment P l a n t .

I.2K-b Raw Water Sampl e w i t h Clp

Rapid Mix

*Ium m Fl occul a to r (0.45 MG)

1 Se t t l i ng Basins 1 ( 2 MG)

IT-, Set t led Sample

Fil t e r s

Fi 1 tered Sampl e

Fluoride

Reservoir ( 3 MG)

Phosphate C1 2

Pumps

Finished Water Pumping Sta t ion Sample

A t average flow of 11 MGD, detention time i s about 60 hours from the i n i t i a l point of chlorine addit ion. Hydraul i c residence time in the treatment plant i s about 24 hours.

Figure A-7. Flow Diagram of Greensboro-Mitchell Water Treatment Plant .

Raw Water Sample

e t t l e d Sample

F i 1 t e r e d Sampl e

c12 Phosphate F l u o r i d e

F in i shed Sample

A t average f l o w of 13.5 MGD, t he d e t e n t i o n t ime i s about 6 hours.

Lime

C12

F igure A-8. Flow Diagram o f Greensboro-Townsend Water Treatmant P l a n t .

I L. Johnson 1 I L . Wheeler 1 L. Raleigh I

1-b Raw Water Sample

Polymer + I

C1 2 A1 urn ? Flume

Caustic or Lime I Flash Mix Y

I Flocculator ( (0.326 M G )

Carbon

Set t l ing Basins (2.286 M G ) w Caustic Settled Sample

I Fi 1 t e r s L--J

ph6sphate Fluoride Fi1 tered Sarnpl e

C l earwel 1 (8.4 M G )

+ i

Pumps

Finished Sample

v

A t an average flow of 7 MGD, the detention time i s 32 hours.

Figure A-9. Flow Diagram of Ral eigh-Bain Water Treatment Plant.

I Neuse River

Raw Water Sample

Carbon c12 A -7 Flash , M i x I ( O . 0 3 8 M G ) Caustic

(0.503 MG)

Sett l ing Basins ( 3 MG) r"l

1 Finished Sample

A t average flow o f 19 MGD, detention time i s 15 hours.

Caustic 1- Settled Sample

Fi 1 t e r Aid

Fi 1 t e rs

C1 Fi 1 tered Sample

phgsphate Fluoride Pre-Cl earwell Sampl e

Figure A-1 0. Flow Diagram o f Raleigh-Johnson Water Treatment Plant.

124

Pump Station Raw Water Sample 1

C12 Carbon

C1 2 L

Settling Basins (2 .632 MG) ,

+ Settled Sample

26 mi. = 9 hour a t 10 MGD

I Filters I c 1 ~h8sohate I3b Filtered Sample

+ b Raw Sample 2 A1 urn

Fl u o h de Caustic Pre-Clearwell Sampl e

Cl earwell (17 MG)

(0.056 MG) Caustic or Lime h

Pump Suction We1 l Fi ni s hed Sample

Rapid Mix

Average detention time in plant i s a b o u t 47 hours a t an average flow of 10 MGD,

Figure A-1 1 . Flow Diagram of Wilmington Water Treatment Plant.

4Yadkin River

Lime A1 urn Air mix

d-b Raw Water Sample

Col 1 ect ion Box a I Flash Mix 1 (0.027 M G )

Set t l ing Basins (2.5MG) u Settled Sample

1

Lime Fi 1 tered Sample

Fl uoride Phosphate Collection Box

(1~:' Clearwell Finished Sample

A t average flow of 18 MGD, detention time i s about 8 hours.

Figure A-1 2. Flow Diagram of Wins ton-Salem Neilson Water Treatment Plant.

126

Raw

Yadkin River Salem Lake KMn04, Carbon

Raw Water Sample

. r n \ Alum, Lime A1 urn L ime

,Fi 1 tered Sarnpl e'

Lime,

Fl uori de + Collection Box

Night b

C1 2 r- v

Clearwell (Open) (6.1 MG) i 4

v

C1 2 W Collection Box

Phosphate 9 Finished Sample

A t average flow of 18 MGD, detention time i s about 13.5 hours.

Figure A-1 3 . Flow Diagram of Winston Sal em-Thomas Water Treatment Plant .

unc-wrri -82-1 79 trihalomethane formation in water …

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