soil vapor intrusion

of Massachusetts Department

ENVIRONMENTAL PROTECTION

Soil Vapor Intrusion...

A Decade of Regulatory Requirements & Experiences

Paul W. Locke

MA DEP Bureau of Waste Site CleanupOne Winter StreetBoston, MA 02108

[email protected]



Late 1980s…

Hillside School,

Needham Mass…

Wow…that can happen?



MADEP Regulatory Response:

1. Place concern on radar screen

2. Incorporate into cleanup standards

3. Obtain “real world” data to gauge scope/parameters of problem

4. Provide tools/toolbox to regulated community



#1: On the Radar Screen…

Training/awareness: agency staff and regulated community

Regulatory requirement to notify MADEP if pathway likely or confirmed



#2: Incorporate into Cleanup Standards

Transport Model

Calc Source Conc in GW

Ceiling Conc

50% Solubility

Lowest of 3 orGW background

or PQL,whatever higher

GWStandard

Air

Groundwater

Lowest of 3or

IAQ Background,whatever is higher

Non-Cancer RiskBased Indoor Air Conc

Cancer Risk BasedIndoor Air Conc

50% Odor Threshold



1993 Standards Transport ModelJohnson & Ettinger

Assumed 10% Henry’s Law Equilibrium Condition

GW to Soil Gas:

Soil Gas to Indoor Air: = 5 x 10-4

“crude and limited application of J&E”



Calculated GW Standards (1993)

Compound Standard (g/L)

TCE 300

1,1,1-TCA 4000

PCE 3000



1996 Evaluation

Are these Standards Really Protective?

Let’s take a Look at our Files…

GW Conc

Soil Gas Conc

Indoor Air Conc



MADEP Records Review

Database Search

DEP Files6000

Potential SitesEvaluated

177

Adequate Data 59 sites

Chlorinated 36 (61%)

BTEX23 (39%)



Petroleum Sites?

Chlorinated Solvent Sites?

Findings: Were the 1993 Standards Generally Conservative & Protective?

☺



Proposed Revisions(2004)

Chemical-Specific Evaluations

Conservative Pathway Scenario

Conservative Site/Soil Properties



Key J&E Inputs (MADEP 2004)

Groundwater• 7 feet below grade;• 1 foot below basement floor

Sand, total porosity • n = 0.43

Building Depressurization • P= 4 Pa (40 g/cm-s2); • 0.45 air exchanges/hour

Vadose Zone Moisture Content • [w] = ????



Moisture Level Below Buildings

Dry Soils?



Vadose Zone Soil Moisture

What is a realistic, conservative value….. beneath buildings?

Little study data available, but….

Fair amount of chemical analytical data from soil samples beneath buildings!



Soil Moisture (v/v) Distribution

0

5

10

15

20

25

30

35

0-5 6-10 11-15 16-20 21-25 >25

Soil Moisture Value (% by volume)

Nu

mb

er

of

Sa

mp

les

*Moisture (w/w) to Soil Moisture(v/v)

0.06



Proposed Revisions to Current MADEP Groundwater Standards

(Soil Vapor Pathway)

Up to an order of magnitude lower for some chlorinated solvents

Public Comment Period Ended December 10, 2004

Stay Tuned…..



#4: Provide Tools & Toolboxes Site-Specific Evaluations

Guidance Documents

Rules of Thumb



Site-Specific Pathway Evaluation

(Mandatory when > Generic GW Standard)

Key Tools:

Soil Gas Assessment

Indoor Air Analysis

Vertical Profiling



F i g u r e 4 - 1 : E v a l u a t i n g I n d o o r A i r P a t h w a y v i a M e t h o d 2

C o n t a m i n a n t s > G W - 2 s t a n d a r d , c o n t a m i n a t e d s o i l s n e a r b u i l d i n g ,

a n d / o r o t h e r e v i d e n c e o f p o t e n t i a l i n d o o r a i r i m p a c t s

I n s t a l l s o i l g a s p r o b e s b e n e a t h

p o t e n t i a l l y i m p a c t e d s t r u c t u r e ( s )

P I D / F I D c o n c o f t o t a l o r g a n i c v a p o r s

< a c t i o n l e v e l s i n T a b l e 4 - 9 ?

G C s c r e e n i n g c o n c o f s o i l - g a s < a c t i o n

l e v e l s l i s t e d i n T a b l e 4 - 1 0 ?

I n d o o r a i r l e v e l s < p u b l i s h e d b a c k g r o u n d

c o n c e n t r a t i o n s i n T a b l e 4 - 1 1 ?

E v a l u a t e c h e m i s t r y o f

i n d o o r a i r d a t a

S a m p l e i n d o o r a i r v i a T O - 1 4 o r A P H m e t h o d

d u r i n g “ w o r s t c a s e ” s e a s o n a l c o n d i t i o n s

C o l l e c t s i t e - s p e c i f i c i n f o r m a t i o n o n

s o i l / b u i l d i n g

C o n d u c t s i t e - s p e c i f i c m o d e l o f i n d o o r a i r

p a t h w a y ( e . g . , J o h n s o n a n d E t t i n g e r )

E v a l u a t e a l l l i n e s o f e v i d e n c e t o d e c i d e i f

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

I n d o o r a i r i m p a c t s a r e n o t l i k e l y ( a b s e n t a n y o t h e r i n f o r m a t i o n o r d a t a t o

t h e c o n t r a r y )

I n d o o r a i r i m p a c t s c o n f i r m e d , l i k e l y , o r c a n n o t b e r u l e d o u t – p r o c e e d w i t h

n o t i f i c a t i o n / I R A / r i s k a s s e s s m e n t / C E P m i t i g a t i o n a s n e e d e d

O p t i o n a l p a t h w a y / s e c o n d a r y i t e r a t i o n s R e c o m m e n d e d f i r s t i t e r a t i o n

N o

N o

Y E S

Y E S N o

Y E S

MA

DE

P R

ecom

men

ded

Ap

pro

ach



MADEP Guidelines for Soil Gas Evaluation:

Compound

Screen out levels ppmV

PID (eV)

FID<10 10-11.4 >11.4

Toluene 11 12 12 10

Ethylbenzene 4 4 4 3

Xylenes 25 26 24 22



MADEP Guidelines for Obtaining Soil Gas Samples

depth togroundwater

buildingfoundation

foundation cracks

enclosed space

vadose zonediffusing vapors

capillary zone

dissolved chemical ingroundwater

Infiltration displaces/ solubilizes soil gases

Negative bias

grass

pavement

place probe below bldg/pavement for

representative samples



Real World Example of Negative Bias: TCE Soil Gas Data from 2 Homes

Date Interior Exterior

9/96 397 / 281 24 / <1 12/96 16 / 80 <1 / <1 3/97 6 / 64 <1 / <1

6/97 19 / 226 <1 / <1 8/97 157 / 594 4 / <1

All data ppb v/v TCE



Obtaining Indoor Air Samples

Winter months usually “worst case” - Other

times may not rule out pathway

frost layer

Furnace combustion

Stack Effects

Vapors

windows closed



Groundwater/Vertical Profiling

Infiltration

VOC plume

fresh water lens

well

groundwater flow



For More Information…..• [email protected] or [email protected]

• Characterizing Risks Posed by Petroleum Contaminated Sites: Implementation of the MADEP VPH/EPH Approachwww.mass.gov/dep/bwsc/files/02-411.pdf

• Indoor Air Sampling and Evaluation Guidewww.mass.gov/dep/ors/files/indair.pdf

• MCP Numerical Standards: GW-2 www.mass.gov/dep/bwsc/files/standard /gw2/gw2.htm