COMPARISONS OF SUB-SLAB SOIL GAS MEASUREMENTS TO MODELED EMISSIONS

FROM SUBSURFACE CONTAMINATION

by

John A. Menatti and Robin V. Davis

Utah Department of Environmental Quality

for

The 16th Annual AEHS Conference on Soils, Sediments and Water

March 13-16, 2006

San Diego, California

Utah Vapor Intrusion ProjectUtah Vapor Intrusion Project

• Project evaluated 6 Utah LUST sites.Project evaluated 6 Utah LUST sites.

• All 6 sites failed the Utah RBCA vapor intrusion-All 6 sites failed the Utah RBCA vapor intrusion-to-indoor air screening evaluation.to-indoor air screening evaluation.

• Johnson & Ettinger Model (J&E Model).Johnson & Ettinger Model (J&E Model).

• Input parameters for the J&E Model are site-Input parameters for the J&E Model are site-specific and include soil type, moisture content, specific and include soil type, moisture content, air-filled porosity, capillary fringe thickness, depth air-filled porosity, capillary fringe thickness, depth to contamination, etc.to contamination, etc.

• Sub-slab soil gas samples were collected at 5 Sub-slab soil gas samples were collected at 5 sites.sites.

• Nested vapor wells were installed and sampled at Nested vapor wells were installed and sampled at 1 site.1 site.

Utah Vapor Intrusion Project LUST SitesUtah Vapor Intrusion Project LUST Sites

1.1. Price Rental, Price Price Rental, Price Aug. 8, 2003Aug. 8, 2003

2.2. Hal’s Chevron, Green River Hal’s Chevron, Green River Nov. 20, 2003Nov. 20, 2003

3.3. Logan Lube, Logan Logan Lube, Logan March 9, 2004March 9, 2004

4.4. Bountiful Bicycle, Woods Cross Bountiful Bicycle, Woods Cross Aug. 26, 2004Aug. 26, 2004

5.5. Wheel-In Market, Salt Lake City Wheel-In Market, Salt Lake City Nov. 22, 2004Nov. 22, 2004

6.6. Gold Cross Ambulance, Salt Lake City Gold Cross Ambulance, Salt Lake City May 10, 2005May 10, 2005

RESULTSRESULTS

The Utah RBCA vapor intrusion screening The Utah RBCA vapor intrusion screening evaluation (J&E Model) at the 6 LUST sites evaluation (J&E Model) at the 6 LUST sites indicated that the vapor intrusion pathway may indicated that the vapor intrusion pathway may be complete and may pose an unacceptable risk be complete and may pose an unacceptable risk to building inhabitants.to building inhabitants.

Sub-slab soil gas sampling and nested vapor Sub-slab soil gas sampling and nested vapor well sampling indicated that the vapor intrusion well sampling indicated that the vapor intrusion pathway was not complete or was not significant pathway was not complete or was not significant at these 6 LUST sites.at these 6 LUST sites.

Utah RBCA Vapor Intrusion Screening Levels Groundwater-to-Indoor Air

Depth Depth to to

GroundGroundWater Water (ft bg)(ft bg)

Clean Clean Medium SandMedium Sand

Silty SandSilty Sand SiltSilt ClayClay

Res.Res. Com.Com. Res.Res. Com.Com. Res.Res. Com.Com. Res.Res. Com.Com.

5 ft5 ft 7070 291291 174174 718718 227227 940940 852852 35223522

10 ft10 ft 7171 292292 174174 720720 229229 945945 892892 36863686

15 ft15 ft 7171 294294 175175 722722 230230 950950 931931 38493849

20 ft20 ft 7272 295295 175175 724724 231231 954954 971971 401340131. Benzene concentrations in groundwater (ug/L) that pass a 1x10E-6 risk vapor intrusion assessment for residential (Res.)

and commercial (Com.) exposure scenarios.

2. J&E Model used to back-calculate these benzene concentrations in groundwater.

Price Rental, Price, UtahPrice Rental, Price, UtahAugust 8, 2003August 8, 2003

Utah RBCA (J&E Model) was used to back-calculate Utah RBCA (J&E Model) was used to back-calculate site-specific soil and groundwater screening levels for site-specific soil and groundwater screening levels for the vapor intrusion-to-indoor air exposure pathway.the vapor intrusion-to-indoor air exposure pathway.

Risk Level = Risk Level = 1 in 1,000,000 (1x10E-6)1 in 1,000,000 (1x10E-6)

Exposure Scenario = Exposure Scenario = Commercial BuildingCommercial Building

Soil Screening Level =Soil Screening Level = 0.4 mg/kg benzene0.4 mg/kg benzene

Groundwater Screening Level = 2,334 ug/L benzeneGroundwater Screening Level = 2,334 ug/L benzene

A paper describing the work at this site was presented at A paper describing the work at this site was presented at the Air & Waste Management Association’s 97the Air & Waste Management Association’s 97thth Annual Annual Conference in Indianapolis, Indiana in June 2004.Conference in Indianapolis, Indiana in June 2004.

PRICE RENTAL

20 Feet

Clayey Silt

Groundwater Contamination = 11,800 ug/L benzene

(Groundwater Screening Level = 2,334 ug/L benzene)

Soil Contamination @ 20 feet bg = 20 mg/kg benzene

(Soil Screening Level = 0.4 mg/kg benzene)

Sub-Slab Soil Gas = 0.85 ug/m3 benzene

(Acceptable Sub-Slab Soil Gas Concentration = 5-50 ug/m3 benzene)

Logan Lube, Logan, UtahLogan Lube, Logan, UtahMarch 9, 2004March 9, 2004

Utah RBCA (J&E Model) was used to back-calculate Utah RBCA (J&E Model) was used to back-calculate site-specific soil and groundwater screening levels for site-specific soil and groundwater screening levels for the vapor intrusion-to-indoor air exposure pathway.the vapor intrusion-to-indoor air exposure pathway.

Risk Level = Risk Level = 1 in 1,000,000 (1x10E-6)1 in 1,000,000 (1x10E-6)

Exposure Scenario =Exposure Scenario = Commercial BuildingCommercial Building

Groundwater Screening Level = 1,000 ug/L benzeneGroundwater Screening Level = 1,000 ug/L benzene

LOGAN LUBE

13 Feet

Silty Clay

Groundwater Contamination = 1,500 – 3,000 ug/L benzene

(Groundwater Screening Level = 1,000 ug/L benzene)

Sub-Slab Soil Gas = 10 ug/m3 benzene

(Acceptable Sub-Slab Soil Gas Concentration = 5-50 ug/m3 benzene)

Slab Attenuation FactorsSlab Attenuation Factors

EPA OSWER Subsurface Vapor Intrusion Guidance (2002) allows EPA OSWER Subsurface Vapor Intrusion Guidance (2002) allows the use of a 10-fold (0.1) slab attenuation factor.the use of a 10-fold (0.1) slab attenuation factor.

San Diego SAM Manual (2004) allows the use of a 10-fold (0.1) slab San Diego SAM Manual (2004) allows the use of a 10-fold (0.1) slab attenuation factor for an “old slab” and a 100-fold (0.01) attenuation attenuation factor for an “old slab” and a 100-fold (0.01) attenuation factor for a “new or improved slab.”factor for a “new or improved slab.”

Sager, et.al. (1997) discussed a study on slab infiltration in 218 U.S. Sager, et.al. (1997) discussed a study on slab infiltration in 218 U.S. homes. Based on the study, he recommended that a 1,000-fold homes. Based on the study, he recommended that a 1,000-fold (0.001) slab attenuation factor be used.(0.001) slab attenuation factor be used.

Reference:Reference:

Sager, S.L., Braddy, L.D., and Day, C.H., 1997, Sager, S.L., Braddy, L.D., and Day, C.H., 1997, The The Infiltration Infiltration Ratio in Vapor Intrusion Calculations, Ratio in Vapor Intrusion Calculations, Proceedings Proceedings of the of the Society for Risk Analysis Annual Meeting, Washington, Society for Risk Analysis Annual Meeting, Washington, D.C., D.C., December 9, 1997.December 9, 1997.

Bountiful Bicycle, Woods Cross, Utah

Bountiful Bicycle, Woods Cross, UtahBountiful Bicycle, Woods Cross, UtahAugust 26, 2004August 26, 2004

Soil contamination remaining under building after vapor extraction remediation was completed = 2,300 mg/kg TPH-G and 900 mg/kg xylenes at 17 feet below the building.

Utah LUST Program Cleanup Level for TPH-G = 1,500 mg/kg and Utah LUST Program Cleanup Level for TPH-G = 1,500 mg/kg and xylenes = 23 mg/kg in soil.xylenes = 23 mg/kg in soil.

Two sub-slab soil gas (SS) samples and one indoor air sample Two sub-slab soil gas (SS) samples and one indoor air sample collected. All concentrations in ug/m3.collected. All concentrations in ug/m3.

ContaminantContaminant SS #1SS #1 SS#2SS#2 Indoor AirIndoor AirBenzeneBenzene <0.58 <0.58 <0.58<0.58 7.77.7TPHTPH <4.1<4.1 <4.1<4.1 175175XylenesXylenes <1.3<1.3 <1.3<1.3 3636

The indoor air sample is higher than the sub-slab soil gas samples.The indoor air sample is higher than the sub-slab soil gas samples.

ASTM RBCA (1995) - National Ambient Indoor Air Concentrations:ASTM RBCA (1995) - National Ambient Indoor Air Concentrations:BenzeneBenzene == 3 - 22 ug/m33 - 22 ug/m3XylenesXylenes == 5 - 48 ug/m35 - 48 ug/m3

Bountiful Bicycle

Ambient Indoor Air Sampling

Wheel-In Market, Salt Lake City, UtahWheel-In Market, Salt Lake City, UtahNovember 22, 2004November 22, 2004

Utah RBCA (J&E Model) was used to back-calculate soil Utah RBCA (J&E Model) was used to back-calculate soil and groundwater screening levels for the vapor intrusion-to-and groundwater screening levels for the vapor intrusion-to-indoor air exposure pathway.indoor air exposure pathway.

Risk Level = Risk Level = 1 in 1,000,0001 in 1,000,000

Exposure Scenario = Exposure Scenario = Commercial BuildingCommercial Building

Groundwater Screening Level = 3,522 ug/L benzene (5 feet Groundwater Screening Level = 3,522 ug/L benzene (5 feet of clay) or 940 ug/L benzene (5 feet of silt).of clay) or 940 ug/L benzene (5 feet of silt).

Soil Screening Level = 1 mg/kg benzene (5-10 feet of clay).Soil Screening Level = 1 mg/kg benzene (5-10 feet of clay).

Wheel-In Market

Sub-Slab Soil Gas = 4.2 ug/m3 benzene and <1.1 ug/m3 MTBE

(Acceptable Sub-Slab Soil Gas Concentration = 5-50 ug/m3 benzene)

3 Feet

Fine Sand with Silt

4 Feet

Lean Clay with Silt

Groundwater Contamination = 3,260 ug/L benzene and 12,300 ug/L MTBE.(Groundwater Screening Level = 3,522 ug/L benzene [5 feet of clay]

or 940 ug/L benzene [5 feet of silt])

Soil Contamination = 3 mg/kg benzene @ 7 feet bg.(Soil Screening Level = 1 mg/kg benzene).

Gold Cross Ambulance, Salt Lake City, Utah Gold Cross Ambulance, Salt Lake City, Utah May 10, 2005May 10, 2005

Utah RBCA (J&E Model) was used to back-calculate soil Utah RBCA (J&E Model) was used to back-calculate soil and groundwater screening levels for the vapor intrusion-to-and groundwater screening levels for the vapor intrusion-to-indoor air exposure pathway.indoor air exposure pathway.

Risk Level = Risk Level = 1 in 1,000,0001 in 1,000,000

Exposure Scenario = Exposure Scenario = Commercial BuildingCommercial Building

Groundwater Screening Level = 720 ug/L benzeneGroundwater Screening Level = 720 ug/L benzene

Soil Screening Levels = Soil Screening Levels = <1 mg/kg benzene<1 mg/kg benzene

1,500 mg/kg TPH.1,500 mg/kg TPH.

Gold Cross Ambulance

Collected 5 Sub-Slab Soil Gas Samples under 5 Buildings

Groundwater Contamination = 88 ug/L benzene.(Groundwater Screening Level = 720 ug/L benzene)

6 Feet

Silty Sand

Soil Contamination = 1.5 mg/kg benzeneand 2,200 mg/kg TPH @ 6 feet bg.(Soil Screening Levels = <1 mg/kg benzene and 1,500 mg/kg TPH)

Sample No.Sample No. BB TT EE XX MTBEMTBE Naph.Naph. TPHTPH

11 <0.3<0.3 4242 3.73.7 15.715.7 <0.4<0.4 NDND 110110

22 <0.3<0.3 2222 1.91.9 8.28.2 <0.4<0.4 NDND 5858

33 <0.3<0.3 1818 1.61.6 6.86.8 <0.4<0.4 NDND 4545

44 <0.3<0.3 3434 2.92.9 11.511.5 <0.4<0.4 NDND 8080

55 <0.3<0.3 2727 2.32.3 10.310.3 <0.4<0.4 NDND 110110

EPA EPA Screening Screening Levels *Levels *

0.30.3

3.03.0

400400

40004000

2.22.2

2222

70007000

7000070000

30003000

3000030000

33

3030

200200

20002000

(Hexane)(Hexane)

Gold Cross Ambulance

Sub-Slab Soil Gas Results (ug/m3)

* Top Number: Indoor Air, 10E-6 Risk, Residential Exposure Scenario

Bottom Number: Sub-Slab Soil Gas

Hal’s Chevron, Green River, UtahHal’s Chevron, Green River, UtahNovember 20, 2003November 20, 2003

Free product (gasoline) plume underlying the Free product (gasoline) plume underlying the Oasis Motel & Café at about 9 feet below the Oasis Motel & Café at about 9 feet below the bottom of basement storerooms.bottom of basement storerooms.

Free product (gasoline) plume underlies Free product (gasoline) plume underlies parking lots and a road at about 14.5 to 17 feet parking lots and a road at about 14.5 to 17 feet below grade.below grade.

11 nested (multi-depth) vapor wells were 11 nested (multi-depth) vapor wells were installed in the basements, parking lots, and installed in the basements, parking lots, and street.street.

Hal’s Chevron

Hal’s Chevron

Hal’s Chevron

Oasis Cafe

Silt and Clayey Silt

Free Product - Gasoline

Basement

Hal’s Chevron

8 Feet

11 Feet

15 Feet

16 Feet

34,000 20,000

Benzene TPH (ug/m3) (mg/m3)

3 <8

V W - 5

Oasis Motel

Silt and Clayey Silt

Free Product - Gasoline

Basement

Hal’s Chevron

980 340

8 Feet

11 Feet

15 Feet

17 Feet

3,400 1,000

V W - 4

Benzene TPH (ug/m3) (mg/m3)

Silt and Clayey Silt

Free Product - Gasoline

Hal’s Chevron

53 <8

50,000 5,300

Parking Lot

3 Feet

7 Feet

11 Feet

15 Feet

V W - 7

280 <12

160 <8

Benzene (ug/m3) TPH (mg/m3)

16 Feet

Silt and Clayey Silt

Free Product - Gasoline

Hal’s Chevron

110,000 30,000

470,000 35,000

Road

3 Feet

7 Feet

11 Feet

15 Feet

V W - 10

450 27

19 <8

Benzene (ug/m3) TPH (mg/m3)

17 Feet

Silt and Clayey Silt

Free Product - Gasoline

Hal’s Chevron

810,000 120,000

Road

4 Feet

8 Feet

12 Feet

V W - 11

1,100,000 110,000

2200 110

Benzene (ug/m3) TPH (mg/m3)

14.5 Feet

EPA-State Regulator

Petroleum Vapor Intrusion Workgroup

The November 2002, EPA OSWER Draft Subsurface Vapor Intrusion Guidance (VI Guidance) presented a process to evaluate the vapor intrusion exposure pathway at contaminated sites.

Basically, the VI Guidance recommended that sub-slab soil gas sampling be conducted if a site fails a J&E Modeling analysis.

The EPA acknowledged that the VI Guidance may be too conservative for use at petroleum hydrocarbon sites.

In late 2003, the EPA formed an EPA-State Regulator Petroleum Vapor Intrusion Workgroup headed up by Joe Vescio (EPA Headquarters).

Robin Davis and I represented Utah on the workgroup.

Biodegradation of Petroleum Hydrocarbon Vapors

The workgroup had many conference calls and compiled an extensive repository of literature on petroleum vapor migration and biodegradation.

Using the literature sources from the workgroup’s reference repository, Robin Davis tabulated and evaluated multi-depth soil gas data from 16 petroleum hydrocarbon sites in the U.S. and Canada.

Robin published her findings in LUSTLine, Bulletin 49, March 2005 and concluded the following:

Biodegradation of petroleum hydrocarbon vapors is a probable mechanism of attenuation in subsurface soils.

The vapor intrusion pathway may not be complete at sites where at least 2 feet of uncontaminated soil overlies the contaminant source and sufficient oxygen is present to facilitate biodegradation.

Biodegradation of Petroleum Hydrocarbon Vapors (cont.)

Robin has continued to scour the scientific literature for additional sites to add to her database.

As of February 2006, she had amassed data from 31 more sites (a total of 47 sites).

Her conclusions are pretty much the same:

2 to 5 feet of clean vadose zone soil overlying the contamination significantly attenuates petroleum hydrocarbon vapors.

The data supports the use of a 100 to 1000 biodegradation factor on the J&E Model.

Robin’s work will be published in an upcoming LUSTLine article and she will be presenting her research at the 18th Annual National Tanks Conference in Memphis, TN next week.

Guidance Documents Incorporating Biodegradation Factors:

Health CanadaOctober 7, 2004

Soil Vapour Intrusion Guidance for Health Canada Screening Level Risk Assessment

Allows the use of a 10-fold biodegradation factor with the J&E Model for petroleum hydrocarbons if:

1. The contaminant source is greater than 13 feet below the building.

2. There is no significant capping that would prevent oxygen migration to below the building, i.e., paved surfaces around the building cover less than 80% of the surface area surrounding the building.

New Jersey Department of Environmental Protection

Vapor Intrusion Guidance October 2005

Allows the use of a 10-fold biodegradation factor with the J&E Model for BTEX vapors in the vadose zone (minimum 2 foot thick vadose zone soil and 4% oxygen).

Nebraska Department of Environmental Quality

Environmental Guidance DocumentFebruary 2002

States that the vapor intrusion pathway for petroleum hydrocarbon contaminated soil and groundwater to indoor air is generally considered incomplete if the contaminated soil or groundwater is greater than 15 feet below the structure.

Wisconsin Division of Public HealthWisconsin Division of Public Health

Chemical Vapor Intrusion andChemical Vapor Intrusion and

Residential Indoor AirResidential Indoor Air

February 13, 2003February 13, 2003

States that petroleum hydrocarbons biodegrade States that petroleum hydrocarbons biodegrade relatively well in unsaturated soils. Therefore, relatively well in unsaturated soils. Therefore, petroleum-related VOCs generally have to be in petroleum-related VOCs generally have to be in “free product” state or groundwater very near, if “free product” state or groundwater very near, if not in contact with, the building foundation to not in contact with, the building foundation to result in vapor intrusion.result in vapor intrusion.

Conclusions & RecommendationsConclusions & Recommendations Biodegradation of petroleum hydrocarbon Biodegradation of petroleum hydrocarbon

vapors in vadose zone soils is well documented.vapors in vadose zone soils is well documented.

Clean vadose zone soils (soil, not gravel) are Clean vadose zone soils (soil, not gravel) are excellent bioreactors for petroleum vapors.excellent bioreactors for petroleum vapors.

A biodegradation factor of 100 to 1000 should be A biodegradation factor of 100 to 1000 should be used to modify the J&E Model for petroleum used to modify the J&E Model for petroleum hydrocarbon vapors.hydrocarbon vapors.

There should be a minimum of 5 feet of clean There should be a minimum of 5 feet of clean vadose zone soil separating the subsurface vadose zone soil separating the subsurface contamination from the bottom of the building.contamination from the bottom of the building.

Sites with free product or preferential pathways Sites with free product or preferential pathways should be sampled, not modeled.should be sampled, not modeled.