Soil Vapor Survey: A Gasoline Plume Beneath A Residence And The Implications For Additional Corrective Action Or Case Closure

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Mabel Walker
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1 Soil Vapor Survey: A Gasoline Plume Beneath A Residence And The Implications For Additional Corrective Action Or Case Closure William R Chapman Senior Geologist VA DEQ NRO Remediation Program 22nd National Tanks Conference and Expo Boston - September 20, 2010

2 Virginia DEQ Petroleum Program Virginia DEQ Divided Into 6 Regional Offices. Northern Regional Office Approx 7400 Open/Closed Pollution Complaint Cases. Approx 300 Open/active Cases. Program Applies to Regulated and Non Regulated, Above and Underground Petroleum Storage Tanks. Homeowner Heating Oil - Commercial Gas Stations - Bulk Terminals.

3 Virginia DEQ Petroleum Program Virginia DEQ Petroleum Program Utilizes a Risk Based Approach (i.e., Identify and Evaluate Risk to Human Health and the Environment). Level of Assessment and Corrective Action Is Dependent on Risk to Current and Future (Conditional) Receptors.

4 Area Specifics Approx 5.3 Million People In DC Metro Area (2008). Typical Urban Mixture - Residential / Commercial / Old / New / Redevelopment.

5 Site Specifics Active Full Service Station at Least Since 1960 s. Current USTs Installed Residential / Commercial Properties Surround Site.

6 Site Specifics Current Pollution Case (PC#) Open Since Two Other PC# s Associated With Service Station. Free Phase / Dissolved Phase Plume Extends Off-site From Service Station. Some Comingling With Upgradient PC#. Soil Excavation / Pump and Treat / SVE. Two Remediation Systems - Service Station (North) and Residential Property (South). Site Work Reimbursed Through Fund (VPSTF).

7 Site Specifics BTEX BENZENE

8 Site Specifics - South 140 South System Free Product Gal On-line Since Q2002S 3Q2002S 4Q2002S 1Q2003S 2Q2003S 3Q2003S 4Q2003S 1Q2004S 2Q2004S 3Q2004S 4Q2004S 1Q2005S 2Q2005S 3Q2004S 4Q2005S 1Q2006S 2Q2006S FP BENZENE MTBE 2.6 Million Gallons Water Treated. 1,330 Gallons Free Phase Recovered. 3Q2006S 4Q2006S 1Q2007S 2Q2007S 3Q2007S 4Q2007S 1Q2008S 2Q2008S 3Q2008S 4Q2008S 1Q2009S 2Q2009S 3Q2009S 4Q2009S 1Q2010S Influent ppb

9 Site Specifics - South MTBE (PPB) BENZENE (PPB) May-02 Nov-02 May-03 Nov-03 May-04 Nov-04 May-05 Nov-05 May-06 Nov-06 May-07 K O P Q Nov-07 May Nov May-09 Nov Dissolved Phase- MTBE avg <1000 ppb Benzene avg <1000 ppb May-02 Nov-02 May-03 Nov-03 May-04 Nov-04 May-05 Nov-05 May-06 Nov-06 May-07 Nov-07 May-08 Nov-08 May-09 Nov-09 K O P Q

10 What to do...what to do... South System Has Significantly Reduced Contaminant Levels On Residential Property. North System Has Reduced Contaminant Levels On Service Station Property. No Confirmed Complaints / Incidents Of Indoor Impacts On North or South Properties. Homeowner Would Like To Use His Backyard. Before Shutting Down South System, Need to Evaluate Remaining Risk to Residence. Conduct Soil Gas Survey Of Residential Property.

11 Murky path with a lot of lights... Develop CSM. Outline Strategy. Identify Resources. Talk To Owner/Occupants.

12 Site Specifics Alluvial Fall Zone (Located Between Piedmont And Coastal Plain). Sand/Gravel And Silt/Clay. Tight Matrix Of Fines, Occasional Thin Layers Of Sand And Gravel. Note: During Probe Installation, Soil From Ground Surface to 4 Feet Was Wet, Between 4 Feet and 10 Feet, Soil Slightly Moist To Moist.

13 Site Specifics - South Three Story Wood Frame Structure >6500 Ft2. Original House Built Expanded Over Time. Basement Floor 5.5 Feet Below Grade In Front / 3.5 Feet Below Grade In Back. 1st Floor Is 2 Feet To 4 Feet Above Grade. Basement Floor Is Concrete Slab And Crawl Space. Numerous Subsurface Utilities. Sump Near Garage.

14 Soil Gas Survey

Soil Gas Survey Two Rounds Of Samples April & August 2010. Ten Multi-level Vapor Points - 3, 6.5, 10.

15 Soil Gas Survey Two Rounds Of Samples April & August Ten Multi-level Vapor Points - 3, 6.5, 10. Sub-slab & Ambient Air Samples. CH 4, CO 2, O 2, PID, C4-C10 Range, TO-15. Remediation System Shut Down Prior To Surveys.

16 Soil Gas Survey Borings Benzene MTBE BTEX VSB-A-5 MDL MDL MDL VSB-A MDL MDL VSB-B-6 MDL MDL MDL VSB-B-13 MDL MDL MDL VSB-C-6 MDL MDL MDL VSB-C VSB-D-5 MDL MDL MDL VSB-D VSB-E-5 MDL MDL MDL VSB-E-13 MDL 6400 MDL VSB-F-5 MDL MDL MDL VSB-F VSB-G-13 MDL MDL MDL VSB-G VSB-H-12 MDL 360 MDL VSB-H VSB-I VSB-I VSB-J-12 MDL 140 MDL VSB-J VSB-A-5 VSB-A-15 No elevated PID until 12. H 2 0 historically at 13. H 2 0 in early 2010 was 10 to C and 8021B analysis (ppb). VSB-B-6 VSB-B-13 VSB-C-6 VSB-C-14 VSB-D-5 VSB-D-14 VSB-E-5 VSB-E-13 VSB-F-5 VSB-F-12 VSB-G-13 VSB-G-15 VSB-H-12 VSB-H-15 VSB-I-12 VSB-I-15 VSB-J-12 VSB-J Benzene MTBE BTEX

17 Soil Gas Survey - 1st Round CO2 O2 J H E I A I A C B D E C G B G D H J I F H G D C F F B E CO2% st Round CO 2 % versus O 2 % J-10 H-3E-3 I-6.5 A-10I-3 A-6.5 C-10B-10D-6.5 1st Round E-6.5 C-6.5 G-10 B-3G-3 CO2 O2 D-10 H-6.5 J-6.5 I-10F-3H-10 G-6.5 D-3 C-3F-6.5 F-10 B-6.5 E O2%

18 Soil Gas Survey - 2nd Round CO2 O2 J B F C E I B D E H A H H A E I I A D G B C F D J G F G C J CO2% nd Round CO 2 % versus O 2 % J-10 B-10F-10 C-10 E-10 I-10B-6.5 D-10E-6.5 H-6.5 A-10 H-10H-3A-6.5 2nd Round CO2 E-3 I-3I-6.5 O2 A-3 D-6.5 G-10 B-3C-6.5 F-6.5 D-3J-6.5G-6.5 F-3 G-3C-3 J O2%

19 Soil Gas Survey Both Rounds Benzene in Soil Gas - A Through J - 1st Round ug/m Benzene between MDL and 42,000,000 ug/m3 ug/m Benzene - 10 Benzene Benzene - 3 Benzene in Soil Gas - A through J - 2nd Round Yes I said 42 million ug/m3...or, MDL and 13,000,000 ppbv Benzene - 10 Benzene Benzene - 3

20 Soil Gas Survey - 1st Round Benzene Toluene Ebenzene MTBE Isooctane I A G J J A H C C D H I B E H B D G I C D F A G F E E F ug/m3 I-10 Benzene did not exceed 640 ug/m3 (200 ppbv) in any 3 points. Several elevated MDLs. Benzene in Soil Gas - A Through J - 1st Round A-6.5 G-10 J-10 J-6.5 A-10 H-10 C-10 C-6.5 D-10 H-6.5 I-6.5 B-10 E-6.5 H-3 B-3 Benzene D-3 G-3 I-3 C-3 D-6.5 F-3 A-3 E-3 G-6.5 F-10 E-10 J-3 F-6.5 B-6.5

21 Soil Gas Survey - 2nd Round Benzene Toluene Ebenzene MTBE Isooctane I H F G A I G J B J B F F E C H A E C A B E I G D D D C ug/m3 I-10 I-6.5 H-10 F-10 G-10 A-10 Benzene did not exceed 680 ug/m3 (210 ppbv) in any 3 points. G-6.5 J-6.5 Several elevated MDLs. Benzene in Soil Gas - A Through J - 2nd Round B-10 J-10 B-6.5 F-6.5 Benzene F-3 E-10 C-6.5 H-6.5 A-6.5 E-6.5 C-10 A-3 B-3 E-3 I-3 G-3 D-3 D-6.5 D-10 C-3 H-3 J-3

22 Soil Gas Survey - 1st Round Benzene Soil Gas at Probe Depths 10

23 Soil Gas Survey - 2nd Round Benzene Soil Gas at Probe Depths 10

24 Soil Gas Survey 1st Round C4 C10 Soil Gas at Probe Depths 10

25 Soil Gas Survey 2nd Round C4-C10 Soil Gas at Probe Depths 10

26 Soil Gas Survey Outdoor Air Benzene 4.2 and 1.4 ug/m3 (1.2 and 0.43 ppbv)

27 Soil Gas Survey Sub Slab Benzene 17 ug/m3 (5.2 ppbv) In VSB-L 3.3 ppbv To 1.4 ppbv Typical Indoor Avg.

28 Soil Gas Survey Sub Slab O 2 > 20% for Both Rounds and Both Locations. PID < 9 ppmv in One Round. Methane < 14 ppmv in One Round. Boring Logs Indicated Native Soil, Gravel, Cobbles, Wet and Dry

29 I-10 H-10 And Another Thing. F-10 I-10 A-6.5 G-10 A-10 H-10 D-10 H-6.5 G-10 A-10 I-6.5 I-6.5 B-10 B-3 D-3 I-3 C-3 G-6.5 J-6.5 B-10 Benzene 1st F-3 E-10 F-6.5 Benzene 1st D-6.5 F-3 A-3 Benzene 2nd C-6.5 H-6.5 A-6.5 Benzene 2nd G-6.5 A-3 B-3 E-3 I-3 F-10 E-10 E-3 D-10 D-3 G-3 C-3 G-3 J-6.5 F-6.5 C-6.5 D-6.5 Benzene conc. between rounds not consistent (i.e. highest location in 1 st was not highest location in 2 nd ). H 2 O was 3 to 4 higher during 1 st round. Was Benzene lower in 1 st round due to increase in H 2 O table?

30 One More Other Thing. ug/m A-3 B-3 C-3 D-3 E-3 F-3 G-3 H-3 Benzene 1st Benzene 2nd I-3 J-3 A-6.5 B-6.5 C-6.5 D-6.5 E-6.5 F-6.5 G-6.5 H-6.5 I-6.5 J-6.5 A-10 B-10 C-10 D-10 E-10 F-10 G-10 H-10 I ug/m3 Some Benzene Soil Gas Samples Had Extremely High Method Detection Limits <64,000 Ug/M3. Removing The Elevated <MDLs From Graph Suggests Lower Soil Gas Benzene Levels In Near Surface Soil.

31 Thoughts on Results Apparent Degradation Of Petroleum Constituents. Comparable Trends Present Between Benzene, C4- C10, Other Constituents. Soil Gas Benzene <1000 ug/m3 From 3 Feet To Ground Surface. Soil Gas Benzene 5.2 ppbv In Subslab Sample. O 2 % In Subslab >20%. No Complaints/Reports Of Odors/Smells In Residence. Dissolved Phase < 1000 ppb Benzene.

32 Thoughts for Next Time Issues With Wet Conditions. Extremely High Detection Limits. Analysis That Provides the Most Help. Time of Year for Soil Vapor Survey. Number of probes and number of points. But for now, I will meet with the homeowner to discuss the results.

33 Paul Revere in today's world: One if by land, two if by sea, and three if by soil gas Questions? Comments? Criticisms?

TECHNICAL MEMORANDUM June 16, 2011

TECHNICAL MEMORANDUM June 16, 2011 Tier 1 Remedial Investigation Results and Tier 2 Sampling Plan Former Salinas Manufactured Gas Plant To: Mr. Henry Chui, Department of Toxics Substances Control From: