VERTICAL SCREENING DISTANCES FOR ETHYLENE DIBROMIDE (EDB) AND 1,2 DICHLOROETHANE (1,2 DCA) AT PETROLEUM UNDERGROUND STORAGE TANK (UST) SITES

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1 VERTICAL SCREENING DISTANCES FOR ETHYLENE DIBROMIDE (EDB) AND 1,2 DICHLOROETHANE (1,2 DCA) AT PETROLEUM UNDERGROUND STORAGE TANK (UST) SITES 25th National Tanks Conference and Expo September 14 16, 2015 Phoenix, Arizona Matthew Lahvis Shell Global Solutions (US), Inc. June Lu SNC Lavalin, Inc. Janice Paslawski SNC Lavalin, Inc. 1

2 DEFINITIONS AND CAUTIONARY NOTE Reserves: Our use of the term reserves in this presentation means SEC proved oil and gas reserves. Resources: Our use of the term resources in this presentation includes quantities of oil and gas not yet classified as SEC proved oil and gas reserves. Resources are consistent with the Society of Petroleum Engineers 2P and 2C definitions. Organic: Our use of the term Organic includes SEC proved oil and gas reserves excluding changes resulting from acquisitions, divestments and year-average pricing impact. Resources plays: Our use of the term resources plays refers to tight, shale and coal bed methane oil and gas acreage. The companies in which Royal Dutch Shell plc directly and indirectly owns investments are separate entities. In this presentation Shell, Shell group and Royal Dutch Shell are sometimes used for convenience where references are made to Royal Dutch Shell plc and its subsidiaries in general. 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3 BACKGROUND use EDB = lead additive; soil fumigant 1,2 DCA = lead additive; commercial chemical/solvent, paints, etc. chemical properties Compound Henry s Law Constant 25 o C Effective Solubility Gasoline b (µg/l) Vapor Pressure (mm Hg) 25 o C Effective Air-Phase Saturation (µg/l) EDB , ,2 DCA , benzene , EDB Br Br 1,2 DCA a VISL calculator - Calculator.xlsm b Falta, Ethylene Dibromide and 1,2-Dichloroethane Contamination from Leaded Gasoline Releases, Ground Water Management - Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Assessment, and Remediation Conference,, pp

4 BACKGROUND: BIODEGRADATION persistence aerobic biodegradation EDB: t 1/2 = days weeks 1,2 DCA: t 1/2 = days > several months anaerobic: EDB: t 1/2 = months 1,2 DCA: t 1/2 = months years; sulfate, methanogenic conditions only co-metabolic biodegradation demonstrated (methane), yet biodegradation may be slowed in the field by the presence of other hydrocarbons EDB Br Br 1,2 DCA KEY EDB and 1,2 DCA biodegrade aerobically biodegradation rates less well understood than BTEX 4

5 BACKGROUND: ANALYTICAL METHODS Method EDB 1,2 DCA GROUNDWATER (µg/l) 8260B SOIL GAS (µg/m 3 ) 8260B TO TO-15 (sim) Screening Level* EDB 1,2 DCA * VISL calculator - KEY separate analytical methods required for groundwater analytical detection limits (DLs) and reporting limits (RLs) in soil gas are generally above risk-based screening levels 5

6 BACKGROUND: OCCURRENCE (EDB) From Wilson and Adair, 2008 KEY EDB concentrations in GW > DLs are a relatively common occurrence in South Carolina and other states 6

7 BACKGROUND: RISK (EDB) EDB risk greater Modified from Wilson and Adair, 2008 KEY EDB represented a greater risk than benzene in groundwater at 25% of sites investigated Natural Attenuation of the Lead Scavengers 1,2 Dibromoethane (EDB) and 1,2 Dichloroethane August 2015 (1,2-DCA) at Motor Fuel Release Sites and Implications for Risk Management (EPA/600/R-08/107) 7

8 BACKGROUND: REGULATORY 2010 US EPA OUST Memo: begin/continue to monitor: - used pre-1986, continued to be stored - threat to DW resources analyze using appropriate methods (Method 8011 EDB) remediate if threat exists share KEY information EPA/Falta studies prompt US EPA OUST to recommend additional risk assessment for EDB and 1,2 DCA 8

9 BACKGROUND: OCCURRENCE # of states monitoring for lead scavengers # of states w/ % s based on estimates or hard data KEY ASTSWMO, Lead Scavengers Survey Report: Prepared by LUST Task Force, August EDB and 1,2 DCA in ground water is a common occurrence, yet states generally do not have hard data to support risk assessment

10 BACKGROUND/MOTIVATION new methodology developed for PVI site screening based on use of vertical screening distances approach recommended in ITRC, US EPA OUST, and California Low Threat Tank Closure Policy historical leaded gasoline releases defined as precluding factor in US EPA OUST & ITRC guidance potential re-opener for sites closed by California Low- Threat Tank Closure Policy Early use of ITRC PVI document (3/26/15) From ITRC PVI Classroom Training (Sept, 2015) Incorporating ITRC doc or referring to directly Staff using, by not formally endorsed 10

11 OBJECTIVES assess PVI risk develop risk-based exclusion distance criteria for use in PVI assessments at petroleumhydrocarbon release sites based on sound science 11

12 DATABASE UST SITES WESTERN CANADA SNC-Lavalin 139 UST sites Western Canada Sites % of database Pb scavengers in groundwater (analyzed) Pb scavengers > DLs in groundwater EDB = 0.5 µg/l;1,2-dca = 0.5 µg/l 7 5 * KEY few sites in Western Canada with EDB and 1,2 DCA > DLs/RLs in groundwater 12

13 DATABASE UST SITES CALIFORNIA (GEOTRACKER) GW # Sites w/ Pb Scavengers Analyzed Detections Soil Gas Detections GW and Soil Gas Paired points County # Total Site (extracted) EDB 1,2 DCA EDB 1,2 DCA Alameda Butte Contra Costa Orange Riverside San Luis Obispo Fresno Salano Santa Cruz Shasta 40 41% GW 32 data, 28% soil-gas 4 data Sutter Tuolumne Kings Lake KEY more common (46%) Los Angeles Mariposa Merced 150 DCA (15% 150 of sites) Napa Sacramento San Bernardino San Diego Santa Barbara Sonoma Ventura Total (%) EDB rarely detected at GW locations where analyzed (3%); 1,2 DCA EDB rarely detected in soil gas (1% of sites) as compared to 1,2 very few (0.1%) sites with groundwater detections for EDB and 1,2 DCA and complementary soil gas data (41%) 95 (3%) 1688 (46%) 733 (8%) 8 (1%) 107 (15%) 423 (11%) March (.1%) 13

14 DATABASE DEVELOPMENT GENERAL ELEMENTS: groundwater and soil gas concentrations soil gas sampling method (vapor probe, monitoring well head space) soil type (presence of fractured rock) surface cover (asphalt, open, building) source type (LNAPL, dissolved) water-table elevation facility type (UST, industrial) sampling dates presence of fractured rock (excluded) vertical separation distances lateral offset (source, monitoring well) analytical method (detection and reporting limits) site operational history (release pre-1986, operating pre-1986) remediation history QA/QC (including leak testing, no on-going remediation, GW wells screened across water table) 14

15 1,2 DCA ALL DATA DISTRIBUTION OF GROUNDWATER CONCENTRATIONS 10 ft from waste oil tank MW Headspace - LNAPL 5 ft from waste oil tank source soil (railroad siding) KEY vast majority of concentrations of 1,2 DCA in soil-gas are ND at source separation distances > ~6 ft, even for relatively significant concentrations in groundwater (i.e., > 100 µg/l) data indicate that PVI risk (screening) at UST sites is likely bounded by benzene (vertical screening distance = 15 ft) March

16 1,2 DCA PAIRED DATA PAIRED DATA < 30 days between sample events < 30 ft between sample locations vapor probe only > 10 ft from source areas (waste-oil tanks) DISTRIBUTION OF GROUNDWATER CONCENTRATIONS KEY empirical data insufficient for derivation of vertical screening distances for 1,2 DCA 16

17 1,2 DCA PAIRED DATA within 3 feet of source KEY soil-gas concentrations orders of magnitude less than predicted by equilibrium partitioning likely an indicator of 1,2 DCA biodegradation in the vadose zone 17

18 EDB WESTERN CANADA SITES W/ HISTORICAL USE OF LEADED GASOLINE KEY NDs in soil gas indicate that PVI is likely not an issue; however, lower soil-gas screening levels are necessary to confirm 18

19 EDB PAIRED DATA KEY again, soil-gas concentrations orders of magnitude below those in equilibrium w/ groundwater are a potential indicator of EDB biodegradation in the vadose zone 19

20 CONCLUSIONS inability to assess screening distances lots of ND data (method DLs and RLs above soil-gas screening levels, especially for EDB) few sites w/detections in groundwater and complementary soil-gas data (i.e., data pairs) empirical data (to date) indicate limited PVI risk biodegradation likely contributing to lack of detections for EDB and1,2 DCA consistent with previous empirical studies showing that the PVI risk is limited above low-concentration (dissolved or weathered LNAPL) sources 20

21 PATH FORWARD research opportunities further data collection at sites with known impacts modeling of soil-gas profiles laboratory column studies new API project (Golder Associates, Scissortail Environmental Solutions, LLC) lit review empirical database evaluation (request for data) 21

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