Sulfate Delivery Using Permeable Filled Borings to Enhance Petroleum Hydrocarbon Biodegradation

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1 Sulfate Delivery Using Permeable Filled Borings to Enhance Petroleum Hydrocarbon Biodegradation California CUPA Training Conference February 8, 2018 Tim Buscheck Chevron Fellow and Sr. Consulting Hydrogeologist Chevron Energy Technology Company

2 Acknowledgements Coauthors UC Davis: Doug Mackay, Nick de Sieyes, Juan Peng, Radomir Schmidt Collaborators Chevron Environmental Management Company: Dave Patten Stantec: Travis Flora Regulatory support Gerald O Regan, Santa Clara Department of Environmental Health 2

3 Sulfate Delivery Using Permeable Filled Borings to Enhance Petroleum Hydrocarbon Biodegradation Outline Remediation History and Objectives Site Background UC Davis Microcosm Study Treatment Strategy Permeable Filled Borings (PFBs) Performance Monitoring Conclusions 3

Former Service Station in Northern California Remediation History and Objectives In 1993 the service station ceased operations; all above and below ground facilities were removed.

4 Former Service Station in Northern California Remediation History and Objectives In 1993 the service station ceased operations; all above and below ground facilities were removed. Remediation technologies applied : Groundwater extraction, excavation, soil vapor extraction, Oxygen releasing compound, Biosparge, Ozone sparge None of these technologies has been effective March 2015 regulatory meeting: Regulators agreed to a sulfate release strategy The remediation objective, based on the CA Low Threat Closure Policy, is benzene <1,000 ug/l in selected monitor wells 4

5 Assumptions: Remediation Objectives Permeable Filled Borings (PFB) and High Pressure Injections (HPI) Locations treatment monitored in selected wells (blue for intermediate, black for deep) most important area within red dashed box U-15 U-12 U-18 U-4 U-1 PFB HPI U-3 Groundwater flow direction has varied significantly in recent years (~10 ft/yr) U-7 NOTE: Size of PFBs and HPI radius of influence not to scale Recent GW flow direction 5

6 Well Remediation Objectives BTEX* and Sulfate in PFB Monitor Wells Pre-Remediation Screen Interval (feet bgs) Benzene (µg/l) Toluene (µg/l) Ethyl Benzene (µg/l) Xylenes (µg/l) mg/l Sulfate *9/4/14 dates U , < /3/05 9/6/13 U , /1/11 U , /1/11 U , /3/5 9/1/11 U-7 (upgradient) ND ND ND ND 737 1,420 9/1/11 9/6/13 TEX concentrations in target wells suggest NAPL is depleted in those compounds Previous mass budget calculations suggest sulfate reduction accounted for 73-95% of total bio-depletion 6

7 Site Background Cross Section for U-4 and U-18 Former USTs Approx. depth below ground surface 0 ft 15 ft PFB monitor wells completed in the intermediate and deep water-bearing zones U-4 30 ft 45 ft Backfill Clayey Sand (SC), Sand with Gravel (SW) & Silty Sand (SM) Clay (CL/CH) U ft Silt (ML) 7

Benzene (μg/l) UC Davis Laboratory Microcosm Results Mixed background levels of sulfate (1,500 mg/l) with benzene (40 mg/l) in lab study with site sediments and groundwater Microcosm Results Added

8 Benzene (μg/l) UC Davis Laboratory Microcosm Results Mixed background levels of sulfate (1,500 mg/l) with benzene (40 mg/l) in lab study with site sediments and groundwater Microcosm Results Added Benzene +Sulfate at start No benzene degradation without sulfate (a), though methane was generated Benzene degradation with sulfate (b) a) No Sulfate b) Sulfate days days Suspect long lag time in microcosms may have been due, in part, to long storage and artifacts of handling of core materials, not initially intended for microcosms 8

hydrated calcium sulfate (CaSO 4 2H 2 O), a widely available mineral HPI Grout seal Gypsum slurry

9 Treatment Strategy Permeable Filled Borings (PFBs) and High Pressure Injections (HPIs) Schematics of the idealized installations PFB cluster Grout seal Bentonite seal Gypsum/gravel Gypsum is hydrated calcium sulfate (CaSO 4 2H 2 O), a widely available mineral HPI Grout seal Gypsum slurry Adapted from neer.org/education/ web-based-classprojects/geoenviron mental-engineering/ 9

10 Treatment Strategy Sulfate Delivered through PFBs and HPIs At time of installation, depth to water ~ 25 ft bgs PFBs created by hollow stem auger in 24, 9-inch diameter borings, Sept-Oct 2015 Backfilled with gypsum/gravel mix (gypsum = CaSO 4 2H 2 O) 8400 pounds of sulfate contained within 15,000 pounds of gypsum Estimated PFB lifetime is 7-9 years for steady groundwater flow HPIs used gypsum powder mixed with hydrant water to create slurry Nine injections, August and October pounds of sulfate contained within 312 pounds of gypsum Average 1600 mg/l gypsum injected, or 890 mg/l as sulfate 10

Crushed gypsum Permeable Filled Borings Options for

Rhyolite 3/8" Lava Porosity (-) 0.49* 0.46 0.48 0.

93 Solid Density (g/cc) 2.31** 2.81* 2.13* 1.95* 1/4" (6.

11 Crushed gypsum Permeable Filled Borings Options for gypsum/gravel mix Physical properties Gypsum 3/8" Granite 3/8" Rhyolite 3/8" Lava Porosity (-) 0.49* Bulk Density (g/cc) Solid Density (g/cc) 2.31** 2.81* 2.13* 1.95* 1/4" (6.3 mm) screen retention 9.40%, passing = 90.60% 40 mesh (0.425 mm) retention 37.00%, passing = 63%" * calculated ** from literature Crushed Granite Crushed Lava Crushed Rhyolite Wikipedia: Rhyolite..the extrusive equivalent to granite rock 11

12 Permeable Filled Borings Delivery and Emplacement of PFBs Bags of pre-mixed gravel/gypsum Augering to depth Most efficient way to get pre-mix into auger Pre-mixed gravel/gypsum Borings above PFB fill were backfilled with ~2 feet of hydrated bentonite followed by cement grout to surface 12

13 Performance Monitoring PFB and HPI Monitor Well Locations PFB Monitor Wells U-1, U-3, U-4, and U-18 HPI Monitor Wells U-12 and U-15 Upgradient Monitor Well U-7 U-15 U-12 U-18 U-4 U-1 PFB HPI U-3 NOTE: Size of PFBs and HPI radius of influence not to scale U-7 Recent GW flow direction 13

14 Concentration (ug/l) Sulfate (mg/l) Sulfate (mg/l) Benzene, TPH-GRO, TPH-DRO and Sulfate vs. Time PFBs provide adequate sulfate to meet demand Toluene, Ethylbenzene and Xylenes each <20 µg/l since September ,000 U-3 10, ,000 1,000.0 TPH-GRO TPH-DRO SGC 1, Benzene Sulfate PFBs installed /11/13 01/11/14 01/11/15 01/11/16 01/10/17 01/10/18 Date 14

15 Concentration (ug/l) Sulfate (mg/l) Benzene, TPH-GRO, TPH-DRO and Sulfate vs. Time PFBs provide adequate sulfate to meet demand Toluene, Ethylbenzene and Xylenes each <20 µg/l since September 2014 U-4 100, , , ,000.0 TPH-GRO Benzene 1, , TPH-DRO SGC Sulfate PFBs installed /11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date 15

16 Concentration (ug/l) Sulfate (mg/l) Benzene, TPH-GRO, TPH-DRO and Sulfate vs. Time Non-benzene demands for sulfate 100,000 U-18 10,000.0 TPH-GRO 10,000 1,000 1, Benzene TPH-DRO SGC Sulfate PFBs installed /11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date 16

17 Concentration (ug/l) Benzene, Toluene, Ethylbenzene, Xylenes and Depth to Water vs. Time 10,000 1, U Benzene Toluene Ethylbenzene Xylenes DTW PFBs installed /11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date Top of Well Screen 17

18 Sulfate (mg/l) Sulfate versus Time for Monitor Wells 8/20/15 is Pre-Remediation Upgradient Well PFB Monitor Wells HPI Monitor Well U-7 U-3 U-4 U-18 U-12 8/20/ /1/2015 3/23/2016 6/17/2016 9/24/ /29/2016 3/23/2017 6/22/2017 9/20/

19 34S-Sulfate (per mil) Sulfur Isotope Ratio ( 34 S/ 32 S) for Sulfate Sulfur isotope results are not available if sulfate was not detected PFB Monitor Wells Upgradient Well Increasing sulfate-reducing conditions U-7 U-3 U-4 U-18 U-12 HPI Monitor Well Gypsum Source /20/ /1/2015 3/23/2016 6/17/2016 9/24/ /29/2016 3/23/2017 6/22/2017 9/20/

20 2H-Benzene (per mil) 34S in Sulfate versus 2H in Benzene March PFB Monitor Wells U U-15 U-12 y = x R² = U-18 U HPI Monitor Wells S-Sulfate δ S (per (per mil) mil) 20

Sulfate Delivery Using Permeable Filled Borings Conclusions Sulfate application has reduced dissolved petroleum hydrocarbon concentrations in areas near PFBs; benzene regulatory goals are met in two

21 Sulfate Delivery Using Permeable Filled Borings Conclusions Sulfate application has reduced dissolved petroleum hydrocarbon concentrations in areas near PFBs; benzene regulatory goals are met in two monitor wells There is isotopic evidence (34S-Sulfate and 2H-Benzene) that PFBs have enhanced sulfate reducing conditions, accelerating hydrocarbon (including benzene) biodegradation Although benzene exceeds 1,000 ug/l in two monitor wells, additional time is needed to satisfy non-benzene sulfate demand and meet dissolved benzene goals Gypsum-filled borings are effective to delivery sulfate as an electron acceptor Funding provided by Chevron Environmental Management Company 21

6. Organic Compounds: Hydrocarbons. General Comments Borden, Canada, tracer test Laurens, SC, gasoline spill Bemidji, MN, crude oil spill

6. Organic Compounds: Hydrocarbons General Comments Borden, Canada, tracer test Laurens, SC, gasoline spill Bemidji, MN, crude oil spill In the subsurface, biogeochemical processes that control contaminant