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
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
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. Remediation technologies applied 1992-2006: 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
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
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-1 36-56 13,000 260 440 180 <0.5 3.6 11/3/05 9/6/13 U-3 36-56 2,100 23 33 5 3.9 9/1/11 U-4 36-56 2,200 7 6 11 1.9 9/1/11 U-18 20-40 6,000 130 180 180 1.5 7.6 11/3/5 9/1/11 U-7 (upgradient) 25-40 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
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-18 60 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 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
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 http://www.geoengi neer.org/education/ web-based-classprojects/geoenviron mental-engineering/ 9
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 2015 180 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 gypsum/gravel mix Physical properties Gypsum 3/8" Granite 3/8" Rhyolite 3/8" Lava Porosity (-) 0.49* 0.46 0.48 0.52 Bulk Density (g/cc) 1.17 1.52 1.12 0.93 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
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
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
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 2014 100,000 U-3 10,000.0 10,000 1,000.0 TPH-GRO TPH-DRO SGC 1,000 100 100.0 10.0 Benzene Sulfate PFBs installed 10 1.0 1 0.1 01/11/13 01/11/14 01/11/15 01/11/16 01/10/17 01/10/18 Date 14
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 10,000.0 100,000.0 10,000.0 TPH-GRO Benzene 1,000.0 100.0 10.0 1,000.0 100.0 10.0 TPH-DRO SGC Sulfate PFBs installed 1.0 1.0 0.1 0.1 1/11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date 15
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 1,000.0 100.0 Benzene TPH-DRO SGC Sulfate PFBs installed 100 10.0 10 1.0 1/11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date 16
Concentration (ug/l) Benzene, Toluene, Ethylbenzene, Xylenes and Depth to Water vs. Time 10,000 1,000 100 U-18 9.00 11.00 13.00 15.00 17.00 19.00 21.00 Benzene Toluene Ethylbenzene Xylenes DTW PFBs installed 23.00 25.00 10 27.00 1/11/13 1/11/14 1/11/15 1/11/16 1/10/17 1/10/18 Date Top of Well Screen 17
Sulfate (mg/l) Sulfate versus Time for Monitor Wells 8/20/15 is Pre-Remediation 1000.0 Upgradient Well PFB Monitor Wells HPI Monitor Well 100.0 10.0 1.0 U-7 U-3 U-4 U-18 U-12 8/20/2015 12/1/2015 3/23/2016 6/17/2016 9/24/2016 12/29/2016 3/23/2017 6/22/2017 9/20/2017 18
34S-Sulfate (per mil) Sulfur Isotope Ratio ( 34 S/ 32 S) for Sulfate Sulfur isotope results are not available if sulfate was not detected 50.00 40.00 PFB Monitor Wells 30.00 20.00 10.00 0.00-10.00-20.00 Upgradient Well Increasing sulfate-reducing conditions U-7 U-3 U-4 U-18 U-12 HPI Monitor Well Gypsum Source -30.00 8/20/2015 12/1/2015 3/23/2016 6/17/2016 9/24/2016 12/29/2016 3/23/2017 6/22/2017 9/20/2017 19
2H-Benzene (per mil) 34S in Sulfate versus 2H in Benzene March 2016-40 -50-60 PFB Monitor Wells U-3-70 -80-90 -100 U-15 U-12 y = 0.4926x - 88.929 R² = 0.6745 U-18 U-4-110 HPI Monitor Wells -120-20.00-10.00 0.00 10.00 20.00 30.00 40.00 34S-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 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