Remedy Analysis for Sierra Army Depot, Building 210 Area Herlong, California Desert Remedial Action Technologies Workshop Phoenix, Arizona Jackie Saling, PE

Outline Site Background Historical Investigations Interim Remedial Activity Pilot Tests Conceptual Site Model Enhanced Reductive Dechlorination Soil Vapor Extraction Conceptual Site Model- Revisited Moving Forward

Site Location and Historical Operations 1942 – storage of supplies and inert materials 1950s – explosives, guided missiles, and fuels Current – storage of war reserves and munitions Activities at the Site fluctuate Located XX miles north of Reno, NV in the ????? Desert Located adjacent to Honey Lake Surrounded by the ??? Mountians Activities included vehicle maintenance, sand blasting, spray painting, steam cleaning, and tank engine fogging Irrigation wells operate near the site How do site feature effect the hydrogeology of the site Building 210 Area

Site Location and Surrounding Features Amedee Mountains Surrounded by Mountains Honey Lake Valley Arid Climate Annual precipitation less than 5” Honey Lake Building 210 Area Diamond Mountains Fort Sage Mountains

Regional Geology Block faulted mountains Diamond Mountains Fort Sage Mountains Amedee Mountains Honey Lake Regional Geology Honey Lake Valley is a 2400 square mile drainage basin. The streamflow comes from the mountains inflitrates ath land surface to become groundwater and , in the driest years accumulate in to Honey The whole depot cover 54 square miles Block faulted mountains Alluvial fans- poorly sorted coarse grained Fine grained lake deposits

Regional Hydrogeology Regional groundwater flow toward Honey Lake Closed hydrologic basin Intermittent streams Surface area of Honey Lake fluctuates Horizontal K:Vertical K 100:1 3982 3984 3986 3988 Building 210 Area Honey Lake

Building 210 Area Vehicle Maintenance Popping furnace Sand blasting, spray painting, steam cleaning, engine fogging Degreasing solvents, oils, sludge

Potential Source Areas TCE and TCA degreaser tanks Possible dumping in ditches behind buildings TCE degreaser tanks Solvent recovery activities Waste discharged to shallow ditch

Site Investigation Timeline 1994 1983 1992 1995 2002 1997 Surface Soil (6 samples) Subsurface Soil (5 borings) Background Soil Subsurface Soil (52 samples) Soil Gas (294 samples) Groundwater (20 samples) Geophysics Hydraulic Testing Groundwater Investigation Plume Delineation Additional Hydraulic Testing Groundwater Treatment Analysis CP Testing (20 locations) Soil Gas (20 samples)

Investigation Findings – Soil and Soil Gas Unsaturated zone consists of interbedded silty sand and poorly-graded sands and gravel Depth to groundwater 95 ft Lower permeability silt zones were encountered from approximately 105 to 155 feet bgs No soil impacts observed TCE in soil gas 10 1 100 Soil gas isocontours developed from 1992 investigation

Investigation Findings - Groundwater TCE in groundwater detected up to 5,000 mg/L in shallow groundwater (95-115’ bgs) Hydraulic conductivity 8 x 10-3 to 3.22 x 10-2 cm/s in shallow groundwater TCE in groundwater near or below criteria in intermediate groundwater (160-170’bgs) 5 500 Building 210 50

Pump and Treat System Layout Building 210 50 24-EX 5 Reinjection Trenches 23-EX 5 21-EX 500 50

Interim Remedial Activity- Pump and Treat Initially a 2 year interim measure. Composed of 3 groundwater extraction wells, air stripper for treatment, discharged to recharge trenches

Pump and Treat Performance Data

Pump and Treat Issues Fouling decreased efficiency of groundwater recovery

ERD Injection Area, 2004 Follow Up HRC Area, 2002 ZVI Injection Area, 2001 SVE Area, 2006 HRC Area, 2000 Building 210 ZVI PRB Area, 2003

Pilot Test – Hydrogen Release Compound® Injection of HRC® into injection wells surrounded by monitoring wells in 2000, follow up 2002 Limited TCE degradation was observed, release rate of hydrogen was not high enough to overcome aerobic conditions

Pilot Test – Zero Valent Iron Injection Conducted in October 2001 Injection of micro-scale into 9 injection points surrounded by monitoring wells TCE concentrations decreased initially, but have rebounded

Pilot Test - Zero Valent Iron PRB Implemented in May 2003 Construction of a micro-scale permeable reactive barrier with 5 injection points B21-73-PZ

Conceptual Site Model Virtually no groundwater movement No connection observed between possible source areas and groundwater impacts identified No recharge to transport contaminants vertically from potential source to groundwater Heavy TCE vapor travel through vadose zone and spread out on top of the groundwater table creating a broad thin groundwater plume Vapor migration transports TCE, no transport in groundwater Significant mass in vadose zone

Site Conditions Building 210 Current Groundwater Plume Figure

Pilot Test – Enhanced Reductive Dechlorination Monthly injections began July 2004, 30% molasses Decreased frequency of injections and molasses concentration over time ERD injections are ongoing

Enhanced Reductive Dechlorination – Operational Data Monitoring Well 77-PZ Decreased to 1% molasses, increased injection volume to 1500 gal/well Decreased to 10% molasses

Enhanced Reductive Dechlorination – Operational Data Monitoring Well 77-PZ Began injection of NaOH

Enhanced Reductive Dechlorination – Operational Data Monitoring Well 77-PZ

Enhanced Reductive Dechlorination – Results Best results with low concentration, high volume injections Long time before reductive conditions were established Effective in decreasing TCE concentrations in groundwater after reductive conditions are established Small injection well ROIs due to the flat gradient, full scale application would require many injection wells and possible groundwater recirculation system Will not address significant mass in the soil vapor

Pilot Test – Soil Vapor Extraction One extraction well Six monitoring points Two passive vents 85 cfm, 50 in H2O at the blower Pilot test ongoing Passive Vent Monitoring Well Extraction Well

Soil Vapor Extraction System - Operation Vacuum extracted air Atmospheric vent

Soil Vapor Extraction – Vacuum Distribution 56 SVE Well 60 61 East-West Cross Section 140 120 100 80 60 40 20 20 40 60 80

Soil Vapor Extraction – Operational Data

Soil Vapor Extraction Groundwater Impact 10 20 30 40 50 SVE Well 500 1,000 Monitoring Well May 2007 1,500

Soil Vapor Extraction Groundwater Impact July 2007 SVE Well 1,000 1,000 500 1,000 1,500 10 20 30 40 50

Soil Vapor Extraction Summary Successful in removing mass from vadose zone and groundwater, 2.1 to 9 pounds TCE removed per month from one extraction well No operational issues, runs 24-7 Vacuum propagation is further to the north and west due to subsurface heterogeneity Ability to reduce TCE concentrations below surface of the water table will be diffusion limited May not be able to reduce groundwater concentrations to regulatory standards

Conceptual Site Model - Revisited ORIGINAL: Virtually no groundwater movement REVISED: Groundwater moving in the SE direction, observed groundwater velocity 0.5 ft/day

Conceptual Site Model - Revisited ORIGINAL: Vapor migration transports TCE, no transport in groundwater REVISED: Updated groundwater model and better understanding of hydrogeology indicates that vapor AND groundwater are transporting TCE. Updated groundwater model shows plume is stable.

Conceptual Site Model - Revisited ORIGINAL: Heavy vapors travel through vadose zone and spread out on top of the water table creating a broad, thin plume REVISED: Plume is not as thin as initially thought due to diffusion of TCE in the groundwater over time

Conceptual Site Model - Revisited No connection observed between possible source areas and groundwater impacts identified No recharge to transport contaminants vertically from potential source to groundwater Significant mass in vadose zone

Moving Forward Groundwater flow direction? Pumping operation on property to the SE? Recharge onsite? Building 210 operations? Geological feature? Full scale soil vapor extraction implementation

Moving Forward Proposed full scale SVE system layout Extraction Well Extraction Well/Passive Vent

Conclusion Numerous technologies tested at the site SVE and ERD are both viable technologies to use at the site SVE- proven technology Best mass removal Low cost Consider and evaluate options to overcome diffusion limitations associated with soil vapor extraction