Technology:
Dual Phase Extraction (DPE)
- 12 DPE wells and six air injection wells arranged in a rectangular grid
- DPE wells installed to depth of 22 to 28 ft bgs (10 ft screen length) and equipped with an electric, submersible (variable-frequency drive) pump,
- SVE vacuum at blower - 42 in WC; SVE air flow rate - 314 cfm
- Groundwater extraction rate - 37 gpm
- DPE radius of influence - 600 to 800 ft, downgradient
- Air extracted by the SVE blower was vented to the atmosphere. Extracted groundwater was pumped directly to a low-profile tray type air stripper to remove VOCs. Air stripper off-gas was released to the atmosphere
- Effluent water was discharged to a storm sewer that flows to a nearby stream.
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Cleanup Authority:
CERCLA - Remedial Action
- ROD signed 1992
- ESD signed 1995
Regulatory Contact:
Stephen Mihalko
Remedial Project Manager
Virginia Department of Environmental Quality
P.O. Box 10009
Richmond, VA 23240
Tel: (804) 698-4202
Todd Richardson
U.S. EPA Region 3
1650 Arch Street (MC 3HS50)
Philadelphia, PA 19103-2029
Tel: (215) 814-5264
E-mail: richardson.todd@epa.gov | Additional Contacts:
Bill Saddington
DSCR Remedial Project Manager
Defense Supply Center Richmond
8000 Jefferson Davis Highway Richmond, VA 23297-5000
Tel: (804) 279- 3781
E-mail: bsaddington@dscr.dla.mil |
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Contaminants:
Chlorinated Solvents
- The highest concentrations of VOCs detected in the upper aquifer were 3300 micrograms per liter (æg/L) for PCE, 890 æg/L for TCE, and 26 æg/L for 1,2-DCE; VOCs were not detected in the lower aquifer |
Waste Source:
Leaks from settling basins that received wastewater from metal plating operations |
Type/Quantity of Media Treated:
Soil and Groundwater/17 million gallons of groundwater recovered and treated
- The plume area was estimated to be 16,000 square feet
- Depth to groundwater - 10 to 15 ft bgs; hydraulic gradient - 0.001 to 0.002 ft/ft; aquifer transmissivity - 374 to 504 ft2/d |
Purpose/Significance of Application:
Use of DPE to treat soil and groundwater contaminated with chlorinated solvents, including PCE and TCE |
Regulatory Requirements/Cleanup Goals:
- Remedial goals for PCE - 5 æg/L and TCE - 5 æg/L, or attainment of an asymptotic trend in contaminant of concern concentrations in groundwater (whichever occurs first)
- The purpose of the DPE treatability study was to collect additional operational data to refine system design parameters, and to evaluate the effectiveness of an air injection system to facilitate air flow through soils exposed by drawdown of the groundwater surface |
Results:
- Total VOC concentrations were reduced by more than 99% in several wells; for example, in two wells located in the plume center initial concentrations of total VOCs were reduced from 1,980 æg/L to 11.9 æg/L and from 1,766 æg/L to 3.5 æg/L
- Total mass of VOC removed - 145 lb:
- Groundwater VOC mass removal rate - 28 lb (0.09 lb/d) total, including 2 lb (<0.01 lb/d) aromatic and 26 lb (0.08 lb/d) chlorinated
- Soil VOC mass removal rate - 117 lb (0.37 lb/d) total, including 70 lb (0.22 lb/d) aromatic and 47 lb (0.15 lb/d) chlorinated
- At the completion of the treatability study, PCE and TCE concentrations remained above the remedial goals in several wells, and increasing VOC concentrations were observed in wells at the outer edge of the radius of influence of the DPE system |
Cost Factors:
- The total cost for the one year treatability study of the DPE system was $538,490, including $134,092 for pre-design investigations supporting DPE design, $73,198 for engineering design of the DPE system, $205,743 in system construction costs (equipment only), $24,309 in startup costs, and $101,148 in operation and maintenance, which included the cost of sample collection and analysis
- The total cost per unit volume of groundwater recovered and treated was $0.03 per gallon (based on 17 million gallons of groundwater) |
Description:
The 640-acre Defense Supply Center Richmond (DSCR) is a military support, service, and storage facility located approximately 11 miles south of the City of Richmond, VA. Since 1942, DSCR has been furnishing and managing general military supplies to the Armed Forces and several federal civilian agencies. Historic and current industrial operations at the DSCR have included repair of equipment, engine rebuilding, and refurbishment of combat helmets and compressed gas cylinders. The Acid Neutralization Pit (ANP) site, located in the northern section of the DSCR, consists of two former concrete settling basins that received wastewater from metal cleaning operations conducted at one of the warehouse buildings. In 1985, when the tanks were closed, they were observed to be cracked and broken. Site investigations determined that the groundwater was contaminated with chlorinated solvents, primarily tetrachloroethene (PCE) and trichloroethene (TCE). The site was placed on the National Priorities List. A ROD, signed in 1995, addressed the contamination at the ANP site, and the results of the Feasibility Study identified DPE as a potentially viable remediation alternative for the site.
A pilot test of the DPE system, along with aquifer testing, was performed in June 1995 to gather site-specific hydrogeologic data and data on air extraction rates and SVE mass removal rates. The results of the testing supported the use of DPE for VOC recovery at DSCR. A full-scale system, consisting of 12 DPE wells and six air injection wells were installed and a treatability study was conducted for one year to evaluate the effectiveness of the full-scale system, including collecting operational data to refine system design parameters, and to evaluate the effectiveness of the air injection system. After one year, the DPE system removed 145 pounds of VOCs, including 117 pounds from the soil vapor and 28 pounds from the groundwater. Although VOC concentrations were reduced in a number of wells, including reductions of more than 99% in two wells located withing the plume, concentrations of PCE and TCE remained above the cleanup goals in several wells. Based on the results of the treatability study, the Army's contractor recommended that the DPE system continue operation and that additional investigations be done to better define the capture zone of the system. The unit cost was $0.03 per gallon based on 17 million gallons of groundwater treated during the pilot test. |
