Dual Phase Extraction (DPE) with Pneumatic Fracturing System
- 20 dual phase, single pump extraction wells installed at the source area
- 41 fracture locations (two pneumatic fracture points installed between each pair of extraction wells)
- Following initial fracturing, a low flow/low pressure compressor provided continuous air injection into each fracture point
- Groundwater extraction rate - approximately 35 gpm on a continuous basis
- Average vapor flow rate - increased from approximately 39 scfm to over 65 scfm, following pneumatic fracturing
State of California San Francisco Bay Regional Water Quality Control Board
Mr. George Lincoln
State of California
Regional Water Quality Control Board
San Francisco Bay Region
1515 Clay Street, Suite 1400
Oakland, CA 94612
Zahra M. Zahiraleslamzadeh
Environmental Project Manager
1125 Coleman Avenue, Gate 1 Annex
P.O. Box 58123
Santa Clara, California 95052
Fax: 408-289- 0195
- Trichloroethene (TCE) is the primary contaminant of concern, with the highest TCE concentration measured in the soil and groundwater during the remedial investigation at 46 mg/kg and 37,000 ug/L, respectively
Storage of waste from vehicle manufacturing operations
Type/Quantity of Media Treated:
Soil and Groundwater
- Depth to groundwater - 8 ft bgs; the first water-bearing zone (A-level aquifer) present at 20 to 50 ft bgs ; second water-bearing zone (B-level aquifer) present 50 to 90 ft bgs
- Sediments underlying the site include marine or basinal clays, coarse channel deposits, and inter-channel silts and clays
Purpose/Significance of Application:
Use of DPE with pneumatic fracturing to remove VOCs from silty clay soils and shallow groundwater
Regulatory Requirements/Cleanup Goals:
- Less than 10 mg/L total VOCs in soil.
- The DPE system removed approximately 1,220 pounds of VOCs from the source area
- VOC mass removed by soil vapor extraction - 782 pounds
- Average source area VOC concentration in groundwater declined from over 12,000 ug/L to less than 800 ug/L
- During first month of operation, about 40% of the mass of VOCs removed was from the vadose zone; by the fifth month, groundwater extraction was removing more VOC mass than SVE
- DPE system shut down June through August 1998 to assess rebound
- VOC concentrations remained relatively constant during shut down and after restart
- 27 confirmation soil samples averaged 0.93 mg/L total VOCs
- The cost to design and install the DPE system with pneumatic fracturing was approximately $300,000.
- Approximate costs for two years of operation and maintenance services, reporting, and analytical fees were $450,000, averaging $225,000 per year. Approximately $100,000 was required for the disposal of spent carbon.
- The unit cost for treatment of the 0.5-acre source area from 0 to 20 feet bgs was $53 per cubic yard of soil (for treatment of 16,000 yd3
The 328 Site occupies approximately 27.1 acres in a primarily industrial and commercial area of San Jose and Santa Clara, California, near the San Jose Airport. The 328 Site was used for manufacturing military tracked vehicles, including assembly and painting operations, from 1963 through 1998. A former waste storage area was the suspected source of VOC contamination of soil and groundwater at the site. The cleanup of the 328 Site was performed in anticipation of future commercial/industrial redevelopment and was conducted by FMC Corporation in accordance with the State of California San Francisco Bay Regional Water Quality Control Board Final Site Cleanup Requirements Order Number 96-024.
A DPE system, which included 20 dual phase, single pump extraction wells, was used to remove VOCs from silty clay soils and shallow groundwater at the site Air flow through the soils was enhanced by pneumatic fracturing (PF) between DPE extraction wells and by supplying continuous low flow/low pressure air to the fractured soils. Over 40 percent of the VOC mass removal occurred from the vadose zone during the first month of operation. Groundwater extraction provided greater mass removal rates than soil vapor extraction by the fifth month of operation. The combination of technologies has allowed soil vapor extraction to be effective in an area that is not well suited for in-situ remediation.