Pump and Treat and Permeable Reactive Barrier
- Groundwater was extracted using three wells and one trench well at an average total pumping rate of 8 gpm
- Extracted groundwater was treated with air stripping and discharged to an on-site storm sewer under a NPDES permit
- The permeable reactive barrier (PRB, treatment wall) is 100% granular iron, 4 ft thick, 40 ft wide, and approximately 13 ft deep; 2 slurry walls are used to route groundwater through the PRB
- Site cleanup requirements order: 10/15/86
|State Point of Contact:|
2101 Webster Street, #500
Oakland, CA 94612
Deborah Hankins, Ph.D.
114 Sansome St., 14th floor
San Francisco, CA 94104
- Maximum concentrations detected in 1986 were TCE (13,000 µg/L), cis-1,2-DCE (19,000 µg/L), Vinyl chloride (1,800 µg/L), and Freon-113 (16,000 µg/L)
Leakage from sub-grade neutralization system
Type/Quantity of Media Treated:
- 38 million gallons treated as of November 1996 (36 million by pump-and-treat and 2 million by PRB)
- Extraction wells are located in 1 aquifer, to a depth of 18 ft (depth to groundwater not provided)
- Transmissivity reported as 370 ft2/day (hydraulic conductivity not provided
Purpose/Significance of Application:
Used P&T for eight years, and replaced this technology with PRB; PRB used for more than three years.
Regulatory Requirements/Cleanup Goals:
- The cleanup goal for the site is to reduce contaminant concentrations throughout the aquifer to levels below the maximum contaminant levels (MCLs) set by the state of California and primary drinking water standards.
- Remedial goals were identified for vinyl chloride (0.5 µg/L), cis-1,2-DCE (6 µg/L), TCE (5 µg/L), and Freon-113 (1,200 µg/L).
- Effluent from the treatment system was required to meet the remedial goals prior to discharge.
- A secondary goal was identified to create an inward gradient to contain the plume.
- The primary goal for the PRB is to reduce contaminant levels in groundwater passing through the wall to the cleanup goals for the site.
- The secondary goal for the PRB is to contain the contaminant plume upgradient of the wall.
- The contaminant plume has been reduced in size at this site, however, contamination remains elevated at three hot spots.
- Average total contaminant concentrations have decreased from 1,609 µg/L in 1986 to 31 µg/L in 1997.
- By 2/95, the P&T system had removed 56 kg of contaminants from the groundwater; from 2/95 to 8/96, the PRB had removed 7 kg of contaminants from the groundwater.
- The contaminant plume has been contained.
- Estimated costs for the P&T system from 1987 to 1995 were approximately $1,343,800 ($325,000 in capital and $1,018,800 in O&M), which correspond to $38 per 1,000 gallons of groundwater extracted and $10,900 per pound of contaminant removed.
- Estimated costs for the PRB system through 11/96 were approximately $762,000 ($5955,000 in capital and $167,000 in O&M), which correspond to $38 per 1,000 gallons of groundwater extracted and $49,400 per pound of contaminant removed.
Intersil operated at the site as a semi-conductor manufacturer from the early 1970s until 1983. The site is currently owned by Sobrato Development Company, and was released to another tenant in 1995. In 1972, Intersil installed a concrete, epoxy-lined, in-ground acid neutralization system at the facility to neutralize wastewater before discharge to a sanitary sewer. In 1982, the California Regional Water Quality Control Board (RWQCB) requested sampling of shallow groundwater and soil near the neutralization holding tank, and Intersil identified chlorinated solvents in the shallow groundwater and soil. Under a state program, a site cleanup requirements order was issued in October 1986.
A pump and treat (P&T) system was operated at this site from 1987 until 1995. The system consisted of three extraction and one trench wells. The wells were installed to a depth of 18 ft and had a design yield of 6 gpm. Extracted groundwater was treated with an air stripper designed to handle a maximum of 40 gpm.In 1993, Intersil examined alternative groundwater remediation technologies based on achievement of two goals. Intersil wanted to minimize the cost of treatment while increasing treatment effectiveness, given that the mass removal by the P&T system had asymptotically declined, and to return the site to leasable/sellable conditions. The selected alternative, approved by the RWQCB, was a PRB. The treatment technologies used at this site have removed contaminant mass and reduced concentrations in the aquifer; however, site cleanup goals have not yet been met.