Pump and Treat of Contaminated Groundwater at Operable Unit B/C, McClellan Air Force Base, California

Site Name:

McClellan Air Force Base

Location:

Sacramento, California

Period of
Operation:

Status: Ongoing
Report covers - 1988 to 1993

Cleanup
Type:

Full-scale cleanup (interim results)

Vendor:

Not Available

Technology:
Groundwater Extraction followed by Aboveground Air Stripping - 7 extraction wells pump to a main treatment plant - Air stripper - design capacity of 1,000 gpm; average flow rate of 250 gpm - Supplemental Treatment - thermal oxidizer and caustic scrubber for offgases; two GAC units in series to polish liquid phase prior to discharge

Cleanup Authority:
DoD

SIC Code:
9711 (National Security)
Point of Contact:
Remedial Project Manager
McClellan AFB Sacramento, CA

Contaminants:
Chlorinated Aliphatics - Trichloroethene (TCE), cis-1,2-Dichloroethene (cis-1,2-DCE), Tetrachloroethene (PCE), 1,2-Dichloroethane (1,2-DCA) - In an area of 7,800 million cubic feet, there is an estimated 33,000 kg of VOCs; percent of total mass for individual constituents is TCE (82.7%), cis-1,2-DCE (0.5%), PCE (16.7%), 1,2-DCA (0.1%)

Waste Source:
Landfill; Underground Storage Tank; Disposal Pit; Open Burn Area

Type/Quantity of Media Treated:
Groundwater - As of 1/94: Over 660 million gallons of groundwater treated since startup in March 1987 - Groundwater subsurface consists of 5 distinct monitoring zones (A through E); evidence points to hydraulic link among 5 zones - Hydraulic conductivity ranges from 2.8 to 30.7 ft/day - Transmissivity ranges from 100-2,000 ft[Sub 2]/day

Purpose/Significance of Application:
Full-scale remediation of groundwater contaminated with VOCs using groundwater extraction and aboveground air stripping.

Regulatory Requirements/Cleanup Goals:
Final cleanup criteria have not been established at this time - Current target is <0.55 ~g/L VOCs for groundwater - NPDES permit - acetone, MEK, and MIK to <1 mg/L and VOCs to <0.5 ~g/L

Results:
- Influent VOC concentrations have decreased from about 60 ppm in 1987 to about 4 ppm in 1993 - The effluent from the treatment system has been below the permitted discharge levels since operation began - As of 3/94, approximately 44,000 lbs of VOCs have been removed since startup

Cost Factors:
- Total Capital Cost in 1987 - $4,000,000 (including over $1,700,000 for the incinerator, air stripper, scrubber, wells, and GAC tanks, and about $1,000,000 for heat exchangers, blowers, pumps, and compressors; control center) - Total Annual Operating Costs - $1,240,000 (including contractor operations, utilities, sampling and analysis, project management) - An estimated total cost for completing the cleanup is not available at this time

Description:
The McClellan Air Force Base in Sacramento, California was established in 1937. Operations at the 3,000-acre facility include aircraft, electronics, and communications equipment maintenance and repair, and a wide variety of hazardous materials have been used at the site. The site was added to the National Priorities List in 1987. Areas of contamination at the site include Operable Unit B (OU B) and Operable Unit C (OU C). Releases from OU B resulted from disposal/release of hazardous substances from landfills, underground storage tanks, storage lots, burial and burn pits. Releases from OU C were attributed to waste disposal activities. Extensive VOC contamination has been identified at the facility. The primary constituents of concern are TCE, cis-1,2-DCE, PCE, and 1,2-DCA.

A groundwater extraction and treatment system including air stripping was installed with operations beginning in 1988. Offgases from the air stripper are treated by thermal oxidation and caustic scrubbing. The effluent from the air stripper is treated using GAC prior to a NPDES- permitted discharge. The 1993 data on the influent to the air stripper show that the VOC concentrations have decreased to about 4 ppm from concentrations of 60 ppm (1987). An estimated 44,000 pounds of VOCs have been removed as of March 1994. The remediation was ongoing at the time of this report and final performance data are not yet available. In addition, the treatment system has been effective in treating groundwater to below the NPDES discharge limits.

The total capital costs for this system are $4,000,000 and the total annual operating costs are $1,240,000. The system has been on line 98% of the time. Problems of scaling and deposition in the air stripper from calcium and magnesium salt precipitation were remedied by changing to 2-inch packing from 1-inch packing in the air stripper. Corrosion was minimized through material changes to nickel-based commercial alloys and change in physical layout to improve flow.