Pump and Treat of Contaminated Groundwater at the U.S. Department of Energy's Savannah River Site, A/M Area, Aiken, South Carolina

Site Name:

Savannah River Site

Location:

Aiken, South Carolina

Period of
Operation:

Status: Ongoing Report covers - 9/85 to 12/93

Cleanup
Type:

Full-scale cleanup (interim results)

Vendor:

C.L. Bergen
Westinghouse Savannah River Company
Aiken, SC

Technology:
Groundwater Extraction Wells followed by Air Stripping - 11 recovery wells at depths to over 200 feet below ground surface - Production air stripper has a design capacity of 610 gpm; operated at 510 gpm - 1993 average flow rate was 479 gpm; average air flow rate was 2,489 cfm - In 1993, 19,500 lbs of VOCs removed; average air emission rate of 2 lbs/hr

Cleanup Authority:
RCRA Corrective Action and State: South Carolina Bureau of Air Quality Control

SIC Code:
9711 (National Security)
3355 (Aluminum forming)
3471 (Metal finishing)
Point of Contact:
G.E. Turner,
DOE Savannah River Oper.
Office Environmental Restoration Div.
Aiken, SC

Contaminants:
Chlorinated Aliphatics - Trichloroethene (TCE), Tetrachloroethene (PCE), and 1,1,1- Trichloroethane (TCA) - Concentrations of volatile organic compounds (VOCs) in groundwater reported as high as 500 ppm - Groundwater TCE concentrations over 48 ppm - Groundwater contains 260,000-450,000 pounds of dissolved organic solvents in concentrations greater than 0.01 ppm, estimated to be 75% TCE - Soil TCE concentrations over 10 ppm - Dense nonaqueous phase liquids (DNAPLs) are present in groundwater

Waste Source:
Surface Impoundment

Type/Quantity of Media Treated:
Groundwater - VOC contaminated groundwater has an approximate thickness of 150 ft and covers about 1,200 acres - Complex hydrogeology arising from heterogeneities in a multilayer aquifer system with discontinuous sand and clay layers - Hydraulic conductivity 9 - 73 ft/day - Transmissivity 175 - 12,500 gpd/day

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

Regulatory Requirements/Cleanup Goals:
Groundwater
TCE - 5 ppb; PCE - 5 ppb; TCA - 200 ppb - Adopted in 1990, based on EPA MCLs - During initial remediation efforts in 1985, the cleanup goal was 99% removal of VOCs over a 30-year period

Air
34 tons/yr VOCs or 7.9 lbs/hr - Based on South Carolina Bureau of Air Quality Control permit

Results:
As of 1993
- Influent concentrations to air stripper decreased for TCE (from 25,000 ppb to about 6,000 ppb) and PCE (from 12,000 ppb to 4,000 ppb) - The total quantity of VOCs removed from 1985 to 1993 is 273,300 lbs - Average VOC removal efficiency for air stripper >99.9%

Cost Factors:
- Total Capital Costs (1990 dollars) - $4,103,000 (including design, construction and installation, engineering, site development) - Total Annual Operating Costs (1990 dollars) - $149,200 (for years 1985 to 1990) (including electricity, maintenance, operation, well sampling and analysis) - Total cost of operation and maintenance is $0.75 per 1,000 gallons treated (198 million gallons per year treated) - An estimated total cost for completing the cleanup is not available at this time

Description:
At the U.S. Department of Energy Savannah River Site, administrative buildings are located within the "A" area and aluminum forming and metal finishing operations have been performed within the "M" area. An estimated 3.5 million pounds of solvents were discharged from these operations between 1958 and 1985, with over 2 million pounds sent to an unlined settling basin. Groundwater contamination beneath the settling basin was discovered in 1981. The primary contaminants were volatile organic compounds (VOCs) at concentrations up to 500 ppm. A pilot groundwater remediation system was operated in 1983, with the full-scale groundwater treatment begun on September 1985. The full-scale technology included groundwater extraction wells and a production air stripper. The design of the production air stripper was based on pilot and prototype air strippers.

While the remediation was ongoing at the time of this report, reductions in concentrations of both TCE and PCE to the air stripper have been noted and the estimated total historical (1985 to 1993) removal of VOCs is over 273,000 lbs. In addition, the average VOC removal efficiency of the air stripper is greater than 99.9%. Contaminated groundwater in the source areas and the areas of the highest VOC concentrations appears to be contained at this time. However, the areas at the fringes of the plume are not as well contained, due to hydraulic factors.

The total capital cost for this application is $4,103,000 and the total annual operating costs are $149,200. DNAPLs were discovered in the groundwater in 1991 and pose a significant limitation to the long-term use of pump and treat, since pump and treat is effective for plume restoration only where DNAPL source areas have been contained or removed. A need for supplemental site characterization to fully define the DNAPL contamination and to redirect ongoing remediation activities has been identified.