Depth to ground water: 8-10 ft. bgs.
Lithology/subsurface geology: Red-brown clay from grade to 8 ft. bgs. Fractured dolomite bedrock begining about 8 ft. bgs.
Hydraulic Conductivity: 3.46 ft/day (bedrock0 to 0.19 ft/day (clay)
Gradient: about 0.001 ft/ft
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Deepest significant ground-water contamination: 45 ft. bgs.
Plume size: Not yet defined, but contamination confirmed in area about one block long and 1/2 block wide
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (66,000 µg/L)
- Trichloroethene (6,400 µg/L)
- cis-1,2-Dichloroethene (19,000 µg/L)
- trans-1,2-Dichloroethene (130 µg/L)
- Vinyl chloride (1,600 µg/L)
- Benzene (7,500 µg/L)
- Toluene (22,000 µg/L)
- Borehole Geophysics
Comments:
Two down-gradient boreholes were video-logged to identify the major fracture zone. This greatly assisted with placing screens to delineate the horizontal and vertical extent of contamination.
- Pump and Treat
- Soil Vapor Extraction
- With Air Stripping
- In Dewatered Zones
- Multi Phase Extraction
Comments:
The dual extraction system (SVE and ground-water extraction) has operated for approximately two years. The system was shut down (9/3/03) to evaluate the plume under steady state conditions and evaluate remedial action options for the entire length of the plume. During active remediation, concentrations of contaminants in the groundwater, at the source area, diminished to the following PCE - 525 ppb, TCE - 151 ppb, cis 1,2 DCE - 341 ppb, and VC - 8.4 ppb. When the system was operating, it removed about 1 lb. of chlorinated solvents per hour. Rush analysis of treated water revealed PCE concentrations of 3 ug/L, with a discharge limit of 50 ug/L. Another rush sampling event revealed PCE concentrations of 10 ug/L, and cis-1,2-DCE concentration of 0.53 ug/L.
Given the lateral extent of chlorinated compounds in ground water, it may not be practical to remediate ground water to below the state ground water quality standards (NR 140 Wis. Adm. Code ). A ground water extraction system will likely be implemented to address contamination beyound the source area.
Althoug the residual plume appears to have pulled away from the water table downgradient from the source area, significant contamination remains at the water table in the source area. Fractures in bedrock have likely enhanced the vertical and lateral migration of the chlorinated compounds. Continued investigation revealed that the chlorinated plume is co-mingled with a second chlorinated plume (primarily PCE). The source of the second plume has not been identified.
Costs:
Site assessment - $32,330 (soil), $57, 609 (ground water)
Design and implementation - $54,869 (soil), $36,460 (ground water)
O&M - About $40,000 over two years
Total costs - $325,000
1. The significant cost savings realized by installing used SVE equipment. The treatment system guilding, air stripper, transfer pump, heater, control panel, exhaust fan, and a portion of the piping were obtained from a leaking UST site. A new submersible pump was purchased, however, to ensure reliability.
2. Limited access and space severely restricted remediation options. There is also a lack of good technologies to remediate chlorinated compounds in clay. Consultants had initially ruled out SVE and an option because of clay's low hydraulic condictivity, but further analysis showed that SVE could remove DNAPL in the rubble zone above the bedrock.
|
