Alluvial deposits (~5.5') overly residual soils (4-8'), which overly bedrock. Three zones were identified in the bedrock: highly fractured fine-grained dolomitic limestone, less fractured fine grained dolomitic limestone, and a course grained, locally highly fractured dolomitic limestone. Karst conditions occur.
Targeted Environmental Media:
 Fractured Bedrock
Contaminant plume extends over an estimated area of 25 acres, with a depth up to 120 below ground surface.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (var)
- 1,2-Dichloroethane (var)
- Vinyl chloride (var)
- Polychlorinated biphenyls (PCBs) (var)
- Fluid Loggings
- Temperature
- Conductivity/Resistivity
- Vertical Chemical Profiling
- Tracer (dye) Test
Comments:
There are suspected karst conditions. Four dye tests were conducted in 1998; two of the injected dyes were detected in the proposed extraction or monitoring wells, the other two were not detected. The results of the test indicated that karst conditions did not influence ground-water flow.
- Pump and Treat
- Other (Natural Attenuation)
Comments:
An initial pump test in 1995 showed that pumping from deeper sections of the bedrock reduced the upward hydraulic gradient and, possibly drew down contamination from the shallow bedrock aquifer. This problem was solved by grouting and packing off sections of the pumping wells. Five extraction wells are operating .
The presence of TCE daughter products, 1,2 DCE and vinyl chloride in the downgradient wells provides evidence that biodegradation is occuring through reductive dechlorination.
PCB's - 0.5 ug/l, cis-1,2 DCE - 70 ug/l, trans-1,2 DCE - 100 ug/l, TCE - 5.0 and vinyl chloride 2.0
A five year review was conducted in Nov. 2002. It was decided that the pump and treat system was removing the source and reducing the plume size.
Annual costs of O&M of the pump and treat system averages $308,000.
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