Geology at the site consists of a layer of glacial till approximately 5 to 9 meters thick that rests on top of a lens of compacted clay known as a lodgment till. The lodgment till is approximately 18 meters thick beneath the site, but pinches out just off the northern and southern site bounds. Beneath the lodgment till lies a fractured quartz-monzonite granite bedrock. The bedrock fractures consist of many sub-horizontal release fractures in the upper sections, connected to steeply dipping fractures that are oriented roughly northeast-southwest and northwest-southeast.
Groundwater flow at the site occurs in the glacial till, or overburden, and the bedrock aquifers. Groundwater flow in the overburden aquifer is governed by the topography and an aquitard, the lodgement till described in the preceding section. As described above, the site lies at the top of a ridge that trends roughly east-west. In the overburden aquifer ground water flow mirrors the surface water flow, in the northern half of the site groundwater flows to the north and in the southern half of the site flows south. On the site ground water does not infiltrate to the bedrock, but instead flows downward towards the lodgment till and then flows horizontally off-site to where the lodgment till pinches out. Groundwater then enters the weathered bedrock via the sub-horizontal release fractures before being intercepted by the steeply dipping fractures. The fracture flow extends over considerable distances and can be significant in volume.
Targeted Environmental Media:
 Fractured Bedrock
The overbuden plume is approximately 490 feet long and 160 feet wide. The extent of the bedrock plume has not been defined.
Major Contaminants and Maximum Concentrations:
- 1,1,1-Trichloroethane (220 µg/L)
- 1,2-Dichloroethene (100 µg/L)
- Trichloroethene (3,000 µg/L)
- Benzene (4,800 µg/L)
- Toluene (9,000 µg/L)
- 4-Methyl-2-pentanone (MIBK) (51,000 µg/L)
- Ethylbenzene (1,500 µg/L)
- Arsenic (80 µg/L)
- Chromium (221 µg/L)
- Manganese (11,400 µg/L)
- Coring
- Chemical Oxidation (In Situ)
- Pump and Treat
Comments:
The remedial actions taken in the overburden aquifer (dual phase extraction and phytoremediation) have substantially reduced the concentrations of contaminants which are a source to the bedrock aquifer. The pump and treat system for the bedrock consisted of pumping one extraction well from from August 21, 2002 to November 4, 2002. Sodium permanganate was then injected into this well with a reduction of many contaminant concentrations except benzene.
MCL and MCLGs were chosen for those chemicals that had them. The other cleanup goals were risk based: 4-Methyl-2-pentanone 1,825 ug/L, Naphthalene 1,460 ug/L, and Manganese 3,650 ug/L (possible reduction to 300 ug/L)
Groundwater monitoring continues at the site to assess the effectiveness of the ground water remedy. The Agency determined that permanganate was not an appropriate oxidant for the site and no longer uses it for bedrock remediation.
http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0101208
Benzene is not susceptible to oxidation by permanganate.
|
