The regional geology in the area of the Site is characterized by the crystalline rock units forming South Mountain to the east and south of the Site, and the Cambrian and Ordovician sedimentary units of the Little Lehigh Creek Basin extending north and west of
South Mountain. The first bedrock unit encountered at the Site consists of carbonate rocks of the Leithsville Formation. Deep sections of weathered bedrock (saprolite) occur above the
competent bedrock of the carbonate units of the Little Lehigh Creek Basin, overlain in some areas in the vicinity of the Site by glacial drift deposits, and generally capped with a soil
horizon. The saprolite varies in thickness from 50 feet to more than 250 feet in the Site vicinity.
The information obtained during the investigations conducted at the Site suggest that the bedrock is highly fractured and faulted in the vicinity of the Site, with the predominant fracture orientations aligned generally
in a north-northeast/south-southwest directions, and faults trending northwest-southeast. A linear ground water depression has been consistently observed for both the shallow and
deeper bedrock extending from an area immediately west of the Site towards the
north-northwest. This feature appears to act as a preferential pathway for the migration of ground water and may be related to the northwest trending dissolution enhanced fault feature.
A bedrock aquifer underlies the Site and is recharged by local precipitation. Ground water beneath the Site flows to the north-northeast, in the direction of the Little Lehigh Creek. Ground water at the Site flows through extensive joints and fractures, and in the case of the carbonates, the solution enhancement of these secondary openings. The depth to ground water at the Site and in the immediate Site vicinity has been observed to range from 105 to 115 feet below ground surface (bgs).
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
The probable DNAPL zone extends to an estimated depth of up to 420 feet below ground surface.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (3,900 µg/L)
- Trichloroethene (400,000 µg/L)
- 1,2-Dichloroethene (43,000 µg/L)
- Vinyl chloride (3,200 µg/L)
- 1,1,2-Trichloroethane (350 µg/L)
- 1,1-Dichloroethene (27 µg/L)
- Chloromethane (2,900 µg/L)
- Borehole Geophysics
- Coring
- Pump and Treat
- Other (Monitored Natural Attenuation of plume outside well captive area)
Comments:
The pump and treat system became operational in February 1997. The system utilized four existing on-site wells (Well 3 (EXW-I), Well 4 (EXW-2), RW-3 (EXW-3) and MW-4 (EXW-4) as extraction points. The system included the following components: an equalization tank, a liquid solid separation unit and sludge handling equipment, an air stripper, liquid phase granular activated carbon units, and a regenerative vapor phase adsorber unit. The system was designed based on an average flow rate of 45 gallons per minute (GPM) and a maximum flow rate of 90 gpm. Treated ground water is discharged to a storm sewer located on site which discharges to an unnamed tributary of the Leibert Creek pursuant to the substantive PADEP National Pollutant Discharge Elimination System (NPDES) requirements.
The site has received a technical impracticability waiver for groundwater cleanup.
The groundwater treatment system is functioning as expected and is providing hydraulic containment for the probable DNAPL zone. Monitoring wells with the historically highest levels of contamination have shown an order of magnitude decrease in contaminant levels. Contaminant levels in the monitoring wells at the plume margin have fluctuated within an order of magnitude. These trends suggest that the overall mass of the contaminant plume is decreasing, but that the area of contamination has largely remained unchanged (2007 5-year review). As of the July 2008 Monthly Progress Report an estimated 130,188,590 gallons of ground water have been treated and discharged by the system. An estimated 9,354 kg of TCE have been removed cumulatively during the time the system has operated.
http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0301744
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