The majority of unconsolidated materials encountered on-site comprise two glacial till units deposited directly above the bedrock surface. The deeper, older till unit is medium to light gray in color and contains abundant rock fragments from the underlying gray shale. This unit has a documented on-site thickness ranging from 0-29 feet. The shallower, younger till unit identified on-site is brown in color and contains reddish-brown sandstone and siltstone fragments. The brown till ranges from 0 to 21 feet in thickness. Soil borings completed just
northwest of the Site also intersect a thin medium to dark brown lacustrine clay unit.
A weathered bedrock zone, between 7 and 10 feet thick, was encountered on-site between overlying unconsolidated materials and competent bedrock. Bedrock
underlying the Site is composed primarily of medium to dark gray shale, interbedded with siltstone and occasional lenses of sandstone. Rock cores collected from on-site locations
indicate that the upper surface of the bedrock is highly fractured and severely weathered in areas. Fractures intersected during rock coring are predominantly horizontal and partially
clayfilled. Vertical jointing within the rocks is well developed with a prominent orientation of north-south. Less developed joints generally trend northeast-southwest and northwest-southeast. This extensively developed system of joints is the main conduit for groundwater movement within these rocks due to the near absence of primary porosity in the shale.
Groundwater was encountered in the glacial till at depths ranging from approximately 6 to 20 feet below the ground surface. The average depth to water encountered was 12 feet below grade. Water levels measured in bedrock
monitoring and production wells during static conditions varied between approximately 10 and 60 feet below the ground surface. The average depth to water measured in the bedrock wells was
approximately 34 feet below grade.
Targeted Environmental Media:
Fractured Bedrock
The vertical and lateral extent is not given in the EPA documentation.
Major Contaminants and Maximum Concentrations:
Acetone (2,200 µg/L) 1,1,1-Trichloroethane (8,800 µg/L) Trichloroethene (1,350 µg/L) Toluene (2,250 µg/L) 1,1-Dichloroethane (865 µg/L) 1,2-Dichloroethene (535 µg/L) 2-Butanone (MEK) (510 µg/L) Carbon tetrachloride (60 µg/L)
Pumping Tests
Coring
Pump and Treat
Other (monitored natural attenuation of overburden groundwater)
Comments:
The current pump and treat system (eight six-inch bedrock wells completed to an average 200 feet bgs) became operational in 2005. The system uses two aqueous phase in-line carbon absorption treatment units.
Cleanup goals are MCLs.
While monitoring has shown a demonstrable decline over time, and, more importantly, significant declines with distance from the site, monitoring has also shown that contaminant values in groundwater remain above standards for VOCs.
http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0201452
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