The Fisher site is underlain by glacial deposits that range from 10 to 30 feet thick across the area. The glacial deposits are unconsolidated sediments with grain size ranging from sandy gravel to silty clay, with sandy silt as the most common sediment type. The deposits are lenticular, and the individual layers are not continuous across the site. The clay content of the glacial sediments is generally higher at the southeastern corner of the site. The glacial deposits are known as the overburden zone at the Fisher site and constitute the uppermost aquifer, where present.
The glacial materials are underlain by sedimentary rocks of the Triassic Brunswick Formation.
Bedrock is mostly sandstone with some conglomerate and shale interbeds. The primary porosity of the bedrock has been filled by compaction and cementation processes; the effective porosity of the bedrock aquifer is, therefore, due to the presence of fractures. Two vertical fracture sets have been identified at the site, oriented northeast-southwest and northwest-southeast in the Brunswick Formation. Core samples, caliper logs, and packer tests indicate that there are two intervals that have significant fracture permeability in the bedrock beneath the site. The upper zone, known as the shallow bedrock zone, is present beneath the bedrock-overburden contact, and extends from approximately 20 feet to 50 feet below ground surface (bgs) across the site (Ref. 5). Beneath this interval, bedrock is less fractured and
does not reliably yield groundwater in the interval from approximately 50 to 70 feet bgs. Beneath this lower permeability interval, another fractured zone is present, generally ranging from 70 to 100 feet bgs.
The lower fractured zone has been designated the intermediate bedrock zone at the site. Deeper zones
within the bedrock aquifer have been subjected to packer and pumping tests in bedrock wells at several locations across the site. Available data do not indicate that significant contamination is present in fractured zones in the deeper portion of the Brunswick Formation.
Water level measurements collected during the packer tests indicate that PW-4 and PW-5 have a larger radius of influence in the intermediate zone than in the shallow bedrock zone, reflecting greater hydraulic interconnection of the
fractures in the intermediate zone.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Bedrock groundwater is contaminated to 100 feet bgs.
Major Contaminants and Maximum Concentrations:
- Acetonitrile (220,000 µg/L)
- Trichloroethene (130,000 µg/L)
- Benzene (74,000 µg/L)
- Chloroform (30,000 µg/L)
- Xylenes (310,000 µg/L)
- Toluene (210,000 µg/L)
- Methylene chloride (3,100 µg/L)
- Tetrachloroethene (3,500 µg/L)
- Carbon tetrachloride (34,000 µg/L)
- 1,1,2,2-Tetrachloroethane (3,200 µg/L)
- Borehole Geophysics
- Vertical Chemical Profiling
- Pumping Tests
- Coring
- Pump and Treat
Comments:
The concentrations given above are from 1984. The bedrock plume is controlled by three production wells open to both the upper and intermediate fracture zones. Their pumping prevents contaminated water from going offsite.
New Jersey Groundwater Quality Standards.
The pump and treat system continues to operate. While the contaminant levels have fallen since 1984, the shallow fractured rock remains highly contaminated and other supplemental remedies are being considered.
http://www.epa.gov/region02/waste/fsfishsfa.htm
|
