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pathways including point routes, and receptors. The CSM is for VOC-containing groundwater associated
with releases from the fire water reservoir and the associated transport pathways.
The fire water reservoir has a capacity of 200,000 gallons and was constructed in 1906. The reservoir is
constructed of concrete and extends approximately 19 feet bgs. Unsaturated soil is present at the fire
water reservoir area to a depth of approximately 12 feet and is underlain by highly fractured bedrock to a
depth of approximately 22 feet bgs. Groundwater is encountered at the soil bedrock contact at
approximately 12 feet below bgs, which is approximately 7 feet above the base of the reservoir. The
results of previous investigations show that the fire water reservoir is the source of solvent releases to the
subsurface. Specifically, solvents, which were discharged to the reservoir, migrated through cold joint
cracks in the sidewalls and possibly the base of the reservoir into the surrounding fractured bedrock (Bzone).
The bedrock surrounding the reservoir consists of a highly jointed and fractured siltstone.
Releases from the reservoir discharged directly into surrounding groundwater present within the fractured
bedrock (B-zone).
Once in the bedrock, dissolved constituents migrated horizontally with groundwater downgradient within
the highly fractured material as well as vertically downward via open joints sets (vertical fractures) that
intersect a prominent bedding plane fracture at the base of the C-zone. The main transport mechanisms
for releases from the reservoir are through the vertical joint (fracture) sets and horizontal bedding planes
in the bedrock. These migration pathways form an interconnected network for groundwater transport.
The horizontal bedding planes (fractures) significantly decrease in frequency with depth. The vertical
joint sets remain open and do not change with depth, but appear to terminate at lithologic contacts
(Engelder and Geisler 1980).
A prominent horizontal bedding plane was identified at an elevation between 515 to 518 feet AMSL (base
of C-zone) beneath the fire water reservoir area. This nearly horizontal feature extends, at a minimum,
laterally to the west and potentially discharges into the B-zone identified near EXB-07 located on South
Cayuga Street.
In the fire water reservoir area, groundwater generally occurs within the upper portion of fractured
bedrock (B-zone) and within a bedding plane fracture encountered at 515 feet AMSL (C-zone).
1.4 PREVIOUS GROUNDWATER EXTRACTION SYSTEM
As detailed in the Record of Decision (December 1994), the remedy selected for the fire water reservoir
area was 2-PHASE Extraction, which removes both groundwater and vapors from wells. This system
consisted of five extraction wells (previously identified as EW-1, EW-3, EW-4, MW-2, and MW-31)
installed downgradient of the fire water reservoir. The extraction wells were completed at depths of
approximately 50 to 65 feet bgs within the C-zone. Groundwater was removed by the extraction wells
using a high efficiency vacuum blower. Extracted groundwater and vapors were piped to an air/water
separator to separate the air and water streams. Groundwater was subsequently treated using activated
carbon to remove the VOCs. The air stream was vented to the atmosphere and the treated water was
discharged to a permitted Outfall #001 located on the western portion of the facility. The system has
been in operation since July 1996 in accordance with the Operation, Maintenance, and Monitoring
Manual dated April 1997, and addendum pages dated July 11, 1997.
This groundwater recovery system was evaluated based on the results of quarterly and semi-annual
sampling events. The sampling events were conducted according to WSP Engineering’s standard
operating procedures (SOPs), with all appropriate quality assurance/quality control measures taken
during the events. The most recent quarterly sampling event occurred on September 4, 2008, and the
results will be presented in the August through December 2008 Semi-Annual 2-PHASE TM Extraction
System Progress Report #25.
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