Highly fractured, cherty Onondaga limestone with very little soil cover. Groundwater transport is through underlying evaporitic shales, which have extensive bedding plane dissolution zones.
There is a disappearing stream about 500 feet from the spill, where surface water infiltrates through the limestone and into the evaportitic shales below. This stream has proven very important to understanding contaminant distribution at the site.
Very rapid groundwater transport has been documented along the bedding plane dissolution zones--3.5 miles in roughly 30 days. Appears to be a lot of dissolution in the underlying shales. One of the slug produced harmonic oscillations in water levels - a splash pool 60 ft. below grade.
Targeted Environmental Media:
Dense Non-aqueous Phase Liquids (DNAPLs) Fractured Bedrock
TCE release (30,000 gallons) from a 1970 train wreck. Dissolved phase plume is over 3.5 miles long and about 0.5 miles wide. One spring at the end of the plume (3.5 miles away) has 1900 ppb.
There is virtually no evidence of TCE degradation at this site--no VC detections, and very low levels of DCE. Presumably, this is due to the oxidizing groundwater environment (assuming much of the shallow groundwater is rapidly infiltrated surface water).
Downward DNAPL penetration has been limited by cherty beds within the limestone. There is some suggestion that the TCE NAPL did not reach the water table.
Major Contaminants and Maximum Concentrations:
Trichloroethene (DNAPL)
Borehole Geophysics
- Natural Gamma
- Caliper
- Video Camera Televiewer
Fluid Loggings
- Temperature
- Conductivity/Resistivity
Vertical Chemical Profiling
Fracture Trace Analysis
GPR Surveys
Coring
Other
Comments:
"Other" refers to a VLF survey to find vertical fractures (likely karst features) which we thought would account for the uneven distribution of contaminants within the plume. We didn't find anything, but that may be because there was nothing to find. As the investigation proceeded, it became apparent that flow along bedding planes was the dominant mechnism for contaminant transport.
Pump and Treat
Comments:
ROD calls for removal of soils (what little there is) and bedrock vapor extraction (BVE). Vadose zone is roughly 60 feet thick during low water events, and BVE pilot testing was extremely successful.
Fracturing would be considered if BVE effectiveness falls off with time.
None provided
As of 10/03 there have been no remediation efforts.
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