Interbedded, fractured and weathered, pelite-sandstone below 3-6 m of till. When the water table is near the top of the weathered bedrock the head gradient is at an angle of only 30 degrees to fracture orientation. When the water table drops deeper into bedrock the head gradient shifts to more closely mirror regional topography, perpendicular to the strike of cleavage. Water table elevation varies seasonally as much as ten feet.
Targeted Environmental Media:
 Fractured Bedrock - Light Non-aqueous Phase Liquids (LNAPLs)
At least three to six thousand gallons of gasoline discharged from an underground tank system in 1999. The bulk of the dissolved gasoline plume moved down gradient along predominant fracture direction. The bedrock plume is 240 m long and 55 m wide terminating along an intermittent stream that is a local ground water discharge point during high water table seasons.
Major Contaminants and Maximum Concentrations:
- Benzene-toluene-ethylbenzene-xylene (BTEX) (LNAPL)
No technologies selected.
- Pump and Treat
- Soil Vapor Extraction
Comments:
Remediation started with recovering 300 gallons of free product from shallow bedrock wells close to the spill in 1999. Approximately 10,000 cubic meters of gasoline contaminated soil estimated to contain 3000 gallons of gasoline were excavated and horizontal SVE lines were installed under structures in October 1999. The SVE system extracted 900 gallons in 2000 during low water table conditions. In the summer and fall of 2000 a shallow bedrock pump and treat system yielded 6 gallons of free product during the time of lowest water level.
None provided
Initial maximum gasoline range organics (GRO) concentration in the bedrock was 4700,000 ppb. Concentrations from bedrock recovery wells fluctuated between 34,000 and 120,000 ppb GRO during 2000.
Cleavage in the water bearing fracture system exerts so much control of ground water flow that contaminant migration across-strike is negligible.
In January, 2004 the state will initiate closeout procedures.
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