The water table is typically 10 to 15 ft below grade and 8 to 12 ft below the top of the bedrock. The overburden is very thin ranging form 0 ft to 4 ft. The bedrock is a fractured, metasedimentary unit. Fractures and cleavage planes are nearly vertical, typically dipping 80 degrees or more. The average bedrock fracture aperature is approximately 120 microns and spacing is 62 cm. perpendicular to fractures. The average bedrock fracture porosity is 0.019%. The matrix porosity ranges from 0.032 to 0.084.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
DNAPLs (PCE) are likely present in the bedrock. Five monitoring wells have had reported PCE concentrations over 10% of solubility (i.e., over 15 mg/L. In addition, rock samples from drilling produced samples where a "sheen" or "oil" was noted. The zone with PCE concentrations over 1% effective solubility provides a general understanding of the potential DNAPL zone, which covers an area of approximately 550 ft by 300 ft in plan view and approximately 130 ft deep.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (1,500 µg/L)
No technologies selected.
- Chemical Oxidation (In Situ)
Comments:
Trenches excavated into the top-of-rock surface were used to deliver the KMnO4 solution. Approximately 281 kg was delivered over a 5 day period. Groundwater monitoring results suggest that essentially all of the KMnO4 was consumed by day 12 of the 28-day test.
It is estimated that approximately 35% of the accessible PCE mass within the target zone was destroyed during the pilot field test. The treated PCE mass is believed to include a combination of DNAPL and dissolved PCE within fractures and dissolved PCE within the outer 5% of the matrix, which is the unfractured portion of the bedrock. The remaining PCE mass is likely in the form of untreated DNAPL and dissolved mass within the outer portion of the bedrock. Additional PCE mass also remains within the interior of the matrix, which was likely not accessed by KMnO4. A significant amount of additional treatment would be required for the ground water within the target zone to approach regulatory standards.
This was a pilot test.
The inefficiency of the destruction of PCE per mass of oxidant, the length of time required for application of oxidant, the total cost per mass of PCE destroyed, and the likelihood that ground water standards would still not be approached for an indeterminate period of time, suggest that full-scale in-situ chemical oxidation of the DNAPL would be technically challenging and relatively ineffective.
In the Spring of 2004 a proposal for a Technical Impracticability (TI) Waiver and pump and treat remediation was submitted to the regulators. The TI waiver was granted in June 2006.
Construction of a groundwater containment system began in October 2010 and is expected to be substantially completed by late spring 2011. The groundwater containment system includes a bedrock well that will pump the contaminated groundwater up through an above ground treatment system and then the clean water will be pumped back into the bedrock.
Trenches excavated into the top-of-rock surface proved to be an efficient and effective means to deliver the KMnO4 solution.
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