The site is underlain by approximately 6 m of poorly sorted silty sands. A pink equigranular and slightly porphyritic, fractured granite lies beneath the silty sands and the water water table is approximately 3 m below the ground surface.
Estimates of effective hydrulic conductivity in the bedrock treatment zone, based on slug tests and packer pressure tests, ranged between 4.3x10-5 to 2.6x10-4 cm/sec. Data from the bedrock coring and packer pressure tests were also used to develop estimates of effective fracture aperture (156 to 349 um) and bedrock porosity (1.03x10-3 to 2.8x10-3). Based on these calculations, the volume of water within the bedrock treatment zone was estimated to be approximately 36,000 liters. Given the observed hydraulic gradient across the bedrock treatment zone, the estimated time to flush one fracture-volume through that zone (assuming all of the fractures are connected) was between 88 and 243 days.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Prior to treatment, the main axis of the plume (PCE and VC) trended approximately 90 m, east to west, and extended to a depth of at least 30 m below the top of the fractured bedrock. The plume is between 20 and 45 m wide.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (1,000 µg/L)
- Pumping Tests
- Fracture Trace Analysis
- Coring
Comments:
outcrop surveys, bedrock core extraction, borehole geophysics, packer sampling and pressure testing and bedrock interconnectivity testing. In general, there was good coorelation among the geophysical measurements, core observations, and influence testing.
- Chemical Oxidation (In Situ)
Comments:
The pilot test involved the injection of 14237 liters of 50% hydrogen peroxide, combined with ferrous sulfate and pH- buffering catalyst. Two injection events were performed, with overlapping performance sampling. Samples collected 30 to 45 days after each injection event showed CVOC concentrations below the treatment objective. However, samples collected 60 to 100 days after each event revealed significant rebound in most areas, at concentrations that approached initial conditions.
This was a pilot test.
Presented at the University of Mass. Conference (Soil, Sediment and Ground Water) Amherst, MA 2005
The injected oxidants primarily influenced the more transmissive fractures whereas the less transmissive fractures were less influenced. Geochemical data and calculations indicate that the peroxide and the catalyst may persist in the subsurface for prolonged (>200 days) periods thus complicating the assessment of rebound.
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