The aquifer over which the grace property lies consists mainly of glacial deposits of two general types: (1) stratified sands and gravels which readily transmit water and (2) an underlying layer of less pervious glacial till which is a dense and relatively impervious mixture of sand, gravel, clay, silt, cobbles and boulders. The glacial deposits are, in turn, is underlaid by bedrock that is comprised of gneisses and schists of the
Nashoba formation. The upper portion of the bedrock, where it has been observed, is weathered
and fractured. This bedrock zone is also transmissive. The primary source of groundwater in the aquifers underlying the study area is precipitation. As precipitation enters the ground, it moves downward through the unsaturated glacial deposits to the groundwater table. For the majority of the Grace property, the groundwater table lies from 20 to 50 feet below the ground surface. However, in the vicinity of the north lagoon, the groundwater table is generally at the ground surface.
The site is on a groundwater divide with part flowing to the northwest and part to the southeast.
Targeted Environmental Media:
 Fractured Bedrock
There are five groundwater plumes at the site. In 2001 the largest was approximately 1,500 feet at its widest and 2,800 feet at its longest.
Major Contaminants and Maximum Concentrations:
- Trichloroethene (26 µg/L)
- Vinyl chloride (420 µg/L)
- 1,1-Dichloroethene (2,900 µg/L)
- Methylene chloride (140 µg/L)
- Benzene (17,000 µg/L)
- Methyl tert butyl ether (190 µg/L)
- Lead (144 µg/L)
- Arsenic (541 µg/L)
- Chromium (5,150 µg/L)
- Manganese (13,000 µg/L)
No technologies selected.
- Pump and Treat
None provided
The pump and treat system has recovered 6,100 pounds of VOCs. The various plumes at the site have been shrinking and declining in concentration--sometimes by orders of magnitude since the 1980s.
The pump and treat system that is currently in place was designed and installed by Grace in 1985. W. R Grace is designing a new groundwater extraction, treatment and discharge system. It is expected that the new treatment system will be constructed and operational by spring of 2011.
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