Geology and Geohydrology at CRREL, Hanover, New Hampshire: Relationship to Subsurface Contamination
1992
Shoop, Sally A. | Gatto, Lawrence W.
Trichloroethylene (TCE) was discovered in three of the industrial wells at CRREL, as well as in two domestic wells in bedrock across the river. This report describes the geohydrology of the CRREL vicinity and the subsurface behavior of TCE as part of the preliminary assessment of the CRREL site. There are three hydrologic units near CRREL-a high permeability esker deposit, lower permeability lake sediments and fractured bedrock. The esker is a high-yield sand aquifer paralleling the river that provides industrial water to CRREL from four wells. The pumping of these wells may induce groundwater recharge from the river. The lake deposits consist of fine-grained silt and sand with some clay, and these cover the esker deposit. These sediments lie above the fractured, folded and metamorphosed volcanics (schist and phyllite) of the Orfordville formation. The free surface water table shows very little hydraulic gradient and appears to be continuous through these units, indicating that they are hydraulically connected. TCE can migrate in the vapor phase, as a soluble component moving along with the groundwater, and as a separate or free phase. Small spills of TCE in the fine-grained soils at CRREL may not have exceeded the retention capacity of the soils and may remain within the soil pores, with a soluble component reaching the groundwater through infiltration. Larger spills may have passed through the saturated soil zone seeking bedrock lows, continuing their downward movement along bedrock fractures. Since the CRREL wells may induce recharge from the river, the possibility of the contamination coming from that direction should not be overlooked.
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