The purge and treat system was constructed during 1995 and 1996 with a start-up in September 1006. System design includes a chromium removal process and dual stage air stripping for volatile organic chemical (VOC) removal. Maximum design flow for the treatment system is 3.2 million gallons per day (MGD). During 2005, the daily average was 2.4 MGD. Treated groundwater is discharged to the Clam River near the old Lake Cadillac Dam.
Groundwater is pumped from 18 purge wells located in two defined water bearing formations referred to as the upper and intermediate aquifers. In 1996, influent VOC concentrations exceeded 600 parts per billion (ppb). Last year, influent VOC concentrations were just over 200 ppb. (One part per billion is approximately equal to one second in 32 years.) Chromium concentrations have been reduced to clean-up criteria and the U.S. EPA has been petitioned for closure of the chromium treatment process.