The Savage Well Superfund Site (Site) is in the Town of Milford approximately ten miles northwest of Nashua. The well is situated approximately two miles west of Milford Center in the Souhegan River floodplain.
The Savage Well was a water supply for Milford from 1960 to 1983, supplying approximately 40 to 45 percent of the town's needs. In February 1983, NHDES detected concentrations of volatile organic compounds (VOCs) in the Savage Well that were above drinking water standards, and the well was shut down. The Site received Superfund emergency monies to temporarily provide bottled water to residents of a nearby trailer park whose water supply well was also affected. The trailer park was subsequently connected to the town's public water supply. The Site was added to the National Priorities List in September 1984.
In 1985, NHDES completed a hydrogeological evaluation of the Site, identifying four manufacturing plants surrounding the well as potentially responsible parties (PRPs) for causing the contamination.
In August 1987, EPA and the PRPs signed a Consent Decree in which the PRPs agreed to conduct the Remedial Investigation/Feasibility Study (RI/FS). The PRPs began fieldwork in the summer of 1988. EPA accepted the RI/FS in 1991, and EPA's Record of Decision (ROD) was issued in September 1991.
In subsequent negotiations, the Site was divided into two areas of remedial responsibility. EPA and the State are undertaking the cleanup of the OK Tool area of the Site where VOCs were released from the now-closed manufacturing facility into the subsurface. The PRPs are responsible for the cleanup of the second area, which includes most of the plume of contaminated groundwater in the Milford-Souhegan aquifer.
The remedial action for the OK Tool portion of the Site differs from the ROD-recommended remedy in that a physical barrier is being used to contain the Dense, Non-Aqueous Phase Liquid (DNAPL) contamination, in conjunction with pumping the groundwater. Also, air sparging and soil vapor extraction were included in the remedy. On December 19, 1996, EPA and NHDES jointly issued an Explanation of Significant Differences to describe these modifications and why they were chosen.
Construction of the1500-foot circumference slurry wall/barrier (containment area) and the treatment plant began in 1997 and was completed in March of 1999.
Since plant operations began (approximately nine years), monitoring well sampling indicates developing trends in contaminant reduction both inside and outside of the containment area. This trend demonstrates that the remediation system is functioning as intended and remediation of the Site is well underway.
After extensive investigations to characterize and delineate source areas inside the containment area, EPA and NHDES performed an in-situ chemical oxidation (ISCO) full-scale pilot test in September of 2003 and 2004. The ISCO test included injection of potassium permanganate into the subsurface. Potassium permanganate destroys dissolved chlorinated solvents such as PCE using oxidizing reactions. These injection events reduce the DNAPL and reduce the cleanup time in the OK Tool area.
Additional investigations to characterize and delineate potential source areas, and their relationship to former waste handling facilities in western part of the
containment area were conducted in 2007 and 2008. The investigations include an expanded area of vertical profiling of the saturated zone in locations where the potential of former DNAPL releases is suspected; soil sampling and soil gas sampling targeting areas in the western half of the containment area. These investigations have aided in finalizing remedies that are being developed and implemented at the site.
The vadose zone soils in the former leachfield are to be addressed through soil excavation and screening followed by chemical oxidation. The saturated zone will be treated by chemical oxidation in a series of injection starting with the deep zone and ending with the shallow zone to reduce the mass of contamination inside the wall.
In accordance with the requirements of the Consent Decree, the PRPs completed construction of a 450-gallon per minute groundwater treatment plant in late fall 2004 to cleanup the plume of contaminated groundwater in the Milford-Souhegan aquifer. The groundwater remediation system continues to operate at an average rate of 400 gpm with treated water being discharged to the subsurface and Souhegan River. The metals treatment system is effectively treating metals, being compliant with both surface water effluent discharge limits established by NHDES and design requirements of the system.