3. SACO Tannery Waste Pits
Site Lead: EPA
Date Deleted from NPL: September 29, 1999
Date of Last Five-Year Review: December 30, 2008
COCs: Arsenic and monochlorobenzene
RAOs: Arsenic concentrations less than 10 µg/L and monochlorobenzene concentrations less than 100 µg/L. MCLs were set as the action levels, or standards, for all groundwater contaminants, except for arsenic at four locations. EPA established Alternate Concentration Limits (ACLs) for four site monitoring wells [MW-l0l (70 µg/L), MW-103 (123 µg/L), MW-111B (64 µg/L), and MW-114B (77 µg/L)] based on the maximum concentrations observed in the four wells during the RI.
Technologies Applied: GW monitoring, source control, excavation
Reported Results: Arsenic concentrations continue to exceed the ACL of 123 µg/L in one of four locations (MW-103) and the 2001 MCL in four of the other five wells in the long-term monitoring program. There does not appear to be a consistent trend in concentrations, with arsenic concentrations at some wells stable over the past twelve years and others fluctuating.
Following the 2005 hydraulic assessment, ME DEP discontinued monitoring for monochlorobenzene except at MW-114A. This was done because for the other eight wells in long-term monitoring, six never exceeded the MCL 100 µg/L and the other two only once each. The MCL has been exceeded slightly at MW-l14A seven times (100-130 µg/L), all since April 2000.
MCLs Achieved? No, arsenic and monochlorobenzene concentrations are still above the MCL, but the restriction on use of site groundwater prevents any exposures.
ICs in Place? Yes, there is restricted site access through state legislation converting it into a wildlife preserve.