SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Jack Badey - 3 - 26 September 2008 Plume Definition The existing network of monitoring wells, coupled with the grab groundwater data presented in the December 2007 report, show that the downgradient extent of the plume is near MW-7, about 800 feet downgradient of the suspected source area, the former Parisian Industrial Services facility. In the Second Quarter 2008 Groundwater Monitoring Results Report, AMEC Geomatrix observes that the field blank obtained immediately prior to obtaining the groundwater sample from MW-7 contained constituents at concentrations similar to past results from MW-7, and the sample from MW-7 did not contain any detectable constituents. AMEC Geomatrix suspects that the samples had been mislabeled in the field. Please indicate the uncertainty about the origin of the entry for MW-7 in future tables. In all of the monitoring wells except one, the mass of PCE exceeds the mass of TCE. This suggests that PCE is slowly degrading into its daughter products. The exception is MW-6, which contains about 10 ug/L PCE, but about 300 ug/L TCE. This well lies south of the estimated plume centerline and may suggest a separate, much older source of PCE, or a separate source of a TCE-rich compound. This ratio of higher TCE concentrations than PCE was also evident in the 2007 grab groundwater samples in the vicinity of MW-6. In the vertical plane, monitoring well MW-5C is screened at about 100 feet bgs and contains about 100 ug/L PCE. The grab groundwater investigation identified concentrations of TCE at a depth of about 145 feet at this location, but did not identify PCE. At a depth of about 70 feet bgs most, but not all, grab groundwater samples contained PCE or TCE in concentrations ranging from 1 to 5 ug/L. Many of these samples did not contain either PCE or TCE at shallower depths. It is unknown at present time if there are separate source areas that have contributed to the PCE and TCE that UniFirst is seeing at these deeper intervals, or if Parisian Industrial Services is the source. To complete this phase of plume definition, UniFirst needs to determine where sewer lines are, their flow direction and to what extent dry cleaning solvents may have been transported from Parisian Industrial Services via the sewer line. UniFirst also needs to propose a reasonable location for an upgradient monitoring well, and should evaluate groundwater- gUaiiiy south of the Parisian Industrial Services in order to help ascertain if the compounds found in MW-6 are from Parisian or from a separate source. Considering the depth and extent of PCE in groundwater, UniFirst also needs to identify where water supply wells are located within a half mile of the facility. Summary In a short amount of time, UniFirst has made significant progress in defining the lateral extent of dry cleaning solvent in groundwater and identifying soil vapor concentrations beneath the UniFirst building. Regional Water Board staff request that UniFirst follow-up on the results of the delineation and provide a work plan to accomplish the following: • Remove vapors from beneath the UniFirst building or provide a work plan to obtain indoor vapor samples. • Evaluate solvent transport through or along sewer lines.