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AUG 20 197 02:55PM CLEPRWATER GROUP P.4/7 <br /> CUE----.RWATER <br /> c POU r, i N C. <br /> FHraa.� ru.f S•.o;rrr <br /> that this additional well would riot provide sufficient information to justify the cost(rneasurcd <br /> primarily in the passage of additional time, as the expense of the well is to be borne by 7-11) <br /> associated with its instalLation. This finding is based oa the following facts: <br /> The well to be installed is slated for an area of the site that has been shown by previous <br /> sampling to be virtually free of contamination. Given site hydrogeology and the sheer fact that <br /> the mass of contaminants dissolved in site groundwater can be shown to be fairly insignificant, <br /> it is not likely that significant contaminant migration has ooewred in the period following the <br /> collection. <br /> Is Even if the well were to be installed, and samples collected confirmed the presence of low <br /> concentrations of contamination, subsequent well installations and sampling would be <br /> complicated by the presence of the confirmed problem at the Southland site. The contemplated <br /> additional well would either tell us that concentrations of contaminants are low, or are below <br /> detectable levels, and that further downgradient exploration is mane problematic by the <br /> presence of 7-11 contarrJnatioa. In other words,the data provided by this installation would <br /> really add nothing to the material collected and evaluated to date. <br /> My review of the file indicates that the information required to complete a formal evaluation for file <br /> closure has already been collected. The effect of source (impacted soil) reruoval has been <br /> documented by the measured decrease of contaminant concentrations in monitoring wells <br /> immediately downgradient of the former[SSTs. Actual measured conceritrations have been quite <br /> low all along. If any additional effort is to be invested in this file,it appears as if this effort would <br /> be best spent quantifying the volume of residual contamination present and completing a basic <br /> evaluation of risk posed by these compounds. It seems as if a RSCA Tier 1 evaluation <br /> accompanied by the residual contaminant volumetric calculation would be the wisest use of <br /> available resources. Additionally, the well survey should be restricted to parcels between the <br /> former CST basin on the subject site and the 7-11,as properties downgradient of the 7-11 are at <br /> risk due to the release at this property,not the subject site. A pleasure of prudence may include the <br /> wateruse assessment of one or two additional parcels to the north and the east, but a 2000 foot <br /> radius seems difficult to technically defend. With your concurrence, a modification in the water <br /> use survey will be docurr onwd. <br />