SITE INFORMATION AND CORRESPONDENCE FILE 2

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Rodger Liston Darpetro Inc. 749 E. Charter Way, Stockton, California Page 2 o15 summary description of contaminant sources , masses or distribution in soil included in this or any other portion of the SCM . The SCM included two cross sections , but had no reference map showing the lines of cross section or boring locations. The SCM section titled 'Groundwater Concepts' refers to hydraulic conductivity determinations obtained by slug tests on monitoring wells MW-4 , MW-5 and MW-6 , which yielded an average conductivity of 2. 94 feet/day as determined by Bouwer-Rice method . This may be an overestimate of the hydraulic conductivity as the test was conducted by adding water to the well when the water table occurred within the screen interval (Driscoll , 1986) . If this is so , then the average seepage velocity estimate of 0 .07203 feet/day would also be an overestimate . The SCM notes that a water sample could not be collected at 45 feet below surface grade (bsg) in HP-2 , but was later collected at 55 feet bsg at the same location , and inferred that the lithology at 45 feet bsg could not transmit water, forcing the ground water to migrate around and under the tight soil . The SCM also noted that dissolved methyl tert-butyl ether (MTBE ) concentrations increased from undetectable concentrations at 39 feet bsg to 2 . 1 micrograms per liter ( µg/I) at 50 feet bsg and to 16 . 5 µg/I at 60 feet bsg in boring 13-3 . CGG interprets these data as indicating northeastward flow of impacted ground water at 55 feet bsg and implied that the known UST releases to the west were potentially the sources of the contaminants . Concerning the interpretation of the HP-2 and B-3 data , EHD notes that several factors can influence the success of obtaining grab groundwater samples and that a number of factors can also influence contaminant distribution , i . e . , soil composition , vadose vs. saturated zone , proximity of source, etc. While an adequate site conceptual model may demonstrate CGG's interpretation to be correct, EHD finds the current SCM to be less than compelling . As discussed during meetings with you and your consultant on 19 June 2002 and on 07 May 2003 , to demonstrate that a plume is impacting your site from another site , a site conceptual model should be prepared that incorporates lithological and analytical data from your site and the adjacent or nearby sites, especially those suspected of being a source of contamination impacting the site . At the 07 May 2003 meeting , you and your consultant agreed to review EHD files for the data from the adjacent or nearby sites . The SCM as submitted contains no data from adjacent or nearby sites . As submitted , the SCM is not adequate to demonstrate migration of a plume onto your site, plume stability or contraction , delineation of the adsorbed and dissolved contaminant masses or vertical extent of impacted ground water. The components and purposes of an SCM were discussed with you and CGG at both meetings . Simply stated , the purposes for such a model are to demonstrate where the contaminants came from , where they