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KEI--P8 8-1013 .R4 October 27 , 1994 Page 9 The subject site is located adjacent to the Sacramento-San Joaquin delta in the Central Valley geomorphic province. The Central Valley is a large, northwestward-trending, asymmetric structural trough that has been filled with as much as six vertical miles of sediment in the San Joaquin Valley. Based on review of regional geologic maps (U. S. Geological Survey Miscellaneous Field Studies Map MF-1401 "Geologic Maps of the Sacramento-San Joaquin Delta, California" by Brian F. Atwater, 1982) , the subject site is underlain by Holocene and/or upper Pleistocene alluvium identified as Alluvium of Calaveras River and Vicinity (Qcr) . The Calaveras River alluvium was deposited by the Calaveras River, Bear Creek and several lesser streams , and has not been described in detail . Based on the results of our subsurface studies, the site and vicinity are underlain by fill materials to a depth of approxi.-- mately 1 to 2 . 5 feet below grade. The fill is in turn underlain by alluvium to the maximum depth explored (72 5 feet below grade) The alluvium underlying the site consists predominantly of an irregularly interbedded sequence of silty clays and clayey silts Poorly graded to moderately graded sand or interbedded sandy silt and silty sand units were also encountered in the borings for the monitoring wells drilled at the site. As of September 1994 , the unsaturated zone is approximately 57 feet thick and consists of interbedded units of silt, silty clay, and lesser amounts of sand. The first water bearing unit beneath the site (first aquifer) consists largely of silt and clay with much lesser amounts of sand. In the six existing monitoring wells, the units immediately above and below the water table consist of silt, except in wells MW10 and MW13 , where clay or silty clay are found immediately above and below the water table. The particle size analysis (sieve only) previously conducted for the soil sample collected from the saturated zone in the boring for monitoring well MW13 at a depth of 65 feet below grade indicates that the sample is composed of 93% fine to medium-grained sand The sample is classified as sand. DISCUSSION AND RECOMMENDATIONS Based on the analytical results of the ground water samples collected and evaluated to date, the extent of the ground water contamination has not been defined, as shown on the attached Figure 2 . Therefore, it appears that an additional monitoring well (s) will be necessary in order to define the extent of the ground water contamination. However, KEI understands that four additional monitoring wells have been proposed at the ad3acent Montgomery 6