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KEI -P88-1013 R6 May 22 , 1996 Page 4 River alluvium was deposited by the Calaveras River, Bear Creek and several lesser streams 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 5 3 feet below grade The fill is in turn underlain by alluvium to the maximum depth explored (72 5 feet below grade) Subsurface conditions are depicted on Geologic Cross-Section A-A' (Figure 8) The location of the cross-section is shown on Figure 7 The alluvium underlying the site consists predominantly of an irregularly interbedded sequence of silty clays, clayey silts, and 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 December 1995 , the unsaturated zone is approximately 46 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 silty sand, silt and clay with much lesser amounts of sand In the eight existing monitoring wells, the units immediately above and below the water table consist of fine grained materials 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 initial ground water samples collected from monitoring wells MW16 and MW17 on December 19 , 1995, and subsequent samples collected during the March 11, 1996, monitoring and sampling event, the extent of petroleum hydrocarbons in ground water appears to be well defined, except for southeast of the site source area, in the vicinity of well MW16 , as shown on the attached Figure 2 Prior to recommending the installation of any addiL.Luiial muiiicuij ziy wells, KEI zecommeridS C hac, weir KW16 and MW17 be added to the monitoring and sampling program in order to verify the initial sampling results In addition, KEI understands that four Hydropunch borings and a monitoring well have recently been installed at the Montgomery Ward site Recommendations for additional work will be made based on the results of the ground water samples collected from the Unocal wells, as well as the 16 recent investigations conducted at the Montgomery Ward site