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e r Monitoring Well Installation Report-Tosco(Former BP)Service Station No 11192- September 3.3 Wellhead Survey Following installation, the well casing elevations and the horizontal coordinates of the new wells and the existing on-site wells were surveyed by Virgil Chavez Land Surveying of Vallejo, Califomia, Licensed California Land Surveyor No 6323 Top of casing and well box elevations were measured relative to mean sea level (MSL), and the horizontal locations of the wells were_ measured with the Geographical Positioning System (GPS)- Well casing elevation data are presented in Table 1 A copy of the surveyor's report is included in Appendix D s 4.4 RESULTS 4.1 Subsurface Conditions Detailed descriptions of the subsurface materials encountered during drilling are presented on the boring logs in Appendix B ' Soil types encountered during installation of MW-8, consisted of clay _ from approximately 15 feet bgs to approximately 5 feet bgs, overlying silt to approximately 24 feet bgs, which in turn overlies silt and silty sand to the total depth of the boring (28 feet bgs) In MW- 9, soils consisted of clay from approximately 1 5 feet bgs to approximately 4 5 feet bgs overlying silt to approximately 8 feet bgs A layer of silty sand was observed at approximately 8 to 17 feet bgs overlying a well-graded sand, interbedded with silt, from approximately 17 feet bgs to the total depth of the boring Soil types in MW-10 consisted of clay from 15 to 5 feet bgs, and silty sand, interbedded with silt, from 5 feet bgs to the total depth explored in MW-10 (29 feet bgs) The subsurface conditions observed during the installation of MW-11 consisted of interbedded clay, silty sand, poorly graded sand and well graded sand observed beginning at a depth 4 feet bgs and extending to approximately 36 feet bgs At approximately 36 feet bgs, a relatively continuous of clay was observed to extended to approximately 68 feet bgs From 68 feet bgs to the total depth explored, silty sand inter-bedded with well graded sand was encountered The subsurface ' conditions observed during the installation of MW-11 generally coincide with the results of the CPT conducted on April 26,200 1_adjacent to (within 5 feet) of MW-11 The boring log for MW-11 is presented in Appendix B - Groundwater`was encountered during drilling at depths ranging from 14 to 19 feet bgs Static groundwater was measured after construction of the wells at approximately 13 feet bgs in all the new wells On August 16, 2001, depth to groundwater in the new and existing wells ranged from 13 07 to 15 07 below the tops of well casings The groundwater flow direction was was determined to be to the north with a gradient of 0 001 to 0 002 ft/ft 4.2 Laboratory Analysis Selected soil and all groundwater samples were analyzed by Sequoia Analytical in Walnut Creek, 14024505-2 6