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Subsurface Investigation and Well Installation Report ARCO Facility No 6100 Tracy, California Page 5 vadose zone contrasts in formation conductivity/resistivity Electrical conductivity/resistivity anomalies were also observed using the 16-inch electrode spacing Spontaneous potential and natural gamma data collected during the logging were not used for geologic interpretations Contrasts in spontaneous potentials and natural gamma radiation do not correlate with changes in lithologies observed in the soil core or the conductivity/resistivity logs Well Installation Western Strata Exploration, Inc returned to the site from September 10 to 25, 2001, to conduct drilling activities using an air rotary casing-hammer drill rig Eight 4-inch diameter PVC wells (MW-2 through MW-9) were installed in four clusters (two each adjacent to borings B-33 through B-36) Well locations are shown on Figure 2 The borings were advanced using a six-inch diameter drill bit advanced ahead of 8 5-inch diameter steel casing The shallow well in each cluster was completed to a maximum depth of 65 feet bgs using 10 feet of 0 02-inch diameter well screen, and the deep well in each cluster was completed to a maximum depth of 95 feet bgs using 20 feet of 0 02-inch diameter well screen A filter pack of#3 LonestarTM sand was placed from the bottom of the borehole to 3 or 4 feet above the top of the well screen Three to 4 feet of bentonite was placed on top of the filter pack and hydrated with clean water to provide a sanitary seal for the wells Neat cement was placed in the annular space around the well casing from the top of the bentonite up to surface grade A watertight locking cap was placed over each well head and a traffic rated vault box was placed over each well Well construction details and California Department of Water Resources (DWR) well completion reports for each well are included in Appendix B Well Development and Surve in Western Strata Exploration, Inc developed well MW-2 on October 12, 2001, under the direction of a Delta representative Well MW-2 was developed for 30 minutes using a surge block Wells MW-3 through MW-9 were not developed because groundwater does not appear to be recharging the wells A groundwater sample was collected from well MW-2 on November 6, 2001 Field Data sheets for groundwater monitoring, sampling, and development are presented in Appendix D Morrow Surveying, Inc of West Sacramento (P L S # 5161) surveyed the locations of all wells and the elevations of wells VW-1 through VW-9, VW-11, VW-12, VW-14, VW-17 through VW-20, and MW-1 through MW-9 to the nearest 0 01 feet mean sea level The locations of borings B-33 through B-38 were also surveyed Wells VW-10, VW-13, VW-15, and VW-16 were inaccessible at the time of the survey Well locations and elevations were established using the Global Positioning System (GPS) Latitudes and longitudes for wells MW-1 through MW-9 and VW-1 through VW-20 were also . established using the GPS A copy of the surveyor's report is presented in Appendix E P 1ARCO161001REPORTS16100-well install report doe