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Soil and Groundwater Investigation Reoort ARCO Facility No 2168 Stockton, California Page 4 Soil samples were collected at five-foot intervals from 0-60 feet bgs in borings/wells MW-1C and MW-8C The soil was continuously sampled from 60 to 120 feet bgs (total depth) at MW-1C and MW-8C The soil at MW-1B and MW-8B was sampled in five to 10 foot intervals with some intervals not sampled, at the discretion of the Delta field representative The wells were drilled using a truck-mounted drilling ng equipped with hollow-stem augers All sampling equipment was cleaned using a LiquinoxTM solution and triple rinsed prior to, and between, each sampling event The samples were collected by driving a modified California-type split-spoon sampler, equipped with four clean 2-inch by 6-inch stainless-steel sleeves, into undisturbed soil using a 140-pound slide hammer falling 30 inches The lowermost, intact sample was retained for analysis The sample ends were covered with Teflon TM sheets and plastic caps and samples were placed in an ice-chilled cooler Each sample was appropriately labeled and identified on a chain-of-custody form Additional sleeves of soil collected at each sampling interval were field screened for volatile organic compounds using a photolonization detector (PID) The soil was also classified using the Unified Soil Classification System Soil classifications, field screening results, blow counts, and other pertinent data are included on the boring logs in Appendix A Monitoring wells MW-1B and MW-8B were constructed using 8 5-inch inside diameter steel conductor casing set from ground surface to 60 feet bgs Monitoring wells MW-1C and MW-8C were constructed using 8 5-inch diameter steel conductor casing set to 85 and 90 feet bgs, respectively The conductor casing was installed by initially advancing the boring with 8-inch diameter hollow stem augers and then enlarging the borehole with 16-inch diameter hollow stem augers The conductor casing was grouted in place using neat cement Following curing of the cement, drilling was completed with 8-inch diameter hollow stem augers inside of the conductor casing to the total depth of the borehole The monitoring wells were installed using two-inch diameter PVC casing with 15 feet of 0 02-inch factory slotted well screen MW-8 was screened from 15 to 30 feet bgs, MW- 1B and MW-8B were screened from 75 to 90 feet bgs, and MW-1C and MW-8C were screened from 105 to 120 feet bgs The existing groundwater monitoring wells are typically screened from 35 to 55 feet bgs A filter pack of#3 sand was placed around the well screen from the bottom of the borehole to 2 to 3 feet above the top of the well screen VolclayTM quick grout, a high yield bentonite slurry, was used as the sanitary seal for the wells VolclayTM was placed using tremie pipe from the top of the filter pack to . 45 feet bgs in wells MW-1B, MW-1C, MW-8B, and MW-8C Well construction details are presented in Table 1 and included on the boring logs in Appendix A Neat cement