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s Former Beacon Station No. 474 May 15, 2000 Stockton, California Results of Additional Subsurface Investigation y the site and completed as a deeper groundwater monitoring well. Monitoring well MW-12 may be used as an air sparge well. Soil borings SBS and SB9 were located south and east, respectively, of the dispenser island area to evaluate lateral and vertical extent of gasoline constituents in the vadose zone and groundwater, and in soil at depths of the historical low groundwater level at the site. Soil borings B8 and B9 were completed as vapor extraction well VW-7 and air sparge well AS-1, respectively. The wells were drilled and installed by V & W Drilling Inc, of Isleton, California using a hollow-stem auger rig fitted with 8-inch diameter, continuous flight augers. The monitoring well MW-12 boring was drilled with 10-inch diameter augers. Soil cuttings were stockpiled on and covered with plastic sheet. Soil samples were generally collected at 5-foot intervals using an 18-inch long by 2-inch diameter split-spoon sampler. Soil samples were field screened with a Thermo Environmental Instruments Inc. organic vapor meter (OVM) to detect and quantify volatile organic compounds using photo- ionization detector (PID) technology. Soil samples to be screened were placed in a plastic bag and sealed to allow any volatile compounds to equilibrate with the headspace. The OVM probe was inserted into the bags and the PID readings, in parts per million (ppm), were recorded on the monitoring well log. Field screening indicated volatile vapors were present at approximately 20 to 35 feet bsg in the MW-10 boring, at approximately 15 and 40 feet bsg in the MW-11 boring, and at 10 to 40 feet bsg in the MW-12 boring. Sediments encountered in the borings consisted of interbedded sand, silt and clay. The sediments were described using the Unified Soil Classification System (LSCS). The USCS classifications are given on the Boring Log Symbol Key contained in Appendix C. The wells were constructed with schedule 40 polyvinyl chloride (PVC) casing and 0.020-inch slotted screen well screen. Two-inch inside diameter (ID) casing and screen were used for 1474.22rpt 4 HORIZON ENVIRONMENTAL INC.