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.kv, <br /> recommended the installation of three additional monitoring wells <br /> in order to define the extent of groundwater contamination. <br />' 3. 0 PROCEDURES <br /> 3.1 Drilling and sampling <br /> Three monitoring wells, MW-6, MW-7 and MW-8 , were drilled in April <br /> 1993. MW-6 was installed approximately 60 feet northeast of MW-4 . <br /> MW-7 was installed approximately 60 feet east of MW-3 . MW-8 was <br /> installed near the northwestern corner of the site. <br /> The borings were advanced to a depth of 70 feet using a truck- <br /> mounted 8-inch hollow-stem auger rig. The Failing F--10 drill rig <br /> and three-man crew were supplied by Great Sierra Exploration. <br /> tDiscrete soil samples were collected at five-foot intervals using <br /> a 140-1b hammer to advance a split-spoon sampler loaded with three <br /> 2 . 5 by 6-inch brass sleeves. The number of blows required to <br />' advance the sampler 18 inches was recorded on the boring log (see <br /> Appendix A) . To avoid cross contamination, the sampling equipment <br /> was washed in a tri-sodium phosphate (TSP) solution and rinsed <br /> twice with water prior to each sampling run. <br /> After removal from the sampler, soil in the bottom tube was <br /> extruded into a plastic bag and screened for volatile organic <br /> compounds using a photo-ionization detector (PTD: Thermo <br /> Environmental 580A . 10. 0 eV, calibrated to isobutylene) , The <br /> reading was recorded on the boring log, and the soil was described <br /> in accordance with the Unified Soil Classification System (Appendix <br /> A) . The samples from 50 and 60 feet in each boring were covered <br /> with aluminum sheets, capped, sealed with tape, and stored on ice <br /> pending transportation to a state-certified laboratory (WEST <br /> Laboratories in Davis) . <br /> 3.2 Well Completion <br /> The borings were completed as groundwater monitoring wells by the <br /> installation of 0.020 screen PVC liner and #3 Monterey sand. All <br /> wells were screened from 55 to 70 feet. The filter pack (#3 sand) <br /> was placed from 53 to 70 feet. Bentonite pellets were used from 51 <br /> to 53 feet and the wells were backfilled to the surface with <br /> Portland Cement. <br /> 3.3 Well surveying <br />■ Well _cut <br /> i <br /> 2 <br />