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3.0 FIELD WORK ' 3.1 DRILLING AND SOIL SAMPLING Between February 23 and 26, 1993, three borings (B-11, MW-1 and MW-2) were ' drilled and sampled on the site as approximately shown on Figure 2. The borings were drilled by Layne-Western Company of Woodland, California (State License C57# 510011), under supervision of EAI geologists. Boring B-11 was drilled to a depth of 50 feet bgs at the center of the concrete slab which formerly contained the USTs. Bonngs MW-1 and MW-2 were drilled to a depth of 70 feet bgs adjacent to the concrete slab and vicinity of the former fuel islands, respectively (see Figure 2) The borings were drilled using 12-inch ' outside diameter continuous flight hollow stem augers. Mike Infurna of the County was on-site dunn& most of the drilling and sampling activities All borings were logged in accordance with the Unified Soil Classification System (see Appendix A). ' Soil samples were obtained from each boring beginning at approximately 5 feet bgs and at approximatelyy 5-foot intervals thereafter until termination. The samples were collected using six 2.5-inch diameter by 3-inch long brass tubes mounted within a 2 5-inch inside diameter split-spoon drive sampler employed in advance of the augers After sample ' recovery, the ends of the lowermost 3-inch long tube were covered with aluminum foil and plastic caps taped over the ends Prior to use, all tubes were washed in a solution of Alconox detergent and tap water, rinsed with tap water and then with distilled water. The f samples were labeled with the sample point identification, EAI project number, depth interval, time and date, individually sealed in "Ziploc" plastic bags, and immediately placed into an ice chest chilled using crushed ice The samples were kept chilled until delivered to the laboratory for analxcal testing All samples were logged on chain of custody record forms (see Appendix Br An HNU Model DL-101 Photoioruzer/Datalogger calibrated against an isobutylene gas standard was used on soil contained in the second tube from the bottom of the shoe, at each sampling interval within the borings to determine if volatile hydrocarbon vapors were emanating directly from the soil Each sample was placed in an airtight "Ziploc" plastic bag. The samples were allowed to sit in the sun, and then the head space in the bags was analyzed using the HNU Photoionizer The results of this testing were recorded on the boring logs (see Appendix A) 3 2 MONITORING WELL CONSTRUCTION Borings MW-1 and MW-2 were converted to ground water monitoring wells MW-1 and MW-2, respectively (see Figure 2) Appendix C contains the County permits issued for construction of the wells All wells were constructed of 4-inch inside diameter flush threaded Schedule 40 polyvinyl chloride (PVC) well casing The wells were designed with I a slotted section (0 02-inch x 2-inch slots) which extended from approximately 48 feet bgs to terrmnation depth of each well The annular space between the borehole wall and well casing was backfilled with grade #3 Monterey sand to about 5 feet above the slotted section A 2-foot thick layer of hydrated quarter-inch diameter bentonite pellets was placed directly on top of the sand pack as a sanitary seal, and the remaining annular space was backfilled with cement and bentonite grout to the surface Flush mounted lockable traffic grates were placed on all the wells. Further, the grates were designed to prevent sheet flow from-entering-the-wells—Appendix-D-contains-the-specific well-construction- details for each well Mike Infurna of the County was present during the grouting of the wells. I Project No 1232 4 ENVIRONMENTAL AUDIT,INC