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1 Januar 2, 1991 San Joaquin County Public,:ealth Services 3 `�/ Y WOW working on the site as part of this investigation will be required to read and sign the plan. SITE CHARACTERIZATION Soil Boring Drilling and Sampling Prior to drilling, Underground Service Alert (USA) - will be notified a minimum of 48 hours in advance of drilling activities. A total of two soil borings will be drilled within this phase of soil characterization (Figure 1). . One soil boring will be drilled on the north side' of the storage tank and the 'other on the south side. Drilling for all borings will be accomplished using a truck mounted CMETM 55 drill rig or equivalent utilizing 8-inch outside diameter hollow-stem augers. The borings will be drilled to a maximum depth of 30 feet below surface grade, or 10 consecutive feet of uncontaminated soil as determined by field screening,- or to the first encountered groundwater. The depth to the regional unconfined aquifer is approximately 65 feet below surface grade beneath the site, and the ground water gradient is anticipated to be to the west. No perched ground water is known to exist beneath the subject site. Soil sampling will be performed while drilling the borings at a five foot interval beginning at 5 . feet below grade to the designed termination 'depth. Soil sampling will be accomplished using a split-spoon sampler (ASTM D 3550 with shoe similar to ASTM D 1586) equipped with three 6-inch by 2.5-inch diameter brass sleeves for soil retention. . The soil samples, will be obtained by driving the sampler with a 140-pound hammer dropping 30 inches in accordance with ASTM D-1586. The lowermost sleeve at each sample interval will be screened fortotal organic vapors with a portable photo-ionization detector (PID) or a Foxboro® OVA 108 flame- ionization meter (FID). Headspace vapor analysis will be performed by first discarding a portion of the soil retained at one end of the sleeve to produce a headspace. The sleeve is then capped and the probe of the,'PID or FID inserted through a hole in the cap and into the head space for analysis. The PID or FID readings will be recorded on the boring logs. ` The uppermost sleeve will be observed for lithology. The middle sample sleeve of the sampler will be immediately sealed with TeflonTm film, capped, labeled, and placed on ice at 40C for transport to a State- certified laboratory. Chain-of-custody procedures will be utilized for all samples 9201-E015.WP EK-6014-1 i I