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i Fs= WESTERN GED-ENGINEERS SECTION 5.4 f FIELD INVESTIGATIVE METHODS y Western Geo-Engineersinvestigation consisted of: 1. Collecting soil and water samples from the excavations left during tank removal; 2. Drillingthree exploratory boreholes (monitor wells 9 through 3); 3. Convrting these boreholes into ground water monitoring wells; 4. Collecting g►ounr! ester samples; 5. Surveying the wPil heads; 6. Collecting grounu water gradient delta throughout this assessment period. SECTION 5.1 EXPLORATORY DRILLING The subsurface investigation consisted of drilling three exploratory borings at , pre-selected locations to help determine the extent of the soil and ground water contamination and whether the contamination had migrated off site. Each boring was drilled using a truck mounted drilling rig (Hogate Drilling) using a ten inch hollow-stem auger. The drilling rig and auger was steam cleaned prior to its use. All lubricated parts that were to enter or were near the boring were lubricated with olive oil. The sampling equipment was washed between each sampling Interval with surgical p. r I i al eves fresh water rinsed and steam cleaned. Relatively undisturbed soil water, within five feet and at the base t he to of the , samples were collected belowp of the borings using a modified California split-spoon sampler equipped with 2" diameter by 6" long clean brass sleeves. Borings were advanced to the desired depth with the hollow-stem auger, then the drill rod- bottom plug-cutter assembly was withdrawn, and the sampler, attached to the drill rod was lowered through the augers to the bottom of the borehole and then driven 18" into the soil with a 140 pound hammer. Soil samples were field checked for the presence of product odor, vapor, and visible product after each sample interval. A hand held Photovac "Tip" photoionizing detector, which was calibrated with 1 ppm benzene prior to drilling each day, was used. At each interval, the liner containing the soil sample having the highest reading from the "Tip" was immediately preserved and labeled by capping the ends of the liner with plastic caps, wrapping the entire liner (sleeve) with aluminum foil wrapping the foil with duct tape and placeing the appropriate label over thS tape prior to placing the samples into an ice chest, which cool samples to 4 C. These samples were then hand delivered to a State and San Joaquin County approved certified laboratory (Eureka Laboratorles, Sacramento, CA.) with chain of custody documentation. The remaining cored soil samples were labeled and used for HCl reamions and sieve, dilatancy, and plasticity using ASTM D2488-84 field analysis procedures. IPillell logs were prepared by a Western Caen-Engineers field geologist, and then categorizon site edthe usinglthe Unified nl'oils The samples were d Classification System and describing lithoivgy. The exploratory boring logs are presented in Appendix A. page 15