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interesting to note that the petroleum-hydrocarbon concentrations <br /> detected in both of these CPT borings were approximately five times <br /> higher at a depth of 70-feet bgs than at 40-feet bgs The only <br /> hydrocarbons and/or VOCs detected in the groundwater samples <br /> collected from 117-feet bgs was 69 ppb TPH-G and 4 6 ppb 1 ,2- <br /> dichloropropane The only concentration detected in any of these <br /> samples which exceeded a California Department of Toxic Substances <br /> Control (DTSC) maximum contaminant level (MCL) for drinking water was <br /> 48 ppb benzene detected in the groundwater sample collected from 70- <br /> feet bgs in boring CPT-13 All of the other concentrations detected were <br /> below DTSC MCLS for drinking water <br /> 6 . 0 DRILLING SOIL BORINGS FOR THE INSTALLATION OF <br /> GROUNDWATER MONITORING WELLS AND COLLECTING <br /> SAMPLES <br /> Between May 3 and May 10, 1999, Gregg Drilling of Martinez, California <br /> drilled soil borings MW-1 through MW-10 at the site using a Mobile B-61 <br /> drill rig equipped with 8-inch diameter hollow-stem augers Groundwater <br /> monitoring wells MW-1 through MW-10 were subsequently constructed in <br /> these borings This drilling was directed by ASE senior geologist Robert E <br /> Kitay, R G <br /> During the drilling of soil borings MW-1 through MW-6, undisturbed soil <br /> samples were collected at vertical intervals of 2 5-feet as drilling <br /> progressed for lithologic and hydrogeologic description and for possible <br /> chemical analyses The samples were collected by driving a split-barrel <br /> drive sampler lined with 2-inch diameter brass tubes ahead of the auger <br /> tip with successive blows from a 140-1b hammer dropped 30-inches One <br /> tube from each sampling interval was immediately trimmed, sealed with <br /> Teflon tape, plastic end caps and duct tape, labeled, sealed in a plastic bag <br /> and stored on ice for transport to Chromalab under chain of custody Soil <br /> from the remaining tubes was described by the site geologist using the <br /> Unified Soil Classification System <br /> Since borings MW-7 through MW-10 were drilled near previous CPT <br /> borings for the installation of groundwater monitoring wells, and since <br /> the sandy sediments present beneath the site presented the possibility of <br /> heaving (flowing) sands during drilling, the bottom of the auger was <br /> plugged with a wooden block and no soil sampling was conducted in these <br /> borings In these borings, the drilling was halted at the desired depth of <br /> Sthe bottom of the well to be constructed, and the wooden plug at the <br /> Franks One Stop Report - June 1999 <br /> -6- <br />