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July 21, 1993 Working To Restore Nature <br /> Fire Engine Company No 2, Stockton, Califorrva <br /> Task 2 Well Installations <br /> o Drill three 10- or 12-inch (whichever appropriate) diameter soil borings to a <br /> maximum depth of 40 feet below grade and convert a minimum of two of the soil <br /> borings to vapor-extraction wells At the location north of the tanks, a dual- <br /> completion well is proposed to provide remedial capability for both the sand and <br /> clayey silt zones containing residual hydrocarbons The second vapor-extraction well <br /> is proposed for installation west of former tank T3 and will be screened in the clayey <br /> silt zone The third soil boring (proposed for drilling at a location approximately 35 <br /> feet north of the north side of the tank cavity) is designed primarily for assessment <br /> purposes and will be backfilled with cement grout However, if field screening of soil <br /> samples indicates that residual hydrocarbons may exist at that location, a third vapor- <br /> extraction well is proposed for construction. <br /> o Drill one 8-inch-diameter soil boring to 10 feet below groundwater (approximately <br /> 55 feet below grade) and convert the boring to a 2-inch-diameter groundwater <br /> monitoring well. <br /> o Collect relatively undisturbed soil samples at 5-foot intervals or lithological changes <br /> from the ground surface to the total depth of each boring Soil samples will be <br /> identified using visual and manual methods and classified according to the Unified <br /> Soil Classification System. <br /> o Develop, purge, and sample the groundwater monitoring well <br /> o Submit the water sample from the new well and a maximum of two soil samples per <br /> boring to a State-certified laboratory for analyses of total petroleum hydrocarbons <br /> as gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylene isomers <br /> (BTEX) using methods approved by the SJCPHS-EHD <br /> o Collect a composite sample from the drill cuttings for analyses of TPHg, BTEX, <br /> corrosivity, ignitabiltty, reactivity, and total lead using EPA Method 7421 to evaluate <br /> disposal options and apprise the City of Stockton of these options <br /> o Contract a licensed surveyor to survey the new and old wells with respect to mean <br /> sea level. <br />`.� 38009-9W 3 <br />