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i ' Project Quarterly Update Report February 21, 1992 Southland, 9110 Thornton Road, Stockton, Cal lorn,a Page 3 Four of the samples collected while drilling MW-20 were analyzed for benzene, toluene, ethyibenzene, xylenes (BTEX), and total petroleum hydrocarbons (TPH)-as-gasoline using ' Environmental Protection Agency (EPA) Method 5030/8020/8015 Three of the soil samples were also analyzed for 1,2-dibromoethane using EPA Method 8240 and total lead using EPA Method 6010 Soil samples collected from the off-site bonngs were not analyzed at the laboratory, as field observations did not indicate the presence of petroleum hydrocarbons rThe wells were constructed with 20 feet of 2-inch-diameter polyvinyl chloride (PVC), 0 02-inch slot well screen, and blank casing The well screen was Installed from 40 to 60 feet below grade for well MW-18 and from 45 to 65 feet below grade for wells MW-19 and MW-20 A sand pack was placed in the annulus to at least 2 feet above the top of the screened Interval The annular space above the sand pack was sealed with between 2 and 3 feet of bentonite, followed by cement grout to the surface The wellheads were secured with locking caps under traffic-rated boxes for protection r2.1.1 Well Development The three wells were developed to improve their efficiency and to provide representative aquifer water samples The wells were developed using a surge and bail technique that alternately pushes and pulls water through the sand pack This process removes fine sod particles smeared on the ' borehole wall during drilling and cleans out the sand pack Following development, the elevation of the top of the PVC well casings for each well was surveyed to mean sea level by a professional, ' licensed surveyor ' 2 1.2 Boring Stratigraphy Generally, the stratigraphy of the sediments at each boring was similar In each boring, a layer of relatively fine-grained sediment consisting of silty clay and clayey silt was encountered between two ' layers of sand containing varying percentages of clay, silt, and gravel The upper sand layer was encountered from surface grade to depths ranging from 34 feet at MW-20 to 40 feet at MW-18 The thickness of the clay/silt layer ranged from approximately 5 feet in boring MW-18 to 19 feet in boring MW-20 The first saturated sediments were encountered within the lower sand layer in boring rMW-18 and MW-19 and at the base of the clay/silt layer at MW-20 Because the water level within the completed monitoring well was within the clay/silt layer, the groundwater in the lower sand layer may exhibit semi-confined to confined conditions The drilling logs are included in Appendix A GROUNDWATER TECHNOLOGY, INC r