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1 3 0 GROUNDWATER MONITQRING In this section, well abandonment procedures for the three JHKA wells, and well installation and groundwater monitoring techniques for the four new wells installed by Dames & Moore in 1990, are ' described Water levels, groundwater gradients, and analytical results for all four rounds of groundwater sampling from the four new Dames & Moore wells are also presented in this section 3 1 WELL ABANDONMENT ' On July 23 and 24, 1990, three existing monitoring wells installed by JHKA (MW-1, MW-2, and MW-3, Figure 2 1)were abandoned at the AFP Site The wells were abandoned because the groundwater ' table had dropped below the bottom of each well Well abandonment consisted of removing the Christy box and associated concrete, then drilling out the four-inch-diameter PVC casing with an abandonment tool that fit inside the 10-inch augers The abandonment tool destroyed the PVC casing as the augers ' were advanced down the boring Auger refusal was met at the top of the stainless steel screen at each well In wells MW-1 and MW-3, the stainless steel screen could not be removed from the boring and the wells were abandoned with the screen in place The total depth drilled at MW-1 and MW-3 was 29 feet and 32 feet, respectively At MW-2, the complete 20-foot section of stainless steel screen was removed and the boring drilled to a depth of 50 feet At each well location, the boring was grouted to the surface with a neat cement mixture containing 2% bentonite The grout was pumped through a ` tremmie pipe and the augers were gradually removed from the boring to minimize the potential for caving Grouting procedures were observed by Elanor Ratliff of PHS-EHD ' 3 2 WELL INSTALLATION AND DEVELOPMENT Between July 25 and August 1, 1990, four new monitoring wells were installed at the site in ' locations requested by the RWQCB (Figure 2 1 and 3 1) DMW-1 serves as an upgradient sampling location while DMW-2, DMW-3, and DMW-4 served as downgradient monitoring points ' Drilling, well installation and well development were performed by Spectrum Exploration of Stockton, California, using a truck-mounted CME-55 drill rig A Dames &Moore Geologist was present ' during all operations to classify soils and to provide any required technical assistance ' Each boring was advanced using 10-inch-diameter hallow-stem augers to a total depth of 81 5 feet Relatively undisturbed soil samples were obtained at 5-foot intervals using a California modified sampler fitted with six-inch-long brass rings One brass ring from each sampling interval was capped, properly labeled, and kept for archival purposes Organic vapor monitor (OVM) readings were taken at each sampling interval from one of the brass rings and recorded on the boring log Drill cuttings were gOTI SAC36 046 11