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i6 <br /> J. R. Simplot Company <br /> Field Report <br /> Groundwater Investigation Program <br /> From April 24 , 1989 through May 10, 1989, three shallow groundwa- <br /> ter monitor wells were drilled, installed, developed, and sampled <br /> and three exploratory boreholes were drilled and logged at the <br /> J.R. Simplot Company, Lathrop, California facility. The three <br /> wells were surveyed on May 10, 1989 . All boreholes and monitor <br /> wells are located in an area surrounding the UST site as indicat- <br /> ed on Figure 1. <br /> Well Installation <br /> Well drilling commenced on April 24, 1989 and all three wells, <br /> designated MW1, MW2, and MW3 were completed and developed on <br /> April 26, 1989. A Central Mining Equipment 55 (CME-55) drill rig <br /> using 10 inch outer diameter, 6. 25 inch inner diameter hollow <br /> stem augers was used to drill all monitor well boreholes. <br /> Cuttings returned by the auger flights were containerized into <br /> labelled 55 gallon steel drums. These drums were stored at the <br /> site pending analytical results. Construction of each well took <br /> place inside the augers, with the screen and casing first lowered <br /> into place and the construction materials (sand and bentonite) <br /> introduced through the annulus. As the construction materials <br /> filled in the borehole, the augers were gradually withdrawn. A <br /> 5% bentonite-cement grout was then mixed at the surface and <br /> pumped through a tremie to fill the borehole from the bottom to <br /> within two feet of the surface. The grout was allowed to harden <br /> overnight, at which point a locking riser and traffic vault was <br /> cemented in place. Construction materials for all wells were of <br /> the same type, as follows: <br /> screen - Schedule 40 flush threaded PVC, 0.010 inch <br /> slot size; <br /> casing - Schedule 40 flush threaded PVC; <br /> caps - Schedule 40 flush threaded PVC for bottom <br /> caps and locking expansion type water tight <br /> caps covered by slip over PVC top caps; <br /> gravel pack - Monterey # 2/16 sand, washed, kilned and <br /> bagged; <br /> seal - 0. 5 inch bentonite tablets; <br /> grout - potable water, Quick Gel bentonite powder and <br /> Portland Type I-II cement <br /> i <br /> All augers, screens, casing and bottom caps were steam cleaned <br /> prior to use in the wells. All grout was placed under the <br />