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• Field Investigation <br />The field investigation included site visits, drilling of exploratory borings and <br />installation of groundwater monitoring wells. A total of 6 borings were drilled to <br />depths of 45 to 105 feet at the locations shown on Sheet 1. The borings drilled on <br />the three lowest benches (fH-210, TH-202, and TH-203) were completed as <br />groundwater observation wells. At these locations a slotted PVC pipe was inserted <br />into the boring to the full depth and backfilled with coarse sand. A 2 to 3 foot thick <br />bentonite seal was placed above the sand. A protective well cover was installed in <br />2 to 3 feet of concrete at the top of the boring. Monitoring well construction details <br />are presented in Appendix A. Thetest holeswere drilled using 4-inch O.D. solid- <br />stem augers powered by struck-mounted drill rig. Six-inch I.D. hollow stem augers <br />were used for boring TH-206 due to caving conditions. The solid augers were <br />• removed at 5 to 10-foot intervals, and samples were obtained with aCalifornia-type <br />(2.5-inch O.D.) drive sampler or 3.0-inch diameter Shelby tubes. Bulk samples of the <br />refuse were obtained off the augers and a bulk sample of typical overburden soils <br />was obtained from near the RDA perimeter. The location of the exploratory borings <br />are shown on Fig. 1. Graphic logs of the borings are presented in Appendix A. <br />Groundwater measurements were made in the borings immediately after <br />drilling and 2 to 3 days after drilling. Water measurements were subsequently <br />performed in borings TH-201, TH-202, and TH-203 about 78 days after drilling. <br />Laboratory Testing <br />Samples obtained during the field investigation were returned to the <br />CTL/Thompson, Inc. laboratory for testing which included: <br />• <br />4 <br />