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8820101-R COT-4 • <br /> approximately 51.5 feet in an attempt to account for sloughing during auger <br /> removal . Unfortunately, significant sloughing occurred, which prevented <br /> installation of the well casing to the full 50-foot depth. The other <br /> borings for Wells MW-1 and MW-2 were both overdrilled to 64 feet with the <br /> casing installed to a depth of 60 feet. Only the MW-2 boring exhibited <br /> signs of free groundwater, which was encountered at a depth of 50.5 feet. <br /> Soil samples were collected using a 2-inch-I .O.-by-16-inch-long modified <br /> California sampler containing four 4-inch long brass tubes. The sampler <br /> was driven ahead of the augers using a 140-pound drop hammer. The average <br /> blow counts required to drive the sampler 12 inches were recorded on the <br /> boring logs provided in Appendix B. After each sample drive, the sampler <br /> was extracted from the boring and the brass tubes removed. The soil <br /> exposed at the ends of each tube was examined for stratigraphy and obvious <br /> presence of contamination. These observations were recorded in the <br /> appended boring logs. In general , the bottom tube was sealed at each end <br /> with aluminum foil , PVC end caps, and electrical tape and placed in cool <br /> storage until delivered to the laboratory. The middle tube was then <br /> Iextruded into a Ziplock bag, sealed and left in the sun for five minutes to <br /> enhance the volatilization of hydrocarbons that may be in the soil . <br /> Subsequently, a headspace reading was taken from the interior of the bag <br /> using a photoionization organic vapor meter. These readings were also <br /> recorded on the appended boring logs. The sampler and tubes were <br /> decontaminated between samples by washing with a low phosphate detergent <br /> followed by a deionized water rinse. <br /> Once completed, the borings were converted to monitoring wells. The wells <br />' were constructed of threaded, 4-inch I.D. Schedule 40 PVC casing with the <br /> screened interval situated over the bottom 30 feet of each boring. <br /> Screening consisted of 0.020-inch horizontal factory slotting. The annulus <br /> around the casing was packed with #3 sand up to a few feet above the top of <br /> the screened casing, followed by 1 foot of hydrated bentonite pellets. The <br /> remaining portion of the annulus was backfilled with cement/bentonite <br /> 5 <br />