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1 vl • The analytical results from the groundwater sample were received on March 26, and because hydrocarbons were detected, Upgradient returned to the site on March 27 to drill the dual- completion monitoring well The boring was drilled with I0-inch-diameter augers to a depth of 75 feet and samples were collected at 5-foot intervals beginning at 10 feet Selected samples were screened with the PID and preserved for laboratory analysis The boring log is included in Appendix B During drilling, first groundwater was again encountered at about 40 feet However, at a depth of approximately 55 feet, drilling slowed abruptly Samples collected at and below this depth consisted of dry, hard, siltstone or"hardpan" that exhibited very poor aquifer characteristics Because of the limited potential of this zone to yield a suitable quantity of water to wells, the decision was made to backfill the boring to a depth of 55 feet with cement grout rather than attempt a dual completion The hole was left open above 55 feet, pending a decision on whether to install well casing above this depth A well box was placed into the hole and cemented to prevent surface runoff into the boring 4.2 Results 4.2.1 Stratigraphy Erne-grained sediment (silt and clay) and coarser-grained sediment(fine- to coarse-grained sand) . were encountered in nearly equal proportions in HP-4 In contrast, VM-4 encountered mostly fine-grained sediment Where visible in samples, sand beds have sharp, erosional bases and are scoured into underlying silt beds The sand beds become finer-grained upward and grade into the overlying silt bed These characteristics are typical of channelized stream deposits and overbank deposits Figure 4 is a cross section through the site, and shows several lenticular channel deposits scoured into adjacent and underlying overbank silt beds There is a thin surficial layer of gravelly-sandy- clay fill dirt, below which brown silt and clay predominate to a depth of approximately 20 feet In the northwestern portion of the site, a fine- to coarse-grained channel deposit is present to a depth of approximately 35 feet This channel becomes thinner to the southeast, and its base rises to less than 30 feet This channel is eroded into the second main fine-grained interval, a light-gray silt bed that is more than 10 feet thick in VM-2 but has been partly eroded by channels in other borings These channel deposits are generally fine-grained and 5 feet thick or less A thick bed of light-brown sandy silt is present from approximately 50 feet to 65 feet, where a dark gray, fine-grained sand bed was encountered in HP-4 As shown in Figure 4, the extent of this sand bed is unknown, because it was not encountered in VM-4 6