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I I72 Discussion p I This report presents the results of a recent CPT investigation, an evaluation of the extent of 1,2-DCA impact in groundwater, and a model of the subject site conditions Soils beneath the site appear to consist of silty and clayey strata, interbedded with predominantly sandy strata, to I the total depth explored These sandy strata appear to be laterally continuous across the site Historically, depth to groundwater in the monitoring wells has ranged from 37 to 81 feet bgs, and flow direction has been variable, but predominantly towards the east, southeast, and northeast I The vertical and lateral extent of dissolved TPHG, benzene, and MTBE appears adequately characterized, and historical analytical data for these compounds show a decreasing trend 1,2-DCA impact is reported in wells MW-13, MW-14, AS-1, and borings CPT-2 through CPT-5, I and CPT-8 The vertical extent of 1,2-DCA impact in the vicinity of wells MW-13, MW-14, AS-1, and borings CPT-2 through CPT-5 appears to be adequately characterized, but additional vertical characterization in the vicinity of CPT-8 is warranted The lateral extent of 1,2-DCA impact has been adequately characterized, except to the east of CPT-5 and to the east and southeast of CPT-8 ' 73 Recommendation Stratus recommends installation of four additional CPT borings (Figure 2) in an attempt to complete characterization of the 1,2-DCA impact One boring (CPT-10) should be situated in the vicinity of CPT-8 to provide additional information on the vertical extent of impact below 85 feet bgs in this area To provide additional information on the lateral extent of impact, one I boring (CPT-11) should be installed east of CPT-5, one boring (CPT-12) should be installed east of CPT-8, and one boring (CPT-13) should be installed southeast of CPT-8 CPT should be utilized for these additional borings, as it provides a continuous log of subsurface conditions, can ' be utilized to collect depth-discrete groundwater samples, and has proven effective at this site in the past ' Locations for the proposed additional CPT borings are shown on Figure 2 Upon approval of this report and these recommendations, Stratus will prepare a work plan for the additional assessment activities 1 1 1 K 1Te,chenIStock,011 I031Reportslscm 04-21,06 doe Page 14 STKATU5 1