ARCHIVED REPORTS_XR0002766 - Laserfiche WebLink

Home Browse Search

3 0 RESULTS OF THE INVESTIGATION r31 Geology and Hydrogeology ' In general, soils observed to the total drilling depth of approximately 160 feet, consisted of massive intervals of clay and silt mixtures, interrupted by relatively thin intervals of sandy soils 1 Saturated sandy soil intervals were primarily observed below the water table at depths of between 70 and 80 feet, 110 and 125 feet, and 140 and 160 feet bgs The interval between 60 and 70 feet bgs includes a sand lense less than two-feet thick beneath the former UST at CPT-1, to the west at CPT-4, and to the south at CPT-5 As such, this sand ' interval appears to be relatively discontinuous and limited in thickness and aerial extent The sand interval between 110 and 125 feet bgs was observed in all six CPT borings at a ' thickness of up to 10 feet The sands observed within this interval were the thickest, most laterally continuous, and present over the greatest aerial extent Sands were also observed between 140 and 160 feet bgs in all six CPT borings, However, these sands appeared interbedded and less massive than the sands in the 110 to 125 foot interval In addition to these three rima rysaturated sand intervals isolated saturated sandy soit units were observed between 45 and 55 feet bgs at CPT-3, and between 130 and 135 feet bgs at CPT- 5 The CPT logs are included in Appendix B ' During the drilling of MW-8A and MW-813, saturated soil was first encountered at a depth of approximately 42 feet bgs Approximately nine days after drilling, the static groundwater was measured at between 39 28 and 39 43 feet bgs The depth-to-groundwater beneath the site ranged from 39 20 feet bgs in MW-4 to 42 88 feet bgs in MW-7 MW-7 is completed above-grade and protected with a monument casing The groundwater elevation beneath the site ranged from ' a high of 22 38 feet below mean sea level (msl) in MW-2 to a low of 22 77 feet below msl in MW- 8B The cumulative groundwater monitoring data are summarized in Table 1 1 Separate groundwater surface maps are included for the shallow-constructed wells (Figure 4) and the deep-constructed wells (Figure 5) Using the shallow-constructed wells, the groundwater gradient is approximately 0 00125 foot/foot in a northeasterly direction Using the deep- constructed wells, the groundwater gradient is approximately 0 00170 foottfoot in a northerly ' direction These groundwater surface configurations are consistent with historical groundwater gradients and flow directions i12 1 1