WORK PLANS - Laserfiche WebLink

Home Browse Search

3.2 Fate and Transport Analysis �r 3.2.1 Geology �. The U.S.D.A. Soil Conservation Service maps the on-site soils as Stockton Clay, which is a fine-textured, dark gray to black clay, deposited by quiescent or slow moving water. The parent material was of mixed origin, but primarily igneous rock. The U.S. Geological Service ~ maps the deeper site geology as "basin deposits", dominated by fine-textured earth materials, and intercalating layers of coarser textured materials, capable of releasing groundwater. Based on site investigation results, the 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. As shown on the stratigraphic cross-section (Figure �.. 12), sandy soil intervals appear to become more massive and laterally continuous with depth. 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.ail six CPT borings; However, these sands appeared interbedded and less massive than the sands in the 110 to 125 foot interval. All of the soil v boring, monitoring well and CPT logs for the project are included in Appendix C. 3.2.2 Hydrogeolo-gy �. Between August 1990 and May 1992, during the installation of MW-1, MW-2 and MW-3, saturated soil was first observed at a depth of between 68 and 70 feet bgs, and the static depth to groundwater ranged from 65 to 67 feet bgs. In May 1994, during the installation of MW-4 and MW-5, saturated soil and static groundwater were first observed at a depth of approximately 60 feet bgs. This suggests that groundwater beneath the site was present under water table conditions, and that the groundwater elevation was on the rise. By January 1996, the continued rise in the groundwater table resulted in the static groundwater elevation ' above the tops of the screened intervals in all five original groundwater monitoring wells. To re-establish a groundwater table monitoring and sampling capability at the site, Ramage Environmental supervised the installation of MW-6 and MW-7 in April 1998, and began .. monitoring and sampling these Wells and the two deep soil vapor extraction wells (VW-1 D and VW-2D). Saturated soil and groundwater were first encountered during the installation of MW-6 and MW-7 at a depth of approximately 43 to 44 feet bgs. Between May 1998 and December 2005, the static depth to groundwater beneath the site has stabilized from between approximately 35 to 50 feet bgs. Between May 1992 and December 2005, the groundwater table elevation rose approximately 23 feet. 14