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i IL Additional Groundwater Investigation and Remediation Feasibility Evaluation Work Plan StocktonCenter Site Authority-University.Park January 25,2005 Page 4 The site shallow subsurface geologic environment has been.explored to depths of up to 135 feet bgs. !. Boring locations for previous phases of investigation with cross-section orientation lines are shown in Figure 3 (Appendix A). Generalized geologic cross-sections depicting interpreted subsurface lith' logies are shown -in Figures 4 and 5 (Appendix A). Interpretations are based upon visual observations from continuous and discontinuous core samples obtained from Geoprobe�' and hollow-stern auger borings to L depths up to 61 feet bgs. Depths up to 135 feet bgs were explored with CPT borings, measuring the soils response to cone bearing pressure, sleeve friction, and dynamic pore water pressure at approximately two- inch intervals.to provide nearly continuous interpretive stratigraphic logs of subsurface soil conditions based on soil behavior type classification charts. The subsurface geology of the site is highly variable, based on the results of drilling. In general, the subsurface is interpreted to consist of clay-dominated sediments with minor, complexly interbedded silty and sandy lenses/beds to depths of approximately 50 to 55 feet bgs. Below 50 to 55 feet the lithology is interpreted to be transitional, composed of a mixture of clayey, sil :. P silty, and sandy sediments, coarsenning downward, to depths of approximately 80/90 feet bgs. Below the last significant clay-rich horizon at L approximately 80/90 feet bgs, CPT soil behavior-type classification .charts infer the sediments to be composed primarily of silt and sand dominated units. i; Initial site groundwater is encountered at a depth of approximately 40 feet bgs. The groundwater gradient has generally been to the southeast at a magnitude of approximately 0.0010 —0.0024 feet/foot (Figure 6, Appendix A). However, rapid shifts in the gradient direction to the east-northeast have been recorded during December on two occasions and may correlate to dynamic interaction between winter/spring recharge events and complex subsurface conditions. 4.0 OVERVIEW OF FIELD, LABORATORY, AND TESTING METHODOLOGY Groundwater investigation and-monitoring activities, to date, have identified variations in site lithology, i groundwater contamination at discrete subsurface depth intervals, and evaluated shallow groundwater contamination and hydrology through time (three site monitoring wells). This work plan proposes additional monitoring wells to temporally evaluate down-gradient groundwater contamination and hydrology, groundwater contamination and hydrology in the source area at a depth greater than evaluated y by the existing shallow monitoring wells, and groundwater characteristics up-gradient of the source area. During installation of the proposed monitoring well borings, various soil sampling and logging activities will be conducted. A proposed deep monitoring well boring up-gradient of the source area, a proposed deep monitoring well boring located in the source area (specifically in the approximate center of the source area), and a proposed deep monitoring well boring in the down-gradient area will be continuously cored. Continuous coring is anticipated to allow careful visual examination of the lithology, allow discrete, selective soil sample collection for analyses of laboratory chemical and physical properties, and allow collection of bulk soil samples for bench scale testing. These procedures will assist in the evaluation of discrete depth contaminant characterization and hydraulic conductivity (permeability of the soil to groundwater and vapor), thereby potentially identifying key contaminant pathways in the.very complex site hydrogeology (and potential means of remediation). In addition, the proposed soil sample analyses will assist in evaluation of total organic content of the site.soil and bench scale testing (described below) intended to evaluate the potential for using ozone injection and/or bioremediation (oxygen infusion, etc.)at the site. LThe overall intent of the proposed work is to evaluate and monitor the extent of the problem and evaluate subsurface physical characteristics so that an appropriate re mediation method for the site can be selected. L i �� CONDOR I