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Work Plan-Soil and Groundwater Remediation + CSUS Multi-Campus Regional Center,Stockton,CA March 3,2003 { Page 3 of 3 1, The January ll, 2002 report recommended quarterly groundwater monitoring, additional lateral and vertical groundwater characterization, and soil over-excavation. The soil over-excavation was a suggested remedial alternative that was most likely to result in rapid mitigation of site contamination. h1 a letter dated April 26, 2002 to Mr. Bailey of CSUS; Ms. Setliff of the SJCEHD agreed with the monitoring and additional groundwater investigation portion of the recommendations, but requested the evaluation of the feasibility of at least two remedial options for the site. Il Condor prepared a Problem Assessment Work Plan (PAWP) for the site dated January 23, 2003, to describe additional groundwater investigation at the site. The PAWP was prepared at the request of Mr. David Rosso for the Trustees of the California State University in response to a letter dated April 26, t 2002 from Ms. Setliff of the SJCEHD. The purpose of the work is to further investigate the lateral and Vertical extent of petroleum hydrocarbon contamination in groundwater at the site through the proposed F. installation of direct push borings to further evaluate the site hydrogeology; collection of discrete interval �. groundwater samples, and installation of at least one shallow monitor well and one deep monitor well to verify the results of the direct push sampling over time. As requested by the SJCEHD, the PAWP also included a remedial feasibility evaluation that compares and discusses remedial techniques for site remediation. Over-excavation and in-situ groundwater remediation has 'been selected to minimize total 'remediation time. Condor has conducted four quarterly monitoring events at the site (December 2001; June, September, and December, 2002); field activities included measurement of water levels and collection of water samples from the three monitor wells, MW-1, MW-2, and MW 3. The quarterly monitoring data indicate that -� !groundwater conditions at the site have remained relatively static. Monitor well MW-1 is located up gradient of the contaminant plume, and, to date, no petroleum hydrocarbon constituents have been detected in the groundwater samples collected from MW-1. Toluene and 1,2-dichloroethane (1,2-DCA) have consistently been detected in the groundwater samples collected from monitor well MW-2; f ' Benzene, ethylbenzene, total xylenes, total petroleum hydrocarbons quantified as gasoline (TPH-G), and '1,2-DCA were also detected in the groundwater samples collected from monitor well MW-2 during the December 2002 monitoring event. A slight petroleum odor has consistently been noted in the field l `inspection samples collected from monitor well MW-3. BTEX, TPH-G, methyl tertiary-butyl. ether I (MTBE), and 1,2-DCA have consistently been detected in the groundwater samples collected•from monitor well MW-3. In addition, tertiary-butanol (TBA) was detected in the groundwater sample collected from MW-3 during the December 2001 monitoring event. The groundwater gradient direction has fluctuated from slightly north of cast to southeast. # 3.0 SITE GEOLOGY Cross sections (Figure 4, Appendix A) through the hydrocarbon impacted soil at the site and are shown in Figures 5, 6, and 7, Appendix A. Soils underlying the site consist predominantly of interbedded clays and silts with interspersed thin beds of sand. Silty and sandy horizons form discontinuous, undulatory 4 interbeds and lenticular features. The clay stratum underlying the site varies in composition from dominantly stiff..to very stiff, fine- grained clay to silty/sandy clay. The silty horizons range in composition from clayey silt to sandy silt; a relatively continuous silty horizon with clay interbeds is present immediately below the former excavation area (Figures 5, 6, and 7, Appendix A) from approximately 14-32 feet below ground surface F '(bgs). This silty horizon appears to pinch out rapidly to the north, east and south of the former excavation G area. ' � 1 4 La CONDOR l f J