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i !y Additional Groundwater Investigation and Remediation Feasibility ty Ev aluatron Work Plan Stockton Center Site Authority-University Park j January 25,2005 Page 2 samples and field observations indicated that petroleum.hydrocarbons were present in site soil and . groundwater down to the approximate total depth of the investigation (36 feet below grade). Based on the results of the Geoprobe® investigation, Condor recommended the installation of three Cone Penetrometer (CPT) borings to investigate the site geology, three direct push borings to collect soil samples, and three i hydropunch borings to collect discrete groundwater samples at depths to be determined by the results of the CPT borings. Condor also recommended the installation of three groundwater monitoring wells to establish the groundwater gradient and to monitor the 'concentrations of petroleum hydrocarbons'in site groundwater. In addition, Condor recommended the completion of a sensitive receptor survey within.a radius of 2,000 feet of the site to investigate the potential for receptors that may be impacted by petroleum hydrocarbons in the groundwater. 'Ms.. Dot Lofstrom of the SJCEHD concurred with the recommendations. ' The approved additional subsurface investigation was conducted in November and December 2001. Results of the work indicated that soil contamination at the site was fully investigated. However, groundwater contamination was present down to the furthest extents of the investigation (approximately Ll 81 feet below the ground surface) and at the lateral bounds of the investigated area, particularly;to the. east. Based on the results of the investigation, Condor recommended quarterly groundwater monitoring, additional lateral and vertical groundwater.characterization, and soil over-cxcavation as an aggressive remedial alternative that was most likely to-result in rapid mitigation of site contamination, as requested by the property owner. Ms. Rebecca 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. ,—, Condor prepared a Problem Assessment Work Plan (PAWP) for the site dated January 23, 2003, and a Work Plan for Soil and Groundwater Remediation dated March 3, 2003 to propose additional groundwater investigation at the site. As requested by the SJCEHD, the PAWP also included a remedial feasibility evaluation that compared and discussed remedial techniques for site remediation. In a letter dated March 13, 2003 to Mr. Rosso, Ms. Margaret Lagorio and Mr.Nuel Henderson of the SJCEHD approved the proposed CPT groundwater investigation described in the PA" and concurred with Condor's recommendation that additional groundwater monitoring wells were needed to characterize and monitor the site. The SJCEHD also approved the proposed soil over-excavation as an interim remedial measure but did not approve the proposed ozone sparging pending the results of additional groundwater characterization. i. Condor has conducted seven quarterly monitoring events at the site (December 2001; June 2002 through March 2003; August and November 2004); field activities included measurement of water levels and collection of water samples from the three site monitoring wells, MW-1, MW-2, and MW-3. A report is currently being prepared, under separate cover, for the latest monitoring event conducted in November 2004. Monitoring well MW-1 is located up gradient of the contaminant plume and, to date, no gasoline constituents have been detected in the groundwater samples collected from MW-1. Samples.;from monitoring well MW-2, located southwest of the former UST location, have generally contained low concentrations of petroleum hydrocarbons constituents. Samples from monitoring well MW-3, located southeast and generally down gradient from the source area, have contained low to moderate concentrations of several petroleum hydrocarbon constituents. The quarterly monitoring data generally indicate that contaminant concentrations in shallow groundwater at the site have remained relatively static. The groundwater gradient direction, however, has fluctuated from east-northeast to just east of south and depth to groundwater has steadily declined from approximately 37.5 feet below ground surface (bgs)to approximately 43 feet bgs. lk�k i� CONDOR