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f t 1 SITE BACKGROUND The site contained three underground storage tanks (USTs) associated with past uses of the site. On July 22, 1998 Henderson Construction of Stockton, California removed all three USTs from the site, each from a separate excavation. A fuel dispenser island was also removed. Tank 6 (TK6)reportedly contained fuel oil for a generator room. Tank 10 (TK10) was reportedly a 10,000-gallon capacity UST formerly containing diesel fuel. Tank 11 (TK11) was reportedly a 1,000-gallon capacity UST formerly containing gasoline. TK10 and TK11 were located adjacent to the north and south end, respectively, of the former fuel dispenser island. TK6 was located approximately 100 feet southeast of TK10, TK 11,, and the fuel dispenser island. On July 23, 1998, a Condor representative was on-site to collect soil samples from the excavations under the direction of Ms. Letitia Briggs of the San Joaquin County Environmental Health Department (SJCEHD). The soil samples were analyzed by APCL of Chico, California. Henderson Construction prepared a brief letter report, dated August 31, 1998, describing the UST removal activities, soil sampling activities, and laboratory analytical results of the soil samples. Field observations and the laboratory analytical results of the soil, samples indicated that further subsurface investigation of the TK6 and TKI1 excavations was not necessary. Field observations and the laboratory analytical results of the soil samples collected from beneath the former location of TK10, however, indicated the presence of diesel range petroleum hydrocarbons. In a letter dated April 28, 2000, the SJCEHD requested the submittal of a work plan to investigate the lateral and vertical extent of contamination at the site. At the request of California State University at Stanislaus (CSUS), Condor subsequently prepared and submitted the Work Plan for Soil and Groundwater Sampling by Direct Push (Geoprobe), dated June 21, 2000. In a letter dated July 7, 2000, Ms. Carol Oz of the SJCEHD approved the work plan (with modifications) and requested that the work be conducted within 90 days and that a report of findings be submitted within 60 days of work completion. l On December 28 and 29, 2000, Condor conducted a limited soil and groundwater investigation utilizing ! Geoprobe® direct push technology at the site. Condor prepared the Preliminary Investigation and Evaluation Report (PIER), dated February 7, 2001, describing the results of the work. Laboratory analytical results of the soil and groundwater 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 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 Hydropunch borings to collect discrete groundwater samples at r depths to be determined by the results of the CPT borings. The purpose of borings was to continue with evaluation of the vertical and horizontal distribution of petroleum hydrocarbon impacted soil and groundwater at the site. Condor also recommended the installation of three groundwater monitor 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 (SRS) within a radius of 2,000 feet of the site to investigate the potentialfor receptors that may be impacted by # petroleum hydrocarbons in the groundwater. In a letter dated April 4, 2001, to Mr. Cliff Bailey of CSUS, Ms. Dot Lofstrom of the SJCEHD concurred with the recommendations contained in the PIER. At the request of Mr. David Rosso for the Trustees of the California State University, Condor prepared the Work Plan - Additional Soil and Groundwater i Investigation, dated October 5, 2001. The proposed work included the installation of CPT borings;'direct