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wells screened in Sand B. Analytical results of recent groundwater sampling events have also shown that other gasoline oxygenates and degradation products have been non-detectable and are not considered COC's. Furthermore, based on the results of the recent quarterly groundwater sampling events, concentrations of Benzene, Toluene, Ethyl-benzene, and Xylene (BTEX) are also below detectable levels in groundwater. As such,none of the BTEX constituents are considered a COC's. 2.2.1 Estimate of Mass Remaining on Site Based on the concentrations provided in SECOR's Additional Assessment Report, there is a total of approximately 2 pounds of MTBE remaining in the shallow groundwater. This estimate is based on the data provided utilizing an affected depth of approximately 15 feet and a porosity of 30%. An additional mass of approximately 0.5 pounds of MTBE remains in the deeper groundwater(Sand B). This mass estimation is provided for planning purposes only since the extent of impact has not been completely defined in all areas. 3.0 SUMMARY OF SITE ASSESSMENT ACTIVITIES Site assessment at the property began in January 1997 with the installation of seven soil borings. In 1998, the USTs,product piping, and dispenser islands were replaced during Site renovation. Compliance soil sampling was conducted for the former southern and northern UST pits. Fifteen GeoProbe borings were later installed in this area. In February 2000, six on-site groundwater monitoring wells were installed and quarterly monitoring and sampling was initiated. In 2001 and 2002, additional GeoProbe borings and groundwater monitoring wells were installed on and offsite. A dual-phase extraction (DPE)test was conducted in June 2004. In 2004, a cone penetrometer test(CPT) investigation was conducted and eight on and offsite borings were installed to depths of up to 100 feet bgs. One onsite groundwater monitoring well was also installed as part of this investigation and an additional four monitoring wells were installed during a pump test in 2005. On January 5, 2005, Stratus submitted a Work Plan for Additional Site Assessment and Evaluation of Remedial Alternatives to the San Joaquin County Environmental Health Department(SJCEHD). The work plan was submitted in response to a request from the SJCEHD to further investigate the presence of MTBE reported in borings CPT-5 and CPT-8, and to evaluate the feasibility of several remedial options. The work plan proposed the installation of two off-site shallow screened monitoring wells, one onsite shallow screened monitoring well, and one off-site deeper screened monitoring well. The work plan also included baseline analysis of selected soil samples for metals and general minerals as well as possible bench scale testing should ozone injection be implemented at the site. The work plan was approved by the SJCEHD on January 31, 2005. On February 2, 2005, Stratus submitted an Injqrim Remedial Action Plan(IRAP)to the SJCEHD proposing to install a groundwater extraction and treatment system at the site to ERG,0406 Page 2 IRAP