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Mr. Soon Kim � Page 3 December 19, 1995 In 1991, at the direction of the.PHS/EHD, Del Monte began an investigation of the soil and groundwater in the vicinity of the Disco site. Del Monte retained CH2M HILL to conduct the investigation. The investigation consisted of a soil-gas survey to assess the extent of volatile- fuel constituents in the shallow soil, seven soil borings to assess fuel constituents in the soil, and the installation of eight monitoring wells to evaluate fuel constituents in the shallow and deep groundwater. The results of the investigation revealed the presence of gasoline constituents in the soil and groundwater. Most of the soil contamination was found below the former tank pit near the groundwater table, between 55 and 75 feet below ground surface (bgs). Significant concentrations of gasoline constituents, including benzene up to 32 mg/L, were encountered in the groundwater. The results of this investigation and a feasibility study are presented in Del Monte's Remedial InvestigationlFeasibility Study(RI/FS)(CH2M HILL, 1992). PHS/EHD further directed Del Monte to define the extent of contamination,install an up- gradient monitoring well and a down-gradient monitoring well pair(one shallow and one deep), conduct aquifer pump tests, and prepare a Corrective Action Plan that addresses both soil and groundwater contamination. In response to PHS/EHD's directive,Del Monte fsubmitted a December 29, 1994, work plan for completing exploratory groundwater sampling, well installation,pump testing, and preparation of a Final Remediation Plan. In April 1995, Del Monte submitted a Problem Assessment Report and Final Remediation Plan (PAR/FRP) to describe the supplemental investigation. The PAR/FRP followed the guidelines of the Tri-Regional Board Staff Recommendations for Preliminary Evaluation and r Investigation of Underground Tank Sites, Appendix A - Reports(Central Valley Regional Water Quality Control Board, 1991). At the direction of PHS/EHD, Del Monte is conducting quarterly groundwater monitoring (since 1991), operating an active remediation system at the Disco site (since February 1995), and conducting a one year ITB demonstration. The remediation system consists of air sparging and soil vapor extraction (AS/SVE). A work plan was submitted to PHS/EHD for the expansion of the soil vapor extraction system (SVE) with the addition of two SVE wells in the source area, and these wells were installed on December 11 and 15, 1995. I Quarterly Groundwater Monitoring Results Quarterly groundwater monitoring was conducted on October 18, 1995 and consisted of taking water level measurements and collecting grab samples for gasoline constituent M analysis. �. Groundwater Gradient Water levels were measured at the site on October 18, 1995, by Del-Tech of Oakdale, California, while the AS/SVE system was not in operation. Shallow groundwater surface i.