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Mr. Soon Kim Page 3 August 11, 1995 102429.AS.T8 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 mg1L, were encountered in the groundwater. The results of this investigation and a feasibility study are presented in Del Monte's Remedial Investigation/Feasibility Study(RDFS)(CH2M HILL, 1992). At the direction of PHS/EHD, Del Monte is conducting quarterly groundwater monitoring (since 1991) and operating an active remediation system at the Disco site (since February 1995). The remediation system consists of air sparging and soil vapor extraction(AS/SVE). 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 submitted a December 29, 1994, work plan for completing exploratory groundwater sampling,. well installation,pump testing, and preparation of an 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 Investigation of Underground Tank Sites, Appendix A - Reports (Central Valley Regional Water Quality Control Board, 1991). Quarterly Groundwater Monitoring Results Quarterly groundwater monitoring consisted of taking water level measurements and collecting grab samples for gasoline constituent analysis.