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1 .0 INTRODUCTION <br /> This document provides a preliminary hydrogcolo�.zic site conceptual model (SCM) and a work <br /> flan for additional groundwater investigations at the former American Forest Products Company <br /> LP (AFP('-LP)facility (Site) in Stockton_ California (Figures 1 and 2). The SCM has been <br /> prepared from existing data in order to guide additional investigation of the lateral and vertical <br /> extent of 1,2-dichloroethane(1,2-DCA) contamination in goundwater. The principal purpose of <br /> the investigation is to provide data that define the lateral extent of 1,2-DCA in groundwater. and <br /> enable site closure to proceed. <br /> 1.1 Project Background <br /> AFPC;-LP operated a maintenance shop associated with a wood manufacturing plant at the site <br /> between 1921 and 1987 (Dames & Moore, 1994). The maintenance shop was used for storage of <br /> piurnhing and electrical parts required for building maintenance. Pump islands and fuel storage <br /> were associated with the maintenance shop, as it was also used for servicing forklifts and motor <br /> vehicles. Three underground storage tanks (USTs) were associated with the maintenance shop. <br /> • "rank 18820001 was located north of the maintenance shop and at the east end of a wood- <br /> frame building. The building was identified as housing electrical equipment and also <br /> served as a lunchroom(Floyd Brown and Associates, 1983), This 10,000-gallon UST had <br /> been used to store diesel fuel, and was removed in 1993 (Advanced Geo l nvironmental, <br /> 1999). Closure for this UST has been provided by the San Joaquin County Environmental <br /> Health Department (SJCFHI), 2007)_ <br /> • "hank 18820002 was located at the cast end of the maintenance shop. This 10,000-Ballon <br /> UST was used for the storage of diesel fuel. and was removed in 1988. <br /> • Tank 18820005 was a 1,000-gallon UST used for storage of waste oil, and was also <br /> removed in 1988. <br /> Soil impacted with total petroleum hydrocarbon (TPH)contamination was excavated and treated <br /> in an on-site bioremediation cell. In 1991, a pump island and associated piping was excavated and <br /> removed from the site. Soil impacts in the vicinity of tanks l 8820002 and 18820005 were <br /> partially rcmediated in 1990. A series of closure request reports (Dames & Moore, 1994, URS, <br /> 2001 and 2002a) have demonstrated that hydrocarbon impacts at the site have been adequately <br /> characterized by a series of investigations, beginning in 1985. However, due to the presence of <br /> 1.2-DCA in groundwater, which has yet to be fully delineated, closure for these tanks has not <br /> been provided by SJCLHD. <br /> 1.2 Report Organization <br /> This report presents the site investigation history and conceptual model, investigative data gap,,.,- <br /> and <br /> apsand proposed additional wells, scope of work, proposed soil boring locations and well <br /> installations, proposed work and reporting schedules, and references. Relevant well construction <br /> details, water level data and historical site analytical groundwater data are presented in the <br /> provided tables. Site details, groundwater elevations, cross sections,soil and groundwater <br /> contamination and proposed monitoring well locations are presented on the provided figures. <br /> 2 <br />