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FORMER AMERICAN FOREST PRODUCTS FACILITY Section No. 1.0 Additional 1,2-DCA Investigation and Site Conceptual Model February 2005 And Second Quarter 2004 Quarterly Monitoring Report Page 1-1 L ' .. 1.0 INTRODUCTION r The principal field tasks described by this report are four quarters of groundwater monitoring and installation and sampling of two additional groundwater monitoring wells at the location of the former American forest Products Facility, 2801 West Lane, Stockton, California (Figure 1). Quarterly groundwater monitoring was restarted at the site with a sampling round conducted in June 2003. The F objective of the groundwater monitoring was to assess changes or stability of concentrations of 1,2- J6" dichloroethane (1,2-DCA) in groundwater. The objective of the well installation was to assess the r downgradient extent of 1,2-DCA. The work described herein was completed in accordance with the requirements presented by San Joaquin County in their letter of April 16, 2003, as well as to provide data demonstrating limited extent and stability of groundwater contaminants as a basis for site closure. This report incorporates groundwater monitoring data through the second quarter of 2004. As such it also serves as the quarterly monitoring report for that period. L r 1.1 BACKGROUND Two underground storage tanks at the site were excavated and removed in 1988. Associated piping was excavated and removed from the site in 1991. Soil impacts were partially remediated in 1990. A series of closure request reports (Dames & Moore, 1994; URS, 2001 and 2002a) has demonstrated that hydrocar- bon impacts at the site have been adequately characterized by a series of investigations, beginning in 1985. 1 Data regarding the extent of 1,2-DCA impacts were presented and site closure was most recently requested in July 2002(URS, 2002).The closure request was based on data that indicate the site meets the ! regulatory criteria for designation as a "low risk groundwater site."These criteria are as follows: • The leak has been stopped and sources removed or remediated; • The site has been adequately characterized; • The dissolved plume is not migrating, and chemical concentrations are not increasing with time; r4, • No water wells, deeper aquifers, surface water, or other sensitive receptors are likely to be impacted; and L • The site represents no significant risk to human health or safety. The above-referenced reports have demonstrated that these criteria have been met at the site with respect to the hydrocarbon impacts. The dissolved hydrocarbon plume shows indications of natural degradation, and the plume is not migrating. There are no water wells in the vicinity that could be impacted by the plume, and the site does not pose a significant risk to water resources, or human health and safety. Subsequent to discussions with the Regional Water Quality Control Board (RWQCB) on February 13, 2002, indicating that closure criteria were met with the exception of delineation of the extent of 1,2-DCA 1 impacts in groundwater, URS presented a work plan (URS, 2002a) to provide data to fill that data gap. The work plan, which proposed a direct-push sampling program at eight locations in the vicinity and downgradient of the former waste oil tank (Figure 2), was approved by the San Joaquin County Public ! K-Wprocess12273MAmerican Forest\Well installation Report revOl.doc Illy