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Former Discharge Area Investigation Report Trinkle and Boys Agricultural Flying Service Facility Tracy, California 1. 0 Introduction The following report presents the methodologies, findings and conclusions of a shallow groundwater and soil investigation conducted by ROY F_ WESTON, INC. (WESTON) as specified in the Former Discharge Area Investigation Work Plan dated July 29 , 1989 as amended by WESTON' s letter to John Menke at the California Regional Water Quality Control Board (CRWQCB) dated April 14, 19-79 . The investigation focused on the determination of the extent of pesticide residues in the shallow soils and groundwater at the Trinkle. and Boys Aqricultural Flying Service (Trinkle and Boo ) facility lacated at 31244 South Highway 33 , Tracy, Califor- nia . _ 2 . 0 Site Background Trinkle and Boys owns and operates an aerial agricultural crop spray application .facility as shown on Figure 1. The site has bean used for the loading and rinsing of aerial applicators since the 19501s. Prior to 1986, rinse water runoff was collected in a low drainage area (identified as the "Gravel Rinse Basin" on Figure 1) southwest of the aerial applicator loading area. Since 1986 , the applicator rinsate has been stored in a large plastic tank for reuse at the facility. In 1986, as part of a district wide investigation of aerial applicators, the CRWQCB gathered shallow soil and shallow ground- -.,ater samples from within the rinse basin area. Analysis of these samples rFvealed the presence of various pesticides and herbicides. Ac, a follow-up to their initial investigation, the CRWQCB, on October 27, 1987 , issued Cleanup and Abatement Order No- 87-734 to Trinkle and. Boys. The Cleanup and .Abatement Order specified that follow-up activities be conducted in an effort to evaluate if pesticide residues, identified by the previous _ sampling, extended deeper into the soil. profile, thereby posing a threat to the beneficial usages of groundwater in the area. This report covers Activities #1 and ##2 as specified by the Cleanup and Abatement Order. Approval of the amended Work Pian was provided by the CRWQCB on April 24 , 1989 . 3 . 0 Field Work Field work consisted of the drilling and installation of three shallow groundwater monitoring wells, the sampling and analysis of groundwater at the three wells and soil sampling and analysis at a total of six borehole locations. Placement of the wells was designed to provide site specific groundwater gradient