ARCHIVED REPORTS_CONCEPTUAL SITE MODEL

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• On December 28, 2001, a flange on a piping manifold, near MW-15A, failed and released less than 10 gallons of red dye diesel. On January 9, 2002, 15 soil samples were collected in and around the spill area. Borings were advanced to approximately 0.5 to 1.5 feet bgs (SECOR, 2002a). • In November 2002, an assessment report and work plan for additional site assessment was submitted which summarized the results of the installation of five offsite monitoring wells (MW-54A, MW-55A, MW-57A, MW-58A, and MW-59A) (SECOR, 2002b). Due to property access complications, MW- 56A was not installed. The objective of the offsite assessment activities was to delineate the lateral extent of petroleum hydrocarbons (including MtBE) in offsite groundwater. MtBE concentrations were detected in the five borings, ranging from 0.6 µg/L (MW-55, MW-57 and MW-59) to 1.0 µg/L (MW- 54). TPHd concentrations were detected in three of the five samples at concentrations ranging from 84 µg/L (MW-55)to 160 µg/L (MW-57). • In August 2002, a construction support activities report was submitted (SECOR, 2002c). This report documented the following activities: 1. Pre- and post-removal soil characterization within the footprint of the ethanol transfer facility excavation. 2. The destruction and proper abandonment of MW-14A and TW-3. 3. The collection of post-remedial soil data in the former dual extraction (DE) area and post- demolition soil data in the card lock area. 4. The segregation, profiling,transportation and disposal of affected soil within the transfer facility excavation. A total of 397 tons of soil was removed from the excavated area and transported to Forward Landfill in Manteca, California. • Between January 21 and 29, 2003, site assessment activities were performed to delineate the vertical and lateral extent of hydrocarbons at the site. The site assessment included advancing 15 soil borings (NSB-0 through NSB-4 and NSB-6 through NSB-15) and installing 5 monitoring wells (MW-61UA, MW-62UA, MW-63A, MW-64B, and MW-65A). Additionally, soil borings PL-1 through PL-9 were advanced using a dutch auger or pneumatic "air knife" tool to approximately 4 feet bgs (SECOR, I2003b). • In March 2003, a 1,000-gallon transmix (tank ID 1842-6) UST was removed and select sidewall soil samples were collected from the tank pit area, under the oversight of the Tracy Fire Department. Results of soil sampling indicated moderate levels of petroleum hydrocarbons along the sidewalls of the tank pit. Soil analytical results are presented in Table 6. On September 3, 2003, monitoring well MW- ' 67UA was installed approximately 50 feet downgradient of the UST, to a total depth of 15 feet bgs with a screened interval of 5 to 15 feet bgs (SECOR, 2004d). • In May 2003, a step-drawdown test and a constant-rate aquifer pumping test were performed to estimate hydraulic characteristics for the Upper A zone and the A zone aquifers beneath the site. Results of the step-drawdown test performed in the Upper A zone indicate the maximum sustainable extraction rate for wells screened in this zone should not exceed 0.9 gallons per minute (gpm). In addition, for effective dewatering,the spacing of wells utilized in dewatering the Upper A zone should not exceed 25 feet from center to center. Results also indicate that extraction from the Upper A zone influenced monitoring well MW-24A, which is screened in the underlying A zone. This suggests that hydraulic communication BLASLAND, BOUCK &LEE, INC. 3124106 engineers,scientists,economists 2-3 J:\D0006\44634-00161022_ConceptuaI Site Model.doc