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m S E C ® R Attachment 2 i Site History ' a Five spills have been documented at the site The first spill occurred on June 9, 1984 h and consisted of 13,000 gallons of gasoline, diesel and heating oil Soil was excavated from the spill area immediately after the spill until no subjective evidence of hydrocarbons remained The second spill was a tank overflow in August 1990 consisting of approximately 300 gallons of gasoline The third spill occurred in August 1998, when an unknown volume of gasoline was released as a result of overfilling tank T-137 The fourth spill occurred in November 1999, when an unknown quantity of red dye diesel was released from a tanker overfill at the loading racks The fifth spill occurred on December 28, 2001, when a flange on a piping manifold failed and released less than 10 gallons of red dye diesel at the site a Between 1983 and 1997, 23 monitoring wells (MW-1 through MW-23) and three piezometers (T-1 through T-3) have been installed at the site Well T-2 has since been , destroyed and well MW-9 has been inaccessible since 1992 With the exception of four wells, all are constructed to monitor the shallow water-bearing zones to depths of 25 to 30 feet belowground surface (bgs) Four wells (MW-12, MW-13, MW-22, and MW-23) were constructed to monitor a deeper water-bearing zone at an approximate depth of 48 feet bgs Geraghty & Miller, Inc (G&M) performed an offsite assessment in August 1993 Twenty soil borings were drilled in the farm field adjacent to the site Groundwater samples collected from all 20 borings were reported as non-detect for total petroleum hydrocarbons as diesel (TPHd), total petroleum hydrocarbons as gasoline (TPHg), benzene and toluene (G&M 1994) r A groundwater remediation system was installed at the site in January 1994 for product recovery and hydraulic containment Extraction of groundwater from five wells on site was initiated in February 1994, and continued until February 1996 Two wells, MW-18 and MW-19, were used for hydraulic containment of the groundwater plume and three wells, MW-14, MW-15, and MW-16, were utilized for product recovery µ�a F a�, A dual phase extraction system (DPE) began continuous operation on March 25, 1996 The DPE system consisted of 14 wells (MW-1, MW-2, MW-7, MW-8, MW-14, MW-15, MW-16, and DE-1 through DE-7), a water knockout tank, an oil/water separator, four granular activated carbon vessels arranged in series for groundwater treatment, and a thermal oxidizer for vapor treatment In May 1997, evidence suggested that the separate phase hydrocarbon (SPH) plume onsite had been substantially diminished by the DPE system In addition, influent water concentrations had declined significantly and influent vapor concentrations had declined to near non-detect levels since system startup The DPE system was shut down in June 1997 Temporary shutdown of the DPE system was approved by Ms Gail Wggett of the Regional Water Quality Control Board (RWQCB) in a meeting on June 2, 1997 3 ,