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,WAkT February 12, 2020 Page 2 of 6 was decided to best utilize the well as a vapor extraction well without modifying the well's construction. As a result MW7 was renamed VW3. On September 18 and 29, 2003, ATC Associates Inc. (ATC) performed short-term and long-term vapor extraction tests, respectively. These tests were performed to evaluate the feasibility of soil vapor extraction (SVE) technology at this site. The results indicated that extracted soil vapor contained sufficient concentrations of vapor phase hydrocarbons, suggesting that SVE would be useful for attenuating the hydrocarbon mass present in the vadose zone. ATC prepared an Interim Remediation Plan on March 25, 2004, recommending the installation of a SVE and air-sparging system to remediate petroleum hydrocarbon impacted soil and groundwater below the site. The SVE system was approved, but the installation of the air sparge system was postponed by the San Joaquin County Environmental Health Department(SJCEHD) due to concerns that the introduction of large volumes of air to groundwater would lead to the movement of dissolved phase hydrocarbons within the capture zone of the nearby domestic well. On January 24, 2005, ATC supervised the installation of VW4 and the destruction of MW10. MW10 became unsuitable for sample collection due to an obstruction in the well casing that could not be removed. In August 2005, the San Joaquin Valley Air Pollution Control District (SJVAPCD) issued an Authority to Construct Permit for the installation of the SVE system. During the week of August 15, 2005, ATC supervised trenching and installation of subsurface remediation piping connecting vapor wells (VW1 through VW4)to a Solleco 250 ECAT electric thermal/catalytic oxidizer. The SVE system was initially optimized to run at a minimum of 600 degrees Fahrenheit at a total flow rate of 235 cubic feet per minute (CFM). The SVE system startup occurred on September 6, 2005, operating with 99.95% destruction efficiency. The SVE system operated on a limited 10-hour per day operating schedule due primarily to reliance of on-site supplied electricity. The system continued to be operated in this mode until dedicated electric service was installed on February 20, 2006, and an automatic timer was installed to allow continuous automatic control. During the first quarter of operation, the system removed an estimated 11,550 pounds of vapor phase hydrocarbons. The amount of hydrocarbons extracted during the first three-month period represented approximately 70 percent of the total vapor phase hydrocarbons removed during the entire 36 months of operation. On September 25, 2008, the system was shut down because sufficient concentrations of petroleum hydrocarbons were not detected at concentrations above laboratory reporting limits in the monthly vapor samples collected during the three previous months of operation. On November 7, 2008, after 43 days of non-operation, the SVE system was restarted and a Rebound Test was performed. This test was used to determine if vapor phase hydrocarbon concentrations within the subsurface would rebound and therefore justify continued operation, or if the system should be shut down indefinitely. Analytical results of influent vapor samples indicated concentrations were so low that if they could be sustained for a 24-hour period, this would result in the extraction of 0.45 lbs. of Gasoline Range Organics (GRO) and 0.03 lbs. of total xylenes per day. Since extractions of this type are characterized by declining concentrations, it was evident that continued operation would not substantially affect the subsurface conditions at the site. Consequently, the system was shut down and has not been restarted since. The SVE system operated from September 6, 2005, through November 7, 2008, for a total of 6,853.5 hours. During this period, the system extracted and destroyed an equivalent of approximately 16,508