SITE INFORMATION AND CORRESPONDENCE

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Mr. Nathan Crum - 2 - 21 October 2010 Valley Pacific Petroleum Se. ,s (pg/L) of total petroleum hydrocarbons as gasoline (TPHg), 16,000 pg/L of benzene, 7,100 pg/L of toluene, 1,500 pg/L of ethylbenzene, 9,000 pg/L of xylenes, and 57,000 pg/L of methyl tertiary butyl ether (MTBE). The TPHg sample was analyzed at a 250 times dilution, and the MTBE sample was analyzed at a 400 times dilution. The sample was not analyzed for TPH as diesel (TPHd). VEW 1 is located 17 feet northeast of source area well MW-8. The Pilot Test Report describes the SVE pilot test conducted between 26 & 29 July 2010. Central Valley Water Board staff conducted a site visit on 27 July to observe the test. Vacuums were alternately applied to each well within the cluster for 18 to 24 hours. Induced vacuum and flow rates were monitored in the other two SVE wells in the cluster and in monitoring wells MW-6R, MW-8, and MW-9R. The monitoring wells are generally screened between 40 and 65 feet bgs. Monitoring results showed that air flow rates were lowest in VEW 1-D and highest in VEW 1-I. The maximum flow rate in VEW 1-I was 190 cubic feet per minute (cfm) at an applied vacuum of 3.5 inches of mercury. At this setting, the induced vacuums measured in monitoring wells MW-6R and MW-8 were 1 .26% and 4.1%, respectively, of the applied vacuum. These wells are 51 feet and 15 feet from VEW-1 , respectively. No induced vacuum was observed in MW9R, which is 39 feet away. Extracted vapors were treated by a thermal catalytic oxidizer. Periodic photo ionization detector (PID) and Tedlar0 bag samples were collected to analyze extracted vapors. Laboratory analytical results of influent vapor samples collected from VEW1-D contained the highest petroleum vapor concentrations. Maximum concentrations included 82,000 micrograms per liter (pg/L) of TPHg, 2,700 pg/L of benzene, 2,400 pg/L of toluene, 250 pg/L of ethylbenzene, 1,040 pg/L of xylenes, and 2,200 pg/L of MTBE. During the 24-hour testing period, Valley Pacific estimates that the SVE system removed about 260 pounds of gasoline hydrocarbons from VEW1-D. A considerably smaller hydrocarbon mass was removed from VEW 1-1 and VEW 1-S, where induced vacuums were considerably higher. Based on an estimated radius of influence (ROI) of 50 feet in the deep extraction well and previous data interpreted to show that most of the vadose zone contamination lies between 40 and 65 feet bgs, Valley Pacific recommends conducting SVE through the existing extraction wells to remediate the soils at the Site. Valley Pacific anticipates that the SVE system is capable of an initial mass removal rate of 400 pounds per day and proposes to prepare a Corrective Action Plan (CAP). Once the system has operated for a time and hydrocarbon vapor concentrations decline, Valley Pacific proposes to re- evaluate the addition of an air-sparging system. Our comments are presented below. 1 . We concur that the pilot test data indicate that SVE will be effective in reducing petroleum hydrocarbon mass at the Site. However, attainment of water quality goals may require the installation of an additional extraction well to address the area of the plume between MW-9 and MW-13, shown on Figure 6 as being outside of the ROI for VEW1. In addition, the persistent sheen and free product observed in monitoring wells