SITE INFORMATION AND CORRESPONDENCE

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�• t 8200 Hwy 99 Speedy Food Mart June 16, 2004 Page '? seal from surface to 270 feet below surface grade (bsg) the operation 6f the well may influence the contaminated groundwater plume. Since dissolved MTBE is highly mobile in groundwater, EHD is very concerned that the water supply well may exert an influence on the plume and could act as a potential receptor. EHD suggests conducting a simple test to determine if there is any hydrogeological communication between the water supply well and MAV13C. An example of such a test could consist of pumping on the water supply well while placing a continuous logging device such as a level-logger in MW13C. A water level drop in MW13C could be construed as positive influence, and pumping should be stopped immediately to prevent further unnecessary migratory influence on the contamination plume. Provide a proposal to EHD that will determine if there is hydrogeological communication between MW13C and the water supply well by July 31, 2004. The lateral extent of the dissolved contamination in the shallow ground water zone is also not defined, and the presence of MTBE in MW12 potentially threatens the private drinking water wells off-site north of the property. MTBE was detected in MW6 at concentration of 20,000 ug/l in October 2000, before gradually dropping to and remaining at non-detect levels since June 2003. The MTBE plume in the vicinity of MW12 appears to have separated from the main body of the contamination, and its leading edge has migrated at least 100 feet down gradient northeast of NRV6. This is a concern of the highest priority to EHD. EHD has approved the installation of two shallow groundwater wells NMI5 and 1N1%V16 northeast of MW12, and the installation of one shallow groundwater extraction well E12 to be installed approximately two weeks after the installation of MW15 and NfW16. EHD directs that the work begin by June 25,2004. As discussed in a telephone conversation on June 17, 2004, EHD agreed the work could be completed under the previously issued well permit SR-35348. A soil vapor extraction (SVE) test was performed at the site using MW1 (screened 60-80 feet bsg) as the extraction well, then switched to VW1 (50 to 70 feet bsg) as the extraction well. The flow rate was 10 to 15 cubic feet per minute (cfm) with a vacuum at 18 to 20 inches of water in 1NAV1, and 20 to 24 cfm with a vacuum of 50 to 58 inches of water in VW1. Influent vapor samples from MWl were as high as 240,000 ug/1 Total Petroleum Hydrocarbons as gasoline (TPH-g), 6,300 ug/l benzene, and 3,800 ug/l MTBE. Influent vapor samples from VEW1 were as high as 66,000 ug/1 TPH-g, 2,400 ug/1 benzene, and 1,700 ug/l MTBE. Groundzero estimated the radius of influence (ROI) to be 30 to 50 feet at depths of 55 to 60 feet. EHD agrees with Groundzero's assessment that SVE is a feasible method for remediation. Submit a work plan for installation of a SVE system to EHD by July 312004. EHD does not agree Groundzero's request to collect additional soil vapor samples from NM and VEW1 to evaluate the effect of the recent groundwater extraction. The SVE pilot test appears to have sufficiently demonstrated the effectiveness of SVE as a remediation technology, and the current groundwater extraction should have only minimal effect on the contamination in the vadose zone. Further testing of vapor samples is not necessary.