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• ti 4.0 MONITORING PROCEDURES AND RESULTS 4.1 Depth to Groundwater The depth to groundwater in each well was measured on April 24 and again on May 8, and the • depths were recorded on the Well Monitor Report (Appendix A) Depths were measured with a Sohnst water level sounder to an accuracy of 0 01 foot In order to utilize water depth data from the spargmg and vapor extraction wells, Upgradient requested and obtained approval from PHS/EHD to survey the site and measure the elevations of the well casings in these wells, which had not been previously done The wells were surveyed on May 8 Water level and casing elevation data are tabulated in Table I and were used in constructing groundwater gradient maps for both days (Figures 8 and 9) The maps are similar in appearance, and indicate that the water table has a natural slope to the northeast of approximately 0 008 ft/ft from SW-2 to MW-4 Tlus natural gradient appears to be affected by • the presence of Yosemite Street to the west of the site, however, causing a flexure in the gradient contours and forming a groundwater "low" beneath the surface of the street We interpret this flexure in the gradient as the result of differential groundwater recharge, caused by the impervious asphalt surface of the street relative to the bare ground that is present on the Conrady property Unable to penetrate the street's surface to the same extent as the natural ground surface, groundwater is 0 4 feet deeper beneath the center of the street than would be anticipated by projecting the gradient contours along the same northwest trend that is observed on the Conrady property 4,2 Hydrocarbons • On the morrung of April 24, prior to injection of the ORC, groundwater samples were collected for laboratory analysis of hydrocarbon concentrations Prior to sampling, all six monitoring wells and both sparging wells were purged, but the sparging wells pumped dry very quickly and were slow to recharge due to ther small screened interval Hence, the vapor extraction wells were not pumped prior to sampling, because, like the sparging wells, they have very short screen intervals in the saturated zone and were likely to pump dry, making sample collection more difficult Twelve to fifteen gallons (approximately 3 casing volumes) were purged from each well, and pH, temperature, and conductivity were measured with a Corning meter to insure that these parameters stabilized prior to sampling (Appendix A) Several of the wells exhibited strong gasoline odors, so after purging each well, the purge pump was immersed in soapy water and the water was pumped through the hoses for several minutes in an effort to prevent cross-contamination between wells A total of 220 gallons of purged water are now stored on site in four 55-gallon drums Samples were collected from each well, including the air sparging and vapor extraction wells, which had not been previously sampled Samples were collected in sterilized vials preserved • 4