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J . ASSOCIATESATC I N C . results were submitted in a Summary Report on Additional Subsurface Investigation, dated August 11, 2004. On January 10 and 17, 2005, ATC supervised the installation of two groundwater monitoring wells (MW-7 and MW-8). The wells were installed hydraulically downgradient with respect to the locations of the former USTs and are the most northerly monitoring wells at the site. A low concentration of xylenes in the groundwater sample collected from MW-7 was the only analyte of interest detected in groundwater samples collected from these wells on January 26, 2005. Refer to ATC's First Quarter 2005 Groundwater Monitoring Event and Well Installation Report, dated April 20, 2005, for additional information. MONITORING WELL SURVEY, SAMPLING,AND GROUNWATER GRADIENT EVALUATION On April 1, 2005, Condor Earth Technologies, Inc. (California-certified Land Surveyor No. 7698) surveyed the locations and elevations of MW-1 through MW-8. The surveyed well casing elevations are indicated in Table 1. ATC personnel performed the latest quarterly groundwater monitoring of eight monitoring wells on April 6, 2005. Field work consisted of measuring depth-to-water levels in all wells, collecting groundwater samples from all wells, and submitting groundwater samples for laboratory analyses. Water level measurements were collected from groundwater monitoring wells MW-1 through MW-8. The depth to water ranged from 7.23 to 8.90 feet below top of well casings. The water level data were used to develop the groundwater elevation contour map (Figure 3). Shallow groundwater flow beneath the site was generally toward the north during the monitoring event. The average hydraulic gradient on April 6, 2005, was calculated to be approximately 0.002 ft/ft or approximately 11 feet/mile. The data indicate a groundwater gradient that is generally consistent with previous groundwater gradients observed at the site. A summary of groundwater monitoring data is presented in Table 1. Groundwater elevations are referenced to feet above mean sea level. Groundwater samples were collected from monitoring wells MW-1 through MW-8. Prior to collection of groundwater samples a minimum of three well casing volumes were purged from each well. The pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected. Samples were then collected from each well using disposable bailers. Purge water was contained in 55-gallon DOT approved drums. Groundwater well purge and sample logs are provided in Attachment 1. The groundwater samples collected from each well were submitted with Chain-of-Custody Record to State-certified Argon Laboratories Inc. (Environmental Laboratory Accreditation Program Certification No. 2359). The samples were analyzed for TPHg by EPA Method 8015M; BTEX by EPA Method 802113; and MTBE, tert-amyl methyl ether (TAME), TBA, di-isopropyl s:\Environmental\17861\reports\2gmr2005.doc 3 ATC Associates Inc.