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July 21, 1991 Harding Lawson Associates • Revised July 25, 1991 17060, 025. 03 Mr. Hal Miller The Southland Corporation Page 2 activities MW-A and MW-7 (formerly MW-B) , near the tank backfill, were destroyed. The remaining 14 HLA wells were left intact. GROUNDWATER SAMPLING On June 10 and 11, 1991, HLA collected groundwater samples from all 14 monitoring wells. Before sampling, we purged at least three casing volumes from each well while monitoring temperature, pH, and conductivity. After those parameters stabilized, groundwater samples were collected with a clean stainless steel bailer, and decanted directly into laboratory-prepared volatile organic analysis (VOA) vials. The samples were labeled and placed into an ice-chilled cooler for transportation, under chain-of-custody, to a state-certified chemical testing laboratory. Between wells, all purging and sampling equipment was cleaned with an Alconox solution and rinsed with de.ionized water. A duplicate sample and a laboratory-provided trip blank were analyzed to provide quality control. CHEMICAL TESTING Samples were sent to Superior Analytical Laboratories in Martinez, California, and analyzed for total petroleum hydrocarbons (TPH) as gasoline, using EPA Test Method 8015; and for benzene, toluene, ethylbenzene, and xylenes (BTEX) , using EPA Test Method 8020 . The results of chemical analyses are presented in Table 1, along with groundwater data from preceding phases of site investigation and characterization. Laboratory data sheets and chain of custody are included in the Appendix. GROUNDWATER GRADIENT Water level measurements were obtained using a chalked steel tape accurate to 0. 01 feet. Well survey and water level data are presented in Table 2 . The water levels in each of the wells have declined relative to previous periodic measurements. Our calculations indicate a northeasterly hydraulic gradient, which is consistent with previous data for the site.