ARCHIVED REPORTS XR0003983 - Laserfiche WebLink

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1' I extent of soil contamination had been delineated by previous stages of the investigation. 2.6 Quarterly Monitoring Program Quarterly monitoring of groundwater at the site began in October 1992. Three of the five wells were monitored at that time; MW-2 and MW-3 were still dry and could not be 71 sampled. Increases in the concentration of most contaminants were noted in the October 1992 event (Table 2). Based on these results, GeoAudit again concluded that additional monitoring wells would be necessary to completely define the extent of groundwater contamination. ' The three additional wells installed in April 1993 were added to the quarterly monitoring program. Well MW-1 and wells MW-4 through MW-8 were monitored at that time, but MW-2 and MW-3 remained dry (Table 2). The gradient continued to be to the southwest. The most recent monitoring event took place in October 1993. As in previous events, a Solinist water meter was used to measure water depth in all wells except MW-2 on October 7, 1993 (Table 3). An attempt was also made to measure the depth in MW-3, but the results yielded a water table elevation more than 2 feet higher than expected, and the data are considered fallacious. After measurements were made, all wells were purged of between 3 ' and 10 gallons of water, using a PVC bailer. Temperature, pH, and conductivity were Pmeasured at one-gallon intervals using a Hydac water analyzer (Table 4). Purge water was stored in a 55-gallon DOT drum on the site. Water samples were collected after at least three well volumes had been purged. Water samples were collected using disposable plastic bailers.Three 40 ml EPA vials were collected from each well and transmitted in a chilled container to Sparger Technology in Sacramento, ` California. No hydrocarbons were detected in MW-5 through MW-8 at a detection limit of 0.3 ppb for BTE&X and 50 ppb for TPH. Moderate concentrations of hydrocarbons were detected in MW-4, and very high concentrations were detected in MW-1 (Table 2). Laboratory results are presented in Appendix C. The concentrations in MW-4 were reasonably similar to those measured in the previous (April, 1993) sampling event, but the concentrations in MW-1 exceed those of April 1993 ' by more than an order of magnitude. Such a large difference is probably not due to differences in calibration of laboratory instruments, and is thought to indicate recent desorption of contaminants from soil into groundwater. ' 2.7 Vadose Zone Remediation Well GeoAudit supervised the installation of remedial well RW-1 in August 1993. Turner Exploration, of Rancho Cordova, California, provided the Mobile Drill B-57 rig and three- man crew. The installation was witnessed by Ms. Mary Mea_vs of PHS/Fi-m- ant] armitinn was witnessed by Mr. Harlin Knoll of PHS/EHD. -- a Ombginl audit Sevirea, 14. FlaA PAiC+1-25.9411.47 7