ARCHIVED REPORTS XR0011199 - Laserfiche WebLink

Home Browse Search

5.4 GROUNDWATER MONT1'ORING ' 5.1 Monitoring Procedures Groundwater monitoring took place on May 23, 1996 The depth to groundwater was measured in all six monitoring wells and in the deep vapor extraction well Depth measurements were recorded on the Well Monitor Report (Appendix C),Prior to sampling, all wells were purged of approximately 3 well volumes (10-15 gallons) before sampling Mr Ron Rowe of PHS/EBD witnessed the purging and sampling ' Two 40-m1 sample vials were collected from each well and were labeled and placed in a cooled ice chest for later delivery to Sequoia Analytical in Sacramento The laboratory report and cham-of- custody form are included in Appendix B ' S 2 Depth to Groundwater ' The normal seasonal nse in the water table was observed during the quarter(Table 1) As of May 23, it had risen over 3 feet from its March level and had reached an average depth of 55 feet ' 5.3 Groundwater Gradient and Flow Direction During the first two quarters of 1995, depth-to-groundwater measurements identified a central trough in the groundwater gradient centered in the vicinity of MW-5 In September, this trough disappeared and the gradient assumed a more planar form, with flow almost due east By December, the trough had ' returned, and was well developed when water depths were measured in February As shown in Figure 6, this trough remained well developed in May, although it shifted slightly to the north of its previous position 5.4 Groundwater Contamination As in the previous four quarters, contaminants were detected in MW-5 (Table 2) The benzene and TPH-g concentrations more than tripled over their values in March, and toluene, ethylbenzene, and xylene were detected Neither ethylbenzene nor xylene had been detected since February 1995, when Upgradient first began collecting groundwater samples For the second time, a water sample from VE-I was analyzed Gasohne, benzene, toluene, and xylene were all detected at significantly lower concentrations than in March, but this well remains the most contaminated ' Gasohne'and all BTEX compounds were detected in the sample from MW-3 at concentrations that are virtually identical to those in MW-5, causing suspicion that the MW-3 sample may have been mislabeled or misidentified by the laboratory The duplicate samples from both MW-3 and MW-5 were 5