ARCHIVED REPORTS_XR0008231 - Laserfiche WebLink

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1 2.0 GROUNDWATER MONITORING, SAMPLING AND ANALYSIS On September 21, 2005, to comply with quarterly groundwater monitoring requirements, and to monitor the plume of impacted groundwater, Ramage Environmental monitored and sampled the three wells 21 Groundwater Monitoring Depth-to-groundwater was monitored to within 0 01-foot using a water level indicator The static depth to the groundwater table, as measured in the three monitoring wells, ranged from 15 50 feet below grade in MW-1 to 27 90 feet below street grade in MW-3 The groundwater surface ' elevation in the three wells ranged from a high of 15 36 feet below mean sea level (msl) at MW-1 to a low of 16 34 feet below msl at MW-3 The resulting groundwater surface appears as a ' regular plane dipping to the northeast at a gradient of approximately 0 0114 foot/foot A groundwater surface contour map is included as Figure 4, the groundwater monitoring data are summarized in Table 3, and the sample information field sheets are included in Appendix A 22 Groundwater Sampling and Analysis Following groundwater level measurements, the wells were purged and sampled The wells were purged with a pump and dedicated disposable tubing until at least three well casing volumes had been removed and/or after groundwater temperature, pH and electrical conductivity values had stabilized Groundwater was sampled from the wells using disposable polyethylene bailers and laboratory-supplied containers Each sample container was transported in an iced cooler with chain-of-custody documentation to Excelchem Environmental Labs (Excelchem), a state of California certified hazardous waste testing laboratory (Certification #2119) Excelchem analyzed ' each groundwater sample for TPH-as-gasoline and benzene, toluene, ethylbenzene, xylenes (BTEX) by EPA Method 8021 B1801 5M, and for MTBE, di-isopropyl ether (DIPE), ethyl tertiary ' butyl ether (ETBE), tertiary amyl methyl ether(TAME), tertiary butanol (TBA), and 1,2- dichloroethane (1,2-DCA) by EPA Method 8260B The highest concentrations of gasoline compounds were detected in the sample collected from MW-1 919 micrograms per liter(µg11) of TPH-as-gasoline, 102 µgll of benzene, 141 µg/1 of ethylbenzene, and 15 9 µg11 of xylenes Only MTBE was detected in MW-2 at 4 2 µg11 and in MW- 3 at 4 2 µg/l The groundwater sample analytical results are summarized in Table 2, the distribution of gasoline in groundwater is shown on Figure 5, and the laboratory reports are included in Appendix B 6