ARCHIVED REPORTS_XR0011983 - Laserfiche WebLink

Home Browse Search

DISCUSSION: MTBE was detected in groundwater samples collected from wells MW-1, and MW-3 through MW-10. Concentrations ranged from 0.60 pg/L up to 69,000 pg/L, with the highest concentration being detected in the sample collected from well MW-6. TPHG and benzene were detected in the sample collected from wells MW-4 (23,000 gg/L, and 5,000 pg/L), MW-8 (460 pg/L, and 190 pg/L), and MW-10 (54 gg/L, and 1.0 pg/L). TPHG was also detected in samples collected from wells MW-5 (710 pg/L), MW-6 (55,000 pglL), and MW-7 (1,400 pg/L). 1,2-DCA was detected in the samples collected from wells MW-9 (19 pg/L), and MW-10 (1.0 pg/L). TBA (590 pg/L) was detected in sample collected from well MW-6. Toluene, ethylbenzene, xylenes, ETRE, and EDB were not detected in any of the samples. This analytical data is generally consistent with previous sampling events, except for wells MW-6, and MW-7, where TPHG concentrations increased significantly relative to the previous quarter and historical data. However, the TPHG concentrations reported for these wells were noted by the laboratory to be due to a single peak at MTBE". During a telephone conversation with the laboratory on November 19, 2002, the laboratory indicated that there does not appear to be any other compounds eluting in the TPHG range other than MTBE. Chromatograms from the analysis of samples from wells MW-6 and MW-7 are included in Appendix C. Groundwater elevations have increased approximately 1.88 to 2.12 feet since the previous sampling event (April 23, 2002). The groundwater flow direction on September 19, 2002, was calculated to be towards the northeast at a gradient of approximately 0.0021 ft/ft. Groundwater flow directions have predominantly been toward the northeast and east during previous monitoring events. The onsite CPT work is scheduled for November 18, 2002, and will consist of advancing one CPT boring, collection of discrete soil and water samples to further evaluate the vertical extent of impact, and to better • characterize the stratigraphy beneath the site. ATTACHMENTS: • Table 1 Groundwater Elevation and Analytical Summary o Table 2 Groundwater Analytical Results for Oxygenates and Additional Compounds o Figure 1 Site Location Map • Figure 2 Groundwater Elevation Contours (Third Quarter 2002) o Figure 3 Groundwater Analytical Summary(Third Quarter 2002) o Appendix A Field Data Sheets • Appendix B Sampling and Analysis Procedures o Appendix C Certified Analytical Reports and Chain-of-Custody Documentation PABA-Arco for URS\54691Quarterly120021Arco_5469_3Q02.doc SrRarus