ARCHIVED REPORTS XR0001151 - Laserfiche WebLink

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en viroso • Ground water samples collected from Wells MWA through MW-10 contained TPPH concentrations ranging from ND to 34,000 ppb Benzene concentrations ranged from ND to 850 ppb A benzene concentration map is presented on Plate 2 • A response to the April 10, 1997 PHS-EHD request for remediation system status is presented below Quarterly Sampling Monitoring Wells MW-1 through MW-10 were sampled and analyzed for Total Purgeable Petroleum Hydrocarbons quantified as gasoline (TPPH) according to EPA Method 8015 (Modified), and benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl-tertiary-butyl-ether (MTBE) according to EPA Method 8020 Additionally, a duplicate sample and an equipment blank were prepared and analyzed for quality control purposes Field monitoring data and chemical analytical data are summarized in Table 1 Blaine's quarterly ground water monitoring report is presented in Appendix A Remediation System Status A soil and ground water remediation system consisting of SVE has been operating at the subject site since September 1992 and has been operating intermittently (pulsing) from September 1993 to present The PHS-EHD letter of April 10, 1997 requested that since the water table has risen at the site to submerge almost the enure screened interval of the wells utilized for SVE, the resulting inefficiency of SVE as a remedial technique must be addressed Field monitoring data summarized in Table 1 indicate that the water table at the subject site began to rise beginning in 1995 Prior to 1995 the depth to ground water tended to fluctuate between approximately 28 to 34 feet below grade (fbg) in site wells utilized for SVE On-site Wells MW-2, MW-3, MW-4, MW-5, MW-7, MW-8, and MW-9 are connected to SVE piping The screen interval of Wells MW-2, MW-3, MW-4, MW-8, and MW-9 is 20 to 40 fbg The screen interval of Wells MW-5 and MW-7 is 25 to 40 fbg Well construction details are presented in Appendix B A plot of hydrocarbon extraction rates versus dates is presented on Plate 3 This data is also presented on Table 2 As shown on Plate 3, hydrocarbon extraction rates began to exhibit asymptotic behavior in the third quarter of 1993, prior to the rise in the water table Recognizing the onset of asymptotic hydrocarbon extraction rates, the prior operator, Fugro West Inc (Fugro), began operating the SVE system intermittently in September 1993 The SVE system has been operated intermittently (pulsing) since that time 97375 2