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Mr. Gabriel Kar* *Project 939-01.09 <br /> April 9, 1992 <br /> Page 3 <br /> The migrant labor housing west of the landfill was inspected and <br /> monitored for landfill methane concentrations, using a Foxboro@ OVA 128 <br /> flame ionization detector (FID). The monitoring effort was focused on <br /> locating and monitoring cracks and points of utility penetrations of floors <br /> and walls, in addition to ambient air monitoring. The instrument detection <br /> limit was 0.4 parts per million by volume (ppmv) of methane. The <br /> equipment maintenance building on the landfill site was also inspected <br /> and monitored for methane intrusion, using the GasTech. <br /> RESULTS <br /> Gas Monitoring Wells <br /> The accumulated data obtained from two recent and two previous <br /> monitoring events for the 12 tri-level gas wells is tabulated in <br /> attachment 1. The monitoring data indicates that methane concentrations <br /> exceeding 5 percent by volume have been detected at all monitoring wells, <br /> except GW-6 and GW-9. A review of the arithmetic averages of the <br /> methane measurements over the last three monitorings (discarding the <br /> first set as potentially atypical) indicates some apparent trends. Wells <br /> GW-6, -7, -8, and -9 along the southern property line appeared to <br /> generally contain the lowest concentrations of methane (between 0 and <br /> 5 percent). Moderate concentrations (between 5 and 30 percent) were <br /> noted along the western property line at GW-2, -3, -4, and -5. Higher <br /> concentrations (above 30 percent) were typically present along the <br /> northern and northeastern property line at wells GW-1, -10, -11, and -12. <br /> Negative gas probe pressures, relative to barometric pressures, were <br /> prevalent on two of the monitoring runs. This effect was probably caused <br /> by rainfall sealing the soil surface, which impedes the lower soil-gas <br /> pressures of the prestorm period from equilibrating with the high <br /> barometric pressures of the poststorm period. The maximum gas <br /> pressure over the last three monitoring events was 1.25 in. w.c. measured <br /> in both GW-21D and GW-1 D. The minimum gas pressure was -2.43 in. <br /> w.c., also measured in GW-2D. Gas pressures were highly variable within <br /> this range, and had no discernible correlation with methane concentration. <br /> PJ9 9390109.EOW <br />