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Graphs for these parameters aro also included in Appendix A. Based on this evaluation, it <br /> appears that the nature of the release at MW-5 is limited to VOCs and possibly chloride <br /> and bicarbonate (i.e., increasing trend). The increasing trend in TDS and EC are probably <br /> due to chloride. The increasing trend in total alkalinity is probably due to bicarbonate. <br /> However, it should be noted that the chloride and bicarbonate levels in MW-5 are lower <br /> than their respective levels in MW-4 and SB-l. Thus the only unambiguous indications of <br /> landfill impact are the low levels of VOCs. Therefore,VOCs are the only valid parameters <br /> indicative of landfill impact. <br /> 3.2 Extent of Release <br /> The extent of a release at a landfill is typically determined through the installation of <br /> additional groundwater monitoring wells. At the Corral Hollow Sanitary Landfill, <br /> however, installing additional monitoring wells is not considered practicable due to the <br /> following reasons. <br /> As previously stated, two groundwater-bearing zones have been identified on site (1) a <br /> shallow perched water-bearing zone within the Corcoran Clay, considered to be <br /> unconfined, in which -4, MW-5, and SB-1 were installed (see Drawing 1); and (2) a <br /> deep regional water-bearing zone which may be semiconfined to confined. The shallow <br /> perched water-bearing zone does not appear to be extensive; rather, it is confined only to <br /> the eastern half of the landfill(see Drawing 2). Groundwater monitoring wells MW-4 and <br /> SB-1 also installed in the shallow perched water-bearing zone do not show any signs of <br /> impact(i.e., no VOCs have been detected). <br /> Because the nature of contamination is limited to onlya few VOCs at relatively low <br /> Y <br /> concentrations) less than their respective MCLS) and the impacted well MW-5 occurs in a <br /> water-bearing zone separated from the deep regional water-bearing zone by a <br /> 200-foot-thick unsaturated zone, the installation of additional wells downgradient of <br /> MW-5 to further determine the extent of contamination is not proposed at this time. <br /> Because of the low concentrations of VOCs and the limited extent of the release (i.e. not <br /> detected in the other shallow perched water-bearing zone wells), it is believed that the <br /> horizontal extent of the VOC-impacted groundwater to be within 500 feet of the landfill <br /> SAC\N�PJM39\09390031.9BG-94\cdg:l Rev.0,4R0/95 <br /> 0939-003.19 3-3 <br />