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3 NATURE AND EXTENT OF RELEASE <br /> The nature and extent of the release are discussed in this section. <br /> 3.1 Nature of Release <br /> Ongoing water quality monitoring conducted at the Corral Hollow Sanitary Landfill has <br /> established that the nature of the release is limited to the northeastern portion of the <br /> landfill. Groundwater impacts are characterized by the consistent presence of relatively <br /> low concentrations of the VOCs, Freon 11, Freon 12, methylene chloride, and PCE from <br /> groundwater samples from only MW-5. <br /> To date, the concentration of Freon 12 has ranged from 8.4 to 71.5 µg/L; Freon 11 from <br /> 0.9 to 9.1 µg/L; methylene chloride from 1.1 to 2.5 µg/L; and PCE from 2.6 to 4.4µg/l- <br /> Chloroform was detected only once at a trace amount during the fourth quarter of 1994. <br /> None of the established MCLS has been exceeded. The MCL is 150 µg/L for Freon 11; <br /> 5 µg/L for both methylene chloride and PCE; and 100 µg/L for chloroform. Freon 12 does <br /> not have an MCL. <br /> WDR Order No. 94-259 and Article 5 2550.8(1) requires that constituents of concern <br /> (COCs) be monitored as part of the EMP. During the fourth quarter 1994, wells MW-4, <br /> MW-5, and SB-1 in the shallow perched water-bearing zone were analyzed for CDCs <br /> along with the monitoring parameters. The COCs and the monitoring parameters are listed <br /> in Table 1. <br /> Two sets of analytical parameters will be monitored as part of the corrective action <br /> monitoring program: COCl and monitoring parameters. COCs are the waste constituents, <br /> reaction products, and hazardous constituents that are reasonably expected to be in or <br /> derived from waste contained in the waste management unit (Article 5, Section 2550.3). <br /> Monitoring parameters include the physical parameters, waste constituents, and reaction <br /> products that provide a reliable indication of changes in water quality due to a release <br /> from a waste management unit (Article 5, Section 2550.9 [e][2]). The monitoring <br /> parameters are a subset of the COCs. <br /> SAC\N-\PJ0M39,09390031.9BG-94\cdg:1 Rev.0,4/20/95 <br /> 0939-003.19 3-1 <br />