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a WASTE DISCHARGE RJPUIREMENTS ORDER NO. -4- SAN JOAQUIN COUNTY FOR POST-CLOSURE AND CORRECTIVE ACTION MONITORING CORRAL HOLLOW SANITARY LANDFILL SAN JOAQUIN COUNTY 21. Sections 20415(e)(8) and (9) of Title 27 provide for the non-statistical evaluation of monitoring data that will provide the best assurance of the earliest possible detection of a release from a Unit in accordance with §20415(b)(1)(B)2.-4. of Title 27. However, Title 27 does not specify a specific method for non-statistical evaluation of monitoring data. 22. The Board may specify a non-statistical data analysis method pursuant to Section 20080(a)(1) of Title 27. Section 13360(x)(1) of the California Water Code allows the Board to specify requirements to protect underground or surface waters from leakage from a solid waste site, which includes a method to provide the best assurance of determining the earliest possible detection of a release. 23. In order to provide the best assurance of the earliest possible detection of a release of non- naturally occurring waste constituents from a Unit, this Order specifies a non-statistical method for the evaluation of monitoring data. 24. The specified non-statistical method for evaluation of monitoring data provides two criteria (or triggers) for making the determination that there has been a release of non-naturally occurring waste constituents from a Unit. The presence of two non-naturally occurring waste constituents above their respective method detection limit(MDL), or one non- naturally occurring waste constituent detected above its practical quantitation limit(PQL), indicates that a release of waste from a Unit has occurred. Following an indication of a release,verification testing will be conducted to determine whether there has been a release from the Unit, or there is a source of the detected constituents other than the landfill, or the detection was a false detection. Although the detection of one non-naturally occurring waste constituent above its MDL is sufficient to provide for the earliest possible detection of a release, the detection of two non-naturally occurring waste constituents above the MDL as a trigger is appropriate due to the higher risk of false-positive analytical results and the corresponding increase in sampling and analytical expenses from the use of one non- naturally occurring waste constituent above its MDL as a trigger. GROUNDWATER DEGRADATION 25. Volatile organic compounds (VOCs)have been detected in monitoring well MW-5 since 1991. Recent groundwater analytical results indicate that tetrachloroethylene(PCE) and vinyl chloride have increasing trends. The fourth quarter 2000 monitoring results show the concentration of PCE was 5.56 gg/l, while the concentration of vinyl chloride was 0.576 µg/1. Other VOCs detected in the fourth quarter of 2000 include trichlorofluoromethane, dichlorodifluoromethane, acetone, benzene, chloroform, 1,1-dichloroethane, cis-1,2- dichloroethylene, 1,2-dichloropropane,methylene chloride, trichloroethylene, methyl tert- butyl ether(MTBE), and o-xylene. Other constituents noted to have an increasing trend at monitoring well MW-5 are electrical conductivity, total dissolved solids, and chloride.