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.Mann-Kendall test, is a nonparametric, rank correlation method which can be used for evaluating correlations between constituent concentrations and time. The test is described in statistical literature (Gilbert, 1987; hollander and Wolfe, 1973) and its use is recommended by the U.S. EPA (Loftin, et al., 1989). As stated previously in Section 6.3, the effectiveness of the capping of the landfill may not be observable for several years. The concentration limit for MW-5 will be no increasing trends. Inorganic Parameters. As described in the Article S Monitoring Program (EMCON, 1992), natural spatial variations in groundwater quality have been identified at the Corral Hollow Sanitary Landfill. Where spatial variations exist, it is inappropriate to designate a single upgradient well (or group of wells) as background because it may not encompass the range of naturally occurring constituent concentrations present at a site. Instead, each well should function as its own background. Therefore, concentration limits for the downgradient wells MW-4 and SB-1 will be calculated based on background water quality data using the tolerance interval method. The tolerance method was approved for use at the Corral Hollow Sanitary Landfill by WDR Order No. 94-259. This statistical method is described in literature (Montgomery, 1985) and in the Article S Monitoring Program (EMCON, 1992). Tolerance limits for the Corral Hollow Sanitary Landfill will be updated on a quarterly basis to provide ongoing definition of water quality for the landfill, as required by WDR Order No. 94-259. Concentration limits for MW-4, as calculated for the first quarter 1995, are shown on Table 2. Concentration limits for SB-1 will be established after sufficient data have been collected For the impacted well MW-5, during corrective action monitoring, inorganic parameters will be evaluated for decreasing trends (and increasing trends in the cases of nitrate-nitrogen and pH) to evaluate the effectiveness of the CAP. Consistent with this evaluation procedure, the concentration limits for inorganic constituents will be "the absence of a statistically significant increasing trend." One exception is nitrate-nitrogen; its depletion in groundwater can be used as an indicator of ongoing landfill impact. Under the anaerobic conditions that are encountered within landfills,facultative microorganisms will use nitrate as an electron acceptor, thus depleting nitrate concentrations. Therefore, a decreasing trend in nitrate-nitrogen concentrations would be indicative of continuing landfill impact. Conversely, increasing nitrate-nitrogen concentrations can be used to indicate the effectiveness of corrective action activities. The concentration limit for nitrate-nitrogen is therefore "the absence of a statistically significant decreasing trend." A second exception is pH, for which both an increasing and a decreasing trend would be indicative of landfill impact. The concentration limit for pH is "the absence of both an increasing and a decreasing trend." SAC\N.\PJ0M3M390031.9BG-94Wb:1 Rev.0,4121/95 0939-003.19 7-2