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August 11, 2000 - 8 - 003-7170 Monitoring well sampling protocols are described in Appendix A. All samples collected and transported to an analytical laboratory will be preserved in a refrigerated cooler and maintained under chain-of-custody protocols. 4.2 Concentration Limits and Background Determination Background values for each monitoring parameter must be established as part of the monitoring program. Concentration limits will be established for each parameter. Concentration limits are used in the detection monitoring program and are not to exceed the background values. In conjunction with appropriate statistical procedures, concentration limits provide the basis for identifying a release from a source. 4.2.1 Synthetic Organic Compounds Concentration limits for synthetic constituents (volatile organic compounds) will be set at the method detection limit. Synthetic constituents are not naturally occurring, and their presence in ground water or surface water, are an indication of impact. 4.2.2 Inorganic Constituents Currently at the site, ground-water data from the site's background or upgradient well defines the background data set and provides the basis for data comparisons. However, at the site, conditions make such comparisons inappropriate because the monitoring data show that concentrations for several of the constituents, including EC, chloride, nitrate, calcium, magnesium, and sodium, are consistently distinguishable among the wells. Since there is no unambiguous evidence of impact (e.g., VOCs have not been confirmed in site wells) the consistent differences in concentrations may be due to natural geologically derived spatial variations in the water quality. Where spatial variations exist, intrawell comparisons should be made instead of using a single background well. In other words, each well should function as its own background. Because only one surface-water monitoring point (pond no. 3) is included in the monitoring program, intrapoint comparisons should also be performed. Concentration limits for the site will be established for each monitoring point using historical data for the individual monitoring points. The method selected to determine concentration limits is the tolerance interval statistical method which is described below. Concentration limits cannot yet be established for general water-quality parameters due to insufficient data. For the establishment of background values, Title 27, Article 1 requires analytical data from all background monitoring points for a period of 1 year (four quarters). When the background data sets are complete,concentration limits for the general water-quality parameters will be calculated. Concentration limits for monitoring parameters will be updated on a quarterly basis as part of routine monitoring for the site. 4.3 Statistical Evaluation Methods The proposed concentration limits for synthetic organic compounds will be set at the analytical detection limit for the analysis. Since synthetic organic compounds are not naturally occurring, their presence in samples from a monitoring well is an indication of a release from the site. Therefore, Roo-37.doc Golder Associates