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;f 1 and reported with 99 percent confidence that the concentration is greater than zero. It is determined from the analysis of the analyte in question in the appropriate matrix. The procedure for establishing the method detection limit is provided in Appendix B of 40 CFR Part 136 as published in the Federal Register of October 26, 1984. Appropriate use of detection limits minimizes confusion in subsequent use of the data. In general, the protocol for determination of the method detection limit is too laborious to permit its routine application in the laboratory. Instead, the "estimated f detection limit" is determined on a daily basis by any one of the several approaches cited in the above reference. It should be noted that detection limits, ne matter how estimated, are highly variable. They depend on the instrument, the analyst, reagent purity, and other factors. In many instances, the detection limit will be dictated by the nature of interferences present in the sample matrix rather than instrumental considerations. D. Assessment Before the significance of analytical data can be assessed, one needs to know how precise, how accurate, and how complete are the data subsets. Precision is amenable to strict definition by the analysis of replicate results according to schemes outlined in the USEPA Bandbook for Analytical Quality Control in Water and Wastewater Laboratories, March, 1979, Chapter 6. Accuracy is .somewhat more i (cult to assess. Spike recovery determinations, regular analysis of laboratory control standards, and use of external check samples contribute to the general assurance that the accuracy of a determination is within acceptable limits. The ultimate accuracy of a determination also depends on factors external to the laborataory such as sampling and storage conditions. Completeness is the most difficult characteristic to assess, depending as it does upon such factors as J representativeness of sampling and subsampling, selection of the appropriate analytical parameters, and scope of the sampling program relative to the size of the environmental question being addressed. While ultimate assessment depends on the experienced judgment of knowledgeable individuals, statistical treat- ment of the data can provide some objective measure of their soundness.. The Federal Register of October 26, 1984, includes required calculations for accuracy on spiked VIII-3 11