Assessment protocols

Assessment protocols. (1) General. The department’s protocols for assessing waterbodies shall be consistent with the state’s water quality standards and federal regulations and be based on relevant scientific information. The department’s protocols may include components such as minimum data requirements, sampling methods, quality control, statistical analysis of data, allowable frequency of exceedance of criteria or thresholds, and use of professional judgment. (2) Sample variability and confidence intervals. (a) For assessment determinations, the department may determine that multiple samples are necessary to account for variability inherent in the waterbody, sampling results, or other conditions. The department may evaluate attainment of criteria or thresholds, using assessment methodology that accounts for both the central tendency of the data, such as the mean or median, and the variability of the samples. (b) The department may apply a confidence interval approach to determine the number of samples needed and to increase certainty in the attainment decision. For metrics expressed as a mean or percentile of a group of samples, the department may use the two-sided 80 percent confidence interval of the mean or percentile for assessment. Other methods of calculating a confidence interval may be applied as appropriate for a specific metric, data type, or statistical goal. Once the confidence interval is determined under this paragraph, it is then compared to the criterion or threshold as specified in par. (c) . (c) When applying an approach under par. (b) , the department shall compare the confidence interval to the applicable criterion or threshold using one of the following evaluation criteria: 1. If the entire confidence interval is attaining the criterion or threshold, no further samples are needed to make the attainment determination. 2. If the entire confidence interval is not attaining the criterion or threshold, no further samples are needed to make the non-attainment determination. 3. If the criterion or threshold is within the confidence interval, the assessment will be deferred until more data can be collected with the goal of narrowing the interval to determine whether subd. 1. or 2. applies. After further data collection, if the criterion or threshold continues to be within the confidence interval, the attainment determination shall be made by directly comparing the sample mean or percentile to the criterion or threshold.