Assessing the TMDL Approach to Water Quality Management (2001) / Chapter Skim
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3 Waterbody Assessment: Listing and Delisting
3 Waterbody Assessment: Listing and Delisting
Pages 32-67
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From page 32... ...
States need to decide what waters should be assessed in the first place, how to create water quality standards for those waters, and then how to determine exceedance of ~ The Clean Water Act Section 305b report the National Water Quality Inventory Report is the primary vehicle for informing Congress and the public about general water quality conditions in the United States. This document characterizes water quality, identifies widespread water quality problems of national significance, and describes various programs implemented to restore and protect our waters (http://www.epa.gov/305b/~.
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Rather, information for decision-making should be based on carefully collected and interpreted monitoring data (Kerr and Dudley, 1981; Yoder, 1997; Yoder and Rankin, 1998~. The committee recognizes that state ambient monitoring programs have multiple objectives beyond the TMDL program (e.g., 305b reports, trends and loads assessments, and other legal requirements)
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34 Assessing the TMDL Approach to Water Quality Management
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The core indicators include baseline biological, chemical, and physical parameters that comprise the basic attributes of aquatic ecosystems supplemented by specific chemical, physical, and bacteriological parameters from water, sediment, and tissue media, depending on the applicable designated users) and watershed-specific issues.
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This is because biological assemblages respond to and integrate all relevant chemical, physical, and biological factors in the environment whether of natural or anthropogenic origin. On the other hand, relying only on biological assessments would not allow precise enough determination of associated causes and sources of impairments to satisfy water quality management needs including TMDL development.
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Data collected can be used to support a number of differ3 In some states, the rotating basin approach is considered to be part of the ambient monitoring program, while in others, it is a separate program. This report assumes the former throughout.
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Waterbody Assessment: Listing and Delisting 39
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40 Assessing the TMDL Approach to Water Quality Management
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The rotating basin approach used by several states is an excellent example of a rigorous approach to ambient monitoring and data collection that can be used to conduct waterbody assessments of varying levels of complexity. For example, this approach can be used to create 305b reports, to list impaired waters, and to develop
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DEFINING ALL WATERS As shown in Figure 1-l, the TMDL process begins with identification of all waters for which achievement of water quality standards is to be assessed. The proposed regulations for the TMDL program (EPA, 1999a)
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These waters are either left out of the decision process and are deemed not impaired by default, or they are included in the decision process with higher error rates. One solution to this problem is to avoid the concept of a valid region for individual monitoring stations entirely and replace it with an approach in which monitoring data are used to develop statistical models of water quality in state waters.
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This approach would combine monitoring data with estimates of water quality based on statistical models. DESIRABLE CRITERIA This section considers the desired features of chemical and biological criteria as surrogates for designated use.
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It should be noted that these numbers are pollutant-specific, and they might vary with season depending on, for example, fish life-stage. Establishing these three dimensions of the criterion is crucial for successfully developing water quality standards4.
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Biocriteria that are regionally relevant would not show those conditions as violations. Fecal coliform counts and algal community parameters such as chlorophyll a are a type of biocriteria, but they are not comprehensive measures of waterbody condition.
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Waterbody Assessment: Listing and Delisting 47 sive, index systems have been developed that focus on characteristics of the biota expected in the particular region where the waterbody is Tocated, including desired fish species and other associated organisms (Box 3-5)
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48 Assessing the TMDL Approach to Water Quality Management
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Recently, the EPA Office of Water has convened a working group of states and other supporting institutions to better define the gradient of biological condition from pristine to highly degraded and link this with operational measures such as numeric biocriteria in a manner that will ensure consistency across state programs. This is referred to as tiered aquatic life uses and is expressed as a biocondition axis.
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This section proposes a mechanism for managing the large number of waters requiring attention by dividing the listing process into multiple smaller steps, as shown in Figure 3-~. Figure 3-l illustrates a framework for water quality management that is more detailed than the conceptualized steps of the TMDL process shown in Figure 1-~.
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__ TOOL Planning _< _~ _Adaptive Implementation it_ < FIGURE 3-1 Framework for water quality management. 51 I Review Use/ Standard
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. Those waterbodies placed on the preliminary list are the object of a more complete assessment that would involve additional monitoring and appropriate analysis of new data to reduce the uncertainty about their condition.
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not be identified in the wait for additional data. The existence of a preliminary list addresses these concerns by focusing attention on waters suspected to be impaired without imposing on stakeholders and the agencies the consequences of TMDL development, until additional information is developed and evaluated.
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Minimum sample sizes and confidence levels have been established, and both chemical and biological data are considered. States will have to decide upon and develop criteria for defining data sufficiency and analytical procedures for placing waterbodies on the preliminary list and the action list.
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Placement of a waterbody on the preliminary list can serve as an indication to stakeholders that action should be taken soon to achieve water quality standards in order to avoid the costs associated with TMDL development. Because of the consequences of movement to the action list, there may be an incentive to keep waters on the preliminary list indefinitely.
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DATA EVALUATION FOR THE LISTING AND DELISTING PROCESS Given finite monitoring resources, it is obvious that the number of sampling stations included in the state program will ultimately limit the number of water quality measurements that can be made at each station. Thus, in addition to the problem of defining state waters and designing the monitoring network to assess those waters, fundamental statistical issues arise concerning how to interpret limited data from individual sampling stations.
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The binomial hypothesis test allows one to take sample size into account. By using a statistical procedure, sample sizes can be selected and one can explicitly control and make trade-offs between error rates (see Smith et al., 2001, and Gibbons, in press, for guidance on managing the risk of false positive and false negative errors)
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. Embedded in the EPA raw score approach is an implication that 10 percent is an acceptable violation rate, which it may not be in certain circumstances.
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In general, alternative statistical approaches transform questions about the proportion of samples that exceed a standard into questions about the center (or another parameter) of a continuous distribution.
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Box 3-6 presents results of several studies in which the error around biological parameters was assessed.
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For chemical parameters, these might include the binomial hypothesis test or other statistical approaches that can more effectively make use of the data collected to determine water quality impairment than does the raw score approach. For biological parameters, these might focus on improvement of sampling designs, more careful identification of the components of biology used as indicators, and analytical procedures that explore bioTogical data as well as integrate biological information with other relevant data.
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The EPA guidance on 303d listing suggests that a simple, but useful, modeling approach that may be used in the absence of monitoring data is "dilution calculations," in which the rate of pollutant loading from point sources in a waterbody (recorded as kg per day in NPDES permits, for example) is divided by the stream flow distribution to give a set of estimated pollutant concentrations that may be compared to the state standard.
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Models that can fib gaps in data have the potential to generate information that will increase the efficiency of monitoring and thus increase the accuracy of the preliminary listing process. For example, regression analyses that correlate pollutant concentration with some more easily measurable factor could be used to extend monitoring data for preliminary listing purposes.
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Assessing the Sustainability and Biological Integrity of Water Resources Using Fish Communities. Boca Raton, FL: CRC Press.
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Assessing the Sustainability and Biological Integrity of Water Resources Using Fish Communities. Boca Raton, FL: CRC Press.
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Appendix I, Ohio Water Resource Inventory (Volume 1~. Columbus, OH: Ohio EPA, Division of Water Quality Planning Assessment.
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MAS/1997-7-1. Columbus, OH: Ohio EPA Division of Surface Water.
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