FIGURE 5-1 Spatial and temporal scales of indicators for various applications.

potentially, to transient contamination of groundwater. Larger spatial scales and longer temporal scales (area B) are of importance in understanding overall sources of microbial loadings to a watershed (that may serve as a water supply) or in studying the contamination of an aquifer or well. Small spatial scales but long temporal scales (area C) may be useful in understanding “typical” conditions at a water supply intake on a river system for the purposes of developing treatment configurations to meet drinking water standards for finished water. Large spatial scales (area D) but short temporal scales may be useful in understanding the occurrence of contamination over a large recreational area under outbreak conditions or from a storm event.

The temporal and spatial requirements for each particular application largely dictate the types of indicators or indicator approaches employed and the methods for measuring these indicators. As discussed throughout this report, particularly in Chapter 6, what is needed is a phased monitoring approach that makes use of a flexible “tool box” in which a variety of indicator methods and approaches are available for measuring a given indicator or pathogen for differing applications and circumstances. In many indicator applications, the level of perceived public health threat will determine the method or methods employed, as well as the spatiotemporal granularity. The indicator method, frequency, and spatial coverage of sampling will have to be “adaptive” in the sense that more frequent samples

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