agement region. It is important to understand that it is easier to develop explicit control strategies as implied by Table 4.8 for sources such as outfalls from sewage treatment plants than for diffuse sources such as rivers, storm runoff channels, or atmospheric inputs.

Lessons from Existing Situations

In developing pollution control systems, much can be learned by studying the existing coastal pollution situation through detailed field observations and computer modeling. This effort will reveal the relative importance of different sources and information about the processes that are currently important in the coastal environment. For example, continuing with the hypothetical example discussed in Table 4.8, if the discharge point of an outfall for a POTW is moved to a new site much further offshore or the treatment is upgraded, then predictions can be made of the new ambient water quality to be achieved by modifying this one source while leaving unchanged all the other sources, such as CSOs, urban runoff, river discharges, atmospheric deposition, and other diffuse sources. Furthermore, when making water quality predictions, engineers usually have some past experience with discharges in the same region to provide data for model calibration and general guidance.

Ambient Water-Quality Objectives

The risk to human health and ecosystems and to our aesthetic appreciation of coastal water is linked directly to ambient water quality, which is often defined by measurable parameters such as concentrations of suspended solids, toxics, nutrients, bacteria and viruses, oil and grease, and dissolved oxygen. For instance, the risk management of pathogens has been systematized by setting standards for surrogates such as coliform bacteria or enterococci bacteria which can be monitored easily. Each individual discharger does not do a risk assessment for pathogens but uses a surrogate of fecal contamination. The deficiency in this approach is the inadequacy of the surrogate for predicting the presence (or absence) of various pathogens and not in the approach itself. (A more detailed discussion of this practice appears in Chapter 2 and Appendix B). Thus, bathing water standards can be set at various levels of bacteria or other appropriate organisms. Such limits constitute an explicit water quality standard used as an objective for engineers who design systems. Similarly, standards (or objectives) may be established to manage many risks. Setting objectives and standards is an important intermediate step for the design of management strategies and engineering systems.

Setting acceptable water-quality or sediment-quality standards for some



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