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Management Measures for Agricultural Sources- Facility Wastewater and Runoff- Large Confined Ani... Page 4 of 8 with the nutrient management measure. The size limitations that define a large unit are based on EPA's analysis of the economic achievability of the management measure. 4. Effectiveness information The effectiveness of management practices to control contaminant losses from confined livestock facilities depends on several factors including: • The contaminant(s)to be controlled and their likely pathways in surface, subsurface, and ground-water flows; • The types of practices(section 5) and how these practices control surface, subsurface, and ground-water contaminant pathways; and • Site-specific variables such as soil type, topography, precipitation characteristics, type of animal housing and waste storage facilities, method of waste collection, handling and disposal, and seasonal variations. The site-specific conditions must be considered in system design, thus having a large effect on practice effectiveness levels. The gross effectiveness-estimates reported in Table 2-9 simply indicate summary literature values. For specific cases, a wide range of effectiveness can be expected depending on the value and interaction of the site-specific variables cited above. When runoff from storms up to and including the 24-hour, 25-year frequency storm is stored, there will be no release of pollutants from a confined animal facility via the surface runoff route. Rare storms of a greater magnitude or sequential storms of combined greater magnitude may produce runoff, however. Table 2-10 reflects the occurrence of such storms by indicating less than 100 percent control for runoff control systems. 5. Confined Animal Facility Management Practices As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure described above. Combinations of the following practices can be used to satisfy the requirements of this management measure. The U.S. Soil Conservation Service (SCS) practice number and definition are provided for each management practice, where available. Also included in italics are SCS statements describing the effect each practice has on water quality (USDA-SCS, 1988). • a. Dikes (356): An embankment constructed of earth or other suitable materials to protect land against overflow or to regulate water. Where dikes are used to prevent water from flowing onto the floodplain, the pollution dispersion effect of the temporary wetlands and backwater are decreased. The sediment, sediment-attached, and soluble materials being transported by the water are carried farther downstream. The final fate of these materials must be investigated on site. Where dikes are used to retain runoff on the floodplain or in wetlands the pollution dispersion effects of these areas may be enhanced. Sediment and related materials may be deposited, and the quality of the water flowing into the http://www.epa.gov/owow/nps/MMGI/Chapter2/ch2-2bl.html 2/6/2009