One way of categorizing the natural systems is to divide them between discharging and nondischarging systems. Discharging systems would include those with a surface water discharge, such as treatment ponds, constructed wetlands, and overland flow land treatment. Underdrained slow rate or soil aquifer treatment (SAT) systems may also have a surface water discharge that would be permitted under the National Pollutant Discharge Elimination System (NPDES). Nondis-charging systems would include slow rate land treatment and SAT, onsite methods, and biosolids treatment and reuse methods. Site topography, soils, geology, and groundwater conditions are important factors for the construction of discharging systems but are often critical components of the treatment process itself for nondischarging systems. Design features and performance expectations for both types of systems are presented in Table 2.1, Table 2.2, and Table 2.3. Special site requirements are summarized in Table 2.1 and Table 2.2 for each type of system for planning purposes. It is presumed that the percolate from a nondischarging system mingles with any groundwater that may be present. The typical regulatory
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