Typical design features and performance expectations for the three basic terrestrial concepts are presented in Table 1.3. All three are dependent on the physical, chemical, and biological reactions on and within the soil matrix. In addition, the slow rate (SR) and overland flow (OF) methods require the presence of vegetation as a major treatment component. The slow rate process can utilize a wide range of vegetation, from trees to pastures to row-crop vegetables. As described in Chapter 8, the overland flow process depends on perennial grasses to ensure a continuous vegetated cover. The hydraulic loading rates on rapid infiltration systems, with some exceptions, are typically too high to support beneficial vegetation. All three concepts can produce high-quality effluent. In the typical case, the slow rate process can be designed to produce drinking water quality in the percolate. Reuse of the treated water is possible with all three concepts. Recovery is easiest with overland flow because it is a surface system that discharges to ditches at the toe of the treatment slopes. Most slow rate and soil aquifer treatment systems require underdrains or wells for water recovery.
Another type of terrestrial concept is on-site systems that serve single-family dwellings, schools, public facilities, and commercial operations. These typically include a preliminary treatment step followed by in-ground disposal. Chapter 10 describes these on-site concepts. Small-scale constructed wetlands used for the preliminary treatment step are described in Chapters 6 and 7.
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