State and local requirements for buffer zones or setback distances from, for example, roads, wells, and property lines should be determined before the site investigation to be sure that the site is of an adequate area. Most requirements for buffer zones or separation distances are based on public health, aesthetics, or avoidance of odor complaints. The potential for aerosol transmission of pathogens has been a concern to some with regard to the operation of land application of wastewater and some kinds of sludge composting operations. A number of aerosol studies have been conducted at both conventional and land treatment facilities with no evidence of significant risk to adjacent populations (Crites et al., 2000). Extensive buffer zones for aerosol containment are not recommended. If the use of sprinklers is planned, a buffer zone to catch the droplets or mist on windy days should be considered. A strip 30 to 50 ft (10 to 15 m) wide planted with conifers should suffice. Odor potential is a concern for facultative-type pond systems, because the seasonal turnover may bring anaerobic materials to the liquid surface for a short period in the spring and fall. A typical requirement in these cases is to locate such ponds at least 0.25 mi (0.4 km) from habitations. Mosquito control for free water surface constructed wetlands may require setbacks from residences unless positive control measures are planned for the system. Recommended setback distances for land application of biosolids are listed in Table 2.21.
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