Because percolate from SR and SAT land treatment can reach groundwater aquifers, the risk of pathogenic contamination must be considered. The removal of bacteria and viruses from the finer-textured agricultural soils used in SR systems is quite effective. A 5-year study in Hanover, New Hampshire, demonstrated almost complete removal of fecal coliforms within the top 5 ft of the soil profile (Reed, 1979). Similar studies in Canada (Bell and Bole, 1978) indicated that fecal coliforms were retained in the top 8 cm (3 in.) of the soil. About 90% of the bacteria died within the first 48 hr, and the remainder was eliminated over the next 2 weeks. Virus removal, which depends initially on adsorption, is also very effective in these soils.
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