Soil Chemical Changes and Infiltration Rate Reduction Under Sewage Spreading

Laboratory and field lysimeters were used to investigate the site and nature of soil‐pore clogging under sewage spreading. The site of clogging was located by determining with a seepage meter the impedance profile at 0.5‐cm depth intervals. Soil samples were analyzed for sulfide, iron, phosphate, total organic matter, polysaccharide, and polyuronide to evaluate possible causative relationships. The infiltration rate loss exhibited three phases: phase I, a slow reduction under aerobic conditions; phase II, a rapid reduction under anaerobic conditions; and phase III, a further gradual decline under anaerobic conditions. The primary site of clogging was the 0‐ to 1‐cm depth of soil. Although sulfide was an indicator of anaerobic conditions, it was not a primary cause of clogging. Accumulations of the other five measured constituents may contribute to clogging in both phase I and phase II. Organic matter was the only probable clogging agent to decline as the infiltration rate was partially recovered in a rest cycle.