Technical Report No. 2
INFILTRATION AND PERCOLATION OF SEWAGE THROUGH OAHU SOILS IN SIMULATED CESSPOOL LYSIMETERS
Melvin K. Koizumi, Nathan C. Burbank, and L. Stephen Lau
August 1966
ABSTRACT
This study investigated conditions contributing to cesspool failure and followed selected parameters to measure the degree of treatment afforded sewage in cesspool disposal. This laboratory study utilized bench scale soil lysimeters and two basic soil types: the Wahiawa Low Humic Latosol and the Lolekaa Humic Latosol. The soils were specimens from areas of potential urban development within known ground water recharge zones. The soils were molded into an “L” shape in the lysimeters to simulate the corner of a cesspool. The lateral soil column was 11 inches wide and the bottom soil layer was ten inches deep. A constant head of 11 inches was maintained in the pool of all for thirty to forty days. Pressures throughout the flow field were determined by piezometers and manometers. The side and bottom drains in the lysimeters allowed separate sampling and flow rate determinations. The Hawaiian soils exhibited typical die-away curves of infiltration with time depending on physical, chemical, and microbial qualities of both the feed and soil. Infiltration rates ranged between 0.7 to 3.6 ft/day. A 99% reduction of the infiltration rate was evidenced by the Wahiawa soil over the experiment-period of 30 to 40 days. Both sewage-fed lysimeters containing the Low Humic Latosol developed a pan-like layer of soil fines approximately 3 cm below the bottom of the cesspools, preventing the penetration of suspended solids after seven days. The Lolekaa soil did not show such changes. Flow nets plotted from pressure readings of the Wahiawa Low Humic Latosol showed that clogging occurred in the 8 to 10-cm zone of the side wall and the soil base of the lysimeters containing this soil. Flow through the lysometer was governed by infiltration, rather than percolation. Visual observation and negative manometer readings showed that unsaturated flow conditions were always present in all of the lysimeters throughout the experimental period. Both domestic and synthetic sewage fed exhibited a 90% reduction in organic nitrogen and a 62 to 96% reduction in COD. The oxidation reduction potential reading (-340 mv) indicated that anaerobic conditions existed within the cesspool: appreciable concentrations of nitrates in the effluent indicated that aerobic conditions existed in the soil mass surrounding the cesspool. The results of this experiment indicate that unless further degradation of the effluent is effected by the soil mass, the incomplete degradation of the sewage makes it a definite hazard to ground water sources. This study presents soil-effluent inter-reaction at a one-foot depth. No conclusive evidence exists to substantiate any further degradation of the effluent by the soil at greater depths to the required U.S. Drinking Water Standards of 45 mg/l of nitrates.