Maintenance of Low Pressure Septic Tank Effluent Distribution Systems

Abstract

Low pressure distribution systems (LPD) are used to provide even distribution of septic tank effluent (STE) in septic system filter fields. LPD systems have been used to prevent surfacing of STE due to clogging of one area of the soil due to overloading, or to provide even distribution in high hydraulic conductivity soils for better treatment of the STE as it infiltrates through the soil. Even distribution of the STE is provided by pumping to pressurize small-diameter holes in the lateral pipe of the soil absorption trenches. The hole diameter is 3.2 mm and the pressure at the small orifi is typically designed for 1.5 m of water head (14.7 kPa). Concern has been expressed regarding clogging of the small-diameter holes. Instrumentation and data logging equipment were installed to measure and record the number and length of pump cycles for two separate and LPD lateral lines. The study has been ongoing since June, 1991, and the pump cycle times have been checked every two weeks. When the pump cycle times appeared excessive, the pressurized distribution pipes were opened and cleaned using a simple drain cleaning device. The cleaning procedure required approximately 30 minutes for two 12 m LPD laterals. Following the cleaning, pump cycle times were reduced. The cleaning was performed at intervals ranging from 35 to 66 weeks. The results of this field study show that a simple pump cycle timer and counter will provide information for maintenance of the pressurized laterals, and that approximately once per year, the laterals may need cleaning.