Provides recommendations for the secondary treatment and safe disposal of septic tank effluent, detailing the design, sizing, and location of soak pits, dispersion trenches, and biological filters based on soil percolation tests.
Recommends practices for the location, sizing, and cleaning of septic tanks for optimal performance.
Quick Reference Values
min distance from drinking water source18 m
min clearance from buildings5 m
min clearance from trees3 m
min depth to ground water table1.5 m below bottom of absorption system
percolation test hole size300 mm square or 150-300 mm diameter
Key Formulas
Q = 130 / √t — Maximum rate of effluent application (l/m²/day), where t is standard percolation time in minutes
Practical Notes
Always conduct a soil percolation test to determine if the soil is suitable for absorption systems; impermeable soils (t > 60 min) require biological filters or upflow anaerobic filters.
Ensure the absorption system is located downstream of any drinking water wells to prevent groundwater contamination.
The absorption area should be kept free of deep-rooted trees to prevent root intrusion and system clogging.