Critical parameters in the design of urban soakaway systems in heavy rainfall regions
The influence of the hydraulic characteristics of subsurface soils in the performance of septicsoakaway systems is studied to achieve a very realistic design. In-situ infiltration tests were conducted on three marked horizons between 0 and 400 cm below the ground surface. Soil samples taken from the same locations were graded and classified, and then hydraulic conductivity was tested using laboratory methods. The three horizons were classified as loam soil, clayey soil and then sandstone. The infiltration rates through these were respectively determined as 52.43, 18.7 and 42.2 mm/hr; while their hydraulic conductivities were 6.49, 4.32 and 9.36 x10-1mm/hr, correspondingly. These results indicate that the middle layer has lower abilities of water absorption and conduction than the others below and above it. This implies that effluent absorption or movement through the medium would be slowed down causing effluent delay and flooding in the surrounding environment. Such failure can be avoided if the system design had taken the hydraulic parameters of the site soils into consideration.
Keywords: hydraulic characteristics, soil, septic-soakaway, heavy rainfall region