Hydraulic Conductivity Estimation Test Impact on Long-Term Acceptance Rate and Soil Absorption System Design

The aim of this paper was to verify the common methods of hydraulic conductivity estimation for soil assessment in respect to wastewater disposal. The studies were conducted on three types of sandy soils. Hydraulic conductivity was determined using a scale effect-free laboratory method, empirical equations and compared with measurements estimated from a laboratory infiltration column with identified head loss. Based on the hydraulic conductivity values, the long-term acceptance rates (LTAR) [1] were calculated. The differences in LTAR values were about one order of magnitude smaller than differences in hydraulic coefficient. The study showed a good convergention of the results obtained from the constant head method (CHM) by solving the Glover Equation for medium and coarse sands. In low permeability soil (fine sand), the best result was obtained using CHM-a with a capillary rise consideration (a is a factor included in the flow in the unsaturated and saturated zones calculated from a capillary rise). From a practical point of view the relatively small value of LTAR underestimation (20%-for constant head method) is responsible for the extended surface area of the system and provides a security margin (the avoidance of clogging risk). The use of the falling head method, based on the Van Hoorn equation, can be said to be highly overestimated. For medium and coarse sandy soils the underestimation of LTAR calculated and based on CHM test determination is 14%–18%. The total cost of soil absorption system (SAS) designed-based on CHM in comparison to that designed-based on real hydraulic conductivity value in Poland is only about 7%–9% higher