Soil Absorption and Treatment of Septic Tank Effluent

Septic tank effluent is inherently high in sodium ions relative to divalent cations (high sodium adsorption ratio). The disposal of septic tank effluent to the soil will cause the sodium ions to disperse the clay colloids, resulting in a physical blocking of the soil pores. Hydraulic conductivity will be reduced and the effluent will fail to dissipate into the soil profile. In designing the disposal system for septic tank effluent it is important to account for both the exchangeable sodium percentage of the soil and the sodium adsorption ratio of the effluent. Where high levels of either ESP or SAR are indicated, amelioration of either the effluent or the soil, or both, are required.