Column Studies of Soil Clogging in a Slowly Permeable Soil as a Function of Effluent Quality

Abstract Clogging as a function of effluent quality was investigated in cores of the very slowly permeable Almena silt loam soil which offers problems for conventional on‐site liquid waste disposal. Undisturbed 60 cm long cores were subjected for approximately 120 days to constant ponding with simulated septic tank effluent, extended aeration effluent and distilled water. Column influents and effluents were monitored with respect to chemical oxygen demand (COD), biochemical oxygen demand (BOD), and solid residue fractions. Column influents differed markedly in COD and BOD content but column effluents had consistently low contents indicating the high renovative capacity of the soil. In situ tensiometric, redox, and flow rate measurements indicated development of the most severe barriers to flow in columns ponded with low BOD aerated effluent, followed closely by those ponded with high BOD septic tank effluent. No barriers developed in columns ponded with water. Total concentrations of solid residue fractions in the two effluents and the cumulative load of solids applied to the columns did not differ significantly, but particle sizes in the aerated effluent were smaller. Increased pore clogging in aerated influent treatments points to the significant role of effluent solids in the clogging process in slowly permeable clayey soils. Additional studies are in progress to better define critical waste characteristics as related to soil clogging.