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WASTEWATER INFILTRATION RATE BEHAVIOR IN POROUS MEDIA AS AFFECTED BY INFILTRATIVE SURFACE ARCHITECTURE: METHODS DEVELOPMENT & EXPERIMENTAL RESULTS

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  701P0104,  . (doi: 10.13031/2013.15778)
Authors:   A. D. Diaz, R.L. Siegrist
Keywords:   clogging zone, infiltration, infiltrative surface, onsite systems, septic tank, wastewater treatment

Understanding of the infiltration rate (IR) behavior of soil-based wastewater treatment systems is crucial to achieving a system design that is hydraulically sound. Loss in permeability at and below the soil infiltrative surface (IS) occurs due to accumulation of pore-filling agents during wastewater application and can cause order-of-magnitude reductions in the clean water IR of a soil IS prior to wastewater application. The rate and extent of the zone of reduced permeability (clogging zone) has been shown to depend on the mass-loading rate of biochemical oxidizable substances and particulate matter. The effective mass-loading rate of these pollutants is thought to depend on the infiltrative surface architecture (ISA), which can be described using quantitative expressions for features such as the degree of exposed soil surface at the IS. Research was completed at the Colorado School of Mines (CSM) to develop methods to enable the study of IR behavior as affected by ISA and to test those methods through completion of initial laboratory experiments. The experimental methods include the following key features: (1) use of 1-D columns packed with various soil media and different infiltrative surface architectures, (2) application of aliquots of a wastewater surrogate material to provide pore-filling agent accumulations equivalent to those experienced under normal operation at increasingly longer periods of operation of months to one year or more, and (3) measurement of IR after each surrogate material addition using deionized water plus salts. In this research, five-centimeter (cm) diameter by 30-cm long columns were used with different degrees of open soil surface equivalent to 29, 51, 80, and 100% open. A clear correlation between IR and ISA was observed when using medium sand, with the greatest open area yielding the greatest final IR. Results with another soil media were supportive of this observation with medium sand. However one media tested was less conclusive due to experimental method limitations.

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