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VADOSE ZONE TREATMENT DURING EFFLUENT RECLAMATION AS AFFECTED BY INFILTRATIVE SURFACE ARCHITECTURE AND HYDRAULIC LOADING RATE

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

Citation:  Paper number  701P0104,  . (doi: 10.13031/2013.15825)
Authors:   K. N. Tackett, K. S. Lowe, R. L. Siegrist, S. M. Van Cuyk
Keywords:   On-site wastewater systems, soil absorption systems, nitrogen, phosphorus, DOC

On-site wastewater systems (OWS) commonly include pretreatment of raw wastewater in a septic tank followed by effluent discharge into a subsurface trench network from which effluent infiltrates and percolates through unsaturated soil before recharging the groundwater under a site. To advance the knowledge base regarding the dynamic and interdependent behavior of hydraulic and purification processes during wastewater effluent treatment in soil systems, a field research project was initiated at the Colorado School of Mines (CSM). In this project, 34 in situ test cells were established in a sandy loam soil at a field test site located on the CSM campus. The experimental design includes five replicates of each of three infiltrative surface architectures for a soil absorption trench and two hydraulic loading rates for domestic septic tank effluent (STE), plus several cells for control purposes. Purification of chemicals and pathogens achieved through infiltration and percolation of the effluent through the vadose zone is being assessed by sampling and analysis of the effluent applied and the soil solution at 60- and 120-cm beneath the infiltrative surface. The time dependent changes in hydraulic behavior associated with permeability changes at the infiltrative surface are also being examined. The focus of this paper is on the fate and transport of organic carbon, nitrogen, and phosphorus during OWS effluent infiltration and percolation through the vadose zone, while details regarding other facets of the research will be presented elsewhere. Test cell operation and monitoring was initiated in spring 2003 and is ongoing. Results to date indicate near complete removal of phosphorus after 60-cm of percolation, and greater than 85% removal of dissolved organic carbon in all test cells. Nitrification commenced to varying degrees in all test cells, leading to a decline in the near 100% removal of nitrogen observed initially. Incipient to continuous effluent ponding on the infiltrative surface was observed within one month of STE loading but this has had no apparent effect on effluent purification processes.

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