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MODELING SUBSURFACE DRIP APPLICATION OF ONSITE WASTEWATER TREATMENT SYSTEM EFFLUENT
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15765)Authors: R. A. Beggs, G. Tchobanoglous, D. Hills, and R. W. Crites
Keywords: subsurface drip irrigation, SDI, septic, onsite wastewater, Hydrus 2D, solute transport
The use of subsurface drip irrigation for the disposal/reuse of septic tank effluent began to gain interest in the 1990s. Using subsurface drip irrigation, effluent can be applied at a lower rate over a larger area and in a more biologically active part of the soil profile than with standard deep infiltration trenches. Subsurface drip irrigation also makes the water and nutrients potentially more available for uptake by plants. Various models developed over the years have been applied to model infiltration, soil nitrogen, and general vadose zone transport scenarios. Based on an evaluation of available models, Hydrus 2D was selected as being capable of adequately modeling the geometry and transport, and having many specific useful features for modeling subsurface drip irrigation. Modeling was then performed for various soils, emitter spacings, depths, and loading rates. Modeling results showed that a system designed for efficient irrigation generally minimized annual nitrate percolation. Nitrification of septic tank effluent prior to subsurface drip application increased nitrate percolation. Nitrification and denitrification rates in the soil profile were enhanced when effluent was applied in a brief daily pulse rather than continuously. Finer soil texture also minimized nitrate percolation. Other results and plans for controlled soil bed tests are presented.
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