Soil Texture Effects On Hydraulic Performance and Nitrogen Treatment of On-Site Wastewater Systems.

State regulatory agencies set standards for the length of onsite wastewater system (OWS) drainfield trenches based on expected hydraulic performance in soils of differing texture. Minimum lot size for homes on OWSs are also specified based on the expected nitrogen (N) load to groundwater. However, the data to support these standards are sparse. Radcliffe and West (2009) suggested design hydraulic loading rates for soil textural classes based on steady-state flow simulated with a 2D HYDRUS model. In a recent field study on a clay soil, Bradshaw et al. (2012) developed a 2D HYDRUS model for N treatment. Our objective was to use this model to test the hydraulic performance and N treatment for all 12 textural classes using two years of weather data from the field experiment. We found that the design hydraulic loading rates of Radcliffe and West (2009) were adequate, except for the sandy clay textural class in which the design rate was too high under actual rainfall conditions. N treatment varied widely among soils. Leaching losses of N were highest in the sand and loamy sand classes (85-97%), intermediate in the silt, silt loam, sandy loam, silty clay loam, and loam classes (57-71%), and lowest in sandy clay, silty clay, clay, clay loam, and sandy clay loam classes (26-40%). Lot sizes were largest in loam textures which had low denitrification losses and intermediate recharge.