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Author: Radcliffe, David E. × Author: Bradshaw, J. Kenneth ×

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    A Nitrogen Model for Onsite Wastewater Systems
    (Georgia Institute of Technology, 2011-04) Radcliffe, David E. ; Bradshaw, J. Kenneth
    A constructed wetland two-dimensional model developed by Langergraber and Simunek (2005) was adapted to onsite wastewater systems (OWS). The model is an optional module in the HYDRUS (2D3D) variably saturated flow model. It predicts the fate and transport of nitrogen (N) species in the drainage trench and surrounding soil of an OWS. It is a multi-component reactive transport model that simulates 12 components and 9 processes. Concentrations of ammonium, nitrite, nitrate (NO3), nitrogen gas (N2), dissolved oxygen (DO), and three forms of organic matter are predicted. The mod-el simulations showed that conditions are dynamic in an OWS as water levels in the trench respond to daily dosing, precipitation, and evapotranspiration. The simulations indicated that NO3 losses occurred during dryer periods when DO concentrations were high enough in the trench for ammonium conversion to NO3, and outside the trench the high DO concentrations slowed denitrification, especially in the dryer area to the side of the trench. Predictions of NO3 losses compared well with an experimental OWS at Griffin, GA.
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    Nitrogen Dynamics in a Piedmont Onsite Wastewater Treatment System
    (Georgia Institute of Technology, 2011-04) Bradshaw, J. Kenneth ; Radcliffe, David E.
    Total Maximum Daily Load (TMDL) analyses of lakes and reservoirs with nutrient impairments commonly identify onsite wastewater treatment systems (i.e. septic systems) as an important potential source of nitrogen (N). In most cases, however, the contribution from on-site wastewater systems (OWSs) is difficult to estimate because of uncertainty about how much of the N is lost due to denitrification. The objective of this study was to quantify wastewater N concentrations in the soil and the extent of denitrification in an OWS commonly used in the Piedmont region. An OWS was installed in Griffin, GA and vadose zone N concentrations were monitored at different depths in the drainfield. Nitrate (NO3-N) concentrations remained low for the first four months after wastewater dosing began and then increased monthly for the next 11 months for all depths beneath the drainfield. The average NO3-N concentration at 90 cm on the last sampling date was 20 mg L-1. Denitrification was characterized in the drainfield by using Cl as a conservative tracer and calculating N/Cl ratios. We estimated that denitrification may account for up to 70% of N removal in OWSs. Currently, we are calibrating a model of the N dynamics using data from our experimental site. Once the model is calibrated, it will be used to estimate denitrification losses by OWSs in other regions by varying the soils and climate data
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    Land use effects on suspended sediment yield in six small Georgia watersheds
    (Georgia Institute of Technology, 2005-04) Bradshaw, J. Kenneth ; Radcliffe, David E. ; Lichtenstein, Karin ; Bakker, Mark ; Jackson, Rhett ; Markewitz, Daniel ; Risse, L. Mark
    In Georgia, over 600 stream segments are scheduled for TMDL development due designated use. Seventy-seven stream segments are listed for excessive sediment. The state does not have quantitative standards for the regulation of sediment concentration. The development of sediment yields using appropriate reference streams with minimum development may be a way to determine what the maximum daily sediment loading should be for impaired streams. This study was initiated to compare water quality in six streams with differing land use. This paper focuses on suspended sediment comparisons among the six streams. Two streams drain areas that are entirely forested and these represent reference streams for the purpose of this study. Two streams drain areas that are predominately agricultural (one dairy and the other a combination of poultry and cattle), and two streams drain areas that are in subdivisions with septic systems. Suspended sediment concentrations (SSC) and stream stage were measured during base flow and storm flow conditions. Annual sediment and water yields were calculated and for each stream for the years 2003 and 2004. Average SSC ranged from 155 to 720 mg/L and was lowest in one of the forested steams and highest in the dairy stream. Sediment yield ranged from 0.91 to 10.11 Mg/ha/yr and was lowest in one of the forested steams and highest in the dairy stream. In general, the forested streams had the lowest sediment yields, the agricultural watersheds had the highest sediment yields, and the suburban streams were intermediate.