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Georgia Water Resources Conference

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Author: Radcliffe, David E. × End date: 2013 × Start date: 2010 ×

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Now showing 1 - 6 of 6
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    Modeling nitrogen in on-site wastewater treatment systems
    (Georgia Institute of Technology, 2013-04) Radcliffe, David E. ; Bradshaw, J. K.
    State regulatory agencies set standards for minimum lot size for homes on onsite wastewater treatment systems (OWTS) based on the expected nitrogen (N) load to groundwater. However, the data to support these standards are sparse. In a recent field study on a clay soil, we developed a two-dimensional model for N treatment. Our objective was to use this model to predict the N treatment for 12 soil textural classes using two years of weather data from the field experiment. We found that soil texture had a strong effect on OWTS performance. Denitrification losses varied widely among soils, from 1% in the sand class to 75% in the sandy clay class. This was due to the effect of water content on denitrification. Leaching losses to groundwater ranged from 27% in the sandy clay class to 97% in the sand class. It was important to consider differences in recharge among soil textural classes in estimating the minimum lot size to protect groundwater. The lot sizes ranged from 0.26 to 1.13 ha and were largest for mediumtextured soils where denitrification and recharge were intermediate.
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    The impact of on-site wastewater treatment systems on the nitrogen load and baseflow in urbanizing watersheds of Metropolitan Atlanta, Georgia
    (Georgia Institute of Technology, 2013-04) Oliver, C. ; Risse, L. Mark ; Radcliffe, David E. ; Habteselassie, M. ; Clarke, John S.
    On-site wastewater treatment systems (OWTSs) are widely used in the Southeastern United States for municipal wastewater treatment. As urban and suburban populations increase, the use of OWTSs is expected to further increase. This region heavily depends on surface waters for its water supply, therefore, the impact of OWTSs on surface water quality and quantity must be investigated. Conventional OWTSs can be potential sources of N pollution for groundwater and streams that can cause human health concerns and stimulate algal growth resulting in eutrophication. The overall goal of this project is to determine the impact of OWTSs on the N load and baseflow in urbanizing watersheds of Ocmulgee and Oconee River basins in Georgia. This paper presents preliminary results of the differences in the N load and baseflow as well as other water quality indicators such as electrical conductivity (EC) and chloride (Cl-) in streams of watersheds impacted by high (HD) and low density (LD) OWTSs. Synoptic samples and discharge measurements of 24 watersheds were taken 3 times per year in fall, spring, and summer under baseflow conditions. EC and Cl- concentrations were significantly higher in HD OWTS watersheds for all three sampling events. N concentrations were not statistically different between HD and LD watersheds for all three sampling events. Baseflow measurements in the fall and spring were not statistically different between HD and LD watersheds, but summer measurements were significantly higher in the HD watersheds. The results indicate the presence of OWTS effluent in streams of watersheds with HD OWTSs, while N analysis indicates a reduction in concentration through dilution and denitrification. However, increased baseflow in watersheds impacted by HD OWTSs results in an increase in total N load. Further analysis is needed to accurately determine and quantify the impact of OWTSs on water quality and quantity at the watershed-scale.
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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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    Correlating Sub-basin Sediment Fingerprints with Land Use in the Southern Piedmont
    (Georgia Institute of Technology, 2011-04) Mckinley, Robert ; Radcliffe, David E. ; Mukundan, Rajith
    This study seeks to further our ability to directly determine sediment provenance by utilizing the sediment fingerprinting technique and Rapid Geomorphic Assessments (RGAs) to determine both sediment contributions from potential sources and the stability of stream channels. Two sub basins of the North Fork Broad River (NFBR) were sampled for suspended sediment. Potential sources fall into three categories 1: surface (pastures and forests) 2: stream banks 3: upland subsurface (dirt roads, construction sites). Three tracers are being used in the study: total Carbon (TC), 15N, and Fatty Acid Methyl Esters (FAME). The Multivariate Mixing Model was used to determine relative contributions from source components. Results from the fingerprinting study were com-pared to RGA data in an attempt to establish a relationship between the two techniques. Currently we have sample data for 7 events in 2009 and 2010. Utilizing TC and 15N, the model output suggests a contribution of about 85% from stream banks and another 10% from pastures. The upland subsurface category is showing only a minimal contribution of about 5%. RGA data collected in 2008 show both tributaries to be unstable with mean stability indexes ranging from 17.2 to 17.6.
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    Streamwater Dissolved Organic Carbon and Total Dissolved Nitrogen: Effects of Timber Harvest in the Georgia Piedmont
    (Georgia Institute of Technology, 2011-04) Markewitz, Daniel ; Jackson, C. Rhett ; Fraser, Noah ; Radcliffe, David E.
    A paired watershed experiment of silvicultural best management practices first initiated in 1973 and harvested in 1974/75 was harvested for a second time in 2004. During the current harvest, BMPs were updated to reflect current guidelines. Stream water yield and physical and chemical attributes were monitored for one year pre-harvest and one year post-harvest. Here we report results for dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations and fluxes. In the treatment watershed, no response to harvest in the discharge-concentration relationship was observed. Based on double mass curves, however, the yield of DOC and TDN increased in the treatment watershed as a result of increased stream water fluxes, although the increased mass of DOC or TDN loss was relatively small.