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School of Civil and Environmental Engineering

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College of Engineering

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Georgia Water Resources Institute

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Georgia Transportation Institute

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Environmental Microbial Genomics Laboratory

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https://finding-aids.library.gatech.edu/agents/corporate_entities/385

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Now showing 1 - 10 of 29

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.
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.
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.
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
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.
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.
Phosphorus and Sediment in Headwater Streams Draining Poultry Operations in the Upper Etowah River Basin, Georgia

(Georgia Institute of Technology, 2007-03) Romeis, Josh ; Jackson, C. Rhett ; Radcliffe, David E. ; Risse, L. Mark ; Bryant, J.

A 1.5-year monitoring program was initiated in January 2005 to support a University of Georgia study aimed at evaluating nutrient trading opportunities for phosphorus (P) in the upper Etowah River basin in Georgia. Twelve first-order streams were instrumented with hydrologic monitoring equipment and automated samplers. Nine streams drain agricultural (AG) watersheds predominated by poultry operations but different in terms of land use history, best management practices, soil test P (STP) concentrations, and other factors. Three streams drain forested (FORS) watersheds. The monitoring program consisted of biweekly grab sampling coupled with stormchasing. From preliminary results, median low-flow and stormflow concentrations of total P (TP) in astreams were 0-1 and 1-3 orders of magnitude greater, respectively, than in FORS streams. The 3 highest median stormflow TP concentrations in AG streams were observed where 3 of the 4 highest STP concentrations were observed. Median low-flow total suspended solids (TSS) concentrations in AG streams were 0-1 order of magnitude greater than in forested streams. Median stormflow concentrations of TSS between the two land use types were within the same order of magnitude. Streamflow, STP, event mean concentrations, and other variables may be important for estimating P loads from agricultural watersheds monitored for the study.
Modeling Phosphorus Loading to Lake Allatoona: Implications for Water Quality Trading

(Georgia Institute of Technology, 2007-03) Radcliffe, David E. ; Lin, Z. ; Risse, L. Mark

Lake Allatoona, a large reservoir north of Atlanta Georgia that drains an area of about 2870 km2, is threatened by excessive algal growth and scheduled for a phosphorus (P) TMDL. In this paper, we use the Soil Water Assessment Tool (SWAT) computer model to estimate the total P load to Lake Allatoona during the periods 1992-1996 and 2001-2004. We also use the model to estimate the contribution from different sources in the watershed. The total P load to Lake Allatoona increased by 20% between the two time periods. The contribution from point sources decreased from 30% to 13% of the total load due to permit restrictions on P for poultry processing plants. The largest nonpoint source of P was estimated to be forest land use in 1992-1996 accounting for 31% of the load and urban land use in 2001-2004 accounting for 50% of the load. Poultry/cattle land use accounted for 18% in 1992-1996 and 15% in 2001-2004. The implications for a program to trade P credits are: 1) point sources and poultry/cattle operations account for similar percentages of the current load, 2) urban development accounts for most of the current P load and should be brought into a trading program, 3) poultry processing plants that have not upgraded to better P removal technology might trade their current load to wastewater treatment facilities that accept their wastewater, 4) cattle in streams and row crops are not large sources according to our model, and 5) there is little net loss of P to streams during transport to Lake Allatoona so distance of a source from the lake may not be important in a trading scheme.
Phosphorus, sediment, and e. Coli loads in unfenced streams of the Georgia Piedmont, USA

(Georgia Institute of Technology, 2005-04) Byers, Harris L. ; Cabrera, Miguel L. ; Matthews, Monte K. ; Franklin, Dorcas H. ; Andrae, John G. ; Radcliffe, David E. ; McCann, Mark A. ; Kuykendall, Holli A. ; Hoveland, Carl S. ; Calvert, Vaughn H., II

Contamination of unfenced streams with phosphorus, sediments, and pathogenic bacteria from cattle activity may be affected by the availability of shade and alternative water sources. The objectives of this study were to evaluate water quality in two streams draining tall fescue/ bermudagrass pastures with different shade distributions, and to quantify the effects of alternative water sources on stream water quality. Loads of DRP, TP, and TSS were measured during storm flow, and loads of DRP, TP, TSS, and E.coli were measured every 14 d during base flow in two streams located in the Piedmont region of Georgia. Our results showed that grazing cattle in pastures with unfenced streams contributed significant loads of DRP, TP, TSS, and E. coli to surface waters (p<0.01). Although storm flow was similar in both streams, loads of DRP, TP, and TSS were larger (p< 0.08) in the pasture with the smaller amount of non-riparian shade. Water trough availability significantly decreased (p< 0.08) base flow loads of TSS and E. coli in both streams. Our results indicate that possible BMPs to reduce P, sediment, and E. coli contamination from beef-cattle-grazed pastures may be to develop or encourage non-riparian shade and to provide cattle with an alternative water supply away from the stream.
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.