Septic System Effects on Lake Lanier

Tracking Phosphorus input to Atlanta’s Water Supply

RBC affiliate Dr. David Radcliffe, a soil scientist in the Department of Crop and Soil Science, will be using his expertise in septic systems, shallow groundwater flow, water quality, and modeling to evaluate certain aspects of Lake Lanier’s water quality. David will be working with RBC affiliates Dr. Susan Wilde, an ecologist in the Warnell School, and Dr. Gary Hawkins, an engineer and extension specialist in Crop and Soil Sciences, to estimate the amount of phosphorus being discharged into the lake by septic systems of lake house homes along the shoreline. The project will develop this estimate through a combination of groundwater and runoff measurements, lake sampling, and modeling investigations.

The groundwater investigation will consist of a two-year study of six lakeshore homes with mature septic systems at least 20 years old. The study will use a curtain drain parallel to the shoreline to intercept the septic system groundwater plume and develop a two-dimensional computer model using data collected from three homes by a pressure transducer and data logger. A transect of wells will be installed and used to determine concentrations of nutrients and bacteria. To estimate how much phosphorus is discharged to the coves as runoff from other sources such as fertilizer, runoff samplers will be installed at 3 sites where convergent groundwater flow and surface runoff during storms seems likely to occur.

For the lake investigation, Dr. Wilde will work with Georgia Tech scientists in deciding what to sample on the lake transects and Dr. Radcliffe will assist in analyzing the collected lake-bottom cores for historical evidence of phosphorous loading.

Nutrient pollution is one of America’s most widespread environmental problems and is caused by excess nitrogen and phosphorous in the air and water. Too much phosphorous in an aquatic ecosystem causes algae to grow faster than the ecosystem can handle. If the homes surrounding Lake Lanier that are on septic systems are put on sewer, there should be an immediate decrease in the phosphorous load because the groundwater flux will decrease with the reduction in loading to the drain field. Over time, there should be a more gradual decrease in load as bound phosphorous desorbs from adsorption sites along the groundwater flow path and dissolved phosphorus concentrations decrease.

Uploaded: 4/25/2018 | Text: Cyra Malec

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