Georgia Water Resources: Groundwater Storage Change and Contamination Risks

The southeastern U.S. is experiencing groundwater decline, and the local geology in southeast Georgia has increased the risk of groundwater contamination, according to research from a NASA DEVELOP team.

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The Georgia Water Resources Team at the University of Georgia geography building. Image Credit: Caren Remillard

At the University of Georgia, a team of young scientists discovered that their region’s geology and contamination patterns can predict where pollution may affect groundwater, holding clues for the future of farmers and urbanites.

The Georgia Water Resources Team, part of NASA’s DEVELOP National Program, used applied sciences to research groundwater treatments in 2015. What they found has serious implications for local Georgia environments and the overall southeastern United States.

“The most important discovery was that the southeastern USA is experiencing groundwater decline, and that the local geology in southeast Georgia has increased the risk of groundwater contamination,” said Dr. Adam Milewski, the project science advisor for the Georgia Water Resources Team. Milewski is an assistant professor of water resources in the Department of Geology at the University of Georgia, and became involved with the project after researching groundwater storage change and dynamics for several years.

Groundwater resources are crucial for providing clean drinking water and supplying industrial and agricultural needs in southwest Georgia, so the entire region can benefit from knowing the relative volume and contamination rate of groundwater reserves.

To determine information about groundwater reserves, the team used data from the Gravity Recovery and Climate Experiment (GRACE) and a model based on depth-to-groundwater, net recharge, aquifer media, soil media, general topography, vadose zone (which is the soil between the surface and the water table), and hydraulic conductivity information. Combined, these terms form the acronym DRASTIC, which defines a method to analyze groundwater contamination risks. The team also created its own model, termed “DRASTICS,” that added sinkhole susceptibility as an analytic factor.

How sinkholes form when limestone dissolves. Image Credit: U.S. Geological Survey

How sinkholes form when limestone dissolves. Image Credit: U.S. Geological Survey

In doing so, the Georgia Water Resources Team was able to observe groundwater trends in local Dougherty County. The geologic aspects of contamination that Milewski described stem from the fact that most of the region’s geology is limestone.

Limestone dissolves easily when it encounters water that is even slightly acidic as most rain is. When this happens, the terrain acquires many “karst features” (a geologic term for the land features such as sinkholes that result from this dissolution). The entire Dougherty County region lies atop a limestone formation, which means that its groundwater falls easily into these karst features and becomes mixed with local contaminants from domestic, industrial and agricultural sources.

Understanding the karst topography and relative risk of sinkholes has many benefits for farmers and other professionals in the area.

Map of the Floridan Aquifer area surveyed for the DEVELOP study. Image Credit: Georgia Water Resources Team

Map of the Floridan Aquifer area surveyed for the DEVELOP study. Image Credit: Georgia Water Resources Team

“The ability to forecast sinkhole development and provide early warning information to farmers, land use planners and those with responsibility for ensuring drinking water quality will allow us to act proactively to protect our water resources and valuable infrastructure,” according to project partner Randy Weathersby.

The Georgia Water Resources Team also discovered that the overall Floridan Aquifer is experiencing a decline in total groundwater storage. The team believes that this decline may be in part due to the local expansion of agriculture and its byproducts, which means that farmers will need to consider groundwater more carefully in the future as part of their crop planning.

On the other hand, the contamination and decline of groundwater has negative implications for the local agricultural industry, as having contaminants in groundwater alters the soil environment.

In addition, karst features, sinkholes and other aberrations in otherwise solid ground make urban planning difficult. The urbanization process, coupled with population growth and urban land expansion, may facilitate increasing levels of high groundwater contamination risk in this area.

“We were impressed by how precisely the GRACE time-series reflected real-time groundwater change,” said Wenjing Xu, a project co-lead for this DEVELOP team. For example, the GRACE data tracked a severe drought that occurred in late 2000s in high detail, which Xu cited as a good illustration of GRACE’s usefulness. Using GRACE data, the team discovered that groundwater storage in the area declined at a rate of approximately 13.2 centimeters per year between 2002 and 2009.

This was not an entirely smooth process, however.

“Although GRACE data is great for groundwater monitoring, it has really coarse resolution,” Xu said.

“We realized the whole Dougherty County is covered by one single pixel and a single pixel cannot provide an accurate picture for groundwater storage change. Besides, groundwater change is not isolated by administrative boundaries,” she said, speaking to the difficulties in analyzing groundwater features on a county-specific basis.

Maps of groundwater storage variation in the Floridan Aquifer from 2002 (A), 2005 (B) and 2009 (C). Image Credit: Georgia Water Resources Team

Maps of groundwater storage variation in the Floridan Aquifer from 2002 (A), 2005 (B) and 2009 (C). Image Credit: Georgia Water Resources Team

As a result, the team scaled up their study to aggregate information from the entire Floridan Aquifer, allowing them to generate a holistic view of southwest Georgia.

This struggle added extra benefits to the end results, however. Thanks to that resolution problem, the information that the Georgia Water Resources Team found will be useful in future planning across the entire Floridan Aquifer, Xu said.

The results from this project likely won’t allow Georgians to reverse the damage already in place. Many of the contamination factors that the team identified in their modified DRASTIC model were based on natural underlying features, and therefore did not include present contaminants.

However, people living in the Floridan Aquifer area can use this data in the future. When city planners are looking to expand an urban area, they can rely on information about possible karst topography to avoid sinkhole disasters. And farmers will be able to look to groundwater contamination and storage data to determine where the soil is best for farming and find locations where they can best minimize agricultural pollution.