By Audry Olmsted
Researchers create toolkit to pinpoint regions at high risk for groundwater contamination
In the Paso del Norte watershed, reliance on groundwater continues to increase dramatically, especially during times of drought. As reliance increases, so does the need to protect this resource from contamination. When visually inspecting the ground, people may not know how easily the aquifer under their feet can be polluted or how their activities affect neighbors around them.
Researchers at New Mexico State University have taken a “drastic” step to create a toolbox to detect the potential risk of groundwater contaminants from on-site septic systems and wastewater treatment systems in the Mesilla Basin aquifer.
“Protecting our water resource is very important,” said Christopher Brown, head of the Department of Geography. “It is extremely expensive and difficult to remediate groundwater pollution. The best thing to do is to protect our water resource and engage in practices that reduce the risk of its contamination, to maintain septic and wastewater treatment systems appropriately and, in the long run, to minimize the number of systems that exist in a particular area.”
All of the surface water in our region is used for agriculture and all of our drinking water comes from groundwater.
“From that perspective, our region is a sole source aquifer region,” Brown said. “All of our drinking water comes from groundwater and considerable areas of our urbanized region are off centralized systems. The potential risk that we are able to document from this has long-term negative impacts on the drinking water viability, quality of life and human health.”
Enter the DRASTIC model.
DRASTIC is an acronym for the components of a standardized risk assessment model used to determine the sensitivity of an aquifer to pollution from a surface contaminant. The DRASTIC model uses ArcGIS to compile data gathered from public sources into layers for seven components. The component layers are hydrogeological factors that affect the capacity of pollutants to reach the aquifer from the ground surface. These factors are: (D)epth to water table, net (R)echarge to the aquifer, (A)quifer media, (S)oil media, (T)opography, (I)mpact of the vadose zone, and hydraulic (C)onductivity of the aquifer. When the layers are ranked, weighted, and overlaid, a pollution risk surface is mapped over the study area.
DRASTIC is a joint project between NMSU’s Departments of Geography and Civil Engineering, the New Mexico Water Resources Research Institute in Las Cruces, Hawley Geomatters in Albuquerque and researchers at la Universidad Autónoma de Ciudad Juárez.
Student Steve Walker, a GIS technician at WRRI who is formulating the model as part of his thesis, is applying the DRASTIC model to an area of 1,032 square miles between Leasburg Dam just north of Las Cruces and the United States/Mexico border at Juárez.
Walker’s DRASTIC modeling work is part of a larger project funded through the Environmental Protection Agency Partnership with the Border Environment Cooperation Commission. In 1998, researchers took the DRASTIC model and customized it for New Mexico, factoring in the region’s geology and weather.
Walker has since taken that model and modified it to meet the needs of the study area.
“The components for the DRASTIC model exist everywhere,” Walker said. “Every region has its own soil types, geology, topography and depth to groundwater. Our idea is to build a toolbox that lets us ask and answer questions about aquifer vulnerability all along the U.S./Mexico border. There are a lot of places in rural areas off a centralized wastewater treatment system that have the potential risk of contamination. Our goal was to create a toolbox that can be used in other regions along the border.”
Once the data from the DRASTIC model are compiled, maps will be generated that show the potential risk of pollution across the study area. Researchers will then focus their educational and outreach activities on the areas with the greatest risk.
Researchers can then offer free outreach and education to people who live in the area.
“Our idea is to focus outreach efforts to educate folks about the proper way to maintain a functioning septic system, or the proper way to abandon a system no longer in use,” Brown said. “We want people to be more prudent about maintaining or abandoning them properly.”
The NMSU team is developing bilingual outreach materials for owners of septic systems. The public can participate in the outreach efforts on a voluntary basis.
Based on what they find through this research project that is deploying the DRASTIC model, Brown said they may share the information with the New Mexico Department of Health.