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January 19, 2017

A regional assessment of untreated groundwater in the Coastal Lowlands aquifer system in the southeastern United States is now available from the U.S. Geological Survey.

The Coastal Lowlands aquifer system ranks fourth in the nation as a source of groundwater for public supply and fifth as a source of private domestic supply, providing about one billion gallons per day for this use. The cities of Houston, New Orleans, Baton Rouge and Mobile are included within the boundaries of the aquifer.

Scientists tested for a broad range of water-quality characteristics of untreated groundwater in the Coastal Lowlands aquifer. Results show inorganic constituents present at high concentrations, meaning at levels exceeding human-health benchmarks, in about 12 percent of the study area. Human-made organic constituents (both pesticides and volatile organic compounds) were not detected at high levels. The study area includes water at the depth used for public supply. The study evaluated untreated drinking water, but compared results to drinking-water quality standards. The full report is available online.

Many inorganic constituents occur naturally in groundwater. The inorganic constituents found at high levels that surpass human-health benchmarks in this study area include arsenic, manganese and the radioactive constituents known as gross alpha activity and radon-222. Total dissolved solids, a measure of the amount of salt in groundwater, was also found at high levels. Concentrations of inorganic constituents can be affected by natural processes as well as by human activities. Results show one or more inorganic constituents present at high concentrations in about 12 percent of the aquifer system and at moderate concentrations (between half the human-health benchmark and the benchmark concentration) in about 18 percent.

The scientists evaluated groundwater quality in the Coastal Lowlands aquifer system by sampling 60 public-supply wells distributed across the aquifer. This study area overlying the Coastal Lowlands aquifer system includes 99,000 square miles along the Gulf Coast in Texas, Louisiana, Mississippi, Alabama and Florida. Land use is composed primarily of agricultural (24 percent) and natural (67 percent) land, with a relatively small percentage of urban (9 percent) land.

Groundwater provides nearly 50 percent of the nation’s drinking water. To help protect this vital resource, the USGS National Water-Quality Assessment, or NAWQA, Project of the National Water Quality Program assesses groundwater quality in aquifers that are important sources of drinking water.

Over the last two decades, USGS scientists have assessed water quality in source (untreated) water from 6,600 wells in extensive regional aquifers that supply most of the groundwater pumped for the nation’s drinking water, irrigation and other uses. This comprehensive sampling, along with detailed information on geology, hydrology, geochemistry and chemical and water use, can be used to explain how and why aquifer vulnerability to contamination varies across the nation.

Map showing location and summary of water-quality results for five principal aquifers currently available.
Map showing location and summary of water-quality results for five principal aquifers currently available. For more details, please refer to the linked resources in this story.

Between 2013 and 2022, NAWQA will continue to assess the quality of the nation’s groundwater by sampling about 2,300 shallow wells and 1,400 deep public-supply wells for a broad range of water-quality constituents. In the future, USGS-led national- and regional-scale modeling will provide a three-dimensional perspective of the quality of the nation’s groundwater that can be used to inform management decisions. More information on USGS regional aquifer assessments can be found in this recent USGS Top Story.

To learn more, visit these websites:
USGS National Summary Circular, Quality of the Nation's Groundwater Quality, 1991-2010
Regional reports on principal aquifers of the U.S.
National Water-Quality Assessment (NAWQA) Project
USGS Groundwater Information

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