The Quality of the Nation’s Groundwater: Progress on a National Survey

New reports assess the quality of drinking-water supplies in five regional aquifers of the nation.

Release Date: December 7, 2017

The U.S. Geological Survey is near the midpoint of a complex undertaking to survey the quality of the nation’s largest drinking-water resource.

Current website: https://www.usgs.gov/news/quality-nation-s-groundwater-progress-a-nation...

This story was updated on April 1, 2020.

Beginning in 2012 and continuing through 2021, the USGS has been extensively sampling groundwater throughout the country and assessing its suitability for drinking water. The latest results from four regional aquifers have become available and have been added to previously released results for eleven regional aquifers.

About half of the nation’s population relies on groundwater for drinking water. As the nation’s population grows, the need for high-quality drinking-water supplies becomes even more urgent.

The USGS has identified 68 principal aquifers—regionally extensive aquifers that can be used as sources of drinking water—across the country. Groundwater pumped from these aquifers provides nearly 50 percent of the nation’s drinking water. Twenty of these principal aquifers account for about 75 percent of the nation’s groundwater pumped for public supply. These aquifers also provide 85 percent of the groundwater pumped for domestic (private) supply. These twenty principal aquifers are being intensively evaluated by the USGS National Water-Quality Assessment Project, which is scheduled to run from 2012 through 2021. Summary results for fifteen principal aquifers are now available online at the links below.

“The National Water-Quality Assessment Project is critical in helping resource managers understand how contaminants are introduced into the environment. This knowledge helps them make informed decisions about how to manage the nation’s water resources,” said Don Cline, USGS Associate Director for Water. “Understanding the quality of our water is critical in sustaining this resource for generations to come.”

A Deep Look at an Unseen Resource

Most consumers receive water that has been treated by local utilities to meet federal drinking-water standards. Understanding what constituents are in source water before it is treated can help decision makers manage and treat water resources. USGS scientists are assessing water quality in source water from wells in principal aquifers across the country.

This comprehensive sampling is focused on public-supply wells that tap deeper groundwater. Along with detailed information on geology, hydrology, geochemistry and chemical and water use, this data can be used to explain how and why groundwater vulnerability to contamination varies across the nation.

These regional aquifer studies provide water utilities and resource managers with information about:

Regulated and unregulated constituents from natural or human sources;
Pesticides, volatile organic compounds, and other constituents of concern for human health;
Present groundwater quality as a baseline for future conditions;
Regional and national statistics on water quality, which provide context for individual wells;
Differences in water quality between the shallow and deep parts of aquifer systems;
Environmental tracers that can be used to understand sources and sustainability of groundwater supplies;
Local, regional and national hydrogeology.

New Regional Aquifer Studies

In-depth, regional-scale assessments conducted or planned for 2012 through 2021 focus on 20 of the most heavily used aquifers in the nation. Groundwater quality results for principal aquifers sampled in 2016 are available today, in addition to those previously available for principal aquifers sampled between 2012 and 2015, and are summarized in the fact sheets below. Almost 1,100 deep public-supply wells were sampled within these aquifers, which were analyzed for a broad range of water-quality constituents.

NEW: The Columbia Plateau basaltic-rock aquifers (northwestern U.S.)
NEW: The High Plains aquifer (west central U.S.)
NEW: The Ozark Plateaus aquifer system (central U.S.)
NEW: The Biscayne aquifer (southeastern Florida)
The Floridan aquifer system (southeastern U.S.)
The Mississippi Embayment-Texas Coastal Uplands aquifer system (south-central U.S.)
Rio Grande aquifer system (southwestern U.S.)
Glacial aquifer system (northern U.S.)
Cambrian-Ordovician aquifer system (north central U.S.)
Piedmont and Blue Ridge crystalline-rock aquifers (eastern U.S.)
Basin and Range basin-fill aquifers (western U.S.)
Valley and Ridge carbonate-rock aquifers and the Piedmont and Blue Ridge carbonate-rock aquifers (eastern U.S.)
Northern Atlantic Coastal Plain aquifer system (east coast of U.S.)
Southeastern Coastal Plain aquifer system (southeastern U.S.)
Coastal Lowlands aquifer system (south central U.S.)

Findings

Contaminants in groundwater have a wide range of sources, both manmade and geologic, as a 2014 USGS water quality summary explains. Most organic (carbon-based) chemicals in groundwater that are of concern for human health are manmade compounds, such as solvents and pesticides. In contrast, most inorganic constituents in groundwater have geologic or other natural sources, although their concentrations in groundwater may be altered by human activities , such as irrigation and groundwater pumping. Some contaminants have both manmade and natural sources. For example, nitrate in groundwater has many natural sources, but nitrate concentrations in groundwater underlying agricultural and urban areas commonly are higher than in other areas, because of contributions from sources associated with human activities.

Groundwater quality of principal aquifers is assessed in the fact sheets by comparing measured concentrations to benchmarks established for drinking-water quality to protect human health and aesthetics, such as taste and odor..

At least one inorganic constituent exceeded a human-health benchmark in 3 to 50 percent of samples collected from the 15 principal aquifers.
Organic contaminants did not occur at levels above human-health benchmarks.
Contaminants from geologic sources—primarily trace elements such as arsenic, fluoride, and manganese—most commonly exceeded human-health benchmarks. In the Biscayne aquifer and the Floridan aquifer system, the trace element strontium—a constituent from geologic sources— was the only trace element to exceed human-health benchmarks.
At least one radioactive constituent exceeded a human-health benchmark in a small percentage of samples in most of the 15 aquifers studied. Exceedances ranged from 0 to 10 percent. The exceptions were the Piedmont and Blue Ridge crystalline-rock aquifers and the Cambrian-Ordovician aquifer system, where exceedances were 30 and 45 percent, respectively.
The nutrient nitrate was the only constituent from manmade sources that exceeded the human-health benchmark, typically in a low percentage of samples (0 to 3 percent). These exceedances occurred in the High Plains aquifer, the Columbia Plateau basaltic-rock aquifers, the Glacial aquifer system, the Rio Grande aquifer system, and the Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers.

Looking Forward

Understanding how natural features and human activities affect groundwater quality helps to predict how and why groundwater vulnerability to contamination varies across the nation. Over the next few years, results will be released for more principal aquifers that are important sources of drinking water for the nation, as the National Water-Quality Assessment Project continues to address three central questions: