Cost-effective strategies for source-water protection and management

Not all water resources are equally vulnerable to contamination. Even areas having similar land uses and sources of contamination can have different degrees of vulnerability and, therefore, different response rates to protection and management strategies. NAWQA findings clearly demonstrate that natural features—such as geology, soils, and hydrology—and land-management practices—such as tile drainage and irrigation—can affect the movement of chemicals over land or to aquifers. Effective management of nonpoint source pollution may, therefore, require targeted strategies based on different degrees of vulnerability rather than uniform treatment of contaminant sources. Linking knowledge on natural features with the use, occurrence, and transport of chemicals through the watershed makes it easier to set priorities in streams and aquifers most vulnerable to contamination and increase the cost-effectiveness of strategies designed to protect water resources in diverse settings.

State of Washington—The Washington State Department of Health, in concert with USGS, assessed the vulnerability of public water-supply wells to pesticide contamination based on geology, well characteristics, land-use activities, and low levels of detection. NAWQA information on pesticide contamination enabled the health department to identify wells with low vulnerability to contamination and obtain waivers for quarterly monitoring required under the Federal Amendments to the Safe Drinking Water Act, 1996. By using the information to meet USEPA requirements for safe drinking water, Washington State was able to protect their drinking-water source while saving at least $6 million in costly additional monitoring. This is an annual savings of as much as $70 per household on small public supply systems that were granted full monitoring waivers.

State of New Jersey—NAWQA data on organic compounds are used heavily in New Jersey’s source-water assessment. USGS and the New Jersey Department of Environmental Protection are developing models to assess the vulnerability of public water supplies (including surface-water intakes and ground-water community and non-community wells) in the State to contamination by regulated compounds.

I coordinate the Upper Mississippi River Source Water Protection Initiative, an effort that will lead to the development of source-water protection plans for public water suppliers within the upper Mississippi River basin. The water quality data that have been generated and documented through NAWQA will figure prominently in the preparation of these plans. The information on certain contaminant levels in various settings within the basin, and the information describing the sources of contaminants provide documentation and solid rationale for identifying source water protection strategies, priorities, and protection measures for public water suppliers. In my opinion, more than any single information source, the Upper Mississippi River NAWQA provides an extremely valuable substantive basis for source water protection in the Upper Mississippi River basin (Mr. David Brostrom, Coordinator, Upper Mississippi River Source Water Protection Initiative, March 2001).

In addition to the examples cited above, more than 30 other states use USGS information to develop source-water protection plans for drinking-water sources. The collaborative projects in these states address nearly 40 percent of the nation’s public water supply, serving more than 90 million people.

USGS information is also used widely by states to develop management plans for constituents, such as pesticides, nutrients, and MTBE. Specifically, state environmental and natural resource agencies prioritize streams and ground-water areas for assessment of these constituents on the basis of vulnerability concepts, contaminant occurrence data, and quality-assurance protocols of the NAWQA Program.

State of Kansas—NAWQA findings on elevated concentrations of atrazine (frequently approaching or exceeding the USEPA drinking-water standard) in water-supply reservoirs in the Lower Kansas River Basin were used by the Kansas State Board of Agriculture as the basis for establishing a pesticide management area in northern Kansas (Delaware River Basin). Within this management area, the State of Kansas called for both voluntary and mandatory restrictions on pesticide usage on cropland to improve water quality. The management area was the first in the nation to focus on reducing atrazine in runoff to streams and reservoirs.

State of Washington—The Washington State Department of Ecology created a Ground Water Management Area to protect ground water from nitrate contamination. The management area covers Grant, Franklin, and Adams counties, located in an intensive agricultural region of the Central Columbia Plateau. NAWQA information and communication of those findings in the USGS publication "Nitrate Concentrations in Ground Water of the Central Columbia Plateau" provided the scientific basis for implementing the management area. As follow-up to the NAWQA findings, USGS works with the Department of Ecology to (1) identify areas with lower nitrate concentrations, which could potentially serve as sources of future drinking-water supplies, (2) statistically correlate nitrate concentrations with natural features and human activities to better assess vulnerability; and, (3) design a long-term monitoring strategy for assessment of changes in nitrate concentrations over time.

State of California—USGS works with the California State Water Resources Control Board and Department of Health Services to assess the vulnerability of public supply wells to contamination. The State uses USGS ground-water-age-dating analyses as one indicator of vulnerability. In addition, on the basis of NAWQA findings on the occurrence of industry-related and petroleum-based chemicals in ground water, the State has included the collection and analysis of VOCs in their vulnerability assessment. More than 200 wells have been sampled in southern California, and these efforts will be extended to northern California and the Central Valley.

State of Idaho—NAWQA information formed the framework for predictive models and maps showing the vulnerability of ground water to contamination by the widely used herbicide atrazine in Idaho. The maps are used by the Idaho State Department of Agriculture to develop its State Pesticide Management Plan. Atrazine data from the NAWQA study in the Upper Snake River Basin were used to calibrate and verify the predictive models, which showed that significant factors associated with elevated atrazine concentrations in ground water were atrazine use, land use, precipitation, soil type, and depth to ground water. These modeling tools aid in the design of cost-effective programs for monitoring and protecting ground-water resources throughout the State.

State of Pennsylvania—The Pennsylvania Department of Environmental Protection works with USGS as a follow-up to NAWQA findings on the prevalence of MTBE in ground water and its potential to contaminate public drinking-water supplies. Through the partnership, consistent and quality-assured data will be compiled, and a qualitative vulnerability rating for MTBE will be developed for different hydrogeologic settings throughout the State of Pennsylvania. The State will use the results to prioritize areas where MTBE should be assessed and where public-supply wells should be tested, and to target inspections of gasoline storage tanks.

National scale—At the request of the USEPA's Office of Ground Water and Drinking Water, the NAWQA Program published a national map that shows the patterns of risk for nitrate contamination of shallow ground water (available in “Nitrate in Ground Waters of the United States—Assessing the Risk, USGS FS-092- 96). By targeting regions with the highest risk of nitrate contamination, resources can be directed to areas most likely to benefit from pollution-prevention programs and long-term monitoring. Use of risk guidelines to locate areas for prevention of contamination also can result in cost-effective management. Once ground water is contaminated, it is expensive and, in many cases, virtually impossible to clean up.

Vulnerability can change over time

NAWQA findings show that the vulnerability to contamination of streams and ground water can differ seasonally in nearly every basin. For example, in streams that drain agricultural areas in many parts of the nation, the highest levels of nutrients and pesticides occur during spring and summer when recently applied chemicals are washed away by spring rains, snowmelt, and irrigation. Excessive amounts of contaminants can also enter streams during storm events. For example, sampling of nutrients and pesticides through a large storm event on the Potomac River in 1996 showed that concentrations and total amounts of nutrients and atrazine can increase during localized large storms, sometimes with overwhelming effects on receiving waters, such as the Chesapeake Bay. In this case, concentrations of individual compounds exceeded USEPA drinking-water standards during and following the extreme storm events. Such information helps water suppliers better understand the role of the short-term and seasonal events, and raises considerations related to timing of withdrawals, mixing, and storage to most effectively deliver high quality water at a minimum cost.