Chicago — The battle for pure ground water may demand closer attention by the states. Experts caution that the natural filtering of underground water by soil and rock has not kept toxic chemicals - and in some cases salt water - from seeping into supplies, particularly in industrialized urban and coastal areas.
States have long had the primary responsibility for controlling ground water, which supplies half the nation's drinking water. But states must raise the issue of water quality to a higher priority and take a careful inventory of the amount and quality of their water resources, water quality experts say.
''The thing suprising to a lot of us is the extent to which organic chemicals have gone in and stayed without breaking down,'' notes Marian Mlay, an administrator in the Envionmental Protection Agency's (EPA) Drinking Water Division.
Hydrologist Jay Lehr, executive director of the National Water Well Association, estimates that only a fraction of 1 percent of the available ground water supply has been contaminated. But he notes that much of the contamination is in densely populated areas, which magnifies its impact.
''The future of our water supply is in the ground,'' he insists. ''If we pollute it, it isn't going to be there for us. If we don't, we'll be in pretty good shape.''
''I believe the situation is soluble and that if we all pull together, we can win this battle by 1990,'' he told an audience of government, environmental, and business officials gathered here for a ''Ground Water in the '80s'' conference sponsored by the Great Lakes Rural Network. ''It's not a crisis situation. We have time to make a careful blueprint.''
In part, the close relationship between underground water in aquifers and wells and surface water in streams and rivers is prodding the new call for better state management. Ground water replenishes 30 percent of surface water and improves its quality by keeping streams moving and dilluting pollutants. Yet an estimated two-thirds of all US lakes and rivers have serious pollution problems. Ground water also faces a constant pollution challenge from 30,000 industrial waste dumps scattered around the country.
Washington has helped protect ground water by such measures as the Safe Drinking Water Act and the Resource Conservation and Recovery Act. The EPA has doubled to almost $8 million the amount it will spend this year on research into how contaminants move and act in ground water.
''There's significant federal legislation for the really horrendous things,'' says the EPA's Ms. Mlay. ''But basically the states must decide to what extent they want to protect what areas. We've been trying to encourage them to look at what they have and make these choices up front. . . . Often it takes political courage.''
''If states are going to act responsibly to protect the quality of ground water, they're going to have to act now . . . alone,'' agrees Jim Tripp, head counsel of the Environmental Defense Fund.
Connecticut is one of the few states with a statewide protection program. The program includes classification of all ground water sites according to the degree of pollution.
Ground water pollution is considered difficult to detect and treat. The contaminants move slowly in a clump sometimes hundreds of feet wide into aquifers and wells and remain in concentrated form. If discovered early, they can sometimes be pumped out and treated. But beyond a certain point, the task becomes uneconomical.
Experts insist that much of the job comes down to setting objectives, mapping the territory, and making tough decisions. Dr. Lehr estimates that as much as 85 percent of all ground water pollution problems have roots in ''gross'' mismanagement of water.