Although groundwater contamination is being detected with increasing frequency in every state, the overall qualitv of the nation's groundwater is good, according to the U.S. Geological Survey's fourth National Water Summary.

But management and protection of groundwater resources remain a challenge, says James W. Ziglar, assistant secretary of the Interior for Water and Science. "Most fresh groundwater meets federal and state drinking-water standards and is suitable for most uses, Ziglar said. "While we can take some comfort from the assurance that most of our groundwater is fit to drink, we must not be complacent."

The report contends that the ability to preserve and protect safe groundwater sources can be met most successfully through a coordinated and cooperative effort between local, state, and federal agencies and private organizations.

"From the information collected by the USGS, in cooperation with more than 950 other federal, state, and local agencies, there is a sound base of data and research on which the states can continue to build strong groundwater management and protection efforts; Ziglar said.

The USGS summary includes these findings:

• Groundwater provides drinking water for 53 percent of the nation's population, including more than 97 per-cent of its rural population.
• Groundwater is the source of about 40 percent of the average annual streamfiow in the United States.
• The national status of groundwater contamination from toxic chemicals and organic substances cannot be measured accurately because ofl a lack of consistent data and basic knowledge of groundwater systems.
• The highest concentrations of contaminants are found at small sites associated with landfills, industrial sites, and chemical and fuel storage sites. Lower concentrations, found over broad areas, are related to such land uses as agriculture, suburban development, and urbaniz-ation.
• Only a small percentage of the total volume of fresh groundwater is contaminated enough to impair use, and most of that is at shallow depths.

USGS spends about half of the $215 million that federal agencies spend each year on groundwater research and investigations.