A federal water quality monitoring program has found that widespread levels of contaminants at very low concentrations are present in many U.S. river basins and aquifer systems. Mixtures of chemical compounds, degradation or breakdown products, and seasonal pulses of chemicals are also present in these water bodies, according to scientists with the U.S. Geological Survey. The scientists provided this information during a 14 May briefing on Capitol Hill, which USGS used to announce the release of a program report, Water Quality in the Nation's Streams and Aquifers - Overview of Selected Findings, 1991-2001.