David K. Mueller John S. Zogorski Sarah J. Ryker Robert J. Gilliom 2002 <p><span>Most </span><span class="searchword">water</span><span>-</span><span class="searchword">quality</span><span> problems we face today result from diffuse "nonpoint" sources of pollution from agricultural land, urban development, forest harvesting and the atmosphere (U.S. Army Corps of Engineers et al., 1999). It is difficult to quantify nonpoint sources because the contaminants they deliver vary in composition and concentrations from hour to hour and season to season. Moreover, the nature of the contamination is complex and varied. When Congress enacted the Clean </span><span class="searchword">Water</span><span> Act 30 years ago, attention was focused on </span><span class="searchword">water</span><span>-</span><span class="searchword">quality</span><span> issues related to the sanitation of rivers and streams - bacteria counts, oxygen in the </span><span class="searchword">water</span><span> for fish, nutrients, temperature, and salinity. Now, attention is turning to the hundreds of synthetic organic compounds like pesticides used in agricultural and residential areas, volatile organics in solvents and gasoline, microbial and viral contamination, and pharmaceuticals and hormones.</span></p> application/pdf en A national look at water quality article