As agreed with their offices, this report describes (1) the human activities that may have contributed to the high turbidity levels in five western Oregon municipal watersheds during and following the storm and (2) the efforts under way by federal, state, local, and private land managers and owners, as well as the affected cities, to ensure safe drinking water during future storms. Human Activities Contribute to Increased Turbidity During Large Storms

Our review of scientific studies and other documents showed that human activities—timber harvests and related roads as well as agricultural, industrial, urban, and residential development—can contribute to elevated sediment levels during large storms. These activities result in soil that is compacted, paved, covered, or cleared of most vegetation. Rain falling on such soil and surfaces can run off into streams, carrying with it eroded topsoil. This sediment from human activities in a municipal watershed, combined with the accelerated erosion that naturally occurs during storms, can shut down a municipality’s water treatment system, as occurred in Salem in February 1996. During storms, this increased runoff moves across barren or disturbed soil, eroding the soil, which can then be transported into streams. However, according to Salem officials, the type of fine sediments after the February 1996 flood would still result in a “treatment challenge” and “may result in finished water exceeding drinking water standards for turbidity.”

	Progress Has Been Made to Ensure Safe Drinking Water During Future Storms

Ongoing federal and nonfederal efforts have made significant progress in (1) mitigating the impact of human activities on water quality and in ensuring safe drinking water for cities in the Willamette and Lower Columbia river basins and (2) involving more key landowners and other stakeholders in discussing, understanding, and addressing watershed issues and concerns and in implementing restoration plans. Nevertheless, some key landowners have not been included in coordination efforts, and many efforts could benefit from a better understanding of, and data on, the condition of the watersheds.
Why GAO Did This Study

Pursuant to a congressional request, GAO provided information on five municipal watersheds in Oregon and the activities that contribute to increased turbidity during large storms, focusing on the: (1) human activities that may have contributed to the high turbidity levels in western Oregon's municipal watersheds in February 1996; and (2) efforts under way by federal, state, local, and private land managers and owners, as well as the affected cities, to ensure safe drinking water during future storms.

What GAO Found

GAO noted that: (1) human activities--timber harvests and related roads as well as agricultural, industrial, urban, and residential development--can contribute to elevated sediment levels during large storms; (2) these activities result in soil that is compacted, paved, covered, or cleared of most vegetation; (3) rain falling on compacted or cleared soil can run off into streams, carrying with it eroded topsoil; (4) in addition, rain falling on roofs, paved roads and parking lots, and other covered surfaces does not penetrate into the ground, thereby increasing the runoff that moves across barren or disturbed soil and eroding topsoil; (5) this sediment can then be transported into streams; (6) the sediment from human activities in a municipal watershed, combined with the accelerated erosion that naturally occurs during storms, can shut down a municipality's water treatment system, as occurred in Salem in February 1996; (7) ongoing federal and nonfederal efforts have made significant progress in: (a) mitigating the impact of human activities on water quality and ensuring safe drinking water to cities in the Willamette and Lower Columbia river basins; and (b) involving more key landowners and other stakeholders in discussing, understanding, and addressing watershed issues and concerns and in implementing restoration plans; and (8) nevertheless, some key landowners have not been included in coordination efforts, and many efforts could benefit from a better understanding of, and data on, the condition of the watersheds.