Why Monitor Water Quality?
The water quality of the North Santiam River is important to more than 170,000 residents of the Salem, Oregon area that rely on the river as their primary source of drinking water. The river normally runs so clear that the City of Salem is able to use a relatively inexpensive and environmentally low-impact water-treatment process called slow-sand filtration. This process uses sand and gravel filters to remove suspended organic and inorganic particles in conjunction with natural biological processes to remove dissolved organic contaminants. If the river turbidity (see inset, right) is greater than 10 NTU, these filters can become clogged. To keep the facility running smoothly, the intake water is tested daily. If the turbidity remains consistently above 10 NTU, the water intakes are closed. During the 1996 flooding, the North Santiam River had turbidity values in excess of 100 NTU at the water-treatment facility intakes. (It is impossible to determine the exact maximum turbidity value b
