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New Boise River Study Confirms High Phosphorous Levels

Boise river contributed 30 percent of total phosphorous to the Snake River system.

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Officials at Boise City Hall have been talking a lot about phosphorous lately--they'll be talking about it a lot more, along with their colleagues in Meridian, Nampa and Caldwell. They have all received a new U.S. Geological Survey report documenting a two-year study of water quality. The bottom line is that scientists found that between September 2008 and October 2010, the Boise River contributed 30 percent of total phosphorous to the Snake River system.

That's a problem. While phosphorous is necessary for plant or animal growth, too much phosphate can choke a waterway with algae and waterweeds, using up huge amounts of oxygen and ultimately threatening fish and aquatic organisms. More importantly, the Environmental Protection Agency is set to unveil new phosphorous restrictions this year. As BW reported last summer (BW, News, "Water, Water," Aug. 3, 2011), recent phosphorous levels at the outtakes of Boise's wastewater treatment facilities had been measured at 5,500 micrograms per liter. The EPA's new guideline is expected to be closer to 70 micrograms per liter, an 8,000 percent targeted improvement.

That's why Boise, Meridian, Nampa and Caldwell commissioned the USGS to quantify how much phosphorous was contributing to the Snake River system.

"We've known all along that the Boise River has a phosphorous problem," said Tim Merrick, science information manager at the Boise USGS office. "But we really didn't know the quantification of how much it was contributing to the Snake."

The baseline data will be an essential tool for regional resource managers to make critical decisions--both economic and environmental. A recent 2.5 percent bump in City of Boise sewer rates was necessary for an immediate $5 million in capital improvements to mitigate phosphorous levels. Long-range improvement to the West Boise Wastewater Treatment Facility could cost anywhere from $67 million to $92 million.

"Our hope is to find the funding to continue this monitoring," Merrick told Citydesk. "We mounted automatic sampling equipment at three different sites, and that's much more efficient than when our technicians had to collect samples."

Merrick said most of the survey work is cooperatively funded. That means partners and the USGS split the cost. For FY 2011, the project costs totaled $162,000.