Boise To Reduce Phosphorus Through Innovative Offset Project

The City of Boise, Idaho plans to begin construction on an innovative means of meeting phosphorus removal requirements this spring. The Dixie Drain contributes about 40% of phosphorus that drains from the Boise River into the Snake River, as reported by the Boise State Public Radio. The drain, dug in the early 20th century, drains farmers’ fields into the river.

The Dixie Drain Phosphorus Offset Project, which has been in the planning stages for more than 4 years, will divert water from the drain into a three-phase treatment facility. Phosphorus will be removed using a simple chemical addition, coagulation, and settling process. The process is expected to remove about 64 kg (140 lb) of phosphorus per day. The treated water will be returned back to the drain.

This strategy will help Boise meet its phosphorus removal requirements under a U.S. Environmental Protection Agency (EPA) discharge permit by treating agricultural runoff in lieu of costly mechanical upgrades at the city’s treatment facilities. Rather than reduce phosphorus by 98% at the city’s two water resource recovery facilities (WRRFs), the city petitioned EPA to reduce their phosphorus output by 94% and achieve the rest offsite via the Dixie Drain project. For every 1 lb not removed at the WRRFs, the Dixie Drain project should remove 1.5 lbs, a Boise State Public Radio article states.

The Dixie Drain treatment facility will be located just upstream from the Boise River’s confluence with the Snake River. The project will remove more phosphorus closer to the problem with a smaller carbon footprint, lower cost per pound removed, and, according to the city, a better environmental outcome for the river. Read more.

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