17-010 Corps invites public comments on Dworshak Long-Term Nutrient Supplementation Program draft FONSI and Environmental Assessment

Published Jan. 27, 2017

AHSAHKA, Idaho – The U.S. Army Corps of Engineers’ Walla Walla District invites public comments on a Draft Finding of No Significant Impact (FONSI) and Environmental Assessment (EA) for the Corps' proposed “Dworshak Long-Term Nutrient Supplementation Program.” Public comments are being accepted from Friday, Jan. 27, 2017, through Monday, Feb. 27, 2017.

The Draft FONSI and EA documents are available on the Walla Walla District website at http://www.nww.usace.army.mil/Missions/Environmental-Compliance/. The Corps will consider all comments submitted as it performs this environmental review.

The Corps proposes to implement a long-term nutrient supplementation program at the Dworshak Dam and Reservoir Project on the North Fork of the Clearwater River near Ahsahka, Idaho. The purpose of the long-term program is to enhance the biological productivity of Dworshak reservoir, primarily to improve the kokanee fishery and to decrease growth of undesirable blue-green algae, which can be hazardous to human and animal health and competes with desirable plankton for nutrients.

In the EA, the Corps considered five alternatives. These alternatives included changing reservoir operation, mixing reservoir sediments, distributing fish pellets or carcasses around the reservoir, applying liquid fertilizer to the reservoir, or taking no action. The Corps’ proposed alternative is to continue applying liquid fertilizer to add nutrients to the reservoir, as was previously done under two pilot studies.

The Corps started a Dworshak Nutrient Supplementation Pilot Project study in 2007 in conjunction with the Idaho Department of Fish and Game (IDFG) to assess the feasibility of increasing the biological productivity of Dworshak Reservoir and abundance of edible phytoplankton (plant-like plankton) by adding inorganic nitrogen liquid fertilizer. The Corps and IDFG agreed to suspend the pilot study in July 2010, restarted it in 2012, and continued it from spring 2012 to fall 2016. Monitoring data collected during this period indicated the effects of the nutrient supplementation were positive compared with data collected from the reservoir before the addition of the nitrogen. A summary report prepared after the 2015 growing season indicated the amount of edible phytoplankton, zooplankton biomass, primary productivity, and kokanee size increased while the amount of toxin-forming blue-green algae decreased. Drinking water has not been affected by nutrient supplementation.

The North Fork of the Clearwater River is naturally nutrient-poor because of the underlying geology, soils and land use. In the years immediately following Dworshak Dam construction completion in the 1970s, the reservoir initially contained plentiful nutrients from the decomposition of organic material that was inundated by rising reservoir water.  However, the amount of nutrients declined after the initial decomposition. The water in the reservoir eventually returned to a nutrient-poor state.

Comments may be submitted no later than Feb. 27 via e-mail to NEPANWW@usace.army.mil. Insert "Dworshak Nutrient Program" in the subject line. Comments submitted by U.S. Mail must be postmarked no later than Feb. 27 and sent to U.S. Army Corps of Engineers, Walla Walla District, CENWW-PPL-C, Dworshak Nutrient Program, 201 North 3rd Avenue, Walla Walla, WA 99362-1876. Questions may be directed to the Environmental Coordinator at 509-527-7265.





Release no. 17-010