The Washington State Department of Ecology has proposed a permanent change to a state water ­quality rule that limits total dissolved gas, and would allow 125 ­percent saturation under certain conditions in the Snake and Columbia rivers.

Currently, TDG must not exceed an average of 115 percent in the forebays of the next downstream dam and an average of 120 percent in the tailraces of each dam. This spring, under a temporary rule change, both Washington and Oregon allowed TDG to average 120 percent in both forebays and tailraces.

The increased TDG levels are being proposed ­following a recommendation by Gov. Jay Inslee’s orca task force that found the extra spill could improve ­juvenile fish migration.

The increased TDG is also part of a flexible spill agreement among federal agencies, states and tribes ­seeking to balance the needs of fish with power ­generation in an effort to resolve spill issues outside the courtroom.

According to Ecology’s analysis of the proposed rule change, a maximum saturation of 125 percent TDG would be allowed only under certain circumstances—if spill activities align with Endangered Species Act requirements; if it’s accompanied by an approved biological monitoring plan that includes nonsalmonid fish species; if biological monitoring continues for at least five years; if the incidence of gas bubble trauma does not exceed 15 percent in nonpaired fins; and if the incidence of gas bubble trauma does not exceed 5 percent in fish that have gas bubbles on 25 percent of the surface area of the fin.

Heather Bartlett, Ecology’s water quality program manager, said in a prepared statement that increased spill has the potential to be a “win-win” for salmon, orcas and power generation.

“We are at a critical time for our orca and salmon. This is a change we can make relatively quickly to help with the long-term recovery efforts,” she added.

According to Ecology’s preliminary report on the proposed rule change, the primary goal of the rule is to improve fish passage for salmon and steelhead migrating downstream in the Snake and Columbia rivers.

“Dams release water through spillways over the dam and fish using the spillways have a better chance for survival compared to those that pass through the dams’ turbines,” the report said. “However, spilling water also increases TDG that can negatively affect aquatic life. This rulemaking amends the TDG limit to allow for greater water flow through spillways for improved salmon ­migration while ensuring that TDG limits minimize ­negative impacts to aquatic life through sufficient ­biological monitoring.”

The report says that because the Flexible Spill ­Agreement allows for additional hydroelectricity ­generation and less spill during peak demand hours for electricity, the added costs and carbon emissions resulting from the extra spill would be offset, and therefore would not change electricity prices or greenhouse gas emissions in Washington.

“Since the Flexible Spill Agreement is revenue neutral compared to the baseline, we do not expect the proposed amendments to result in net costs” at the U.S. Army Corps of Engineers dams that BPA operates, it said.

As for benefits, the report uses a 2017 Fish Passage Center estimate that expects a “mean annual increase” of up to 146,000 adult spring Chinook and up to 116,929 steelhead returning to the mouth of the Columbia River, depending on the level of spill.

The new proposed rule language says TDG criteria may be adjusted to aid fish passage over hydroelectric dams when spilling for anadromous juvenile fish passage as of the 2020 spill season. The criteria are intended to allow increased fish passage without causing more harm to fish populations than caused by turbine fish passage.

The maximum TDG saturation level of 125 percent is calculated as the average of the two highest hourly TDG measures in a calendar day during spillage for fish.

Beginning in 2021, plans must include monitoring for nonsalmonid fish species and must continue for a minimum of five years.

The proposed rule change would delete ­temperature requirements in order to comply with a 2018 U.S. District Court stipulated order of dismissal of a lawsuit involving the Northwest Environmental Advocates, which filed a ­lawsuit against the U.S. Environmental Protection Agency and the Washington Department of Ecology.

The agency will accept comments on its proposal until Sept. 26 (CU No. 1913 [11.5]).

Comments will be accepted online, or by mail to Susan Braley, WA State Dept. of Ecology, Water Quality Program, P.O. Box 47600, Olympia, WA 98504-7600.

Comments will also be accepted in person during a hearing at 1:30 p.m. on Sept. 16 at the Washington State School for the Blind, Fries Auditorium (Old Main Building), 2214 E. 13th St. in Vancouver.

An online seminar is scheduled for 1:30 p.m. Sept. 19.

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.