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Alaska Fish & Wildlife News
December 2005

Mixing Zones

By Doug Vincent-Lang
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A natural mixing zone, where fresh glacial water from the Katzehin River mixes with the seawater in Lynn Canal. Photo by Riley Woodford

Editorial: Mixing Zones
By Doug Vincent-Lang

Nearly every wastewater discharge to Alaska’s surface waters has a permit that includes provisions for a mixing zone. Mixing zones are areas where treated wastewater is authorized by Department of Environmental Conservation (DEC) to combine with a water body. The most common mixing zones are for placer mining, seafood processing and municipal wastewater treatment systems.

About two years ago, the DEC began a process to rewrite Alaska’s mixing zone
regulations. Under existing regulations, establishment of mixing zones is prohibited in salmon and selected high value freshwater fish spawning areas. However, in recent years it has become clear that this absolute prohibition was unnecessarily restrictive, in that some mixing zones could be permitted in spawning areas when it could be demonstrated that they would not cause harm to fishery resources or their uses.

Department staff, including several from our former Habitat and Restoration Division, were actively involved in the rewrite of these regulations. Only after their concerns were addressed did we offer ADF&G’s support of the revised proposed rules currently out for public review. ADF&G believes that the new rules allow for responsible development of Alaska’s resources while protecting fish and wildlife and their uses.

Our input was well-received and has been incorporated into the new proposed rule. Under the rewrite, DEC is proposing to repeal the existing regulations and adopt revisions that would:
1) reorganize the mixing zone regulations to improve clarity and reduce redundancy;
2) expand the prohibition on mixing zones in spawning areas to include lakes;
3) create exemptions to the prohibition on mixing zones in fish spawning habitat;
4) require consultation with ADF&G and the Alaska Department of Natural Resources/Office of Habitat Management and Permitting (ADNR/OHMP) if mixing zones are proposed in spawning areas;
5) require ADF&G approval of mitigation plans that would offset adverse impacts of mixing zones on aquatic resources if a mixing zone is found within a state refuge, sanctuary, or critical habitat area (collectively referred to as special areas);
6) define a mitigation process and require ADNR/OHMP approval of mitigation plans for a mixing zone in spawning areas outside of special areas; and
7) update a reference to federal technology-based effluent limitations.
The proposed regulations also include for the first time a definition for shellfish. You can learn more about the proposed changes by visiting the DEC Division of Water web site at

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Doug Vincent-Lang

Given the protection provided in the new proposed rule for fish and wildlife and their uses, ADF&G is supportive of DEC’s new proposed rule and is comfortable with the level of flexibility that the rule provides.

Doug Vincent-Lang is the assistant director of the sportfish division at the Department of Fish and Game

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(907) 465-4256

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