Chapter 173-201A WAC (Natural Conditions)

Ecology is proposing revisions to Chapter 173-201A WAC, Water Quality Standards for Surface Waters of the State of Washington.

We are proposing revisions to the parts of the surface water quality standards that address natural conditions. We have natural conditions provisions because conditions in some water bodies naturally do not meet water quality criteria. For example, a naturally low-flowing stream in a natural prairie without any human alteration may have seasonally higher temperatures than the limit set to protect fish. Water bodies may not meet the limits set to protect aquatic life because of natural processes or seasonal conditions. 

We are proposing a new method to calculate natural conditions criteria, called a performance-based approach. We've proposed a definition for this method and a new section to describe it. Also, we are providing a draft rule document with details about how to calculate natural conditions criteria using the performance-based approach. 

In addition, we are proposing the following changes:

• Updating minimal allowances for local and regional human impacts to fresh and marine waters for dissolved oxygen and temperature when the natural conditions represent the water quality criteria. We are also adding a definition for "local and regional sources of human-caused pollution."
• Updating the natural conditions criteria language to limit use to aquatic life criteria and describing methods for determining natural conditions criteria values.
• Updating how site-specific analyses must be conducted and other minor changes to the site-specific criteria section to reflect the latest guidance.