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TO: - Chehalis Basin Partnership
FROM: - Kahle Jennings, Department of Ecology Representative
SUBJECT: - Comparison of Dissolved Oxygen Criterion
for Washington State and Idaho
After the discussion at the last Partnership meeting I posed the following question to my contacts within Ecology for issues related to the state water quality standards:
"The state of Idaho has not been delegated authority under the Clean Water Act (CWA) to set state water quality standards so Idaho's water quality standards are set by the U.S. Environmental Protection Agency (USEPA). In Washington State the Department of Ecology has been delegated authority by USEPA under the CWA to set water quality standards.
The dissolved oxygen criterion for Idaho has been set at 6.0 mg/l. Immediately across the border in Washington State, the dissolved oxygen criterion is 8.0 mg/l. How can 6.0 mg/l of dissolved oxygen be sufficient for fish on one side of the border and on the other side of the border they suddenly require 8.0mg/l? This discrepancy is being cited as an example of how Washington State (Ecology) manipulates science so regulations can be more restrictive than necessary, as evidence that Ecology is unreasonable, and that the results are costing Washington citizens money and costing the state lost business opportunity. If we are all using the same science, how can EPA justify setting a standard of 6.0 while Ecology requires 8.0 in Washington? Or reversing the question, how can Ecology justify setting a criterion of 8.0 while EPA allows 6.0 in Idaho to protect the same species?"
This is the response I have received from my contacts:
There are a number of different reasons for this apparent discrepancy. The most significant reason is that Idaho's dissolved oxygen criterion of 6.0 mg/liter is only part of the story. Idaho has two other dissolved oxygen criteria that must also be taken into account.
First, Idaho also has a salmonid spawning Intergravel Dissolved Oxygen (IGDO) minimum criterion of 5.0 mg/liter, with a seven-day average of not less than 6.0 mg/l. IGDO is measured in the gravel, not in the water column. EPA says that there is typically a 3.0 mg/liter difference between the two. So, in order to get 5.0 or 6.0 mg/liter of dissolved oxygen in the gravel (also part of Idaho's standards), they need about 8.0 or 9.0 mg/liter of dissolved oxygen in the water column above the gravel. This is pretty similar to Washington State's current dissolved oxygen criteria of 8 and 9.5 mg/liter in the water column
Secondly, Idaho's criteria includes a one-day minimum of not less than 6.0 mg/l or 90% of saturation in the water above the gravel, whichever is greater . For example, if the water temperature is 16 degrees Celsius at an elevation of 1000 feet, dissolved oxygen saturates at 9.5 mg/liter, and 90% of that is about 8.5 mg/liter. So the 90% saturation clause may kick in long before a river ever reaches 6 mg/liter dissolved oxygen and require that there be 8.5 mg/liter of dissolved oxygen in the water.
Washington State has actually established a special seasonal dissolved oxygen criterion of 5.0 mg/liter between June 1 and September 15 each year for that portion of the Chehalis River that includes the section between the Cities of Chehalis and Centralia. This special dissolved oxygen criterion - which is 3.0 mg/liter lower than the normal 8.0 mg/liter criterion for dissolved oxygen -- was established in recognition of the fact that dissolved oxygen in this part of the river is normally lower than 8.0 mg/liter in the summer due to natural conditions (very slow rates of flow and stratification of the water into different temperature layers). Ecology is actually quite sensitive to "real-life natural conditions" that affect water quality, and considers these natural conditions when establishing the Washington State Water Quality standards.
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