Evaluating Revisions to Oregon’s Water Quality Standards for Turbidity – A Murky Process

Oregon is in the process of reviewing and revising its essentially thirty-year-old water quality standards for turbidity, a change that would impact a wide range of water users and wastewater dischargers. Among the challenges that will face Oregon’s Department of Environmental Quality (DEQ) in developing a revised standard is how to distinguish background turbidity levels from anthropogenic sources, particularly in the state’s water bodies that have high seasonal and geographic variability. Turbidity is notoriously difficult to measure, monitor, and establish water quality standards for, especially in mountainous areas where runoff, erosion, and glacial flow can cause significant fluctuations in turbidity levels even without direct human involvement. As a result, Oregon’s revised standards, as considered during the public review process and as eventually adopted, could provide a framework for other western states to evaluate as they consider revising their own standards.

Technical and Legal Background to Water Quality Standards for Turbidity

Turbidity is a measure of the cloudiness or lack of clarity of water, caused by the scattering or absorption of light by sediment, algae, or other particulates suspended in water. Chronic and high levels of turbidity can impair photosynthesis and stunt aquatic growth,[1] thereby negatively affecting aquatic life and other “beneficial uses” of water bodies. The amount of turbidity is generally determined by the number and size of particles in the water, and is typically measured in Nephelometric Turbidity Units (NTU). Some water bodies, such as small streams, have significant natural variability of turbidity. In the dry season, many streams are often exceptionally clear, measuring as low as 1-2 NTU. There is far greater variability in the wet season, and turbidity can go as high as hundreds or even thousands of NTU as runoff from banks and culverts cloud the streams.

Clean Water Act (CWA) Section 303(c) requires states to develop water quality standards for a range of contaminants, review and update those standards every three years, and submit the standards to EPA for review and approval.[2] A state’s water quality standards, once adopted and approved, become central components of a range of CWA permits and programs. For example, water quality standards are incorporated into the state’s National Pollution Discharge Elimination System (NPDES) permits under CWA Section 402 and dredge and fill permits under CWA Section 404, are the yardsticks that a state uses in its certification analysis under CWA Section 401 and in determining whether to list water bodies under CWA Section 303(d), and form the foundations for pollutant loading allocations under the state’s total maximum daily load (TMDL) programs.

Water quality standards are comprised of designated uses of water bodies, water quality criteria that are necessary to protect those uses, and antidegradation components.[3] Water quality criteria are expressed in either numeric or narrative form, although EPA’s regulations favor the use of numeric criteria where possible.[4] The numeric approach is typically feasible in circumstances where in-stream pollutants are predominantly due to anthropogenic discharges from discrete sources, such as end-of-pipe discharges from facilities. Some states have implemented so-called “absolute” numeric limits for turbidity, such as North Carolina, which has a general standard of no more than 50 NTU stream, with more restrictive numbers for lakes, reservoirs, or water bodies designated as trout waters.[5]

Although this approach has obvious benefits from the perspective of consistent regulatory oversight, the inherent variability of turbidity in many streams, particularly in areas with high precipitation or mountainous geography, cause significant difficulties in using an absolute numeric standard for turbidity. As a result, some states employ a true “narrative” approach, such as Georgia, where where “[a]ll waters shall be free from turbidity which results in a substantial visual contrast in a water body due to a man-made activity.”[6] Due to difficulties in implementing and enforcing this sort of ambiguous and highly site-specific standard, many states have employed a so-called “relative” approach to their water quality standards for turbidity, where the standard is X% over a perceived background level, depending on the beneficial use and often with a graduated X% increase depending on natural conditions. Although the relative approach ostensibly melds a hard – albeit site-specific – numeric limit with flexibility to address background conditions, it too presents difficulties for regulators and the regulated community alike. As described below, developing and measuring a relative criterion can have significant practical and technical difficulties.

Oregon’s Current Water Quality Standard for Turbidity

Oregon currently employs a fairly straight-forward “relative” water quality standard for turbidity. The rule states that “no more than a ten percent cumulative increase in natural stream turbidities may be allowed, as measured relative to a control point immediately upstream of the turbidity causing activity.”[7] The regulation also allows exceptions for certain “limited duration activities” or emergencies, including activities certified or permitted under CWA Sections 401 or 404.[8] The “ten percent cumulative increase in natural stream turbidities” component of the rule is similar to several other western states, and is based on a 1976 EPA recommendation.[9]

DEQ has barely changed the current water quality standard for turbidity in over thirty years. The last change to the rule occurred in 1990, when DEQ shifted from a measurement using Jackson Turbidity Units (JTUs) to NTUs, which allowed the agency to measure turbidity with more precision (from approximately 25 units down to below 1 unit). Due to concerns regarding the reliability and practicality of the existing standard, DEQ first sought to revise the water quality standard nearly ten years ago, and, in 2005, proposed a draft revision to the rule that was not adopted.

DEQ’s current effort to revise its rule is based on a range of what the agency refers to as “policy and implementation challenges inherent in the current standard.”[10] Among these concerns is the fact that, because many small streams are very clear throughout the year, a 10% increase is often less than 1 NTU – an increase that is both difficult to detect and of dubious impact on the streams.[11] Additionally, the imprecision of some terms in the rule, such as what constitutes a “control point” and what should be construed as “limited duration activities,” which are essentially exempt from the rule, have created difficulties in implementing the rule.[12] DEQ’s primary goals in revising the standard are to create a well-reasoned, clear, and defensible rule of general applicability that will accommodate the state’s variability of water quality, reflect the best technical information, and protect the beneficial uses of the state’s water bodies.

Difficulties in Revising Turbidity Water Quality Standards

Developing a sensible and clear water quality standard for turbidity necessitates an understanding of the background levels for the water bodies in question against which anthropogenic causes will appear in the data. The devil is in the details, of course, and streams are notoriously variable; defining “background” can at times present a formidable challenge. For example, glacial streams may have variability of many hundreds of NTU over the course of a short period of time, especially in the summer when glacial melts occur, whereas non-glacial streams tend to be less turbid during those times. Additionally, even in non-glacial streams the impact of tributaries to the stream in question can complicate how and where one establishes background – taking measurements too close to a tributary can skew the background data that the standard is based on.

The challenge of dealing with wide variation in turbidity data is compounded by instrument limitations. DEQ acknowledges that interpretation of data is often difficult because different instruments and collection techniques vary widely. These challenges are the subject of ongoing discussions and public meetings with DEQ.

DEQ’s Currently Considered Proposals for a New Turbidity Water Quality Standard

DEQ is currently considering proposing “Relative Numeric Criterion for Protection of All Aquatic Life Uses.”[13] One proposal floated during a recent meeting was as follows:

The weekly average turbidity may not exceed 3 NTU above the weekly average background turbidity. If the weekly average background turbidity is greater than 30 NTU, the weekly average turbidity may not exceed 10% above the weekly average background turbidity. Where there are insufficient data to calculate a weekly average turbidity, turbidity in a single sample may not exceed 20 NTU above background turbidity when background turbidity is 0-100 NTU, or 20% above background turbidity when background turbidity is greater than 100 NTU.

Special summertime criteria is also suggested: “Median turbidity in the summer may not exceed 3 NTU more than one time every five years. If median turbidity in the summer under natural conditions is greater than 3 NTU, median turbidity in the summer shall not exceed 1 NTU above natural conditions.” These approaches suggest that much work will need to be done in defining and refining the meaning of natural, background turbidity, especially in the case where there is insufficient data to calculate weekly averages. The data acquisition tasks and the resources that these rules would entail could be significant.

DEQ is considering site-specific criteria for the Hood River and its tributaries, which experience high summer turbidity originating from the glaciers on Mount Hood. The median flows of Coe and Elliot Creeks near Mount Hood range between 35 and over a hundred NTU in the summer, with the highest turbidity levels approaching 1,000 NTU. Clearly, the final standard would need to be adequate to deal with the challenges posed by such streams. The proposed standard does not account for non-glacial rivers such as the Powder River or the Malheur River, which appear to be chronically turbid. DEQ recognizes site specific problems where natural conditions far exceed the contemplated turbidity standards, and with those rivers in particular, acknowledges that there is insufficient data at this time to suggest site-specific criteria. The drawback of any such site-specific variances, of course, is that they necessitate years of data from multiple locations, a technical feat that requires substantial resources.

DEQ also is proposing a “migration corridor” criterion designed to protect the migration of salmon and steelhead in certain river corridors at their critical times of migration, and cool water species. The corridors currently under consideration are the Columbia River, the lower 50 miles of the Willamette River, portions of the Snake River, the Lower John Day River and certain small reaches of the Grand Ronde, Coquille, and Coos River basins. For these corridors (or others, however finally defined), the draft criteria says, “[m]edian turbidity in the summer may not exceed 5 NTU more than one time every five years. If median turbidity in the summer under natural conditions is greater than 5 NTU, median turbidity in the summer shall not exceed 1 NTU above natural conditions.”[14]

The host of anthropogenic factors influencing turbidity in streams needs somehow to be disentangled from background, “natural conditions” in order for any of DEQ’s proposals to work. For example, the distinction between activities like hauling, dredging, vegetation removal, and dam releases, all of which are “anthropogenic” must be distinguished from small landslides, deposition of organic materials or dust, groundwater and nutrient infusions, and other natural influences. This would have to be done within an accuracy of a handful of NTU. DEQ acknowledges the current limitations on the accuracy of turbidity measurement and significant data gaps that will present challenges to regulation.

Conclusion

DEQ’s approach may likely become a template for other states to review as they consider revising their water quality standards for turbidity. How Oregon addresses the inherent variability of turbidity daily, seasonally, and geographically in areas of the state’s mountainous landscape will be of particular interest to regulators in other western states that may be considering revisions to their standards, such as Washington. Since a great deal of non-point source activity creates turbidity, the implications of this rulemaking are significant. It is well-worth the public’s being engaged with DEQ’s efforts on this project as it moves ahead with this process. DEQ has encouraged public participation in its review process and provides further information regarding its process on its website.

For more information on this article, please contact Douglas MacDougal, Meli MacCurdy, or any other member of Marten Law’s Permitting and Environmental Review, Water Quality, or Water Resources practice groups.