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Assessment Methodology Updates

Methodology updates

EPA regulations require states to describe the methodology, data and information used to identify and list water quality limited segments requiring TMDLs. Oregon's assessment methodology contains the "decision rules" DEQ uses to compare data and information to existing water quality standards to develop the biennial Integrated Report pursuant to Clean Water Act Sections 303(d) and 305(b) and OAR 340-041-0046. The methodology builds on DEQ's protocols from previous 305(b)/303(d) assessments. 

Before each reporting cycle, DEQ updates the assessment methodology to revise existing and develop new methods. Oregon statute requires that DEQ publish the Integrated Report assessment methodology prior to the start of drafting the Integrated Report.

DEQ has set a strategic vision for the Water Quality Assessment program composed of short-term and long-term priorities. Short-term updates will be taken on in the next two assessment cycles. Long-term updates will be developed in coordination with WQ program goals.

Short-term updates

​DEQ is committed to making updates to the biocriteria methodology based on peer review recommendations received in 2018. DEQ has updated its reference screening protocols, identified additional reference site data, and incorporated new data into its reference screening process.  DEQ is exploring the option of a new or revised model, multi-metric index, and additional supporting lines of evidence. This work fulfills DEQ's commitment to EPA to pursue additional steps and lines of evidence to increase confidence in DEQ's interpretation of its biocriteria narrative.​

DEQ has convened a scientific technical workgroup for the assessment of ocean acidification and hypoxia. The objective of the workgroup is to assist DEQ in developing methodologies for assessing the impacts of ocean acidification and marine dissolved oxygen in Oregon's territorial waters for future Integrated Report cycles.

Meeting materials 

Freshwater streams that flow directly into the ocean are currently assessed using the freshwater indicator bacteria, E. coli. To better align with data collected by DEQ's Beach Monitoring program, the existing method for assessing bacteria in these streams will be revised to include the use of Enterococcus as a bacteria indicator to make determinations whether the recreation use is being met. 

Additionally, the current coastal contact bacteria methodology reads “more than 10% of all samples within any 90-day period exceed 130 Enterococci organisms per 100 mL (as expressed in rule) using the 10% raw score method, based on a minimum of 5 samples".  In practice, this means that any one exceedance in a 90-day period can trigger an impaired listing. DEQ will revise the method to use the binomial 10% exceedance rate to be consistent with the freshwater assessment. ​

Oregon does not have specified data minimums for delisting assessment units for temperature. In the 2022 cycle, this led to several assessment units to be delisted with only 1 or 2 years worth of data. DEQ is developing minimum data requirements for temperature delisting to ensure beneficial use protection. ​

​Oregon's methodology for listing segments of waterbodies as “impaired" for toxics does not currently include a method for assessing toxics data in tissue other than mercury. Category 5 listings are based on either water column concentrations of toxic pollutants, or on fish advisories issued by the Oregon Health Authority (OHA). DEQ is developing a method to assess support of the fish consumption (Fishing) beneficial use using data collected from aquatic tissue samples by interpreting Oregon's narrative criteria for toxic substances OAR 340-041-0033(1).​

DEQ will evaluate the use of guidance values, or concentrations for toxic compounds that do not have WQ criteria that DEQ may use in application of Oregon's Toxic Substances Narrative (340-041-0033(2)). ​

Long-term updates

​​The current assessment method of the Narrative Criteria ORS 340-041-0007(9) lacks specific details and protocols. To support a determination of impairment by aquatic weeds or algae, terms such as “excessive growths” and “dominate the assemblage” must be clarified and a weight of evidence approach defined. This update will add clarity to the existing methodology.

​​DEQ historically listed waterbodies based on excessive amounts of algae (i.e. benthic/floating algae). DEQ is exploring multiple lines of evidence that may be used to assess attainment of this criteria. This update will provide clarity and a clear weight of evidence approach to remove “excessive algae” listings. Lines of evidence may include: methods for visual estimation of algae, periphyton biomass thresholds, algae community composition, and other supporting WQ information such as nutrients, diel dissolved oxygen and/or pH.

In conjunction with protocols for excessive algae, DEQ plan to develop a weight of evidence approach for nutrient impairment.  Possible lines of evidence could be diel DO/pH, phosphorus/nitrogen concentrations together with chlorophyll (water column and benthic), phytoplankton community structure, and macroinvertebrates.​

​​​DEQ is coordinating with EPA to determine, where no numeric criteria exist (i.e. phosphorus, nutrients, sediment), whether attainment of TMDL targets/benchmarks may be used to identify where waterbodies have been restored and beneficial uses are currently being supported.

​​Sedimentation is a significant cause of impaired waters in Oregon.  Development of a sedimentation benchmark and corresponding assessment methodology would require peer review. A methodology to assess suspended and bedded sediment would build on current knowledge and procedures for implementing the narrative criterion. ​

Public process

The 2024 reporting cycle will have a robust public process. There will be an opportunity for public comment on the Draft Assessment Methodology, anticipated in early-2023. 

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Supporting Documents for Methodology Updates