Turbidity Standards

DEQ establishes water quality standards to protect aquatic plants and animals and other beneficial uses of Oregon waters, such as drinking water and recreation. Increased turbidity, or “cloudiness” of the water, can negatively impact these uses.

DEQ is in the process of revising the water quality standards for turbidity based on the best available science regarding the effects of turbidity on beneficial uses, in particular aquatic life. DEQ also will address a number of issues that have made it challenging to implement the current turbidity standard across all of DEQ’s water quality programs, such as better definition of what is allowed for a limited duration exceedance and duration and frequency of exceedances that would violate the standard.  

Turbidity Rulemaking Current Standard Turbidity Technical Review Turbidity Advisory Workgroup

Document Archive Background Contact

Turbidity Rulemaking

DEQ last reviewed its water quality standards for turbidity in 2005 and 2006. The standard ultimately was not revised at that time. DEQ's current review will build on the turbidity effects analysis that was conducted at that time and documented in the Draft Technical Basis for Revising Turbidity Criteria. DEQ will incorporate new research and data, any data that is received and screened through the Call for Data process and address comments received in 2005 from the Independent Multidisciplinary Science Team. 

• Turbidity Rulemaking Fact Sheet PDF

Current Standard

Turbidity Rule (OAR 340-041-0036)

Turbidity (Nephelometric Turbidity Units, NTU): 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. However, limited duration activities necessary to address an emergency or to accommodate essential dredging, construction or other legitimate activities and which cause the standard to be exceeded may be authorized provided all practicable turbidity control techniques have been applied and one of the following has been granted:

1. Emergency activities: Approval coordinated by the Department with the Oregon Department of Fish and Wildlife under conditions they may prescribe to accommodate response to emergencies or to protect public health and welfare;
2. Dredging, Construction or other Legitimate Activities: Permit or certification authorized under terms of section 401 or 404 (Permits and Licenses, Federal Water Pollution Control Act) or OAR 14l-085-0100 et seq. (Removal and Fill Permits, Division of State Lands), with limitations and conditions governing the activity set forth in the permit or certificate.

Stat. Auth.: ORS 468.020, 468B.030, 468B.035 & 468B.048
Stats. Implemented: ORS 468B.030, 468B.035 & 468B.048
Hist.: DEQ 17-2003, f. & cert. ef. 12-9-03

Turbidity Technical Review

DEQ prepared a review summarizing the scientific literature and data on the effect of turbidity on beneficial uses.  The document will assist DEQ in developing a revised turbidity criteria based on the best available science.  The document was reviewed by a panel of scientific experts with expertise in stream, lake, estuarine ecology, hydrology and aquatic biology.

• Turbidity Technical Review  PDF

Turbidity Advisory Workgroup

DEQ has convened a turbidity advisory workgroup to provide input on policy, economic and other implications of rule options for revising the water quality standards to address turbidity.

Document Archive

• Draft Technical Basis for Revising Turbidity Criteria PDF (2MB)
• IMST Review of Oregon Department of Environmental Quality's Technical Basis for Revising Turbidity Criteria PDF (DEQ Water Quality Division, October 2005 draft)
• February 17, 2010 Public Meeting Presentation PDF
  

Background

Turbidity measures the “cloudiness” of water using the penetration of light through water. Increased levels of turbidity are caused by matter sediment and other matter suspended in the water column. Scientific literature indicates that turbidity reduces growth of aquatic plants and interferes with the ability of fish to catch prey. Increased turbidity levels also reduce the desirability of waters for recreational uses. High levels of suspended sediment, usually measured as turbidity for regulatory purposes, can cause public drinking water treatment systems to shut down and increase operation and maintenance costs. 

Contact

For more information, contact Aron Borok at Oregon DEQ at (503) 229-5050 or by e-mail.

To receive periodic updates on this effort, sign up on DEQ's GovDelivery listserv for turbidity (see the green envelope above on the left hand side of this web page.)

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