Liberte Environmental Associates

NPDES Permits Potentially Affecting Water Quality

Final NPDES Wastewater Permits - Issued by Oregon Department of Environmental Quality

This list consists of permit documents* (see end) made available by Oregon DEQ and is not all inclusive. All documents are PDF except where indicated.

Durham Sewage Treatment Plant (STP): Final NPDES Wastewater Permit Related Documents

Durham STP - Final Permit

Durham STP - Final Fact Sheet

Durham STP - Final Fact Sheet: Supplemental MS4

Current Draft Tualatin Watershed TMDL - Public Comment Periods ends on November 30, 2011.

Existing Tualatin Watershed TMDL - Finalized in August 2001.

Permitted Mixing Zone Size for Toxicity:

Waterbody: Tualatin River at about River Mile (RM) 9.2 just upstream of the confluence with Fanno Creek.

Acute Mixing Zone Radius: 10 feet in all directions from the diffuser.

Acute Mixing Zone Surface Area: Estimated SA is 2,234 square feet based on a diffuser length of about 96 feet.

Chronic Mixing Zone Radius: 100 feet in all directions from diffuser (at least this is what the permit language allows despite the channel being only 200 feet wide).

Chronic Mixing Zone Surface Area: Estimated SA is 9,600 square feet based on a diffuser length of about 96 feet (i.e., SA is about 96 by 100 feet if only the downstream direction is considered).

Chronic Mixing Zone Volume: DEQ does not provide Tualatin River MZ depth in the fact sheet so MZ volume is not yet determinable.

The NPDES Fact Sheet (p. 13) describes the primary Durham Outfall Diffuser as follows:
"3.1. Durham AWTF
The Durham AWTF Outfall (D001) discharges to the Tualatin River at river mile 9.2, just upstream from the Fanno Creek tributary. The river channel at this point is described as being approximately 200 feet wide. Effluent is discharged through a 96-foot wide multi-port diffuser that was laid on the bottom of the river nearly in the center of the channel. The diffuser has twelve evenly spaced ports."

*LEA Disclaimer for compiled, unlocked and OCR documents: From time to time LEA will post on this website scanned documents, and additional documents otherwise limited in accessibility. Accordingly, LEA may use document unlocking and optical character recognition (OCR) capabilities to provide accessible, tagged text documents for use by people with visual impairments, and also provide searchable documents. The unlocking and OCR processes are not faultless, and hence LEA cannot guarantee document perfection. However, taking these caveats into account, document accessibility is greatly increased. LEA also posts the original document where necessary, as obtained by LEA, such that users may compare any potential imperfections in the unlocked and OCR documents.

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