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Portneuf River Subbasin

Data Details
Hydrologic Unit Code 17040208
Size 1,360 square miles (870,400 acres)

Water Bodies with EPA-Approved TMDLs (Category 4a)

Beaverdam Creek; Bell Marsh Creek; Birch Creek; Cherry Creek; Clear Creek; Deer Creek; Dempsey Creek; East Creek; East Fork Mink Creek; Garden Creek; Goodenough Creek; Hawkins Creek; Hawkins Reservoir; Indian Creek; Inman Creek; Kinney Creek; Little Toponce Creek; Lower Bell Marsh Creek; Lower Dempsey Creek; Lower Gibson Jack Creek; Lower Hawkins Creek; Lower Inman Creek; Lower Marsh Creek; Lower Middle Marsh Creek; Lower Mink Creek; Lower Pebble Creek; Lower Walker Creek; Marsh Creek; Middle and Lower Pocatello Creeks; Mink Creek; North and South Forks Pebble Creek; North Fork Inman Creek; North, South, and Middle Forks Toponce Creek; Pebble Creek; Pocatello Creek; Portneuf River; Rapid Creek; Sawmill Creek; South Fork Mink Creek; South Fork Pocatello Creek; Toponce Creek; Twentyfour Mile Creek; Upper and Lower Garden Creek; Upper and Lower Goodenough Creek; Upper and Lower Jackson Creeks; Upper and Lower Moonlight Creek; Upper Cherry Creek; Upper Middle Marsh Creek; Upper Pebble Creek/Big Canyon; Upper, Lower, and Middle Toponce Creek; Webb Creek; West and North Fork Rapid Creeks; West Fork Mink Creek; Yellow Dog Creek

Beneficial Uses Affected Cold water aquatic life, salmonid spawning, primary and secondary contact recreation
Major Land Uses Agriculture, rangeland, urban
Date Supplement Approved by EPA April 2001
EPA Approval Letter
Date Revision/Addendum Approved by EPA

September 2010
EPA Approval Letter

Subbasin Characteristics

The Portneuf River subbasin is located in southeast Idaho. The Portneuf River is approximately 100 miles long and drains an area of roughly 1,360 square miles. The subbasin is primarily in Bannock and Caribou Counties but has small portions in Bingham, Power, and Oneida Counties as well. Marsh Creek is the only major tributary to the Portneuf River.

1999 and 2001 Subbasin Assessment and TMDL

The Portneuf River subbasin has numerous documented water quality problems that affect beneficial uses: 27 stream segments in the subbasin were listed on the 1994/1996 §303(d) list, including the main stem Portneuf River, 16 tributaries, and Hawkins Reservoir. All segments include sediment as a pollutant of concern and roughly half are listed for nutrients. The main stem Portneuf River is also listed for bacteria, flow alteration, and oil and grease. Hawkins Reservoir is listed for dissolved oxygen. Evidence indicates that other pollutants, such as temperature, metals, and PCBs, may also be impairing waters in the Portneuf River subbasin.

Information collected through the Beneficial Use Reconnaissance Program indicates that several streams on the §303(d) list (Gibson Jack, Mink, Walker, Bell Marsh, Goodenough, upper Garden, Dempsey, Pebble, and Toponce Creeks) are supporting their beneficial uses; DEQ recommends these streams be removed from the §303(d) list.

1999 and 2001 TMDL: Pollutants for Which TMDLs Were Developed
TMDLs were prepared for fecal coliform, oil and grease, suspended sediment, total inorganic nitrogen, and total phosphorus from nonpoint and point sources.

2010 Addendum

This document addresses water bodies in the Portneuf River subbasin that are on Idaho’s 2008 §303(d) list, including carryovers from previous lists (2002, 1998, and 1996) and also revisions to assessment units with approved TMDLs or that have been delisted. Exceedances of sediment targets in the Portneuf River subbasin are widespread. Nutrient loading in the subbasin is more difficult to summarize but was documented in assessment units from both main stem and tributary sites. E. coli loading from tributaries is widespread in the subbasin.

2010 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Cherry Creek tributaries Bacteria (E. coli)
Cherry Creek Bacteria (E. coli)
Dempsey Creek Bacteria (E. coli)
Beaverdam Creek Sediment
Garden Creek Bacteria (E. coli)
Indian Creek Bacteria (E. coli)
Marsh Creek Bacteria (E. coli), total phosphorus, total nitrogen, sediment
Kinney Creek Sediment
Mink Creek Sediment
Portneuf River/td> Bacteria (E. coli), sediment, total phosphorus, oil and grease
South Fork Pocatello Creek Sediment
Hawkins Reservoir Dissolved oxygen, total phosphorus, total nitrogen

Subbasin Document(s)

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DEQ Pocatello Regional Office
444 Hospital Way, #300
Pocatello, ID 83201
Ph: (208) 236-6160
Fax: (208) 236-6168
Toll Free: (888) 655-6160

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