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Palouse River Subbasin

Data Details
Hydrologic Unit Codes 17060108
Size 407 square miles (260,641 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a) Big Creek, Cow Creek, Crane Creek, Deep Creek, East and West Forks Rock Creek, Flannigan Creek, Gold Creek, Hatter Creek, Idlers Rest Creek, Paradise Creek, Rock Creek, South Fork Palouse River
Beneficial Uses Affected Cold water, salmonid spawning, primary and secondary contact recreation, agricultural water supply, domestic water supply, industrial water supply, wildlife habitat, aesthetics
Major Land Uses Agriculture, grazing, forestry, residential, recreation, urban, pasture, agribusiness
Date Paradise Creek TMDL Approved by EPA February 1998 Approval Letter
Date Approved by EPA March 2005
Date Cow Creek TMDL Approved by EPA February 2006 Approval Letter
Date South Fork Palouse River TMDL Approved by EPA October 2007 EPA Approval Letter
Date Cow Creek Addendum Approved by EPA April 2014 Approval Letter
Date Paradise Creek TMDL 2015 Bacteria Addendum Approved by EPA November 2016 Approval Letter
Date Palouse River Subbasin 2017 Temperature TMDL Approved by EPA August 2017 Approval Letter

Subbasin Characteristics

The Palouse River subbasin is a sparsely populated area with one major town, Moscow, and several other small towns and communities, including Potlatch, Princeton, and Harvard.

The economy of the Palouse is dominated by agriculture and two universities: the University of Idaho and Washington State University. Forestry, livestock, grazing, construction, and recreation are other economic factors. All of these affect water quality to some degree. The Palouse prairie is one of the most productive agricultural areas in the world and agriculture is and will continue to be the dominant economic driving force in the subbasin. Preventing the rich, fertile soil of the Palouse prairie from eroding and keeping it intact on the landscape is the major theme of this document. This goal is not only key to maintaining and improving water quality but also to maintaining the economic life force of the Palouse.

1997 Paradise Creek Watershed Assessment and TMDL

Paradise Creek flows from its headwaters on Moscow Mountain in north Idaho, through the city of Moscow, and across the Washington/Idaho border to the South Fork Palouse River near Pullman, Washington. The watershed is approximately 36 square miles (23,038 acres). As an interstate water, Paradise Creek must meet Washington’s water quality standards at the state line, in addition to meeting Idaho’s standards. According to Washington’s water quality standards, Paradise Creek must be protected for salmonid spawning, primary contact recreation, and domestic water supply, among other things. Salmonid spawning, primary contact recreation, and domestic water supply are not supported by Paradise Creek.

Paradise Creek receives pollutants from several sources, including nonirrigated croplands, grazing lands, construction, urban runoff, roads, and timber harvest. In addition, Moscow’s wastewater treatment plant and the University of Idaho’s aquaculture facility discharge to the creek through National Pollutant Discharge Elimination System permits.

TMDLs were developed for Paradise Creek for all of its listed pollutants except for flow and habitat alteration. The US Environmental Protection Agency does not believe that flow and habitat alteration are pollutants as defined by the Clean Water Act. Since TMDLs are not required for water bodies impaired by pollution but not pollutants, TMDLs were not developed for flow or habitat alteration. However, flow and habitat alteration will be addressed through pollution control activities implemented to control the other pollutants addressed in this TMDL.

1997 TMDL: Stream and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Paradise Creek Sediment, total phosphorus, temperature, bacteria, ammonia

2005 Subbasin Assessment and TMDL

The pollutants in the Palouse River subbasin are from nonpoint sources, including sheet and rill erosion, solar radiation, cattle and other livestock, fertilizers, and septic systems. There are no point sources within the §303(d) stream watershed boundaries.

Some listed pollutants were found to not be impairing beneficial uses for specific streams and are recommended for removal from the §303(d) list. It is recommended that nutrients be removed from the §303(d) list for Big, Deep, Gold, and Rock Creeks and part of Hatter Creek. The document also recommends that sediment and bacteria be removed as listed pollutants for Big Creek and temperature be removed as a listed pollutant for Rock Creek.

2005 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Big Creek Temperature
Deep Creek Bacteria, sediment, temperature
Flannigan Creek Bacteria, nutrients, sediment, temperature
Gold Creek Bacteria, sediment, temperature
Hatter Creek (upper) Bacteria, sediment, temperature
Hatter Creek (lower) Bacteria, nutrients, sediment, temperature
Rock Creek Bacteria, sediment

2005 Cow Creek Watershed Assessment and TMDL

Cow Creek is considered both a 2nd- and 3rd-order tributary of the Palouse River in the southern part of Latah County and northern part of Nez Perce County, Idaho. The creek flows primarily southwest for about 18.5 miles before it enters Union Flat Creek. The watershed is approximately 32.8 square miles (21,000 acres). A sewage lagoon facility is located along Cow Creek just downstream of the city of Genesee.

Low flow periods in Cow Creek between July and September coincide with periods of diurnal dissolved oxygen exceedances in both the intermittent and perennial reaches of the watershed. This TMDL is intended to manage in-stream phosphorus concentrations, reduce aquatic plant growth, and enhance dissolved oxygen during the mid- to late-summer critical flow period between July and September.

The Genesee wastewater treatment lagoon is the only point source permitted to discharge in the Cow Creek watershed. In February 2005, the US Environmental Protection Agency (EPA) issued a National Pollutant Discharge Elimination System (NPDES) permit to the City of Genesee allowing discharge year-round. Historically, the city only discharged from November to July. The city anticipated the need to discharge year-round due to increasing influent flows and required lining of the lagoons to eliminate seepage. The new permit requires the city to monitor effluent quality and the receiving surface waters of Cow Creek. Surface water monitoring is required for temperature, pH, total phosphorus, and ammonia.

This TMDL provides a wasteload allocation for the wastewater treatment lagoon for total phosphorus of 0.60 kilograms/day during the annual critical low flow period of June through September.

The primary nonpoint sources of pollutants in the Cow Creek watershed are nonirrigated croplands and grazing lands. The entire length of Cow Creek and its tributaries typically receive pollutants from agricultural fields during rainfall and snowmelt. Nutrients associated with sediment also enter the creek at these times from fields and unstable banks. During the summer low-flow periods, portions of Cow Creek experience temperature increases and low dissolved oxygen concentrations.

A TMDL was developed for nutrients (total phosphorus) for Cow Creek. TMDLs were not developed for temperature or habitat alteration. It is recommended that Cow Creek remain on the §303(d) list for temperature and that a temperature TMDL be deferred until additional data can be collected to determine if a TMDL is needed.

EPA does not consider habitat alteration to be a pollutant as defined by the Clean Water Act. Since TMDLs are not required for water bodies impaired by pollution but not pollutants, a TMDL was not developed for habitat alteration.

2005 TMDL: Stream and Pollutant for Which TMDLs Were Developed

Stream Pollutants
Cow Creek Total phosphorus

2007 Palouse River (South Fork) Watershed Assessment and TMDL

The South Fork Palouse River drains from the southern slope of Moscow Mountain, skirts the south side of the city of Moscow, and enters Washington upstream of the city of Pullman. The watershed is approximately 30 square miles (19,200 acres). Most of the wetlands and floodplains in the Palouse prairie have been eliminated by modern land use, urbanization, and transportation infrastructure. These activities have affected instream flows, channel sinuosity, and habitat diversity. In addition, the topography, soils, and climate make the Palouse River subbasin very susceptible to erosion. Land uses that contribute excess sediment, nutrients, and bacteria to the river can degrade water quality. Total maximum daily loads were established for E. coli bacteria and temperature throughout the watershed, and for sediment and nutrients in specific portions of the watershed. In addition to nonpoint source load allocations, wasteload allocations were developed for February and March for Syringa Mobile Home Park and Country Homes Mobile Park, both of which discharge small amounts of wastewater to the river from wastewater lagoons. These are included with the load allocation in the existing load.

2007 TMDL: Stream and Pollutants for Which TMDLs Were Developed

Stream Pollutants
South Fork Palouse River E. coli, nutrients, sediment, temperature

2013 Cow Creek Addendum

This addendum addresses the outstanding temperature impairment listing included in Idaho’s 2010 Integrated Report for Cow Creek in the Palouse River subbasin. The addendum provides a TMDL load allocation that calls for an increase in riparian shade to restore stream temperatures to natural background conditions. The addendum also provides a TMDL wasteload allocation for the City of Genesee wastewater treatment facility based on the wastewater treatment facility effluent discharge data required to be reported by the city’s 2005 US Environmental Protection Agency National Pollutant Discharge Elimination System (NPDES) permit.

Two assessment units of Cow Creek were originally placed on the 1998 §303(d) list of impaired waters, and subsequent lists, for reasons associated with temperature criteria violations and carried forward to the 2010 Integrated Report. The Idaho Department of Environmental Quality has developed temperature TMDLs for one of these assessment units and has recommended delisting the other due to a lack of water in the channel during the critical time period.

2013 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Cow Creek Total phosphorus

2016 Paradise Creek Bacteria TMDL Addendum

This addendum addresses previously approved fecal coliform bacteria TMDLs that are updated to Escherichia coli (E. coli) bacteria TMDLs to reflect changes in recreation use criteria. Existing E. coli bacteria loads were determined from surface water sampling from May 2013 through April 2014. The E. coli target of 126 cfu/100 mL and existing E. coli levels were compared to determine the reduction needed to bring water bodies into compliance. Non-point source load allocations and point source wasteload allocations are provided. Two assessment units of Paradise Creek were originally placed on the 1994 §303(d) list of impaired waters, and subsequent lists, for reasons associated with bacteria criteria violations. The TMDL addendum addresses the following assessment units: Paradise Creek-urban boundary to Idaho/Washington border (ID17060108CL005_02) Paradise Creek-forest habitat boundary to urban boundary (ID17060108CL005_02a)

2016 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Paradise Creek E. coli bacteria

Subbasin Document(s)

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DEQ Lewiston Regional Office
1118 F St.
Lewiston, ID 83501
Ph: (208) 799-4370
Fax: (208) 799-3451
Toll Free: (877) 541-3304

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