Protecting Public Health and the Environment.

Hangman Creek Subbasin

Subbasin at a Glance

Hydrologic Unit Code 17010306
Size Approximately 15 square miles (9,500 acres)

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

Hangman Creek and tributaries

Beneficial Uses Affected Cold water aquatic life, secondary contact recreation, salmonid spawning
Major Land Uses Timber management, residential development, livestock grazing
Date Approved by EPA

September 2007
EPA Approval Letter

Subbasin Characteristics

The Hangman Creek subbasin is located above the Coeur d’Alene Tribal boundary, where the rolling hills of the Hangman Creek valley meet steep mountainsides. The subbasin is forested, although some openings have been created for other land-use activities. The primary land use is timber management, with residential development along major roads and livestock grazing at lower elevations; 77% of the subbasin is privately owned and the remaining 23% is federal national forest ownership.

2007 Subbasin Assessment and TMDL

The document addresses two assessment units within the Hangman Creek subbasin. Sediment, temperature, and bacteria TMDLs were developed for seven named streams within these two assessment units. These streams include Hangman, South Fork Hangman, Tenas, Martin, Conrad, Hill, and Bunnel Creeks. The pollutants originate solely from nonpoint sources.

Sediment was determined to be present in excessive quantities and impairing the cold water aquatic life use designation. Sediment generated from roads, mass failures, and streambank erosion was characterized to determine the amount of sediment load reduction needed to restore beneficial uses. The target load capacity was set at 50% above natural background.

Temperature TMDLs were written following data that revealed exceedances of Idaho's numeric water quality temperature standard. Solar radiation was determined to be the factor most easily controllable and manageable in reducing stream temperatures. A decrease in solar radiation requires an increase in stream shading. Potential natural vegetation (PNV) was selected as the desired target for the TMDL. If the targets are achieved, yet stream temperatures are warmer than numeric criteria, it is assumed that the stream’s temperature is natural, and natural background provisions of Idaho water quality standards apply.

Bacteria TMDLs were written because water quality monitoring data indicated that the beneficial use of secondary contact recreation was not being fully supported. The source of bacteria is unknown. Further monitoring will be needed to determine the source of contamination. Known possible sources include domesticated and wild animals and/or human contributions from recreation or septic systems.

Some water bodies in this subbasin were also listed for habitat alteration and/or nutrients. No TMDL was completed for habitat alteration as a matter of DEQ policy. This document recommends delisting for nutrients due to recent data showing low levels of total phosphorus.

2007 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Hangman Creek
Sediment, temperature, bacteria
South Fork Hangman Creek
Sediment, temperature, bacteria
Tenas Creek
Sediment, temperature, bacteria
Martin Creek
Sediment, temperature, bacteria
Conrad Creek
Sediment, temperature, bacteria
Hill Creek
Sediment, temperature, bacteria
Bunnel Creek
Sediment, temperature, bacteria

Subbasin Document