Water Quality Improvement Project
Selah Ditch is east of the Cascade Mountains in Yakima County, Washington
State. It is about one mile north of the city of Yakima. Climate in
the area is generally mild and dry. Most precipitation comes during the
late fall to early spring months.
Selah Ditch is a man-made drainage canal, originally made for dewatering a
high water table to allow the city of Selah to continue to grow. It
collects water from point and nonpoint sources: mainly irrigation supply water,
irrigation runoff, urban storm water, and industrial/municipal discharges.
It then discharges into the west side of the east fork of Taylor Ditch.
Water quality issues
Based on studies and water samples, Selah Ditch was placed on Washington
State's 1996 and 1998 303(d) lists due to violations of the state water quality
standards for ammonia, chlorine, and dissolved oxygen. On the 2004 list the ditch was
listed only for fecal coliform bacteria and temperature. Studies found
impaired levels of dissolved oxygen, but due to insufficient data it was not
listed for dissolved oxygen.
Why this matters
Fecal coliform is a type of “bacteria” common in human and animal
waste. It can make people sick and cause the closure of shellfish harvesting
beds. Bacteria can get into our waters from untreated or partially treated
discharges from wastewater treatment plants, from improperly functioning septic
systems, and from livestock, pets and wildlife.
Water temperature influences what types of organisms can live in a
waterbody. Cooler water can hold more dissolved oxygen that fish and other
aquatic life need to breathe. Warmer water holds less dissolved oxygen.
Threatened and endangered salmon need cold, clean water to survive.
Status of the project
The Department of Ecology, with the help of local groups in the watershed,
developed a total maximum daily load (TMDL) report. The report provided results
of water quality studies on the ditch, recommendations for bringing the water
quality up to meet state standards for fecal coliform bacteria and temperature,
and an implementation strategy on how to accomplish the recommendations.
Ecology sent the finalized TMDL to EPA for approval. EPA approved
the document in September 2006.
Wasteload allocations were applied to the publicly-owned treatment works (POTWs) and
stormwater discharges through their National Pollutant Discharge Elimination
System (NPDES) permits and best management practices (BMPs). For temperature
issues, mainly due to solar radiation, the recommendation was
application of load allocations in the form of increased shading over parts of
Past chlorine problems have been eliminated due to the city of Selah's POTW converting to
ultraviolet (UV) disinfection. Past
ammonia problems have not continued, so there is insufficient data to warrant a
Selah Ditch Multiparameter Total
Maximum Daily Load: Technical Assessment (Ecology publication)
Selah Ditch Multiparameter Total Maximum Daily Load: Water Quality Improvement Report
Little Klickitat River Watershed Temperature Total Maximum Daily Load
Teanaway Temperature Total Maximum Daily Load – Submittal Report (Ecology
WRIA 39: Upper Yakima
Watershed Information (Water web site)
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Last updated May