Water Quality Improvement Projects (TMDLs) > Yakima Watershed Area Projects > Selah Ditch Area Multi-parameter Project

Water Quality Improvement Project
Selah Ditch Area:
Multi-parameter

Introduction

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Selah Ditch is a man-made drainage canal, originally made for dewatering a high water table to allow the city of Selah to continue to grow.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 some 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 the ditch.

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 continued listing.

Technical information

Selah Ditch Multiparameter Total Maximum Daily Load: Technical Assessment (Ecology publication)
www.ecy.wa.gov/biblio/0510020.html

Selah Ditch Multiparameter Total Maximum Daily Load: Water Quality Improvement Report (Ecology publication)
www.ecy.wa.gov/biblio/0610040.html

Related information

Little Klickitat River Watershed Temperature Total Maximum Daily Load (Ecology publication)
www.ecy.wa.gov/biblio/0203031.html

Teanaway Temperature Total Maximum Daily Load – Submittal Report (Ecology publication)
www.ecy.wa.gov/biblio/0110019.html

WRIA 39: Upper Yakima Watershed Information (Environmental Assessment Program web site)
www.ecy.wa.gov/apps/watersheds/wriapages/39.html

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