Water Quality Improvement Project
Wilson and Cooke Creeks:
The Wilson Creek sub-basin is east of the Cascade Mountains in Kittitas
County, Washington State. It drains most of the area surrounding the city of
Ellensburg, as well as the agricultural lands and forests to the north and east
of the city. The climate in the sub-basin area is semi-arid, with an average
annual rainfall of 8.9 inches. The sub-basin covers approximately 244,500 acres
(394 sq. miles) of land.
Land uses in the sub-basin vary from forestland, range, and intensively
irrigated agriculture to urban and suburban areas. The sub-basin contains a
network of supply canals, diversions, irrigation return drains, and numerous
natural creeks, such as Cooke Creek. Water from
the Yakima River is directed through
the sub-basin by three large irrigation supply canals. The sub-basins’ natural
creeks are ultimately used as the conduits for irrigation return flows.
Water quality issues
Studies indicated that the downstream portion of various creeks in the Wilson Creek sub-basin violated
Washington State water quality standards for fecal coliform bacteria. (See
Study Area map)
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.
People can help keep bacteria out of the water. Keep livestock away from
creeks and implement best management practices (BMPs) to prevent runoff from
agricultural fields. Properly collect, bag, and
trash dog poop. Check your on-site sewage system to make sure it is maintained
and working properly.
Status of the project
Ecology, with the help of local groups, developed a total maximum daily load
(TMDL) report. The report included results of water quality studies and
monitoring; recommendations for helping the water quality to meet the state
water quality standards; and an implementation strategy to determine how to
accomplish the recommendations. Ecology sent the finalized TMDL to EPA for
approval. EPA approved the document in July 2005.
The national pollution discharge elimination system (NPDES) permits issued to
the city of Kittitas after September 30, 2006, had more stringent requirements
for fecal coliform bacteria levels in the waste water than previously. The
city also upgraded its municipal wastewater treatment plan. Concentrated
animal feeding operations (CAFOs) are not allowed to discharge pollutants to the
waters of the state except under extreme circumstances. A single load
allocation was set for all non-point sources of fecal coliform pollution in the
sub-basin. Human contribution of fecal coliform bacteria was expected to
be reduced through implementing BMPs.
Unless otherwise specified the following documents are Ecology publications.
Wilson Creek Sub-Basin Bacteria Total Maximum Daily Load (Water Cleanup
Plan): Submittal Report
Wilson Creek Sub-basin Bacteria Total Maximum Daily Load Detailed
Wilson Creek Sub-Basin Fecal Coliform Bacteria Effectiveness Monitoring Water
Quality Study Design (Quality Assurance Project Plan)
Wilson Creek Sub-basin Bacteria Total Maximum Daily Load: First Water Quality
Post TMDL Monitoring Report
Focus on Wilson Creek Sub-basin Bacteria TMDL
WRIA 39: Upper Yakima
Watershed Information (Water web site)
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