Water Quality Improvement Project
The Similkameen River begins in the Cascade Mountains between British
Columbia (BC) and Washington State. The Pasayten River flows north out of
Washington to join the Similkameen River in British Columbia. After
crossing the border, the Similkameen River becomes a tributary of the
Okanogan River at Oroville, Washington.
Mining, forestry, agriculture, and recreation are the major land-use
activities in the Similkameen watershed.
Water quality issues
The Similkameen River is listed on the Washington State 303(d) list
because it does not meet the human health criteria for arsenic. The
major source of arsenic appears to be a legacy resulting from historical
mining activities, mostly in British Columbia between Hedley and the
U.S. border. Washington State sources are Palmer Lake, likely from
periodic flooding and sediment deposit by the Similkameen River,
possible inputs from Sinlahekin Creek, and re-suspension of contaminated
Why this matters
Arsenic is a naturally-occurring element found in soil and
minerals. It is also commonly found in products such as wood
preservatives, pressure-treated lumber, pesticides, automobile
batteries, and light-emitting diodes (LEDs). Arsenic cannot be destroyed
in the environment - it can only change its form.
Stormwater runoff and industrial wastewater discharges carry arsenic into our
downstream waters. All of us are exposed to arsenic through the air we breathe,
the water we drink, and the food we eat. Higher exposure to arsenic can cause
health problems, depending on the type, amount, and method of arsenic ingestion.
Status of the project
It was determined that the Similkameen River naturally exceeds the EPA
arsenic criteria upstream of the areas disturbed by mining near Hedley, BC.
Under these circumstances, natural conditions constitute the water quality
criteria. Because arsenic levels naturally exceed criteria, the loading capacity
for the river is set equal to the natural background concentration of arsenic.
The Department of Ecology developed a total maximum daily load (TMDL) study
and report for the Similkameen River from the international border between
Washington State and British Columbia (river mile 27.1) to the river’s mouth
near Oroville, Washington, including Palmer Lake outlet and other tributaries to
the river within Washington. An arsenic monitoring plan was suggested for the
Similkameen River. The plan recommends: 1) periodical review of Canadian
federal/provincial water quality monitoring data for the Similkameen; 2)
renewing arsenic monitoring of the river in Washington if and when cleanups
begin; 3) analyzing inorganic arsenic in Similkameen River and Palmer Lake fish
to assess human health risk; and 4) conducting a study of arsenic sources and
cycling in Palmer Lake.
After responding to public comments, the TMDL report was submitted to EPA for
approval. EPA approved the TMDL on February 17, 2004.
Unless otherwise noted, the following documents are Ecology publications.
Lower Similkameen River Arsenic Detailed Implementation Plan
Lower Similkameen River Arsenic Total Maximum Daily Load: Submittal Report
Quality Assurance Project Plan - Similkameen River and Palmer Lake Investigation of Arsenic in Fish Tissue
A Total Maximum Daily Load Evaluation for Arsenic in the Similkameen River
Similkameen River and Palmer Lake Investigation of Arsenic in Fish
Effects of Small-Scale Gold Dredging on Arsenic, Copper, Lead, and Zinc Concentrations in the
WRIA 49: Okanogan Watershed Information (Water web site)
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