Water Quality Improvement Project
The Okanogan River originates in the Cascade Mountains north of the
international border between British Columbia (BC) and Washington State.
On the BC side the Okanogan River is made up of a series of lakes and a
free-flowing river coming from Lake Osoyoos, which straddles the
boundary. Once it crosses the border into Washington it flows 78 miles
to its confluence with the Columbia River.
The Okanogan River’s primary tributary is the
Similkameen River, which enters
the Okanogan River just downstream of Oroville, Washington. The
Similkameen River normally contributes three-quarters of the combined
flow in the Okanogan River. About 20 small tributary streams also drain
the 2,600 square miles of the Washington portion of the basin. The basin
is lightly populated. Agriculture, forestry, mining, and recreation are
the major land-use activities in the Okanogan watershed.
Water quality issues
The Okanogan River and several tributaries are listed on Washington
State's 303(d) list of impaired waters because they do not meet the EPA
human health criteria for DDT and PCBs in edible fish tissue, as well as
for non-attainment of Washington's chronic criteria for DDT in water.
When water bodies are placed on the 303(d) list, the Clean Water Act
requires that the state develop a Total Maximum Daily Load (TMDL) for
that waterbody. The TMDL determines the extent of the pollutant
problem in the water, and establishes the maximum load of that pollutant
that the water body can accept without violating the state's surface
water quality standards. The TMDL is accompanied by a
implementation strategy or plan, worked out between the state and local
citizens, governments, and special interest groups, to help the move the
water body to clean water.
Why this matters
DDT is a pesticide that was widely used from the mid-1940s
until 1958, when the U.S. Department of Agriculture (USDA) began a
program to phase it out for its insect control programs due to concerns
about its persistence in the environment and toxicity to non-target
organisms, such as aquatic life. In 1972, the U.S. Environmental
Protection Agency (EPA) banned DDT for all uses except for emergencies.
Despite the ban, DDT persists in the environment. Soils containing DDT can
end up in streams and other surface water bodies through erosion. As DDT is
transported to streams, it is absorbed by the plant and animal life within the
stream system and then moves up the food chain. DDT biomagnifies at higher
levels in each step of the food chain (plants, aquatic biota, fish, humans). DDT
can also be found in ground water, as water infiltrates through contaminated
soils into aquifers.
Pesticides and polychlorinated biphenyls (PCBs) can be toxic to fish
and wildlife that use a contaminated water body.
In the past, PCBs were used as coolants and lubricants in electrical
equipment such as transformers and capacitors. The United States banned the
manufacture of PCBs in 1977 because they build up in the environment and can be
harmful to humans and wildlife. PCB exposure can occur if you:
- Eat food, including fish, meat, and dairy products that is contaminated
- Drink PCB-contaminated water.
- Breathe air near hazardous waste sites that contain PCBs.
Because DDT, PCB and other legacy chemicals are found everywhere now –
cities, farms, forest roads, etc. - control of stormwater runoff or movement of
soils by wind or vehicles is paramount in controlling spread of the chemicals.
The Okanogan watershed was one of Washington State’s first Total Maximum
Daily Load (TMDL) efforts. Studies on DDT, PCB, arsenic, mercury, and
other pollutants started as early as 1980. Because these pollutants are
so hard to remove from the environment, Ecology has developed
containment strategies as well through TMDLs.
What has been done
A TMDL project was conducted for the portion of
the river that flows through Washington State. It was determined that the source
of these contaminants appeared to be from historic agricultural and industrial
activities common throughout the Okanogan River watershed.
The chemical characteristics of DDT and PCBs cause them to be classified as
persistent, bioaccumulative toxins. They are a legacy of past activities,
because the United States and Canada banned their use over 25 years ago. Due to
their legacy nature mitigation of the DDT and PCB contamination, both directly
and indirectly, has already occurred in the Okanogan Basin. Direct actions
include banning these materials from use; indirect actions include irrigation
improvements that have reduced the loss of agricultural topsoil that potentially
could carry pesticide residues to the Okanogan River and associated waterbodies.
The DDT and PCBs in the lower Okanogan River Basin TMDL continue to promote
community actions that address DDT and PCB contamination, along with new actions
of source identification and development of management strategies to address any
sources of contamination subsequently revealed.
Status of the project
EPA approved the TMDL for the Lower Okanogan River in February 2005. The
project is currently in implementation. Preliminary monitoring in 2009 and 2011
indicated that DDT levels were slightly reduced. Ecology will continue to
monitor until 2015, then revise the implementation plan if needed.
Unless otherwise specified, the following documents are Ecology publications.
DDT and PCBs Total Maximum Daily Load: Water Quality Improvement Report
Lower Okanogan DDT PCB Detailed Implementation Plan
Quality Assurance Project Plan: Okanogan River DDT and PCB Total Maximum Daily
Load Effectiveness Monitoring
Lower Okanogan River Basin
DDT and PCB Total Maximum Daily Load: Water Quality Effectiveness Monitoring
Okanogan Pesticide Collection Partnership: Keeping Pollution Out of the Water (Ecology water quality story)
WRIA 49: Okanogan Watershed Information (Environmental Assessment
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