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TMDL Case Study: Tualatin River Watershed
A groundbreaking TMDL process in Oregon identifies the chain of command among federal, state and county agencies, and underscores the importance of technical
advisory groups in shaping – and reviewing – TMDLs.
The Tualatin River watershed in northwestern Oregon was one of the
first TMDL-regulated watersheds in the United States. TMDLs were set in 1987-88 following
the resolution of a lawsuit based on the Clean Water Act ( Northwest Environmental
Defense Center v. Thomas). As a result of this lawsuit, a consent decree was agreed upon which included "both a timetable for certain Oregon actions and a requirement for EPA action if Oregon did
not comply." (Lindley, 1998).
Based upon existing knowledge, TMDLs were set for the main stem of
the Tualatin River by the
Oregon Department of Environmental Quality (DEQ). Summer flow rates
were averaged for the
tributaries and the mainstem of the river so that concentrations
would not exceed 70 micrograms
total phosphorus (TP)/L and 1 mg ammonia (total of NH 3 and
NH 4 )-N/L.
Standards were in effect only during the low-flow, warm season period, from
approximately May 1 through October 31, which covered the peak period of algal growth.
At the time the TMDLs were set, the river averaged over 1 mg
TP/L and
over 5 mg ammonium (total of NH 3 and
NH 4 )-N/L
in the summer.
The ammonium-N was essentially all released from wastewater treatment
plants along the river.
Compliance was achieved by installing nitrification ponds in the
plants, which collect wastewaterand allow the ammonium-N to convert to nitrate. Nitrate does not
directly decrease levels of dissolved oxygen (DO) when released into the river; however,
indirectly it can through encouraging algal growth.
Phosphorus (P) control has been much more challenging. While the bulk
of the phosphorus entering the river in 1987 was from wastewater treatment plants,
inputs from nonpoint sources were also significant. A concerted effort to reduce nonpoint sources
of phosphorus was clearly necessary, addressing the three dominant land uses in the watershed.
Forestry is practiced on the mountainous fringe, agriculture in the foothills and valley floor;
and the urbanized area is primarily near the river in the center of the valley floor.
A Designated Management Agency (DMA) representing each of the three
categories of land use was assigned responsibility for developing and implementing both
monitoring and BMP plans to restore beneficial uses for the river by lowering nonpoint source pollution.
The urban DMA is the Unified Sewerage Agency (USA) which collects and
treats nearly all the sanitary sewer discharge in the valley. USA also is responsible for
stormwater management inthe urban areas of the county. The agricultural DMA is the Oregon
Department of Agriculture (ODA), which passed its primary responsibility to the Washington
County Soil and Water Conservation District (SWCD) as Washington County roughly encompasses the entire
Tualatin Watershed. The forestry DMA is the Oregon Department of Forestry
(ODF).
Oregon Department of Environmental Quality (OR
DEQ) set acceptable loads – expressed as median monthly concentrations – for streams passing through
primarily forested watersheds at 20 micrograms TP/L. Streams passing through agricultural areas were set
at 50 micrograms TP/L; and the lower portion of the Tualatin River was set at 70 micrograms TP/L.
The Tualatin watershed drew on the technical resources available in
the valley in an effort toevaluate and understand the river system. The SWCD appointed a
Technical Advisory committeeto assist with agricultural issues related to the TMDLs. However,
membership rapidly grew toinclude representatives of urban systems and forestry, as well as
Oregon DEQ. An intense periodof meetings followed which brought all involved parties to a high
level of technical awareness in terms of monitoring, interpretation, objectives of the program, and
BMPs.
A second feature of the effort was the Tualatin River Research
Advisory Committee (TRRAC).
Beginning in 1991, the TRRAC met each spring to discuss the plans for
the upcoming summermonitoring and research, and met again each fall to discuss the
monitoring results. All partiesinterested in the technical developments in the watershed were
invited. The discussions brought all three DMAs up to date with results of a joint United States
Geological Survey (USGS)/Oregon Graduate Institute research project, as well as other water
quality research that hadoccurred in the watershed over the previous year. Decisions related
to monitoring and BMPimplementation could be made rapidly and effectively following these
meetings, prior to formal publication of results in many cases.
The Unified Sewerage developed new, highly effective chemical methods
of P removal whichbrought summertime wastewater treatment plant
(WWTP) effluent
concentration averages down to 50 micrograms
TP/L from values over 7,000 micrograms TP/L.
Although costly, this effectively eliminated P pollution from WWTPs. Concentrations in the mainstem of
the river dropped to between 100 and 150 micrograms TP/L in the summer, still
approximately twice the target TMDL concentration. The remainder was derived from natural sources
and human nonpoint source activities. Approximately six years of research and monitoring
of groundwater inputs, surface water inputs and runoff inputs led to this
determination.
BMPs have been
instituted, with some ongoing monitoring conducted to assess the long-term
impacts of these BMPs on water quality. Current estimates of natural background levels,
derived from valley sediments and P-rich geology in the surrounding mountains, indicate
that it may be very difficult to lower mainstem TP concentrations below 100 micro-grams/L.
Comments: Tualatin Watershed, Oregon
"In our work with TMDLs in the Tualatin Valley, our overall
objective was to link the best science quickly and directly to
the applications in the field. We formed a Technical Advisory Committee
(TAC), a group of scientists from a wide array of
disciplines, to answer questions from our other committees,
which were composed mainly of farmers.
The TAC helped guide us in decision-making. It also provided
the Tualatin River Subbasin Local Agricultural Water
Quality Advisory Committee with the specific scientific and
technical data needed to write the annual Tualatin River Sub
basin Agricultural Water Quality Management Area Plan
required by the Oregon Department of Environmental
Quality. Where the answers were not available from current
knowledge, we worked to get the best quality of applied
science done to answer those questions. Because of this
strong involvement of scientists with the public, citizens
living in the watershed are generally much more comfortable
with the regulations and the results." -- Dick
Kover, Director, Washington County, Oregon, Soil and
Water Conservation District
The TMDLs for both TP and ammonia are currently under review. More
recently, temperature impacts have come under scrutiny. This has led to the implementation
of temperature TMDLs on many tributaries of the Tualatin during the summer months. The
pollutant is heat energy. Temperature TMDLs are calculated based on heat energy loadings from solar
radiation and point sources. Solar radiation heats unshaded water directly as well as
soils, pavements, roof tops, etc., which in turn heat runoff waters. Point sources such as industrial
and municipal wastewater treatment plants and power plants can also discharge heated water.
For temperature TMDLs, it is much better to monitor temperature continuously, as temperature
can change significantly from season to season, day to day, or hour to hour.
(Oregon DEQ 1999. Upper Grande Ronde River Subbasin TMDL.)
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