Section 319
NONPOINT SOORCE PROGRAM SUCCESS STORY
Forestry, Agricultural and Urban Stormwater Best Management Practices
Improve Reservoir s Water Quality
\A/ato hnH I n n oH Water quality in the Cascade Reservoir, 70 miles north of Boise in
VVdierDOQy improved central Idaho, has been impaired by phosphorus loading from various
sources, including forestry operations, agricultural activities and urban
Stormwater runoff. By upgrading forest roads and implementing a series of best management practices
and drainage improvements, project partners have achieved 70 percent of the needed reductions in
phosphorus. Although phosphorus levels do not yet consistently meet standards, data show that water
quality is improving.
Problem
The U.S. Bureau of Reclamation (USER) created
Cascade Reservoir in 1949 for flood control and
water storage. The reservoir averages 26.5 feet
deep and is 21 miles long and 4.5 miles wide at
the widest point. Approximately 65 percent of the
reservoir's watershed is steeply sloped forestland,
while the land adjacent to the reservoir and major
tributaries is used predominantly for agriculture
(22 percent). Urban and residential areas make up
another 13 percent of the total land area. Two rivers
(North Fork Payette and Gold Fork) and four creeks
(Mud, Lake Fork, Boulder, and Willow) all discharge
into the northern end of the reservoir (see Figure 1).
The Cascade Reservoir has been plagued with
excessive algae blooms, which have degraded
fish habitat and impaired swimming and boating
uses in the reservoir. Eutrophication was especially
apparent in 1993 and 1994 when dense mats of
blue-green algae formed in the reservoir. In 1993
23 cattle died after ingesting toxins produced by the
algae. A substantial fish kill occurred in 1994. Water
quality studies identified phosphorus as the source
of the problem. Idaho Department of Environmental
Quality (IDEQ) added the reservoir to the state's
Clean Water Act section 303(d) list of impaired
waters for phosphorus and initiated a phased total
maximum daily load (TMDL) in 1995.
Studies showed that point source pollution from
wastewater treatment plants (WWTPs) and a
fish hatchery contributed about 10 percent of the
phosphorus loading to the watershed. Nonpoint
source (NPS) pollution from forestry, agriculture, and
urban areas contributed an estimated 84 percent,
and poorly functioning or failing septic tanks were
the source of the remaining 6 percent. The Cascade
Subwatersheds of Cascade Reservoir
Boulder &
Willow Creeks
West
Mountain
0 5 10 15 20 25 Miles
Figure 1.
Watershed map
delineating
the Cascade
Reservoir and
its five main
tributaries.
Reservoir Phase II Watershed Management Plan
outlines a need to reduce by 37 percent (30 percent
reduction, plus a 7 percent margin of safety) the
total phosphorus loads entering the lake throughout
the watershed to bring the reservoir into compliance
with water quality standards. IDEQ completed an
implementation plan for the Phase II TMDL in 2000.
Project Highlights
The two primary point source implementation proj-
ects are complete. The Idaho Department of Fish
and Game's (IDFG's) fish hatchery modified its food
type and feeding practices and installed a sediment
pond to treat discharge water, which allowed the
hatchery to meet its phosphorus reduction goal.
In 2001 the city of McCall completed a project to
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remove 100 percent of its WWTP effluent from the
watershed by instead using the effluent to supple-
ment summer irrigation water.
Project partners have either completed or initiated
a variety of NPS pollution reduction projects. For
example, several projects addressed forestry-
related sediment runoff along more than 109 miles
of forest roads by graveling 81 miles, closing
3.5 miles, paving 0.1 mile and installing road drain-
age upgrades on 24.7 miles. USER created wet-
lands along Cascade Reservoir, which have reduced
nutrient, bacteria and sediment loading from the
surrounding areas. USER also stabilized more than
3,000 linear feet of eroding shoreline since 2000.
Urban and suburban projects included improving
drainage and adding stormwater filters in the cities
of Donnelly and McCall. McCall created wetlands to
indirectly treat stormwater and operates a street-
sweeping program. Idaho Parks and Recreation
added a sediment basin at a public boat launch and
upgraded several vault toilets.
To reduce streambank erosion caused by cattle
grazing on public land, nearly 100 percent of grazing
allotments on public forested lands are now under
grazing management plans. Other agricultural
projects include improving irrigation and grazing
management by excluding livestock from sensi-
tive areas, planting trees and shrubs, and better
managing wetlands and uplands for wildlife habitat.
Valley Soil and Water Conservation District (SWCD)
and IDEQ initiated an education outreach program,
Lake-A-Syst, which teaches homeowners how to
minimize impacts on the reservoir.
Results
The Phase II TMDL identified an overall reduction
goal for point source loading of 4,455 kilograms
per year (kg/year) total phosphorus. With the
completion of the McCall WWTP project, estimat-
ed point source reductions from this project total
3,947 kg/year. When combined with the previous
reductions accomplished by the IDFG fish hatch-
ery, 100 percent of the total point source reduction
goal has been achieved.
Additionally, the TMDL specified that total phospho-
rus loads from NPS pollution should be reduced by
11,141 kg/year. The total of measured and esti-
mated NPS reductions of total phosphorus equals
6,421 kg/year (approximately 58 percent of the total
NPS reduction goal). Overall, between point and
NPS reductions, 70 percent of the load reduction
goal has been met.
Median water column total phosphorus and chloro-
phyll a concentrations have consistently decreased
in all years since 1994 except 2001 (an exceptional
drought year). The improving water quality observed
indicates that the magnitude of water quality
impairment is decreasing. Although overall total
phosphorus levels are declining, concentrations still
routinely exceed the target level (0.025 milligram
per liter). Figure 2 shows that, while the many areas
in the Cascade Reservoir watershed are close to
meeting standards, a few of the tributaries still have
elevated phosphorus levels.
D 25th-75th Percentile
3 015
O
.C
Q.
CL
I
* Median 1 Min-Max -Average ^^— Standard
4
_J
'
rr
1 |_| -J- ± n
^ ^ | — < > — L*J
North Fork Lake Mud Boulder W How Gold Fork GAR052 GAR053
Payette Fork Creek Creek Creek River
River
Figure 2. Total phosphorus concentrations in the
Cascade Reservoir (sites GAR052 and GAR053) and its
tributaries between May and September 2003-2007.
Partners and Funding
Project partners include local residents, IDEQ,
IDFG, Idaho Department of Lands, Idaho Parks
and Recreation, U.S. Department of Agriculture's
Natural Resources Conservation Service and Forest
Service, USER, Boise Cascade Corporation, Valley
SWCD and the cities of McCall and Donnelly.
Several public groups, including the Cascade
Reservoir Watershed Advisory Group and the
Cascade Reservoir Technical Advisory Committee,
have reviewed and assessed all phased TMDL
documents. Since 1996, project partners have used
approximately $2 million in section 319 grants to
implement best management practices, including
forest road upgrades, grazing management activi-
ties and stormwater treatment wetlands.
\
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-09-001H
June 2009
For additional information contact:
Leslie Freeman
Idaho Department of Environmental Quality
208-634-4900
leslie.freeman@deq.idaho.gov
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