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Section 319
NONPOINT SOURCE PROGRAM SUCCESS STORY
Forestry, Agricultural, and Stormwater Best Management Practices
Improve Quality of Reservoir
Waterbodv Imoroved Water Quality in the Cascade Reservoir, 70 miles north of
Boise in central Idaho, has been adversely affected by
phosphorus loading from various sources, including forestry operations and agricultural
activities. By upgrading forest roads and implementing grazing best management practices,
project partners saw a 57 percent reduction in phosphorus, exceeding the 37 percent
reduction goal.
Problem
The Cascade Reservoir has been plagued with
excessive algae blooms that have degraded
fish habitat and caused poor water quality
for swimming and boating. Water quality
studies identified phosphorus as the pollutant
of concern in the watershed, and as a result
the reservoir was added to the state's 303(d)
list for phosphorus. Point source pollution
from wastewater treatment plants and a fish
hatchery contributed about 10 percent of the
phosphorus loading to the watershed. Nonpoint
sources like 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 Reservoir Phase II Watershed
Management Plan outlined a need to reduce
phosphorus by 37 percent throughout
the watershed to bring the reservoir into
compliance with water quality standards.
Project Highlights
In 1995 the Idaho Department of Environmental
Quality initiated a phased total maximum daily
load (TMDL) process to address concerns
about excess phosphorus. Forestry implemen-
tation projects addressed road-related sedi-
ment runoff along more than 109 miles of road
Before: Drain ditch leading
to Cascade Reservoir prior
to installation of BMPs.
After: Drain ditch after
cattle have been removed
from the ditch area and
vegetation reestablished.
by graveling 81 miles, closing 3.5 miles, paving
0.1 mile, and installing drainage upgrades on
24.7 miles of road. Agricultural implementa-
tion projects addressed grazing and irrigation
management through livestock exclusion,
fencing, tree and shrub planting, and wildlife
habitat management. Urban and suburban
implementation projects included the creation
of wetlands as indirect treatment measures
for stormwater discharges, as well as imple-
menting parking lot upgrades and drainage
improvements as direct stormwater treatment
measures.
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Summary of Estimated Phosphorus Loads and Reductions for Point and Nonpoint
Sources in the Cascade Reservoir Watershed, 1994 through 2002
Point Sources
McCall Wastewater Treatment Plantb
Idaho Fish and Game fish hatchery
Point source totals
Nonpoint Sources
Forestry
Agriculture
Urban and suburban
Septic systems
Unidentified and natural sources
Nonpoint source totals
Grand Total
Total Load
(kg/yr)
3,947
726
4,673
8,840
11,740
4,423
2,205
8,508
35,716
39,881
Projected Reduction
(kg/yr)a
3,947
508
4,455
2,652
3,485
1,359
1,544
2,134
11,174
15,121
Reduction Achieved
to Date (kg)
3,947
508
4,455
2,675
745
255
838C
80
4,593
8,540
Percent of Reduction
Achieved to Date
100%
100%
100%
101%
21%
19%
38%
4%
41%
57%
a Contains management, natural, and background loading.
b Construction of winter storage pond is not yet complete. Storage and delivery systems will be completed and tested.
Additional options for effluent use are being investigated to ensure that the system will operate with no discharge to North
Fork Payette River in extreme water years.
c The 838 kg figure used assumes that all septic-to-sewer hookups completed included proper decommissioning of the septic
tanks. This assumption has yet to be validated. Septic decommissioning is being evaluated.
Results
Initial monitoring data indicate a 57 percent
reduction in phosphorus, exceeding the 37 per-
cent reduction goal. The reductions achieved
have resulted in improved water quality condi-
tions in the reservoir. Improved dissolved oxy-
gen conditions were observed in the reservoir
in 1999, 2000, and 2001. Continued reductions
in phosphorus from nonpoint sources are
expected through the participation of partners
throughout the watershed.
Partners and Funding
This project's success has been ensured
through the broad participation of agencies and
the local project sponsors. Partners include the
Idaho Department of Lands, USDA's Natural
Resources Conservation Service and Forest
Service, Boise Cascade Corporation, Valley
Soil and Water Conservation District, City of
McCalls, and local residents. Project costs from
1997 to 2004 totaled more than $20 million.
Section 319 grants accounted for approximately
$1.05 million in project funds and were used to
implement best management practices, includ-
ing forest road upgrades, grazing management
activities, and stormwater treatment wetlands.
I
5
Q
'. U.S. Environmental Protection Agency
\ Office of Water
a Washington, DC
EPA841-F-05-004C
July 2005
For additional information contact:
Todd Maguire
Nonpoint Source Management Program
Idaho Department of Environmental Quality
208-373-0115 • todd.maguire@deq.idaho.gov
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