Q
A
NONPOINT SOURCE SUCCESS STURY
Csfclifornifc
Regulatory Actions and Stakeholder Involvement Reduce Diazinon
Levels in Butte Slough
Waterbody Improved
Widespread use of the pesticide diazinon resulted in elevated
concentrations that were toxic to aquatic invertebrates and exceeded
water quality standards in Butte Slough. As a result, Butte Slough was placed on California's Clean Water Act
(CWA) section 303(d) list of impaired waters for diazinon in 2002. The California Central Valley Regional Water
Quality Control Board (Central Valley Water Board) initiated the Irrigated Lands Regulatory Program (ILRP)
in 2002, and in 2003 the Central Valley Water Board adopted the diazinon total maximum daily load (TMDL)
for the Sacramento River watershed. Outreach and education efforts were coordinated to promote ways to
address the problem. Watershed stakeholders implemented best management practices (BMPs) to manage
the use of diazinon and other pesticides. Diazinon concentrations decreased, resulting in the Central Valley
Water Board's recommendation to remove Butte Slough from the impaired waters list for diazinon in 2016.
Problem
The 9-mi!e™!ong Butte Slough flows between Butte
Creek and the Sutter Bypass in Butte County in
California's Central Valley (Figure 1). Butte Slough
discharges to, and diverts flood water from, the
Sacramento River, California's longest river. Butte
Slough receives large volumes of agricultural runoff
during winter storms and is dominated by agricultural
return flows during the summer irrigation season.
The Butte Slough watershed contains extensive
almond and stone fruit orchards. In 1994 diazinon lev-
els were found to exceed water quality standards. For
decades, growers used diazinon as a dormant spray in
orchards during winter months to control wood-boring
pests. Diazinon is highly toxic to aquatic life; exposure
to even low concentrations of the pesticide (one part
per billion or less) can cause genetic damage in fish
and reduce their reproductive success.
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Project Highlights
A collaborative effort that included voluntary and
regulatory approaches motivated the agricultural com-
munity to address the diazinon impairment. In 1996
the Sacramento River Watershed Program (SRWP), a
nonprofit corporation, was developed from a grant
from the U.S. Environmental Protection Agency (EPA)
Region 9. The SRWP connected groups and individuals
concerned about the health of the watershed. SRWP
activities included research, monitoring and continual
assessment of water quality, and outreach and education.
Figure 1. Butte Slough (shown in green) is in the
Sacramento Valley of California.
In 2001 the SRWP Organophosphorus (OP)
Pesticide Focus Group completed its Water Quality
Management Strategy (Strategy) for diazinon in the
Sacramento and Feather rivers. The Strategy summa-
rized two years of research on OP pesticide concerns
and presented an implementation plan to reduce
diazinon runoff. An Agricultural Implementation
Group composed of commodity boards, pesticide
registrants and farm organizations worked to imple-
ment the Strategy. For example, growers replaced
flood irrigation with sprinkler systems, installed filter
strips, planted cover crops, and transitioned to pest

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Figure 2. Micro-sprinklers and
cover crop BMPs reduced
diazinon in runoff.
management practices
that limit diazinon use
(Figure 2).
In 2002 the Central
Valley Water Board's ILRP
initiated efforts to regulate
agricultural discharges.
The ILRP allows growers to
attain regulatory compli-
ance through coalition
groups. The Sacramento
Valiey Water Quality
Coalition organized to represent and educate grow-
ers about water quality problems and BMPs, monitor
water quality, and meet ILRP requirements. In 2003
the Central Valley Water Board adopted a diazinon
TMDL. for the Sacramento and Feather rivers, which
included requirements for dischargers in the Butte/
Sutter Basin, and began to regulate diazinon as a waste
discharge from irrigated lands.
The TMDL arid ILRP requirements played a key role
in motivating the agricultural community to imple-
ment BMPs. In 2003 EPA and pesticide manufactur-
ers developed local label restrictions for agricultural
uses of diazinon. Then, in 2004, the EPA Pesticide
Program, under the Federal Insecticide, Fungicide, and
Rodenticide Act, cancelled the registration and sale of
diazinon pesticides for indoor use, nonagricultural out-
door use (lawns and gardens), and certain agricultural
uses. In 2006 the California Department of Pesticide
Regulation (DPR) adopted dormant spray regulations
for agricultural applications. The regulations prohibit
diazinon application within 48 hours of a forecast
storm, or when soils are saturated.
Results
Growers reduced diazinon runoff to Butte Slough
by implementing BMPs to comply with the diazinon
TMDL, ILRP requirements, DPR regulations, and pes-
ticide label changes. Water quality samples collected
since 2000 show that diazinon levels in Butte Slough
meet water quality standards. None of the 61 water
samples, including 19 samples collected in the
dormant season, exceeded standards (Figure 3). This
long-term data set provided the Central Valley Water
Board with sufficient weight of evidence to propose
removing Butte Slough from the 2016 impaired
waters list for diazinon.
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Conditions in 1994
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1-hour average criterion for diazinon (0.16 fig/L)
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~ Jariuary-94	February-94
O Results {(J.g/L)
• Nondetect Results (ug/L}
March-94
Conditions in 2000-2006
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1-hour average criterion for diazinon (0.16 iig/L)
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Jan-00Jan-01Jan-02Jan-03Jan-04Jan-05Jari-Q6
O Results (|ig/L)
• Nondetect Results (ug/L)
Figure 3. Samples show many exceedances in 1994
(before restoration), and none in 2000-2006 (after
restoration).
Partners and Funding
Since 1991, EPA has awarded $7.6 million In special
appropriation funds to develop the SRWP. CWA section
319 grants supported several projects that addressed
diazinon in the Sacramento River watershed, including
a $219,000 grant awarded in 1997 to support ongoing
SRWP planning and outreach/education efforts. A 2002
state bond-funded grant for $932,680 was awarded
to the Coalition for Urban/Rural Environmental
Stewardship for projects that provided education, out-
reach and technical assistance to orchard growers and
agricultural commissioners. CWA section 319 grants
supported Centra! Valley Water Board staff time to
address diazinon in the Sacramento River watershed; it
also provided funding to continue SRWP planning and
outreach/education efforts. The Central Valley Water
Board's ILRP continues to work with Sacramento Valley
Water Quality Coalition to improve surface waters that
can be affected by pesticide runoff.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-17-001X
November 2017
For additional information contact:
Danny McClure, Central Valley Regional Water Quality Control
Board, Region 5
916-464-4751 • Danny.McClure@waterboards.ca.gov
Holly Grover, Central Valley Regional Water Quality Control
Board, Region 5
916-464-4747 • Holly.Grover@waterboards.ca.gov

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