Section 319
NONPOINT SOURCE PROGRAM SOCGESS STORY
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Reducing Pesticide Use Contributes to Restoration of San Diego Creek
\A/qtprhnrl\/ Imnrnx/prl Run°ff from residential aha agricultural activities contributed
r "'*"' to high levels of pesticides (diazinon and chlorpyrifos) in
California's San Diego Creek. As a result, the state added a 7.83-mile segment of the creek
to its Clean Water Act (CWA) section 303(d) list of impaired waters in 1998. Project partners
conducted education and outreach programs that led watershed stakeholders to implement
best management practices (BMPs). As a result of these efforts, diazinon and chlorpyrifos
levels have declined, prompting California to propose removing these two pesticides from
the list of impairments on the 7.83-mile segment of San Diego Creek in 2014.
Problem
San Diego Creek is in the Newport Bay watershed
in central Orange County on the Southern California
coast (Figure 1). The watershed is surrounded by
the Santa Ana Mountains to the east and the San
Joaquin Hills to the west. Monitoring data indicated
that pesticides were present in a 7.83-mile seg-
ment of San Diego Creek (Reach 1) extending from
Newport Bay upstream into Irvine, and likely con-
tributed to the creek's failure to support its benefi-
cial use of warm freshwater habitat. Consequently,
in 1998 the segment was placed on the California
CWA section 303(d) list as impaired for pesticides.
Diazinon and chlorpyrifos were first linked to water
column toxicity in San Diego Creek during a state-
sponsored investigation in 1999 and 2000. At the
time, plant nurseries in the San Diego Creek water-
shed treated their nursery stock with pesticides to
comply with a state-imposed quarantine targeting
fire ants. High levels of diazinon and chlorpyrifos
caused Reach 1 to violate water quality standards.
The bioaccumulation of these compounds can
adversely affect the health and reproductive success
of aquatic organisms and their predators, and can
pose a human health threat. The investigation identi-
fied runoff from nurseries as the primary source of
the diazinon and chlorpyrifos in San Diego Creek.
In 2002 the U.S. Environmental Protection Agency
(EPA) established total maximum daily loads
(TMDLs) for San Diego Creek and Newport Bay
by consent decree, which the Santa Ana Regional
Water Quality Control Board adopted in 2003.
These TMDLs established numeric targets for
diazinon and chlorpyrifos and outlined a series of
implementation actions to reduce pesticide loading.
Newport Bay Watershed
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Peters Canyon Wash
6 Nursery Implementation Actions
Impaired Water
Figure 1. San Diego Creek is in Southern California's 154-square
mile Newport Bay watershed.
Project Highlights
Between 2006 and 2009, Orange County
Coastkeeper (OCCK) collaborated with the
University of California Cooperative Extension
(UCCE) on the Orange County Nurseries Water
Quality Improvement Project, which focused on
reducing pesticides in runoff from plant nurseries
and agricultural sites in the San Diego Creek water-
shed. The program (1) educated residential pesticide
users and small nurseries about alternative ant
control strategies, (2) improved irrigation and imple-
mented erosion/sediment control procedures at
nurseries to prevent potting mix (with incorporated
pesticides) from reaching waterbodies; (3) encour-
aged municipalities to implement Integrated Pest
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Management (IPM) strategies to reduce pesticide
use through landscape design, plant selection and
use of nontoxic alternatives for pest control; and
(4) created a demonstration center to train land-
scape architects, master gardeners and municipal
staff about IPM.
In 1990 the Regional Board issued Waste
Discharge Requirements (WDRs) to large nurseries
to address excessive nutrient discharges. In 2005
and 2006, these WDRs were revised to include
the TMDL limits on diazinon and chlorpyrifos.
As a result, the nurseries switched to alternative
products and implemented BMPs to retain sedi-
ment (and associated bound pesticides) on-site
and to reuse the sediment in their potting mix (see
Figure 1 for nursery implementation action sites).
Additionally, the 1996 Food Quality Protection
Act directed EPA to begin using more stringent
standards when registering pesticides—largely
because of public health concerns. This led to the
phase-out of diazinon and chlorpyrifos for most
uses by 2005 (Figure 2).
Results
Monitoring data collected between 1999 and 2011
show that water column toxicity caused by diazi-
non and chlorpyrifos has been reduced to levels
that are no longer detrimental to the waterbody's
beneficial uses. While San Diego Creek contained
diazinon concentrations as great as 400 nanograms
per liter (ng/L) in 2001, concentrations have steadily
decreased and now meet both the TMDL chronic
and acute load allocation (nonpoint source) limits
of 45 and 72 ng/L, respectively. Similarly, chlorpy-
rifos levels were as high as 100 ng/L in 2002 but
by 2003, levels had declined and have consistently
mettheTMDL load allocation chronic (12.6 ng/L)
and acute (18 ng/L) limits since 2003 (except for
exceedances in December 2008 due to a heavy
storm event).
Sediment toxicity data show steady declines in
pesticide concentrations, particularly between
2001 and 2005, when many agricultural and non-
agricultural uses of pesticides were phased out.
Additionally, the TMDL required Orange County's
stormwater National Pollutant Discharge Elimination
System co-permittees to implement a monitoring
program for diazinon and chlorpyrifos, and for water
column toxicity. These data show that water quality
has improved.
Reported Diazinon and Chlorpyrifos Use in Orange County (1995-2009)
100,000
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Figure 2. Pesticide reduction efforts led to significant decreases
in diazinon and chlorpyrifos use.
On the basis of these data, the state will propose
to remove Reach 1 of San Diego Creek from the
state's 2014 list of impaired waters for both diazi-
non and chlorpyrifos. This segment remains listed
as impaired for toxaphene (a banned insecticide),
selenium, sedimentation/siltation, nutrients and
fecal coliform. The upstream, Reach 2 segment
of San Diego Creek remains listed as impaired for
unknown toxicity, nutrients, sedimentation/siltation
and indicator bacteria.
Partners and Funding
Partners in the water quality restoration effort
include the State Water Resources Control Board,
Santa Ana Regional Water Quality Board, Southern
California Edison, Orange County, OCCK, UCCE,
large commercial nurseries, California Department
of Pesticide Regulation and EPA. Two EPA CWA
section 205(j) and 319(h) grants funded five years
of diazinon, chlorpyrifos and toxicity data col-
lection. To date, California has invested at least
$306,758 in CWA section 319(h) funds to help
nurseries implement BMPs to reduce pollutant
loads. Grants under the California state bond pro-
grams supported BMP implementation to reduce
pesticides in the watershed. Water quality out-
reach to small nurseries was funded in part by a
$372,000 grant from the state's Agricultural Water
Quality Grant Program.
UJ
(9
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-12-001TT
October 2012
For additional information contact:
Doug Shibberu, Santa Ana Regional Water Quality
Control Board
dshibberu@waterboards.ca.gov • 951-782-7959
Wilson Yee, EPA Region 9
yee.wilson@epa.gov • 415-972-3484
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