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Reducing Endosulfan Use in the Imperial Valley Drains Area
Watprbnrh/ Imnrnvpd Ths lmperial Vallev Drains, an extensive gravity flow drainage
system consisting of 1,450 miles of ditches, was listed as
impaired for the pesticide endosulfan in 1996. In 2000, the U.S. Environmental Protection Agency
(USEPA) began phasing out endosulfan. The 2005 Imperial Valley Drains Sediment Total Maximum
Daily Load (TMDL) and Implementation Plan required growers to implement improved sediment
best management practices (BMPs) to reduce runoff and decrease subsequent endosulfan
bioaccumulation in fish. Water quality has met the state standard for endosulfan since 2001. Fish
tissue samples no longer exceeded standards for applicable beneficial uses: warm freshwater
habitat and commercial or recreational collection. As a result, the Imperial Valley Drains were
delisted for the endosulfan impairment in 2012.
Problem
The imperial Valley Drains system consists of 1,450
miles of ditches that drain 500,000 acres of agricul-
tural land into the New River, the Alamo River and
the Saltan Sea in southern California. The Saltan Sea
watershed (Figure 1) is one of the most productive
agricultural centers in the world, with crops grown
year-round, irrigation tail water comprises most of the
flow in the imperial Valley Drains, with lesser inputs
from storm water flows, groundwater, and industrial
effluent discharges. The Saltan Sea watershed is also
a major center for avian biodiversity in the American
Southwest, supporting over 350 species and averaging
over 1.5 million birds annually. Use of the pesticide
endosulfan was widespread in the Imperial Valley
during the 1980s and 1990s. It attached to sediments
and bioaccumulated in fish tissue, and was toxic to
wildlife species, particularly fish and birds. Monitoring
showed that levels of endosulfan in fish tissue samples
exceeded standards for applicable beneficial uses (warm
freshwater habitat and commercial or recreational
collection), prompting California to add Imperial Valley
Drains to the Clean Water Act (CWA) section 303(d) list
of impaired waters for endosulfan in 1996.
Story Highlights
With increasing regulations and concerns over toxicity,
the annual use of endosulfan in Imperial Valley
steadily declined (Figure 2). USEPA began phasing out
endosulfan in 2000. In 2005 California's Colorado River
Figure 1. Imperial Valley farmland (red outline) and
monitoring locations (dots).
Basin Regional Water Quality Control Board (Colorado
River Water Board) adopted the Imperial Valley Drains
Sedimentation and SiItation TMDL and Implementation
Plan, which began requiring growers to implement
improved sediment management practices to reduce
delivery of suspended sediment to the Imperial Valley
Drains. Because sediment is the primary carrier for
endosulfan to the drains, BMPs that reduce sediment
transport to the drains also reduce pesticide transport
and subsequent endosulfan bioaccumulation in fish.
The implementation plan established four phases,
each with increasingly lower Interim numeric targets,
'Niland 2 Drain
I	Bfbrain
Puhiicej(^\ Pumice Drain 2
¦fly Mayflower
El Centra^entra'Jj'
South Central *-
Barbara Worth1
Peach
Warren,
\
iGreeson

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Table 1. Phases and interim targets for attainment of
Imperial Valley Drains per sediment TMDL.
Phase
Time Period
Estimated Percent
Load Reduction1
Interim Target
TSS (mg/L)
l
2005-2006
10%
376
2
2007-2009
25%
282
3
2010-2012
20%
226
4
2013-2015
12%
200
1 The reduction required in the average concentration at the end of each
phase, beginning with the 2002 average concentration of 418 mg/L.
over a 12-year schedule to allow farmers time to reach
the numeric total suspended solids (TSS) goal of 200
milligrams per liter (mg/L) (Table 1). The Imperial Valley
Farm Bureau developed a program for compliance
with the TMDL and assisted farmers in the Imperial
Valley Drains watershed with installation of BMPs,
supported in part with CWA section 319 grant funds.
Under the Imperial County Farm Bureau's (ICFB)
Voluntary TMDL Compliance Program, farm plans are
submitted to the Colorado River Water Board. The
top five BMPs implemented by farmers to control
the amount of sediment and pesticides in agricul-
tural runoff in 2014 were: (1) agricultural tailwater
structures; (2) irrigation water management; (3) land
leveling, including field at proper grade near the
drain box; (4) pan ditches (wide, flat-tail ditches); and
(5) plastic sheeting used to control erosion. In 2014,
farmers submitted 5,953 farm plans; and as of 2019,
nearly 100 percent of farmers in the Imperial Valley
Drains watershed are enrolled in the program.
Results
Monitoring data in the Imperial Valley from 1985
through 2014 shows a steady decline in endosulfan
concentrations found in fish tissue collected from the
Imperial Valley Drains (Figure 3). Additionally, with con-
cerns over toxicity and increasing regulation, farmers
moved away from endosulfan use; after 2007, there
was little to no application of endosulfan in Imperial
Valley. Since 2014, its application has stopped entirely.
In 2012, the Colorado River Water Board recommended
delisting endosulfan from the impaired waters list
for Imperial Valley Drains, based on several lines of
evidence, including the National Academy of Science
Water Quality Criteria (1972) maximum total endosulfan
Annual Endosulfan Agricultural Use in Imperial County
S16000
Figure 2. Endosulfan use overtime.
Imperial Valley Drains Endosulfan In Fish Tissue
2000
1750
Numeric Target (100 ng/Kg)
I	Rose
Holtville
,	Central
!	S. Central
:	Rice
i	Verde
1	Pumice
¦	Mayflower
,	Peach
Target
an-85 Feb-89 Mar-93 Apr-97 Jun-01 Jul-05 Aug-09 Oct-13
Figure 3. Fish tissue samples (1985-2014).
concentration of 100 micrograms per kilogram (|ig/Kg)
(wet weight) in tissue samples for protection of aquatic
life from bioaccumulation. The delisting was approved
by the State Water Board and USEPA.
Partners and Funding
The Colorado River Water Board, one of nine
Regional Water Quality Control Boards in California,
is responsible for implementing the federal CWA and
state water quality regulations in the area. The ICFB
developed the Voluntary TMDL Compliance Program in
response to the Regional Board's Imperial Valley Drains
Sedimentation and SiItation TMDL and Implementation
Plan. The Imperial Irrigation District (IID) supplies
nearly all water used by municipalities and agricultural
operations in the Imperial Valley Drains watershed.
Water is diverted at Imperial Dam on the Colorado
River through the 82-mile Ail-American Canal, which
11D operates and maintains. With more than 3,000
miles of canals and drains, 11D is one of the largest
irrigation districts in the nation.
^edsj^ U.S. Environmental Protection Agency
0** Office of Water
^ Washington, DC
WJ
EPA 841-F-19-001KK
pRot^° November 2019
For additional information contact:
Francisco Costa
Colorado River Basin Regional Water Quality Control Board
760-776-8937 • francisco.costa@waterboards.ca.gov
Chris Monary
State Water Resources Control Board
916-322-7782 • chris.monary@waterboards.ca.gov

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