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Endosulfan Reduction and Removal in the Alamo River Watershed
\A/atprhnrl\/ lmnrn\/prl Endosulfan, an organochlorine pesticide used in agriculture, binds to
sediments and can bioaccumulate in fish tissue when transported to
waterbodies. Endosulfan was detected in Alamo River fish tissue samples beginning in 1978. The U.S.
Environmental Protection Agency (USEPA) began phasing out endosulfan in 2000. The Alamo River
Sedimentation/Siltation Total Maximum Daily Load (TMDL) was adopted by the Colorado River Basin
Regional Water Quality Control Board (Colorado River Water Board) in June 2001. The Imperial County
Farm Bureau (ICFB) developed a Voluntary TMDL Compliance Program to assist Imperial Valley farmers
in implementing best management practices (BMPs) to reduce sediment-bound pesticide runoff. Based
in part on significantly reduced endosulfan concentrations in fish tissue samples, the Alamo River was
delisted for endosulfan in California's 2012 Integrated Report.
Problem
Saltan
Sea
The Alamo River originates about a kilometer over the
border into Mexico and flows north into the United
States for 57 miles through the Imperial Valley (in central
Imperial County) before draining into the Salton Sea
(Figure 1). The Alamo River subwatershed, Impaired
for sediment/siltation, pesticides and other pollutants,
Includes approximately 340,000 acres within the Imperial
Valley. Irrigated agriculture is the major land use and is
Identified as a major source of pesticide and sediment
Impairment to the river. Due to low precipitation, the
water in the Alamo River consists almost entirely of
agricultural drainage from farms.
The organochlorine pesticide endosulfan was widely
used during the 1970s and 1980s in the region. Because
endosulfan has a strong tendency to bind to sediments,
the transport of sediments from land is the primary path-
way for endosulfan to reach receiving waters. Organisms
bioaccumulate endosulfan from the environment and
through the food-web; concentrations of endosulfan in
fish tissue have been previously associated with its con-
centrations in sediment. Endosulfan was detected in fish
tissue samples beginning in 1978. The numeric target for
endosulfan in fish tissue is 100 micrograms per kilogram
([ig/Kg), as established in the 1972 National Academy
of Sciences (NAS) Water Quality Criteria. The Colorado
River Water Board adopted a listing of the Alamo River
as impaired by endosulfan on the Clean Water Act (CWA)
section 303(d) impaired list in the 2010 assessment cycle.
~ Watershed Boundary
Monitoring Sites
O Outlet
ฎ Drop 6
Drop 10
International Boundary
Brawley
Imperial County
E Centra
ป -U S-
Cam 1 |Ve*icฐ
10 Miles
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Figure 1. California section of the Alamo River watershed
(red outline) and monitoring stations.
Story Highlights
USEPA began phasing out endosulfan in 2000, and the
Alamo River Sedimentation/Siltation TMDL was adopted by
the Colorado River Water Board in June 2001 and became
effective in june 2002, The TMDL has an overall goal of
reducing sediment loads in Alamo River by 53 percent.
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BMPs that reduce sediment transport also reduce endosulfan
transport to these waters. Concerns over endosulfan toxicity
and increasing regulations led farmers in the Imperial Valley to
instead use different pesticides, thereby rapidly reducing the
use of endosulfan (Figure 2). All farmers stopped using endo-
sulfan in 2014, and the use of endosulfan on any crops became
unlawful after July 2016.
Implementing the TMDL relies on controlling runoff from
Imperial Valley farms. To help farmers implement irrigation
BMPs to reduce runoff, the Imperial County Farm Bureau (ICFB)
developed the Voluntary TMDL Compliance Program. In this
program, dischargers in the Alamo River and other Imperial
Valley subwatersheds participate in a coalition. Implementing
California's Irrigated Lands regulatory program included
adopting about 25,000 BMPs on over 5,000 Imperial Valley
farm fields (478,000 acres of farmland in the Imperial Valley
are covered by program). Growers submitted over 6,000 farm
plans to the program annually. Nine outreach and education
seminars were held annually. The top five BMPs that farmers
reported using to reduce sediment and pesticides in runoff
are: (1) adherence to Imperial Irrigation District (IID) Regulation
No. 39 for Agricultural Taiiwater 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 to control erosion.
Results
Endosulfan in the Alamo River was delisted based on fish tissue
concentration levels that remained well below the 1972 NAS
tissue guideline of 100 jig/If for the protection of aquatic life
uses. Since 2001, tissue concentrations have been largely below
the reporting limit (Figure 3), and endosulfan has not been
detected in water samples. The Colorado River Water Board
adopted the delisting of the Alamo River for endosulfan, which
was documented in the Final California 2012 Integrated Report
(303(d) List/305(b) Report).
Partners and Funding
The Colorado River Water Board, one of nine Regional Water
Quality Control Boards in California, is responsible for imple-
menting the federal CWA and state water quality regulations in
the area. The ICFB developed the Voluntary TMDL Compliance
Program in 2001 in response to the Imperial Valley Drains
Sedimentation and SiItation TMDL and Implementation Plan.
CWA 319 grants to ICFB and collaborating agencies helped
implement the Voluntary TMDL Compliance Program to
Annual Endosulfan Agricultural Use in Imperial County
END05ULFAN
18000
16UUU
14000
12000
1UUUU
Figure 2. Endosulfan use has declined.
Alamo River Endosulfan in Fish Tissue
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Numeric Target (100
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~ AR/IB
O AR/IB <ฃ 10
Notes: AR = Alamo River; IB = International Boundary; Drop 10 = Brawly; Drop 6 = Holtville; Outlet
= where Alamo River drains into the Salton Sea; < RL - sample taken was below the reporting level.
Figure 3. Endosulfan levels at each monitoring station from
1978 through 2012 on the Alamo River.
decrease runoff of sediment-bound pesticides in Imperial
Valley. CWA 319 grants were awarded in 2000-2006 for
Imperial Valley pollution control and totaled $1,748,557.
11D manages more than 3,000 miles of drains and canals, making
it one of the largest irrigation districts in the country. They
supply almost all the water used by agricultural or municipal
activities. 11D is authorized by state law to provide urban runoff
treatment services and is implementing a plan to treat urban
runoff using constructed wetlands.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-19-001LL
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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