United States Office of Water EPA 916-F-01-030
Environmental Protection (4606) July 2001
Agency
Source Water Protection
Practices Bulletin
Managing Large-Scale Application
of Pesticides to Prevent
Contamination of Drinking Water
Pesticides (including insecticides, herbicides, and fungicides) contain a variety of chemicals
used to control pests, insects, and weeds. They are used in a variety of applications to reduce
the damage to plants by insects and other pests, and to control overgrowth of undesirable plant
species. This fact sheet describes measures to prevent the contamination of drinking water
sources from large-scale pesticide application for agricultural use. Prevention measures for
small-scale pesticide application (e.g., on lawns, schools, golf courses, and parks) are addressed
in a separate fact sheet.
SOURCES OF PESTICIDES
Pesticides are applied to crops by aerial spraying, topsoil application (granular, dust or liquid
formulations, or spray using truck or tractor-mounted equipment), soil injection, soil
incorporation, or irrigation. Aerial spraying and topsoil application pose the greatest risks for
pesticides to enter surface water bodies from runoff. Soil injection and incorporation pose the
greatest likelihood for ground water contamination because pesticides placed in the soil are
subject to leaching. The
application of pesticides
through irrigation
(chemigation) can also
cause ground water
contamination; for example,
an irrigation pump may fail
while the pesticide-metering
equipment continues to
operate and cause highly
concentrated pesticide
levels to be applied to a
field. Pesticides can reach
ground water through
drains, sink holes, and other
conduits as well.
Excess rain or irrigation
water can wash pesticides from plants and soil. This can, in turn, run off into streams.
Pesticides can leach into the soil if plants are watered or rainfall occurs soon after application.
Some pesticides resist degradation by microbes in the soil and will eventually leach into the
ground water.
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WHY IS IT IMPORTANT TO MANAGE PESTICIDES NEAR THE SOURCES OF
YOUR DRINKING WATER?
Pesticides contain a variety of organic and inorganic compounds. By nature, they are
poisonous, and while they can be safely used if manufacturers' usage directions are followed,
they can, if mismanaged, seep into surface water and ground water supplies. They can be
difficult and expensive to remove, and, if inhaled or consumed, be hazardous to human health.
The synthetic organic chemicals in pesticides have been linked to serious health problems
including cancer, liver and kidney damage, reproductive difficulties, and nervous system
effects.
Once a water supply becomes contaminated with a pesticide, treating it can be very difficult and
costly. Treating the water supply is a lengthy process and is not always successful. Using an
alternative water source may also be costly and impractical. For example, it would be very
expensive to connect to another public water system, and drilling new wells does not
necessarily guarantee that the new ground water source will not be contaminated.
AVAILABLE PREVENTION MEASURES TO ADDRESS PESTICIDES
Prevention measures are available to protect source waters from pesticide contamination. They
range from simple, common sense housekeeping activities to more complex activities such as
constructing storage facilities. The most effective pesticide prevention measures encompass
both simple and complex practices to reduce the potential for pesticides to move into source
waters. The prevention measures can be divided into those that protect surface water from
pesticide runoff and those that protect ground water from leaching or percolation.
Please keep in mind that individual prevention measures may or may not be adequate to prevent
contamination of source waters. Most likely, individual measures should be combined in an
overall prevention approach that considers the nature of the potential source of contamination,
the purpose, cost, operational, and maintenance requirements of the measures, the vulnerability
of the source waters, the public's acceptance of the measures, and the community's desired
degree of risk reduction. The following are the more conventional prevention measures used to
avoid contamination from pesticides.
Integrated Pest Management (IPM) is the use of all means
of pest control (chemical and non-chemical) in a compatible
fashion to reduce crop losses. Pesticides are the last line of
defense and are used only when pest levels are causing
sufficient damage to offset the expense of the application.
IPM includes regular field scouting or
monitoring to check levels of pest
populations and their damage to
determine management needs, be it
pesticide application or other
management actions. Scouting can be accomplished by a trained farmer or a
crop consultant. IPM also includes non-chemical control measures such as
mechanical, cultural and biological controls, sanitation, and pest-resistant
plants are highly recommended. Wherever possible, it is preferable to use
crop rotation, select resistant plant varieties, clean tractors and combines thoroughly between
fields to reduce weed seed introductions, and use cultivation to control weeds. Efforts should
be made to maximize the benefits of naturally occurring biological controls and use pesticides
only when necessary. Many insecticides are broad spectrum materials that also affect
beneficial insects and arthropods.
Diorhabda elongata
Alfalfa pest
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Proper Pesticide Application
If pesticides must be used, proper handling and application according to the EPA-approved
label are essential. Select an effective pesticide for the intended use and, where possible, use
products that pose lower human and environmental risks (i.e., low-persistence). Read the
pesticide label for guidance on required setbacks from water, agricultural drainage wells and
tile networks, buildings, wetlands, wildlife habitats, and other sensitive areas where
applications are prohibited.
Never start an application if a significant weather event such as rainfall is forecast; the rainfall
may cause drift or soil runoff at the application site. Pesticide application just before rainfall or
irrigation may result in reduced efficacy if the pesticide is washed off the target crop, resulting
in the need to reapply the pesticide.
Ways to Reduce Pesticide Use
Crop rotation reduces pesticide use by breaking up
the pest cycle. As crops are rotated, pests such as
insects and weeds cannot adapt to the changes in
nutrient sources. Insects will move to another
location where they can find food. Weeds will
become dormant until the right condition returns.
Crop rotation also increases crop yields and lowers
irrigation and fertilizer cost. Pesticide rotation
reduces the risk of pesticide-resistant pests. As
pesticides are used year after year, pests develop
immunities to them, resulting in increased
application of pesticides.
Corn - wheat- fallow rotation
Soil incorporation involves placing the pesticide into the top two inches of soil by tillage,
where it is less likely to be removed by surface runoff, reducing runoff by as much as two-
thirds compared to surface application. Post-emergence application is the application of
pesticides after the plant emerges from the soil; it requires a much smaller amount of pesticide
(as compared to the labeled rate) for the same pest control. Post-emergence application of
pesticides should be done during low periods of rainfall; spring or windy conditions may reduce
the time available for application.
Early pre-plant application is the application of pesticides before the plant emerges from the
soil. This application, using less than the labeled rate, can reduce potential pesticide runoff by
up to one-half When used in early April, pre-plant applications can provide effective control
and the applied pesticides will be less vulnerable to spring and early summer runoff. If
additional control is needed with a pre-emerge or post-emerge product, spot treatment should
be practiced.
Split application, with one-half to two-thirds of the pesticide applied prior to planting and one-
half to one-third applied at planting, can reduce pesticide runoff by up to one-third. If good
weed control is achieved with the pre-emergence
application, the post application may not be
necessary. Wherever feasible, the use of reduced
rates for pesticide application or combination
| products (containing less toxic chemicals) will also
help reduce runoff of the more toxic chemicals.
Very low applications of pesticides may not be
effective for high weed infestations or very wet
springs.
Ultra low-volume pesticides
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Proper Pesticide Storage and Handling
Pesticide storage is key to preventing ground water contamination. If pesticides are stored in
intact containers in a secure, properly constructed location, pesticide storage poses little danger
to ground water. You must follow directions for storage on pesticide labels, although the
instructions are usually general, such as
"Do not contaminate water, food or feed
by storage or disposal." Some States,
including Maryland, New Hampshire,
North Carolina and Washington, have
regulations on the storage of small
quantities of pesticides. Nearly half the
States have regulations for the storage of
large tanks of pesticides. Secondary
containment, such as an impermeable
(waterproof) floor with a curb and walls
around the storage area, will minimize
pesticide seepage into the ground or
Pesticide storage tanks spreading to other areas if a liquid
pesticide storage tank leaks. The capacity
of liquid tank secondary containment should be sufficient to contain the volume of the largest
tank. Dry pesticides should be protected from precipitation. An operator should always be
present when pesticides are being transferred.
Proper mixing and loading practices can also prevent contamination of ground water and
surface water by pesticides. Mixing and loading on an impermeable concrete surface allows
most spilled pesticides to be recovered and reused. The impermeable surface, or pad, should be
kept clean and large enough to hold wash water from the cleaning of equipment, and to keep
spills from moving off-site during transfer of chemicals to the sprayer or spreader. Ideally, the
pad should slope to a liquid-tight sump that can be pumped out when spills occur.
Spill clean up is another important prevention measure. Dry spills should be promptly swept
up and reused. For liquid spills, recover as much of the spill as possible and reuse the pesticide
as intended. If a spill involves soil around the mixing pad, it may be desirable to remove some
contaminated soil, which can be spread on fields under certain circumstances if allowed by your
State pesticide regulatory agency (usually the Department of Agriculture). In addition, clay,
sawdust, or cat litter should be available to absorb unrecovered liquid from concrete pads.
Finally, an emergency response plan for the site is important - to know where the runoff water
will flow, how to handle a particular chemical, and whom to call for help.
Improper disposal of pesticide containers can lead to ground water contamination. To prevent
ground water contamination, use returnable containers and take them back to the dealer as often
as possible. Pressure-rinse or triple-rinse nonreturnable containers immediately after use, since
residue can be difficult to remove after it dries, and pour the into the spray tank. Puncture
nonreturnable containers and store them in a covered area until they can be taken to a container
recycling program or a permitted landfill. Contact the Ag Container Recycling Council at
www.acrecycle.org or 877-952-2272 for more on a recycling program near you. Shake out
bags, bind or wrap them to minimize dust, and take them to a permitted landfill. Do not bury or
burn pesticide containers or bags on private property.
FOR ADDITIONAL INFORMATION
These sources contain information on pesticide management measures. All of the documents
listed are available for free on the Internet. Contact local government authorities in your area to
see if there are ordinances in place to manage pesticides. You should also contact the Natural
Resources Conservation Service (NRCS), Conservation District, and Agricultural Extension
Service representatives in your area. They can provide more information on pesticide
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management and cost-share programs, such as the Environmental Quality Incentives Program
(EQIP), the Conservation Reserve Program (CRP), and the Conservation Reserve Enhancement
Program (CREP), to assist in financing source water protection measures.
Extox Net FAQs. Pesticides: How They Affect You and The Environment. Retrieved March 8,
2001, from the World Wide Web: http://ace.orst.edu/info/extoxnet/faqs/.
Extox Net FAQs. Pesticide Residues in Drinking Water. Retrieved March 8, 2001, from the
World Wide Web: http://ace.orst.edu/info/faqs/safedrink/pest.htm.
Florida Department of Agriculture and Consumer Services and Florida Department of
Environmental Protection. Best Management Practices for Agrichemical Handling and Farm
Equipment Maintenance. (1998, May) Retrieved May 30, 2001, from the World Wide Web:
http: //www. dep. state. fl .us/water/slerp/nonpoint_stormwater/documents/pubinfo .htm#Be st
Management Practices
Iowa State University, University Extension. Pesticides, Drinking Water, and Human Health.
Retrieved March 8, 2001, from the World Wide Web:
http://hermes.ecn.purdue.edu: 800 l/cgi/convertwq?6608
David Kammel et al. Midwest Plan Service, Iowa State University Agricultural and Biosystems
Engineering Department, Designing Facilities for Pesticide and Fertilizer Containment, First
Edition. 1991. Cost if $15 plus shipping. Retrieved May 11, 200, from the World Wide Web:
http://www.mwpshq.org/catalog.html
Maryland Department of Agriculture. Storage and Transport. Retrieved May 30, 2001, from
the World Wide Web: http://www.mda.state.md.us/plant/storage.htm
Maryland Department of the Environment. Buffer Protection and Management Ordinance,
Baltimore County, MD. Retrieved May 22, 2001, from the World Wide Web:
http :/www .epa.gov/owow/nps/ordinance/language .htm
Massachusetts Department of Food and Agriculture, Pesticide Bureau, Storage, Mixing and
Loading of Pesticides: Guidelines. Retrieved May 30, 2001, from the World Wide Web:
http://www.massdfa.org/pesticides/waste/index.htm
NCSU Water Quality Group. Guidance on Controlling Agricultural Sources ofNonpoint
Source Pollution. Retrieved January 23, 2001, from the World Wide Web:
http://www.bae.ncsu.edu/bae/programs/extension/wqg/.
New Hampshire Department of Agriculture. Markets and Food, Regulations: Disposal and
Storage of Pesticides and Pesticide Containers. Retrieved May 30, 2001, from the World Wide
Web: http: //www. state .nh .us/agric/ar&l .html
Penn State Pesticide Education Program. The Fate of Pesticides in the Environment. Retrieved
January 23, 2001from the World Wide Web: http://www.pested.psu.edu/fact8.html.
Purdue University, Conservation Technology Information Center. Conservation Technology
Information Center Home Page. Retrieved May 22, 2001, from the World Wide Web:
http://www.ctic.purdue.edu/KYW/wspartners/statewscontacts.html.
Purdue University, Conservation Technology Information Center. Know Your Watershed: State
Watershed Contacts. Retrieved May 22, 2001, from the World Wide Web:
http://www.ctic.purdue.edu/KYW/wspartners/statewscontacts.html.
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Purdue University Cooperative Extension Service. Pesticides and Container Management
(PPP-21). (1992, December) Retrieved May 30, 2001, from the World Wide Web:
http://www.agcom.purdue.edu/AgCom/Pubs/PPP/PPP-21.pdf
Texas A&M, Texas Agricultural Extension Service. Pesticide Characteristics that Affect
Water Quality. Retrieved February 15, 2001, from the World Wide Web:
http://entowww.tamu.edu/extension/bulletins/water/water_01 .html.
Texas A&M, Texas Agricultural Extension Service. Reducing the Risk of Ground Water
Contamination by Improving Pesticide Storage and Handling. Retrieved January 23, 2001,
from the World Wide Web: http://agpublications.tamu.edu/catalog/index.html.
United States Environmental Protection Agency, Region 5 Water Division. Electronic
Compendium of Groundwater Protection Ordinance. (1998, October). Retrieved May 22,
2001, from the World Wide Web: http://www.epa.gov/r5water/ordcom/.
U.S. EPA, Region 5. SOFTWARE For Environmental Awareness. (2000, August). Retrieved
January 24, 2001, from the World Wide Web: http://www.epa.gov/seahome/.
U.S. EPA, Office of Water. Model Ordinances to Protect Local Resources: Links. Retrieved
May 22, 2001, from the World Wide Web:
http://www.epa.gov/owow/nps/ordinance/stormwater.htm.
U.S. EPA, Office of Water. Model Ordinances to Protect Local Resources: Storm Water
Control Operation and Maintenance. Retrieved May 22, 2001, from the World Wide Web:
http://www.epa.gov/owow/nps/ordinance/stormwater.htm.
University of Georgia College of Agricultural and Environmental Sciences Cooperative
Extension Service. Your Drinking Water: Pesticides. Retrieved January 23, 2001, from the
World Wide Web: http://www.ces.uga.edu/pubcd/C819-6W.html.
University of Nebraska Extension Service. Best Management Practices to Reduce Atrazine
Runoff from Corn Fields in Nebraska. Retrieved January 25, 2001, from the World Wide Web:
http://www.ianr.unl.edu/pubs/Water/gl323.htm.
University of Nebraska Extension Service. Best Management Practices for Agricultural
Pesticides to Protect Water Resources. Retrieved January 23, 2001, from the World Wide
Web: http://www.ianr.unl.edu/pubs/water/gl 182.htm.
Vermont Department of Agriculture. Food and Markets web site on regulations on the control
of pesticides. Section XIII deals with storage, transportation and disposal. Retrieved May 30,
2001, from the World Wide Web: http://www.state.vt.us/agric/VTregs91 .htm
Washington State Department of Agriculture. Pesticide Management: Storage (non-bulk and
bulk storage). Retrieved May 30, 2001, from the World Wide Web:
http: //www. wa.gov/agr/pmd/pe sticide s/storage .htm
Wisconsin Department of Agriculture, Agricultural Chemical Cleanup Program. Containment
of Pesticides and Fertilizer. Retrieved May 30, 2001, from the World Wide Web:
http ://datcp. state. wi .us/static/accp/contain.htm
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