Decision Aids / TEX*A*Syst / Reducing Contamination by Improving Pesticide Storage and Handling

B.L. Harris, D.W. Hoffman and F.J. Mazac, Jr.

  1. Do you store pesticides on your land?
  2. Do you use or store any agricultural chemicals near a water well?
  3. Are chemicals stored on a permeable surface such as wood, gravel or soil, or are chemicals stored on an impermeable surface with no curb?
  4. Do you have any chemical containers that are rusted, damaged or leaking?
  5. Are chemicals stored in an area where containers could become damaged or where a chemical spill could occur?
  6. Are chemicals stored in a location that is unlocked and open to vandalism or to children?
  7. Do you fill the sprayer tank directly from a water well?
  8. Do you fill a sprayer tank with a hose that does not have a check valve, or put the hose in the tank so that it is below the liquid line during filling?
  9. Do you leave the sprayer tank unattended when filling?
  10. Do you mix or load chemicals upslope or within 150 feet of a water well?
  11. Do you have a concrete pad with a curb to contain spills during the mixing or loading of chemicals?
  12. Do you wash the sprayer tank out and dump the rinsate on your land less than 150 feet from a water well?
  13. Do you apply pesticides without reading the label first?
  14. Has it been longer than 5 years since you attended a pesticide applicator training?

If these questions create doubt about the safety of your management practices, this publication will provide helpful information.

Pesticide Handling Overview

Pesticides play an important role in agriculture. They have increased farm production and enabled farmers to manage more acres with less labor. Taking voluntary action to prevent pesticide contamination of ground water will help ensure that pesticides remain available for responsible use.

Pesticides work by interfering with the life processes of plants and insects. Some pesticides are also toxic to humans. If a pesticide enters a water supply in large quantities, which could happen with spills or back-siphonage accidents, acute health effects (toxic effects apparent after only a short period of exposure) could occur, depending on the toxicity of the pesticide. Contaminated ground water used for drinking water supplies may cause chronic exposure (prolonged or repeated exposure to low doses of toxic substances). Chronic exposure may be hazardous to humans and livestock.

Normally pesticides are not found in water supplies in high enough concentrations to cause acute health effects, which can include chemical burns, nausea and convulsions. Instead, pesticides usually occur in trace amounts, and the concern is for the chronic health problems that may result from prolonged exposure.

Proper pesticide management on your property is an important step toward preventing ground water contamination. This guide will provide information about the following areas:

  1. Pesticide storage
  2. Mixing and loading practices
  3. Spill clean up
  4. Container disposal
  5. Other management practices
  6. Evaluation table

Pesticide Storage

If stored in a secure, properly constructed location, pesticides pose little danger to ground water. Common sense suggests keeping pesticides out of the way of activities that might knock over a jug or rip open a bag. Short-term storage (during a season) poses a lower risk than year-round storage, but storage for any length of time can be a risk to ground water.

Secondary containment includes an impermeable (waterproof) floor and walls around the storage area. This will minimize the amount of pesticide seeping into the ground if a bulk liquid pesticide storage tank leaks.

If a spill does occur, an impermeable concrete floor should prevent chemical seepage into the ground. Putting a curb around a concrete floor also will prevent chemicals from spreading to other areas.

A mixing or loading pad provides secondary containment during the transfer of pesticides to spraying equipment or nurse tanks.

Building a New Storage Facility

Building a new facility just for pesticide storage may be expensive, but it is usually easier than trying to modify areas meant for other purposes. When building a new facility, keep in mind a few principles of safe pesticide storage.

  • Locate the building downslope and at least 100 feet away from your water well. The distance from the well should be greater if the site has sandy soils or fractured bed-rock near the soil surface. The risk of pesticides contaminating ground water is influenced by properties of both the pesticide and the soil on which it is spilled or applied.
  • Drain surface water to a confined area because, in the event of a fire, contaminated surface water can be collected more safely.
  • Locate the mixing and loading area close to your storage facility in order to minimize the distance that chemicals are carried.
  • Provide a well-drained building foundation or secondary containment floor that is high above the water table. The finished soil grade should be 3 inches below the floor and sloped to provide surface drainage away from the building. The subsoil should have a low permeability.
  • Keep large drums or bags on pallets and off the floor. Shelves for smaller containers should have lips to keep the containers from sliding off. Steel shelves are easier to clean than wood if a spill occurs. Store dry products above liquids to prevent wetting from spills.
  • Provide a containment area large enough to confine 125 percent of the contents of the largest bulk container, plus the displaced volume of any other storage tanks in the area.
  • Keep the storage area or building locked for security. Preventing unauthorized use of pesticides reduces the chance of accidental spills or theft. Post signs or labels to identify the area as a pesticide storage area. Labels on the outside of the building will give firefighters information about pesticides if they must respond to a fire or a spill. Also, it is a good idea to maintain, in a separate location, a list of the chemicals and amounts stored.
  • Provide adequate road access for deliveries and emergency equipment.
  • Keep pesticides separate to prevent cross-contamination. Herbicides, insecticides and fungicides should be kept on separate shelves or in separate areas.

For information on other factors to consider in the design of a storage facility, such as ventilation, water access, temperature control and worker safety, contact your county Extension office or the Texas A&M University Department of Agricultural Engineering.

Modifying an Existing Storage Facility

Remodeling an existing facility to serve as pesticide storage may be less expensive than building a new facility, but remodeling can be complicated. When existing buildings must accommodate other activities, also using them to store pesticides could compromise the safety of people and the environment. Storing chemicals in a separate facility reduces the risk associated with fire or accidental spills. Never store pesticides inside a wellhouse or in a facility containing an abandoned well.

Even if you decide to improve your current storage building, applying the above principles can be expensive. Compared to the cost of a major accident or a lawsuit, however, storage improvements are a bargain. Also, note that the last five items listed in the section above are important points to remember for existing storage facilities.

The least expensive alternative you may have is to reduce the amounts and types of pesticides stored. If that is not practical, consider how stored pesticides can be protected. Sound containers are the first defense against a spill or leak.

When modifying a structure, it is important to note that the building should have a solid floor. If liquid pesticides are stored the building also should have a curb. The modified structure should be large enough to hold 125 percent of the contents of the largest full container, plus the displaced volume of any other storage tanks in the area.

When modifying an existing structure, label windows and doors to alert firefighters to the presence of pesticides and other products stored in the structure. It is always a good idea to keep a list of the stored chemicals and amounts in a separate location.

If a fire should occur, consider where the surface runoff water will go and where it might collect. For example, adding a curb around a floor can help confine contaminated water. In making the storage area secure, also make it accessible in order to help get chemicals out in a hurry.

Mixing and Loading Practices

Ground water contamination can result even from small spills in the mixing and loading area. Small quantities spilled regularly in the same place can go unnoticed, but the chemicals can build up in the soil and eventually reach ground water. By mixing and loading on an impermeable concrete surface most spilled pesticides can be recovered and reused.

A Mixing and Loading Pad

Figure 1. Farm-sized pesticide facility. Source: Farm-Sized Mixing/Loading Pad and Agri-chemical Storage Facility, by D.W. Kammel and D. O’Neil, presented at Summer Meeting of the American Society of Agricultural Engineers, June 24-27, 1990.

Figure 1. Farm-sized pesticide facility. Source: Farm-Sized Mixing/Loading Pad and Agri-chemical Storage Facility, by D.W. Kammel and D. O’Neil, presented at Summer Meeting of the American Society of Agricultural Engineers, June 24-27, 1990.

Containing pesticide spills and leaks requires an impermeable or waterproof surface for mixing and loading. The surface, or pad, should be large enough to contain leaks from bulk tanks, to hold wash water from cleaning equipment, and to keep spills from transferring chemicals to the sprayer or spreader. (See Figure 1.)

The size of the pad depends on the equipment used. The pad should provide space around the parked equipment for washing and rinsing. Having several rinsate (rinse water) storage tanks allows the user to keep rinsate separate from other chemicals. That way, the rinsate can be used as mixing water on subsequent loads.

Always keep the pad clean and dispose of pesticides properly so that rainfall will not mix with spilled pesticides and cause contamination. Storage of rainfall increases the required size of the sump.

Locate the pad next to the storage area. Make sure that any water from the pad moves away from the well. At sites where runoff water could reach the well, construct a diversion to another area.

For help in constructing a mixing and loading pad, contact your county Extension office or the Texas A&M University Department of Agricultural Engineering.

Better Management on an Existing Mixing and Loading Site

Spills and leaks are bound to occur from time to time. Even if there is no impermeable mixing and loading pad, the risk of contamination can be minimized by following some basic guidelines.

  • Avoid mixing and loading pesticides near any well. One way to do this is to use a nurse tank to transport water to the mixing and loading site. Ideally, the mixing site should be moved within the field of application each year to avoid build-up of spilled pesticides in the soil.
  • Avoid mixing and loading on gravel driveways or other surfaces that allow spills to sink quickly through the soil. A clay surface is better than sand.
  • Install a back-siphon prevention device on the well or hydrants to prevent reverse flow of liquids into the water supply.
  • Leave an air gap of 6 inches between the hose and the top of the sprayer tank. Never put the hose in the sprayer tank.
  • Supervise sprayer filling. For restricted-use and state-limited-use pesticides, a trained and licensed applicator must supervise operations.
  • Consider using a closed handling system, which transfers the pesticide directly from a storage container to the application equipment (through a hose, for example). This will ensure that humans and the environment are never inadvertently exposed to the pesticide.
  • Use rinsate for mixing subsequent loads.

Spill Cleanup

Promptly sweep up dry spills and reuse the pesticide as it was intended. Dry spills are usually easier to clean.

For liquid spills, recover as much of the spill as possible and reuse it as it was intended. It may be necessary to remove some contaminated soil from clay pads and spread it on fields. Have clay, sawdust or cat litter available to adsorb unrecovered liquid from concrete pads. Have an emergency response plan for the site. Know where the runoff water will go, how to handle a particular chemical, and whom to call for help.

Container Disposal

Unwashed and improperly stored containers can lead to ground water contamination if chemical residues leak onto the ground. Some guidelines that can help prevent this problem include the following:

  • Use returnable containers and minibulks, and take them back to the dealer as often as possible.
  • Pressure-rinse or triple-rinse containers immediately after use, since residue can be difficult to remove after it dries. Pour the rinse water into the spray tank. Puncture containers and store them in a covered area until you take them to a permitted landfill.
  • Recycle plastic and metal containers whenever possible.
  • 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.

Other Management Practices

Reducing pesticide waste makes financial as well as environmental sense, but it means more than just reducing spills. It also means not buying more than you need to apply, keeping records of what is on hand, and using older products first.

  • Buying only what is needed makes long-term storage unnecessary. Storing pesticides during cold weather can make someof them useless.
  • Record keeping may seem unrelated to ground water contamination, but knowing what pesticides have been used in the past and what is currently on hand allows for better purchasing decisions. Keep records of past field application rates and their effectiveness. Along with field records, add information such as the manufacturer’s name and address, chemical types and handling precautions. This information can be important if you must respond quickly to an accident.
  • Using older products first keeps any inventory current and effective. Before using chemicals that have been stored for a few years, though, check with your county Extension agent about possible restrictions on their use.

Evaluation Table

The following table can be used to help agricultural producers and rural homeowners determine the risk that drinking water on a given property will be contaminated as a result of the management practices being used. For each category on the left that is appropriate, read across the right and circle the statement that best describes conditions on your land. Allow 15 to 30 minutes to complete the worksheet, and skip any categories that do not apply. Note any high risk ratings and take appropriate actions to remedy them. Strive for all low or low to moderate risk ratings.

Pesticide Storage and Handling: Assessing Drinking Water Contamination Risk

Pesticide Leachability Chart


Air gap: An air space (open space) between the hose or faucet and water level, representing one way to prevent backflow of liquids into a well or water supply.

Anti-backflow (anti-back-siphoning) device: A check valve or other mechanical device to prevent the unwanted reverse flow of liquids back down a water supply pipe into a well.

Backflow: The unwanted reverse flow of liquids in a piping system.

Back-siphonage: Backflow caused by formation of a vacuum in a water supply pipe.

Closed handling system: A system for transferring pesticides or fertilizers directly from a storage container to application equipment (through a hose, for example), so that humans and the environment are never inadvertently exposed to the chemicals.

Cross-connection: A link or channel between pipes, wells, fixtures or tanks carrying contaminated water and those carrying potable (safe for drinking) water. Contaminated water, if at a higher pressure, enters the potable water system.

Micrograms per liter: The weight of a substance measured in micrograms contained in 1 liter. It is equivalent to 1 part per billion in water measure.

Milligrams per liter (mg/l): The weight of a substance measured in milligrams contained in 1 liter. It is equivalent to 1 part per million in water measure.

Parts per billion (ppb): A measurement of concentration of one unit of material dispersed in 1 billion units of another.

Parts per million (ppm): A measurement of concentration of one unit of material dispersed in 1 million units of another.

Pesticide: A chemical intended to prevent, destroy, repel or mitigate any pest.

Rinsate: Rinse water from pesticide or fertilizer tank cleaning.

Secondary containment: Impermeable floor and walls around a chemical storage area that minimize the amount of chemical seeping into the ground from a spill or leak.

Sump: A pit or reservoir serving as a drain or receptacle for liquids.

Toxicity: The quality, state or degree of being poisonous.

Contacts and References

For additional information contact your county Extension agent or National Resources Conservation Service office, the Texas Department of Agriculture, or the Texas Natural Resources Conservation Commission.

  • The Texas Pesticide Law; The Texas Pesticide Regulations
  • Rinse and Recycle: It Makes Good Sense published by the Texas Natural Resources Conservation Commission, Texas Department of Agriculture, Texas Agricultural Extension Service, and U.S. Environmental Protection Agency. Publication No. TWC/C91-09 2/93.