Evaluate the need, method, and frequency of chemical control. Use pesticides only when necessary and only in amounts that will adequately control pests. Pesticides that are applied less frequently and in low concentrations are less likely to leach into the groundwater. Where possible, select pesticides that are less toxic and less persistent.
Identify the vulnerability of the soil.
Well-drained or sandy soils low in organic matter have a high potential for groundwater contamination.
Consider the location of the pesticide application in relation to surface water and groundwater.
Keeping pesticides away from water sources helps prevent their introduction into groundwater. Consult your local county Extension office or Soil Conservation Service to determine the depth to groundwater in your area The proximity of a water well to a pesticide source is an important factor. Movement of pesticide residues associated with runoff into streams and rivers can also ultimately contribute to groundwater contamination under certain conditions.
Become familiar with pesticides that may leach.
Pesticides with a high potential for leaching are more likely to contaminate groundwater. For example some carbamate pesticides are more likely to leach and cause groundwater contamination than other pesticides. Check the pesticide label for warnings about potential to<> leach to groundwater. Pesticides that are relatively stable, highly water soluble, and not adsorbed on soil particles have the greatest potential to leach through the soil.
Your local county Extension office or the Environmental Protection Agency can provide information on the leaching potential of different pesticides.
Consider the vulnerability of the area.
Determine the relative susceptibility of the soil to leaching. Pesticide movement is affected by soil texture, permeability, and organic matter content. Determine, to the extent possible, the depth of the water table and the relative permeability of the geologic layers between the soil surface and the groundwater. Sinkholes and large soil fractures can be especially troublesome because they allow surface water to quickly reach groundwater with little natural soil filtering.
Follow the directions on the pesticide label.
Many pesticide labels contain use instructions or precautions to avoid groundwater contamination. If you do not follow the label directions, you risk contaminating the groundwater. Always read pesticide labels carefully.
Apply the pesticide at the appropriate time.
Fewer applications are required if they are carefully timed relative to stages in the pest's life cycle. Information on proper timing of pesticides is available from your local county Extension office or the Environmental Protection Agency.
Measure the pesticide properly and carefully.
Avoid the temptation to use more product than the label directs. More product will not do a better job of controlling pests. It only increases the cost of pest control, the resistance of pests to chemical controls, and the risk of groundwater contamination.
Calibrate and maintain equipment properly.
Correctly calibrating application equipment before applying pesticides reduces the chances of applying too much. Check your application equipment regularly for leaks, malfunctions, and calibration accuracy. You will save money and help prevent groundwater contamination.
Avoid spills and back-siphoning.
Avoid spills, especially near wells or other water sources. Prevent back-siphoning of pesticide-contaminated water into the water source by keeping the end of the fill hose above the water level in the spray tank. Install a backflow device (such as an air gap or check valve) on the filling pipe to prevent backflow problems. The potential for pesticide contamination is greater from storage, mixing, loading, disposal, and equipment-cleaning sites than from the field application.
Direct the application to the target site.
Avoid over-spraying the ground and possible drift to reduce the risk of groundwater contamination.
Leave buffer zones around sensitive areas.
When mixing, applying, storing, or disposing of pesticides (including cleanup), consider the location of groundwater-sensitive areas. These include sinkholes; wells and groundwater recharge areas; and springs, streams, ponds, wetlands, and other surface water. Establishing thick vegetation, such as turf or pasture grasses, or leaving an untreated border are two ways to provide a buffer zone between a pesticide-use or handling site and a sensitive area.
Dispose of pesticides properly.
Triple rinse or pressure rinse pesticide containers and return the rinse water to the spray tank. Follow the label for proper disposal of leftover pesticide so it does not cause groundwater problems. Good planning is the best insurance against pesticide disposal problems. Buy and mix only the amounts you need. Never dispose of pesticides or pesticide containers near a water source, in sinkholes, in abandoned wells, or where there is a shallow water. table.
Store pesticides safely.
Store pesticides in their original containers in a cool, well-ventilated, protected location away from pumps and water sources.
Maintain records of pesticide use.
Maintain records, by date, of the identity and quantity of pesticides applied to each area. Delay irrigation after pesticide applications.
Because pesticides frequently move with water downward through the soil, irrigation should not immediately follow pesticide applications. For example, delaying irrigation for one or more days after applying a pesticide can reduce the risk of the pesticide reaching the groundwater. On the other hand, some moisture may be necessary to activate certain herbicides and, thus, hasten their intended action and consequent metabolism.
Consider weather and runoff.
Runoff should be avoided by not applying immediately prior to a heavy or sustained rain and not using an excessive amount of irrigation water. Avoiding runoff will reduce soil erosion and pesticide entry into the surface and groundwater. This is especially critical for clay soils that are subject to rapid runoff.
Exercise care when practicing chemigation.
Particular care should be used when practicing chemigation. The irrigation water may carry the pesticides downward through the soil into groundwater Devices should 'be used to prevent possible back-siphoning of the pesticides into the water supply system.
Check the well system.
Consider the location and condition of wells Properly seal new wells and inspect old wells to ensure the seal is adequate. This will help keep contaminated surface water from entering the well and groundwater. Also, consider the method of the well construction, including the type of materials adjacent to the casing, the grade or slope to or from the well, and maintenance.
Use Integrated Pest Management (IPM).
Integrated Pest Management (IPM) is a recommended alternative to purely chemical pest control. IPM integrates available pest control techniques in an economically and ecologically sound manner. IPM uses scientifically sound strategies, such as economic thresholds and pest monitoring, to determine the proper time for pesticide applications.