Protecting Water Resources from Contamination

Objectives:

1. Increase awareness of the potential for contamination of groundwater and surface water resources as a result of irrigated agriculture.
2. Increase familiarity with terminology, processes and pathways associated with common agricultural sources of water resource contamination.
3. Increase understanding and application of best management practices to reduce risk of groundwater or surface water contamination.

Key Points:

1. Water losses due to surface runoff or deep percolation can transport sediments, salts, and/or agricultural chemicals to groundwater or surface water.
2. Efficient irrigation and management to optimize rainwater can reduce runoff and deep percolation (leaching) losses.
3. Physical, chemical and other properties of the soil and potential contaminants affect the relative risk of water contamination.
4. Safe and appropriate storage, handling and application of agricultural chemicals and wastes are key to reducing risk of contamination.

Assess your knowledge:

1. Briefly describe some best management practices that can reduce runoff losses and deep percolation losses of irrigation and/or rainfall.
2. What is the difference between a conservative constituent and a non-conservative constituent? List some examples of each.
3. Briefly describe some BMPs for agricultural chemical handling, and explain how they can prevent contamination of water resources.
4. What is the role of a chemigation check valve? How does it work?
5. How can soil fertility testing be a tool in preventing water contamination?

BMPs to Prevent Pesticide Contamination of Water Resources

Groundwater and surface water resources are active components of a dynamically interrelated hydrologic system.  In Texas, there are increasing demands on limited water resources, thus it is especially critical that they be protected from contamination.

Pesticides are important tools in controlling weed, disease, and insect pests in agricultural production, as well as in lawns, sports fields, landscapes and other green industry applications.  Pesticides are also used to control insect and rodent pests in our living and working environments.  Careful and appropriate handling and use minimize risk of environmental contamination and exposure to pesticides.

Compiled by Dana Porter, PhD, PE, Department of Biological and Agricultural Engineering and Texas A&M AgriLife Research and Extension Center – Lubbock.

Pesticide properties that affect Risk of Contamination

• Solubility determines how readily a chemical dissolves in water.
• Adsorptivity determines how strongly a chemical is adsorbed to soil particles.
• Volatility determines how quickly a chemical will evaporate in air.
• Degradation describes how quickly a chemical breaks down due to biological and environmental factors.

Local conditions that affect Risk of Contamination

Soil texture affects how quickly water moves through soil, how much water can be stored in the soil, and relative particle surface area for chemical adsorption. Coarse (sandy) soils pose higher risk of groundwater contamination than finer textured soils (loam and clay soils).

Organic matter in soil reduces water pollution risk, because it increases chemical adsorption potential and supports higher populations of microorganisms for biodegradation of pesticides.

Topography, soil structure, soil surface condition and soil moisture affect water movement into and through the soil, influencing relative risks of leaching contaminants to groundwater or runoff of contaminated water to surface water.

Distance from groundwater and surface water resources, depth to groundwater, and the proximity of abandoned or poorly constructed water wells affect risk of contamination.

Pesticides in the Environment

After application, pesticides may be evaporated (volatilized), adsorbed onto soil particles, broken down by sunlight (UV degradation), broken down by microorganisms (biodegradation), taken up in or attached to plants, or dissolved in water.

Pesticides dissolved in water may be transported to groundwater through leaching or to surface water through runoff. Pesticides adsorbed to soil particles also may move to surface water through erosion and sedimentation.

Pesticides in water may also undergo evaporation, UV degradation or biodegradation. They may become diluted or dispersed in the water. They may even move within the groundwater or surface water.

Best Management Practices

Integrated Pest Management (IPM)

Optimize pest management strategies, chemical selection and application timing for efficient and effective control. Consider crop rotations, tillage practices, planting and harvest dates, and other strategies as applicable to achieve good crop results while minimizing the need for pesticide applications. Check with your County Extension IPM or Agriculture Agent for specific IPM recommendations.

Pesticide storage, handling and disposal

• Read and follow the pesticide label.
• Store, handle, mix, apply and dispose of chemicals according to label instructions – not near water wells or water drainage areas.
• Purchase and mix only the amount of chemical that is required to minimize need for disposal.
• Contain and clean spills quickly to minimize risk of water contamination.
• Consider installing a concrete pad, detention storage or berms to contain chemicals, spills and rinsates in the mixing and tank filling area.
• Avoid spraying, mixing and rinsing tanks near a wellhead; use a longer hose or use a water spigot away from the wellhead, if possible.

Pesticide application

• Read and follow label directions!
• Calibrate, clean and maintain all application equipment properly.
• Follow all label instructions regarding registered crops, application rates, methods and timing of pesticide application.
• Observe all restrictions on location, soil types, depths to water table and other limitations as noted on the label.

Additional Best Management Practices

Manage irrigation to minimize potential for runoff or deep percolation (leaching) losses. Consider usingconservation tillage, setback areas, vegetative filter strips, contour farming and other practices as appropriate to reduce runoff losses from irrigation or rainfall.

Practice wellhead protection. Prevent back-siphoning; use adequate backflow protection devices in mixing chemicals and filling tanks. Use backflow protection (chemigation check) valves in chemigation operations. Properly close abandoned water wells.

Plan ahead to minimize risk. Identify water wells, surface drainage and other potential pathways for contamination. Avoid using, storing or mixing pesticides near these areas.

Identify potential sources of contamination, including chemical storage and mixing areas. Secure these areas to minimize risk of accidental spills.

Prepare an Emergency Response Plan.

References

• Pesticide Properties That Affect Water Quality (B-6050)
• Chemigation Equipment and Safety (L-2422)
• Reducing Herbicides in Surface Water Best Management Practices (L-5205)
• Chemigation and Water Quality Protection Information on the Internet