Chemigation as a Source of Ground Water Contamination
If proper safety measures are not taken, ground water can be contaminated when irrigation water containing pesticides is allowed to backflow into the well supplying the water. Pesticides that flow back into the well can mix with, and move in the normal flow path of, ground water. If the well also supplies drinking water, the pesticide residues will immediately contaminate the drinking water. If the well provides only irrigation water, pesticide residues can be transported in ground water as it flows to drinking water wells.

Chemigation Defined
Chemigation is defined in the California Food and Agricultural Code Section 13142 (opens in new browser window) as a method of irrigation whereby a pesticide is mixed with irrigation water before that water is applied to the crop or to the soil. Section 13142 is part of the Pesticide Contamination Prevention Act, which is designed to prevent further pollution of ground water used for drinking water supplies from the agricultural use of pesticides.

Chemigation is also defined by the Department of Pesticide Regulation (DPR) in Section 6000 of Title 3 of the California Code of Regulations (Definitions), which similarly describes chemigation as the application of pesticides through irrigation systems.

Product Labels Require Backflow Prevention Devices for Chemigation
The increased use of pressurized irrigation systems, such as macro-sprinkler, micro-sprinkler, and drip systems, facilitated the injection of chemicals from a fixed point of application. The prevention devices listed on the pesticide labels and their approved alternatives are part of an integrated system that, in addition to preventing backflow into wellheads, also assures proper metering and application of pesticides through properly designed irrigation systems.

In 1987, the United States Environmental Protection Agency (U.S. EPA) issued Pesticide Registration (PR) Notice 87-1 (opens in new browser window) to clarify label requirements when chemigation is a method of application. This notice required registrants to revise the labeling of pesticide products registered under the Federal Insecticide, Fungicide, Rodenticide Act (FIFRA) (opens in new browser window) and intended for application through irrigation systems (chemigation) to include "additional use directions and other statements." According to FIFRA , it is unlawful for any person to use any registered pesticide in a manner inconsistent with its labeling. Pesticides not labeled for chemigation applications must contain language indicating that the product cannot be applied through an irrigation system. Thus, it is illegal to apply pesticides by chemigation if "additional use directions and other statements" specific for chemigation are not contained on the label. When using chemigation as a method of application, the user must conform to the requirements for backflow prevention stated on the label, except as provided in U.S. EPA's memorandum listing approved alternatives.

After the initial PR notice, U.S. EPA received comments indicating a wider range of acceptable devices for backflow prevention. As a result of this information, the U.S. EPA released a memorandum listing chemigation equipment that could be used as alternatives. In some cases, the alternative equipment was less expensive, more reliable, or more available than some of the equipment initially approved as acceptable devices. For example, even though a label specifically states to use an injection pump to chemigate a pesticide, use of a Venturi system is a legally approved substitute. Any chemigation equipment that is required on pesticide product labeling that has no listed alternative(s) is still required as a component of the chemigation system.

DPR Backflow Prevention Regulations
The DPR regulation for backflow prevention in 3CCR section 6610 states that each service rig and piece of application equipment that handles pesticides and draws water from an outside source shall be equipped with an air-gap separation, reduced pressure principle backflow prevention device, or double check valve assembly. Backflow protection must be acceptable to both the water purveyor and the local health department.

This rule, established in 1977, was intended to clarify responsibilities for connection to public water systems, so the language reflected requirements in the Health and Safety Code. The requirement for public water systems is still applicable but connections to non-public water systems, such as domestic and irrigation wells, is now more appropriately covered by U.S. EPA label language requirements. In contrast to public water system wells where there is generally constant pressure, non-public system wells run intermittently, and thus require different backflow prevention components.

In 2001, DPR issued two enforcement letters, ENF 01-12 (PDF, 39 kb) and ENF 01-28 (PDF, 398 kb), to clarify that the EPA label language is appropriate protection for chemigation systems connected to stand alone domestic and irrigation wells. These letters affirm DPR's adoption of the EPA label language and include a list of alternative components.

Who Is Required to Have Backflow Prevention Devices?
Anyone applying a pesticide through an irrigation system is required to have functional backflow prevention devices installed. The components differ depending on the type of connection. If you are connected to a municipal system and use the water for irrigation, you must conform to California Department of Health Services (DHS) (PDF, 184 mb, opens in new browser window) regulations for connection to municipal systems. These requirements can also be obtained from local County Health Departments (opens in new browser window). If your water source is a stand alone well, you must comply with the label language for the pesticide product, except when there are alternatives approved by U.S. EPA. For example, a Venturi system can substitute for a positive displacement injection pump. Contact your local County Agricultural Commissioner (California Department of Food and Agriculture page opens in a new browser window) if you have any questions.

• Chemigation Initiative menu
• DPR chemigation publications
• Educational materials
• Required chemigation safety devices
• Related links