Chemigation safety measures

Chemigation is the process of applying an agricultural chemical (fertilizer or pesticide) to the soil or plant surface with an irrigation system by injecting the chemical into the irrigation water. Depending on the type of agricultural chemical applied, chemigation may be referred to as fertigation, herbigation, insectigation, fungigation, etc.

Chemigation, like other chemical application methods, has its advantages, limitations and risks that you must consider when deciding which method of application is best. The greatest risk of chemigation is the potential for accidental backflow of all or part of the chemical into the irrigation water source if the system is not properly set up, operated and maintained.

To reduce nitrate leaching losses, apply a portion of a crops nitrogen (N) requirement with irrigation water. Both University of Minnesota and Minnesota Department of Agriculture crop specialists recognize this as a best management practice for high-nitrogen-use crops grown on coarse textured soils.

Before installing any chemigation equipment, get specific details on the required safety devices and measures from the MDA.

Chemigation has three main ways of potentially polluting irrigation water sources if safety devices aren’t correctly functioning.

1. The chemical in the supply tank and in the irrigation pipeline could flow or be siphoned back into the water source when the irrigation system shuts down (Figures 1 and 4).

2. The chemigation system could continue to inject the chemical into the irrigation pipeline when the irrigation system shuts down. This causes the chemical solution to flow back into the water source or spill onto ground (Figure 2).

3. The chemigation system could shut down while the irrigation system continues to operate and force water back into the chemical supply tank causing it to overflow and spill onto the ground (Figure 3).

The chemigation operator and farm manager/owner are responsible for minimizing these and other pollution risks by using proper safety devices and management measures.

While injecting a pesticide, you must provide an MDA-approved reduced pressure zone (RPZ) backflow preventer or two check valves in series in the main irrigation water supply pipeline of any system directly connected to an irrigation water well or a surface water source. If you only intend to inject fertilizer, you can use a single MDA-approved check valve in the main pipeline.

Locating and installing the check valve

Locate the check valve(s) or RPZ assembly between the point of chemical injection and the irrigation water supply pump. Their main purpose is to keep the water and chemical mixture from flowing back or being siphoned back into the water source.

Install check valves with fittings that allow for easy removal for maintenance or repair. You can install a check valve(s) assembly as a portable unit and move it to other permitted irrigation systems.

Required components

Each check valve assembly must contain an:

• Air vacuum relief valve.

• Automatic low-pressure release drain on the water-supply side of the check valve flapper.

• Inspection port that can easily be opened to inspect the check valve flapper and the low pressure drain when the irrigation system is shut down.

Air vacuum relief valves

The vacuum relief valve allows air to enter the pipeline when the water stops flowing. This prevents the creation of a vacuum that siphons the water and chemical mixture downstream of the check valve back into the water supply.

Low-pressure drain

The low-pressure drain must:

• Be located on the bottom of the pipeline on the supply side of the check valve.

• Have a fully functioning drain opening that’s at least 3/4 inches in diameter.

• Open automatically whenever the irrigation water flow stops. This provides a secondary safety backup for preventing any chemical and water mixture from entering the water source if the check valve leaks.

You must also position the drain outlet or direct the drainage to flow away from the well or surface water source during shutdown. Use a hose, pipe or open conduit to direct the drain discharge.

Approved models

Approved check valve assemblies must meet MDA design and operating standards and be certified by an independent testing laboratory.

Approved check valve models

Features of check valve assemblies:

• Quick-closing by spring action.

• Water-tight seal.

• Constructed of corrosion-resistant material or protected to resist corrosion.

• Easy to maintain and repair.

The chemigation injection system must be interlocked with the irrigation system’s power or water supply so it will shut down anytime the irrigation system or pumping plant stops operating or the water flow is disrupted.

In all cases, this measure must prevent chemicals in the supply tank from being injected into the main irrigation pipeline after the water supply stops flowing.

Electric motors

If you use electric motors for both the irrigation and chemigation systems, interlock the control panels for the two systems. You must set up the interlock so the injection pump motor stops whenever the irrigation system or pump stops.

Internal combustion engines

Irrigation pumps driven by an internal combustion engine can be interlocked with an injection pump via belting to the drive shaft or an accessory pulley on the engine. Electrically powered injection pumps should connect to the engine’s generator or electrical control system.

Flowing water or water pressure

Some chemigation systems use flowing water or water pressure to power the injection meter or pump. In most cases, these systems will stop injecting a chemical when the irrigation water supply stops flowing.

Solenoid valves

If chemical flow from the supply tank could possibly continue after shutdown, provide a normally closed solenoid valve in the chemical injection line, preferably on the suction side of the injection meter. The solenoid valve must be interlocked and powered by the irrigation system control panel, water supply pressure or the injector power supply.

The chemical injector discharge line/hose must contain a positive closing check valve, which won’t allow flow either way when the injection system isn’t operating.

The check valve must be located between the injection meter and the point of the chemical injection into the irrigation pipeline. This valve should do both of the following:

1. Stop the flow of water from the irrigation system into the chemical supply tank if the injection system stops.

2. Prevent gravity flow from the chemical tank into the irrigation pipeline following an unexpected shutdown.

Two-way protection

To provide two-way protection, the valve should have a watertight sealing check valve with a minimum opening (cracking) pressure of 10 pounds per square inch. It should also be constructed of material that’s resistant to corrosion from agricultural chemicals.

Risks and dangers

If irrigation water is allowed to flow back into the chemical supply tank, it could overflow the tank, causing the chemical solution to spill onto the ground.

If the chemical solution in the supply tank is allowed to flow into the irrigation pipeline by gravity or be siphoned when the irrigation system isn’t operating, it could pose a potential danger to the crop or leak onto the ground. Then, it could get into a surface or groundwater source.

The irrigation system must contain a low-pressure shutdown switch or device with similar operating characteristics on the main pipeline.

This switch shuts down the irrigation system and the chemigation system if the operating pressure drops to an unsatisfactory level for proper agricultural chemical distribution.

The chemigation supply tank must not be located closer to an irrigation well than the distance specified by Minnesota law. Likewise, the separation distance from a surface water source must be no less than that specified for an irrigation well, unless other state or federal regulations are more applicable.

Specifications

In addition, the chemigation supply tank must be safeguarded according to the following MDA specifications:

• House the chemigation supply tank in a secondary containment (dike) unit if the tank storage meets at least two of the following conditions: a) The supply tank has a rated capacity of more than 1,500 gallons, b) the tank is located within 100 feet of a water supply and c) the supply tank storage is located at the site for more than 30 consecutive days.

• The minimum required capacity for a secondary containment unit is 125 percent of the tank capacity (110 percent if under a roof). Its walls and base may be made of ferrous metal, reinforced concrete, solid reinforced masonry, synthetic lined earth or prefabricated metal or synthetic materials. Synthetic liners must have a minimum thickness of 30 mils.

• The unit must be leak-proof and built to withstand the hydrostatic pressure from the release of a full tank. The walls or base must not contain a drain. Design specifications.

The chemical supply tank must be constructed from fiberglass, polyethylene, stainless steel or other materials that are resistant to the chemical being stored and resistant to degradation by sunlight.

If not contained in a secondary unit, locate and landscape the tank so any leaks are directed away from entering the water source. Also, protect the tank from damage from farm machinery and livestock.

All sites being treated with a pesticide through the irrigation system must be posted with signs during the entire chemigation treatment.

What to put on signs

Signs must contain:

• The signal word from the pesticide label (e.g. Danger, caution, etc).

• Name of the pesticide.

• Date of treatment.

• Reentry date as described by the pesticide label.

If the pesticide you’re using in chemigation has more restrictive instructions for posting on the label, you must completely follow the label instructions.

Pesticide information from the Environmental Protection Agency (EPA)

Where to post signs

Signs must be:

• Posted at usual points of entry.

• Posted at property corners immediately adjacent to public transportation routes or other public or private property.

• Placed no greater than 100 feet apart for a field that’s adjacent to a public area such as a park, school or residential area.

If the label describes more restrictive instructions for posting, you must completely follow those restrictions.

Hoses, clamps and fittings

All components in contact with the chemical mixtures should be constructed of materials that are chemically resistant and resistant to sunlight degradation. The pressure rating of all components should be adequate to withstand all operating pressures. Hoses and fittings should be protected from mechanical damage.

Injection line strainer

Install a strainer on the chemical suction line/hose to remove foreign materials that could plug or damage the injection meter/pump or chemical injection line check valve.

Injection line flow sensor

An injection line flow sensor installed just upstream from the chemical injection line check valve and interlocked with the injection device can shut down the injection system if flow in the injection line ceases. 

This safety measure would prevent continuous operation after a line or hose ruptures or disconnects, an injection device loses prime or fails, a supply tank is emptied or an injection port becomes plugged. You could also interlock the flow sensor with the irrigation system to shut down the whole system if injection line flow stops.

Two-way interlock

A two-way interlock between the irrigation system and the injection system can stop either system if the other system also stops. This interlock will eliminate untreated areas in the field by stopping the irrigation pump and sprinkler system if the injection system stops or malfunctions.

The interlock can be done electrically or with a flow sensor on the discharge side of the chemical injection device. When there’s no flow in the injection line, the irrigation system and pumping plants will shut down.

Solenoid valve

For added safety, you could install a normally closed solenoid valve on the suction side of the injection device to provide a positive shut down on the injection line when not in use. The solenoid valve must be interlocked with the injection device power supply to open or close properly.

Bleed valve

You can use a bleed valve, located upstream and next to the injection line check valve, to relieve locked-in pressure in the chemical injection line anytime the line is to be disconnected. This will prevent the operator from being sprayed with the chemical in the line during line removal.

Calibration equipment

A calibration tube or in-line flow meter installed on a chemigation system can provide an easy way to measure the flow rate of the chemical being injected into the irrigation system.

A calibration tube is typically a clear tube with markings in milliliters or fluid ounces that’s used with a stopwatch to measure the flow rate. Place the tube on the suction side of the injection device with the necessary valves and fittings so the injection rate can be checked during a chemigation.

Install in-line flow meters in either the suction or discharge side of the injection device. Its markings are typically expressed in flow units of volume per time.

Injection port location

When possible, locate the port for chemical injection higher than the chemical supply tank but lower than the lowest sprinkler outlet to prevent siphoning from the tank. In all cases, the injection port must be located downstream from the main pipeline check valve.

Injection meter/pump location

When available and possible, locate the injection meter or pump within the chemical supply tank containment unit.

Portable chemigation system and chemical supply tank

Install the chemigation injection meter/pump and chemical supply tank onto a portable trailer or truck. Construct a secondary containment unit of appropriate size on the bed of the trailer or truck.

Chemigation system location

When developing a new irrigation system, locate the irrigation well at least 150 feet from the chemigation system, chemical supply tank, injection port, power interlock controls, etc.

• Periodically observe the irrigation system’s water distribution pattern and conduct a water distribution test of the spray pattern. Remember that the uniformity of the chemical distribution will be no better than the distribution of the water.
• Adjust the irrigation system (such as the end gun) to prevent spray from going beyond the boundaries of the target field.
• Shut the irrigation system down if wind will carry chemical drift off-target.
• Manage the irrigation system to prevent runoff or deep percolation of the water-chemical mixture.
• Don’t chemigate in areas containing wetlands and other surface water bodies.
• Don’t apply any pesticide that’s not labeled for use in an irrigation system. Such applications are illegal and may adversely affect wildlife, non-target plants and water quality.

Inspect all components of the chemigation and irrigation system before each use. If components aren’t working at the time of inspection, repair or replace them before chemigating.

Routine inspections should minimize the potential for failure of any component during chemigation. You must keep a record of inspection dates for the Minnesota Department of Agriculture (MDA).

Follow the procedures listed below to inspect the irrigation pipeline check valve, low pressure drain, injection line check valve, low-pressure switch and the power interlock. RPZ backflow preventers and some other types of check valves will require a different approach to inspection. Contact MDA staff for directions on inspecting if assistance is needed.

Inspection procedures

1. Connect the chemigation system to the irrigation system, but leave the chemical injection line/hose disconnected from the injection port check valve.

2. Start the irrigation pump and pressurize the irrigation system to its normal operating pressure.

3. Observe the injection line check valve to see if any water is leaking back out the inlet side of the check valve. You should not observe any leakage when the irrigation system is operating or shut down.

4. Connect the chemical injection hose to the injection check valve and start up the chemigation system. Only operate the chemigation system with clean water.

5. Turn down the main pipeline control valve (reducing the operating pressure) until the low pressure switch shuts down the irrigation system. The pressure switch should be set to cause the irrigation pump and system to shut down when the normal operating pressure has been reduced by 25 to 50 percent. If no flow control valve is present, shut the power off to the pump and/or irrigation system.

6. Immediately after shutdown, check to see if any water is flowing from the low pressure drain(s). Some drainage for a short period of time after shut down is normal; then drainage should stop.

7. Check to see if the chemigation injection device has stopped operating. This device should stop when the irrigation system and pump shut down. If the chemigation system has an agitation system, this unit does not have to shut down when the injection device stops.

8. Open the inspection port at the main pipeline check valve assembly after the low pressure drain has stopped flowing. Inspect for any leakage from the check valve flapper. You should not observe any leakage coming from the downstream flapper. Also check for proper functioning of the flapper valve assembly.

Direct suppliers to closely monitor the delivery of products to a supply tank. Before filling, make sure they first check the condition of the supply tank and plumbing.

Fill the supply tank to no more than 95 percent of capacity. Monitor the inventory of product contained in the supply tank between chemigations to determine if the supply tank is leaking.

Triple-rinse pesticide containers at the time of use and add the rinse water into the supply tank. Rinse over the opening of the supply tank to minimize risk of spilling on the ground.

To facilitate safe monitoring of the chemigation operation, don’t allow the irrigation system to spray water and the chemical solution into the chemigation equipment area. This may mean plugging a couple nozzles on the irrigation system near the chemigation site.

Accurately calibrating the chemical injection device is essential for proper application. Periodically re-check the calibration setting of the injection device.

Follow calibration procedures described by the chemical label, chemigation equipment manufacturer or University of Minnesota Extension.

Minor differences in injection rate over an extended period can cause the chemical application to be too high or low. This may produce unsatisfactory results or cause potential pollution or crop damage when making high applications.

Immediately apply leftover pesticide mixtures to another crop or site listed on the label or remove it from the supply tank and store it in an appropriate place and in a marked container for later use.

Rinse out the empty tank, and apply rinsing water to the irrigated crop or another labeled site. You can get more specific information on storage or disposal from the Minnesota Department of Agriculture (MDA).

If your tanks contain leftover N solution that you’re not planning to use in the next week or two, remove the N from the supply tank or relocate the tank away from the water source, unless safeguarded according to MDA and Minnesota Department of Health requirements.

Injection equipment

Flush the chemigation injection device, hoses and check valve with clean water after each use. Flush cleaning water into the irrigation system while it’s operating so the cleaning water will be applied to the field. Clean the strainer after each chemigation.

Irrigation system

After you complete the chemigation event and clean the chemigation system, operate the irrigation pump as long as necessary to flush the irrigation system of the chemical solution. This may take 10 to 15 minutes for most systems.

If an accident occurs, regardless of size:

• Avoid personal contamination.

• Take action to keep the potential spill to a minimum.

• Immediately report the incident to the Minnesota Duty Officer at 1-800-422-0798 for assistance.