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Grower Training Manual for Backflow Prevention in Chemigation of Pesticides Grower Training Manual for
Backflow Prevention in
Chemigation of
Pesticides

Revised 3/17/03

By

The Center for Irrigation Technology
California Agricultural Technology Institute
California State University, Fresno

David F. Zoldoske, Director
Tim Jacobsen, Education Specialist
Edward M. Norum, Agricultural Engineer



For

Environmental Monitoring Branch
Department of Pesticide Regulation
California EPA




March 2003


2
DPR Grower Training Manual for Backflow Prevention

Table of Contents

Introduction.3
Pesticide Label Requirements for Chemigation......3
Alternatives Devices that also Comply with the Label ..7
Maintenance, Calibration, and Safety.11
Appendix.13



3
Introduction

The purpose of this manual is to familiarize those involved with injecting pesticides into
irrigation systems with the equipment requirements mandated by the federal government
and stated on the pesticide label. The manual will cover the legal requirements as well as
discuss practical ways to satisfy the requirements.

Chemigation, or the addition of chemicals to irrigation water, has probably been around
for as long as both irrigation and chemicals have been used in agriculture. Chemigation
became more widely used in the 1970s with the adoption of center pivot irrigation
systems in the Midwest. The federal government began regulating chemigation in 1988
when the EPA adopted a label improvement program for labeled agricultural pesticides.
That program requires labels that permit chemigation to contain specific language
describing equipment the application system must contain to prevent backflow into the
water supply. Backflow prevention is necessary to prevent pesticide contamination of
surface water supplies as well as ground water. Since 1988, the EPA has approved
additional alternative backflow prevention equipment and many states have instituted
guidelines to help growers come into compliance with the federal requirements.


Pesticide Label Requirements for Chemigation

The following is the actual text of the language found on every EPA label for pesticides
that are approved for application by chemigation.

1. The system must contain a functional check valve, vacuum relief valve, and low
pressure drain appropriately located on the irrigation pipeline to prevent water
source contamination from backflow. Chemigation valves are available that
have been designed to satisfy these three requirements (Figure 1). A chemigation
valve consists of an air/vacuum relief valve and a low pressure drain valve located
immediately upstream of a check valve. This valve should be mounted
immediately adjacent to the discharge head of the pump.

4


Figure 1: Chemigation valve (mainline check valve, vacuum relief
valve, and low pressure drain)


2. The pesticide injection pipeline must contain a functional, automatic, quick-
closing check valve to prevent the flow of fluid back toward the injection pump.
This smaller check valve is located in the line between the pesticide injection
pump and the irrigation pipeline (Figure 2). It functions to prevent the flow of
water back towards the pesticide supply tank and prevents pollution spills.




Figure 2: Quick-closing check valve on pesticide injection line


3. The pesticide injection pipeline must also contain a functional, normally closed,
solenoid-operated valve located on the intake side of the injection pump and
electrically connected to the system interlock. The purpose of this valve is to
prevent fluid from being withdrawn from the supply tank when the irrigation
system is either automatically or manually shut down. The valve also will
Vacuum
Relief
Valve
Low
Pressure
Drain
Valve
Check
Valve
Injection
Line Check
Valve
To Irrigation
System
From
Pesticide
Injection
Pump
5
prevent water from entering the pesticide tank when the injection pump is not
operating. The valve is to be located at the pesticide tank to isolate the tank from
the irrigation line and prevent accidental spills (Figure 3).




Figure 3: Normally closed solenoid valve


4. The irrigation pipeline must include a functional pressure switch which will stop
the water pump motor when the water pressure decreases to the point where
pesticide distribution is adversely affected. Pressure switches come in many
configurations and prices and are commonly available from an irrigation supply
store. An example of one type is shown in Figure 4.




Figure 4: Pressure switch


5. The system must contain functional interlocking controls to automatically shut
off the pesticide injection pump when the water pump motor stops. These
controls shut off the injection pump when the pressure switch indicates a drop in
Solenoid
Valve
Low
Pressure
Switch
6
irrigation system pressure that will affect the distribution uniformity of the
pesticide application. The interlock can be electrical or hydraulic.

6. Systems must use a metering pump, such as a positive displacement injection
pump (e.g., diaphragm or piston pump) effectively designed and constructed of
materials that are compatible with pesticides and capable of being fitted with a
system interlock. Most pesticide injection pumps meet these criteria.
Centrifugal pumps do not meet these criteria for a metering pump.

Figure 5: Schematic of a pesticide injection system with the eight required items.








(A) Mainline Single Check Valve
(C) Air/Vacuum Relief Valve
(G) Pesticide Injection Pump
(E) Interlocking System Controls
(H) Injection Line Check Valve

(B) Low Pressure Drain

(F) Solenoid Operated Valve
(D) Pressure Switch

(C)
(A)
(B)
(H)
(E)
(G)
(D)
(F)
Irrigation
Pipeline
Pesticide
Injection Line
Electrical
Connections
Pesticide
Supply Tank
Well Pump
and Wellhead
7
Alternative Devices that also Comply with the Label

EPA allows for some modifications of the equipment list, which, in some cases, may
simplify the system. The following is a list of required devices and the approved
alternatives for those devices.

Air Gap The most reliable form of backflow prevention is an air gap, a physical air
separation between the pesticidally treated water and the water supply. No additional
backflow protection is required if the water for the irrigation system leaves the pump
discharge head and flows into a standpipe before the pesticide injection point. The
disadvantage to an air gap is that any pressure built by the water system is lost to
atmosphere at the point of discharge. The end of the pipe must be two pipe diameters
above the level of the standpipe to qualify as a proper air gap (Figure 6).


Figure 6: Air gap


Gooseneck Pipe Loop Another alternative is a gooseneck pipe loop structure with a
vacuum relief valve located 24 above the highest water emission point in the field. This
structure will also serve as adequate backflow protection and takes the place of the
chemigation valve (mainline check valve, vacuum relief valve, and low pressure drain
valve). The gooseneck pipe loop must be located in the main water line immediately
downstream of the water pump. The bottom side of the pipe at the loop apex must be at
Two Pipe
Diameters
8
least 24 above the sprinkler or any other type of water emitting device. The loop must
contain a vacuum relief valve on the top of the pipe at the apex of the pipe loop. The
pesticide injection port must be located downstream of the apex of the pipe loop and at
least 6 below the bottom side of the pipe at the loop apex.

Venturi A venturi can replace the positive displacement pesticide injection pump to
draw pesticides into the irrigation water (Figure 7). A venturi is a non-mechanical device
that uses negative pressure created in the body of the device to introduce liquids into the
irrigation pipe. A 15 to 40 psi pressure drop across the venturi is required to make the
unit function. Normally the venturi is installed across a pressure reducing valve or a
booster pump and takes advantage of the difference in pressure between the inlet and
outlet. The venturi can also be installed in a bypass configuration with a small booster
pump. See Appendix for complete details.



Figure 7: Venturi installed in bypass configuration


Additional Vacuum Relief The solenoid controlled valve on the pesticide tank may be
eliminated if an additional vacuum relief valve is installed between the positive
displacement pesticide injection pump and the pesticide injection line check valve
(Figure 8). This valve must be elevated at least 12 above the highest fluid level in the
pesticide supply