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Chemigation. Guy Fipps – Extension Agricultural Engineer Shay Simpson – Extension Associate 8 th Annual Southeast Texas Grounds Maintenance Conference October 25, 2001. Regulations.

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Chemigation

Guy Fipps – Extension Agricultural Engineer

Shay Simpson – Extension Associate

8th Annual Southeast Texas Grounds Maintenance Conference

October 25, 2001


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Regulations

  • Administrative Rules of the Texas Department of Licensing and Regulation (TDLR): Chapter 76 – Water Well Drillers and Pump Installers

  • Texas Natural Resource Conservation Commission (TNRCC):

    • Chapter 290 – Public Drinking Water

    • Chapter 344 – Landscape Irrigation

  • Local Ordinances


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TDLR Chapter 76.1007Water Well Drillers and Pump Installers

Section 76.1007. Technical Requirements - Chemical Injection, Chemigation, and Foreign Substance Systems


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TDLR Chapter 76.1007

All irrigation distribution systems … into which any type of chemical … or other foreign substances will be injected into the water pumped from wells shall be equipped with an in-line, automatic quick-closing check valve capable of preventing pollution of the ground water.


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Check Valve

  • Body constructed of:

    • Cast iron

    • Stainless steel

    • Cast aluminum

    • Cast steel

    • Material and design of sturdy integrity

  • Materials should be corrosion resistant or coated to prevent corrosion


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Check Valve

  • Valve working pressure rating shall exceed the highest pressure to which the valve will be subjected

  • Valve shall be installed between the pump discharge and the point of chemical/foreign substance injection


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Other Required Devices Installed between the pump discharge and the check valve

  • Vacuum-relief device

  • Automatic low pressure drain

    • At least ¾ inch in diameter

    • Flush with inside surface of pipe bottom

    • Outside opening be at least 2 inches above grade

  • Inspection port

    • Minimum of 4 inch diameter orifice


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TNRCC – Chapter 290Public Drinking Water

Appendix I: Assessment of Hazards and Selection of Assemblies


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Irrigation With Chemical Additives

  • Health hazard

  • Required assembly

    • Reduced-pressure principle backflow prevention assembly (RPBA)


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Irrigation Without Chemical Additives

  • Non-health hazard

  • Required assembly*

    • Double check valve backflow prevention assembly (DCVA)

    • Atmospheric vacuum breaker (AVB)

    • Pressure vacuum breaker (PVB)

  • *Where greater hazards exist reduced-pressure principle backflow prevention assembly is required.


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TNRCC – Chapter 344Landscape IrrigationProposed Revision

An irrigation system which adds any chemical with any kind of injection device associated with it has a potential for introducing toxic substances into the water supply and is, therefore, considered to be a "high health hazard" installation.


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Proposed Revision

Such an irrigation system must not be connected to any potable water supply except through an industry-approved "high health hazard" backflow prevention device, such as an appropriate pressure-type vacuum breaker backflow preventor or a reduced pressure principle backflow prevention assembly.


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Proposed Revision

The backflow prevention assembly must be tested upon installation and, at least, annually, thereafter, in accordance with §290.44(h)(4) of this title (relating to Water Distribution).


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Reduced-Pressure Principle Backflow Prevention Assembly

  • RPBA

  • RPZ

  • RP


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RPBA

  • Protects against back-siphonage & back-pressure

  • Can be under constant pressure

  • Must be 12 inches above grade

  • Must be tested upon installation and annually if in high hazard applications


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RPBA

  • Installed horizontally

  • 4 test cocks

  • 2 shut off valves

  • At least 2 (psi) zone pressure difference

  • Double seated relief valve


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Chemigation

The process of injecting an approved chemical into irrigation water and applying it through the irrigation system to a crop or field.


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Chemigation

  • Fertigation

  • Insectigation

  • Fungigation

  • Nematigation


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Advantages of Chemigation

  • Uniformity of application

  • Precise application

  • Economics

  • Timeliness

  • Reduced soil compaction and crop damage

  • Operator safety


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Disadvantages of Chemigation

  • High management

  • Additional equipment


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The US EPA’s Label Improvement Program (LIP)

  • Effective April 1988

  • Labels must state whether product is approved to be applied through the irrigation system

  • Application instructions are provided

  • Requires use of specific safety equipment and devices designed to prevent accidental spills


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Example Labels


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Summary of Chemigation Equipment Requirements


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1. Irrigation Pipeline

  • Check valve between well and injection points*

  • Vacuum relief valve between check valve and well

  • Low pressure cut off

  • Low pressure drain*

*Alternative safety equipment may be substituted

approved by EPA, March 1989.


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2. Injection Hose

  • Anti-back flow injection valve – 10 psi

  • Normally closed solenoid valve between injection pump and chemical tank*

  • A metering type injection pump*

*Alternative safety equipment may be substituted

approved by EPA, March 1989.


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3. Power Interlock

  • Interlock injection pump and water pump power

  • Interlock normally closed solenoid valve and injection pump power


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Management Practices for Chemigation

  • Flushing injection system

  • Flushing irrigation system

  • Monitoring

  • Calibration check

  • Chemical compatibility

  • Prevent runoff

  • Prevent application to surface water


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Chemigation Pumps

  • Mechanical

    • Piston (positive displacement) pumps

    • Diaphragm pumps

  • Venturi meters


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Piston/Positive Displacement Pumps

Discharge flow rate will not change as the irrigation pipeline pressure varies

  • Flow rates cannot be adjusted while operating

  • Used to inject fertilizer

  • Not easily adjusted for insecticides, fungicides and herbicides


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Diaphragm Pumps

Discharge flow rate not constant with significantly varying discharge pressure

  • Easy to adjust flow rate while operating

  • Zero leakage


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Venturi Meters

Variations in flow rate from the water supply will change the rate of injection

  • Reduced diameter throat tube

  • Velocity changes in throat create vacuum to pull chemical into stream

  • Requires additional hardware for injection


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Important CharacteristicsChemigation Pumps & Components

  • Accuracy to within + or – 0.5 percent

  • Calibration tube

  • Adjustable while running

  • Durable – stainless steel valve balls – Niton seals

  • Agitation capability

  • Accessibility of repairs

  • Appropriate size chemical tank/tanks


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Calibration of Equipment

  • Small differences in injection rates make large differences in total amount of chemical applied

    • Results in insufficient or excessive application

      450 gallons/minute = 1 acre-inch/hour

      27,000 gallons = 1 acre-inch


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Example Calibration


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Precipitation Rate

  • Amount of water applied per unit time

  • Meter method

  • Area flow method

  • Catch can method


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Example of Precipitation Rate


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Distribution Uniformity

  • Provides an analysis of water application over area irrigated

  • Expressed in percent

  • 70 to 80% is considered good


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Distribution Uniformity(DU) (%)

  • Ratio: dry vs. wet areas

  • Based on irrigation system hardware

  • Easy to measure using catch devices

  • Limiting factor when producing good schedules

  • Limiting factor for good chemigation application


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The Eight Steps of an Audit

Site Selection Step 1: Obtain site data

Step 2: Rank the sites

Field Work Step 3: Inspect the site

Step 4: Prepare for the irrigation system tests Step 5: Perform irrigation system tests

Step 6: Calculate base irrigation schedule

Follow-up Step 7: Prepare reports, adjust schedule

Step 8: Review performance


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Landscape Irrigation Auditing and Management (LIAM)Short Course

http://irrigation.tamu.edu


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