(Center Pivot Spray Irrigation System)
Spray irrigation technology with "Center Pivots" and "Linear" systems can be used to remediate groundwater contaminated with volatile organic compounds (VOC). The technology is commonly used to apply irrigation water to vegetable and row crops. While the systems were introduced to irrigate hilly terrain and excessively well-drained soils, the technology has been adapted in both groundwater quality and quantity management areas as a best management practice. This technology severely reduces water application rates and leaching relative to flood irrigation techniques.
The systems consist of an elevated pipeline with nozzles placed at close intervals. Groundwater is pumped through the pipeline and sprayed uniformly over a field as the pipeline pivots or linearly passes over the cropped area. The typical pump rate is between 800 and 2,000 gallons per minute (gpm). These self-propelled systems are highly mechanized and have low labor and operating requirements. The systems do not require level ground and startup costs are low.
The sprinkler method applies water over the irrigated area with a fine spray (see the photograph below). Water coverage over the irrigated area is controlled by the speed with which the "pivot" or "linear" systems travel across the field. The heart of the sprinkler irrigation system is the nozzle, which is a small opening through which a high-velocity stream of water is emitted. As the high-velocity water stream leaves the nozzle, it strikes an impact pad and forms a thin film of water.
Center Pivot Spray Irrigation System
The system used in the SITE demonstration program was a center pivot and was located on a seed corn field in Hastings, Nebraska. The system was equipped with off-the-shelf, fog- producing impact pads for improved volatilization efficiency. The thin film of water produced by these pads breaks up into small droplets as it leaves the impact pad. Droplet size depends on the stream pressure and design of the impact pad.
A stratified water droplet collector (SWDC) simultaneously collected spray at four fall heights above ground level, and was specifically contracted for this project by the Dutton-Lainson Company in Hastings, Nebraska. With this device, droplets were collected at heights of 1.5, 4.5, 7.5, and 10.5 feet above the ground surface. Twelve SWDCs were installed parallel to the pivot arm to determine average volatilization efficiencies along the 340 nozzles on the pivot arm.
The sprinkler irrigation system is capable of remediating VOC-contaminated groundwater. Removal rates in excess of 95 percent have been demonstrated for groundwater containing ethylene dibromide (EDB), trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and carbon tetrachloride (CT). The method will efficiently volatilize all common volatiles in groundwater which may originate from landfills, degreasers, dry cleaners, electrical industries, gas stations, or refineries. The residuals are transferred to the atmosphere, where they are dispersed and most are rapidly degraded in ultraviolet light.
The technique may be limited to individual groundwater VOC concentrations that are less than 1 part per million if residual concentrations of VOCs are mandated to be near or below the maximum contaminant level prior to reaching the ground surface. Otherwise, the technique can be used in any agricultural setting where sufficient groundwater and irrigatable land are available.
The Center Pivot Spray Irrigation system was accepted into the SITE Program in late 1995. Under a University of Nebraska project funded by the Cooperative State Research Service of the Department of Agriculture, field tests were completed in the summers of 1994 and 1995 in a seed corn field in Hastings, Nebraska.
The technology was demonstrated under the SITE Program in July 1996 at the North Landfill Subsite in Hastings, Nebraska. The 50-acre site is a furrow-irrigated corn field underlain by commingled plumes of groundwater containing EDB, TCE, TCA, CT, 1,1-dichloroethene, trans-1,2-dichloroethene, and chloroform. The primary goal of the demonstration was to determine the efficiency of the system to remediate VOCs in groundwater to concentrations below the maximum contaminant levels. The results of this demonstration will be available in a Demonstration Bulletin and Innovative Technology Evaluation Report to be published early in 1997.
Clients involved in large pump-and-treat projects at several military bases are investigating the suitability of the system to their specific site situations. Potential clients include the U.S. Navy, the Army Corp of Engineers, and several state agencies. The technology is currently being used at the Lindsey Manufacturing site in Nebraska and at some grain elevators being remediated by Argonne Laboratory.
EPA PROJECT MANAGER:
Teri Richardson
EPA SITE Project Manager
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7949
Fax: 513-569-7105
TECHNOLOGY DEVELOPER CONTACT:
Roy Spalding
University of Nebraska - Lincoln
Water Center/Environmental Programs
103 Natural Resources Hall
P.O. Box 830844
Lincoln, NE 68583-0844
402-472-7558
Fax: 402-472-9599