Unique Approach for Sizing a Reclaimed Water Spray Irrigation System Maximizes Benefits

In 2004, the City of Raleigh Public Utilities Department (CORPUD) initiated a reclaimed water spray irrigation system project to irrigate approximately 130 acres of its existing 1,030-acre farmland used in the past to land apply Class B biosolids. Unlike typical land application or reclaimed water irrigation systems, the primary driver was not to minimize surface water discharge, but rather to maximize crop yield to achieve maximum uptake of applied nutrients and protection of the underlying aquifer. This paper focuses on the alternative approach used to design and implement this spray irrigation system and the resulting benefits gained from this unique system.By sizing a spray irrigation system to maximize crop yield and nutrient uptake and carefully designing the layout of the irrigation system to avoid unsuitable soils and landscape features, CORPUD was able to demonstrate that the irrigation system will be maintained well below the hydraulic limitations of soils and minimize nutrient migration to the underlying aquifer. This unique reclaimed water irrigation system will provide several additional benefits, including:Reducing wastewater treatment plant effluent discharge nitrogen and phosphorus loadings.Significantly reducing crop impacts from droughts.Offsetting additional flow to the wastewater treatment plant from a new groundwater remediation system.Providing a dependable and reliable source of water, even in cases of severe drought.Meeting the need of the existing agricultural fields without creating additional water supply demands.