ASSESSMENT OF RECYCLED WATER IRRIGATION IN CENTRAL OAHU

Although water recycling has been practiced successfully in Hawaii for over 70 years, the fate of constituents applied over unconfined aquifers has been questioned. Water recycling through irrigation has demonstrated the multiple benefits of wastewater reuse including a reduction of the demand on potable aquifer sources and the beneficial reuse of water and nutrients. The preferred reuse method under study on Oahu is irrigation, because c urrent and past water recycling projects utilize reclaimed water on golf courses and agricultural land. The Honolulu Board of Water Supply (HBWS) has taken a cautious approach toward allowing recycled water use over potable water aquifers because of concerns over degrading or contaminating the underlying, high-quality groundwater. HBWS has concerns regarding the migration of constituents, including pesticides and trace organics. As a result, HBWS has developed a project to investigate potential impacts of irrigation with recycled water in Central Oahu. The purpose of the project is to determine the level of protection of water quality that exists when recycled water is used for crop or turf irrigation.The project was initiated with a literature review and research plan in December 2000. The current status of the project is described including a detailed water quality characterization of recycled water and alternative irrigation water sources. Preliminary results from an 18 month field study are reported in which the percolate water quality from plots irrigated with recycled water is compared to the percolate from plots irrigated with control groundwater.