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Author      Title/Abstract      

Results of Assessment of Recycled Water Irrigation in Central Oahu
Author: Ron Crites
Date: 6/105
AWWA 2005 Annual Conference

The overall objective of this study was to evaluate the percolate water quality differences between irrigation with recycled water and the local groundwater, which is the current source of irrigation water. A significant difference in the percolate water quality could indicate a potential cause of concern. No significant difference would indicate that there is no cause for concern when irrigating with recycled water. The results from the percolate water were used to model the impacts on groundwater quality. The Honolulu Board of Water Supply (HBWS), the municipal water utility for the island of Oahu, State of Hawaii, is exploring the use of recycled water as one of their water supply options. Opportunities exist for irrigating with category R-1 recycled water (oxidized, filtered, and disinfected to achieve significant reduction in viral and bacterial pathogens) for agricultural and horticultural uses as an alternative to groundwater. Many of the potential reuse areas are on lands over the potable water aquifers in Central Oahu. The concern regarding aquifer protection that resulted from historic effects on groundwater from agricultural pesticides has been a potential roadblock to implementation. To evaluate the potential effects from irrigation with R-1 water, the HBWS has conducted a scientific study to determine the level of constituent removal from R-1 water using typical irrigation practices on soils. This paper summarizes the results of the year and a half long field research and demonstration project in Central Oahu. In 2000, the HBWS launched a water recycling program through the purchase of the Honouliuli Water Reclamation Facility. This facility currently produces R-1 water that is irrigated on golf courses and median strips over brackish groundwater in the caprock area of the Ewa plain. Previous studies (Dugan and Lau, 1981; Lau, et al., 1975) had been sponsored by the HBWS and the City and County of Honolulu to determine the feasibility of water reuse. The authors concluded that the nitrogen balance results were 60.4 percent uptake by the Bermuda grass, 39.4 percent loss to denitrification, and 0.2 percent leaching (Dugan and Lau, 1981). The authors reported 94 percent removal of total organic carbon (TOC).