WRRCTMR No.80 Groundwater Recharge with Honouliuli Wastewater Irrigation, Ewa Plain, Southern Oahu, Hawaii

Abstract

The Ewa caprock aquifer has been a long-standing water source for southern Oahu, but the freshwater viability of the aquifer is being threatened with the gradual increase in the salinity level of pumped caprock aquifer water in recent years. Concern over enhancing the freshwater quantity and quality of the Ewa caprock aquifer prompted a consortium of agencies to sponsor a demonstration Groundwater Recharge with Treated Wastewater Effluent project. The project, located in a sugarcane field on the Ewa Plain, consists of two California grass plots and four sugarcane plots, each approximately 0.5 acre in size. One of the California grass plots is to receive, by overhead sprinklers, 4 in./day of nearby Honouliuli WWTP primary effluent, 5 days/wk; the other, one-half this application rate. Two of the sugarcane plots are scheduled to receive 10 in. of primary effluent by flood irrigation twice a week, the other two plots, once a week. Shallow and deep monitoring wells within, upstream, and downstream of the plots will be sampled and analyzed for various constituents. Baseline analyses of monitoring wells and Honouliuli WWTP effluent samples have been conducted.