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Groundwater Recharge and Availability in the Pearl Harbor Aquifer, Oahu, Hawaii
The Pearl Harbor aquifer is the most important aquifer on the island of Oahu and currently supplies about 100 million gallons per day of fresh groundwater mainly for public supply. Decisions related to future infrastructure development and alternate sources of fresh water, including desalinization, will depend on the long-term sustainability of the groundwater resources in the Pearl Harbor aquifer. The current estimate of sustainable yield used by the Hawaii State Commission on Water Resource Management (CWRM) is based on a simple equation that does not account for aquifer heterogeneities and the spatial distribution of withdrawals. Salinity of water pumped by some wells in the eastern part of the Pearl Harbor aquifer have risen in recent years, although recent pumpage from the area is near the CWRM-estimated sustainable yield. It is critically important, from both economic and resource standpoints, to have an accurate understanding of how much fresh groundwater in the Pearl Harbor aquifer can be developed for future needs.
The overall objective of the study is to provide the BWS with a tool that can be used to (1) effectively manage groundwater pumping from the Pearl Harbor aquifer and (2) develop long-range plans for future development of resources in the Pearl Harbor aquifer as well as alternate sources of fresh water. The tool will be in the form of a three-dimensional numerical groundwater model capable of simulating the distribution of salinity in the aquifer and the response of the freshwater lens to user-specified pumping conditions.
Relevance and Benefits
The results from this study are necessary for the proper management of the groundwater in the State. The study is consistent with the USGS Science Strategy to provide scientific information to manage water resources and to protect our quality of life. A water-related mission that supports the overall mission of the USGS is to provide the hydrologic information and understanding needed for the best use and management of the Nation's water resources for the benefit of the people of the United States. This study will provide information needed for water-use permitting and land-use planning.
To meet the objective of this study, the USGS will (1) provide updated estimates of groundwater recharge from infiltration of rainfall and irrigation water in the Pearl Harbor area, (2) refine the estimate of the amount of inflow entering the aquifer, (3) evaluate the hydrologic effectiveness of known and other potential valley-fill barriers in the area, (4) conduct two synoptic water-level surveys, (5) quantify the hydraulic properties of the aquifer, (6) develop a refined numerical groundwater model, and (7) provide training for BWS personnel on the use of the numerical model.