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Hanawi Stream near Nahiku, Maui, Hawaii.


Map of Maui showing area included in study
Map of Maui showing location of study area

Ground-Water Data Management, Iao and Waihee Aquifers, Maui, Hawaii

Project Chief: Stephen Gingerich

Project Period: March 2002 through September 2007

Cooperator: Maui County Department of Water Supply

Problem:  The Iao and Waihee aquifers, in the vicinity of Wailuku, Maui, are the source of over 75 percent of the ground water that is pumped for municipal purposes on Maui. The Iao and Waihee aquifers, as delineated by the State of Hawaii Commission on Water Resource Management, are currently pumped at about 18 and 4.6 million gallons per day (Mgal/d), respectively. The Commission on Water Resource Management has set a sustainable yield for the Iao aquifer at 20 Mgal/d. Data has shown that water levels in the Iao aquifer have declined to nearly one-half of the predevelopment water levels, chloride concentrations of the pumped water from at least two of the wells in the area has risen to levels above the U.S. Environmental Protection Agency secondary drinking water guideline of 250 milligrams per liter, and the transition zone of the freshwater lens has risen from about 823 feet in 1985 to 667 feet in 2007. More comprehensive water-resource data are needed to quantify the stress on existing supplies and to better model and evaluate possible water-supply management options.

Objectives:  The objective of this study is to provide quarterly updates of rainfall, pumpage, water level, and chloride-concentration data for the Iao aquifer area.

Relevance and Benefits:  An important part of the USGS mission is to provide scientific information to manage the water resources of the Nation and to enhance and protect our quality of life. The future health and welfare of the Nation's population is dependent upon a continuing supply of uncontaminated fresh water. To help assess Mauiís groundwater resources in the Iao aquifer area, the USGS will monitor rainfall, pumpage, and groundwater levels and chloride concentrations in wells. These data will be used to determine long-term trends in water levels, rainfall, and effects of pumping on water levels and chloride concentrations. The study results will provide some of the information needed by the cooperator and other state and county agencies to implement effective water-resource management decisions.

Approach:  The objective of this study will be met by compiling and reporting trends in rainfall, pumpage, water-level, and chloride-concentration data.

Plans for Fiscal Year 2007:  Continue data compilation and reporting activities. Publish quarterly updates on the World Wide Web at

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