The Response of the Iao Aquifer to Ground-Water Development, Rainfall, and Land-Use Practices Between 1940 and 1998, Island of Maui, Hawaii

The complete report is available as an Adobe Acrobat (.pdf) file (2,226 Kb).

The complete report requires Adobe Acrobat Reader (free) to be viewed.

Abstract

Ground water pumped from the Iao aquifer has been used for agricultural purposes since 1948, and domestic purposes since 1955. In 1990, the Hawaii State Commission on Water Resource Management established a value of 20 million gallons per day for the sustainable yield of the aquifer. Water-level data from observation wells throughout the aquifer and information on the depth to and thickness of the transition zone between freshwater and saltwater at the Waiehu deep monitor well indicate that pumping rates near the sustainable yield value of 20 million gallons per day could result in salt-water intrusion in some pumped wells.

Since the introduction of pumpage in 1948 and the reduction of recharge in 1980, water levels have declined, chloride concentrations of the pumped water have increased, and the transition zone between freshwater and saltwater has risen. Water levels declined by about 18 feet between 1940 and 1998 in the area near Iao Stream, and by as much as 6 feet between 1977 and 1997 in the vicinity of the major well fields near Waiehu Stream. Chloride concentrations of pumped water have risen at all the well fields, but are presently below the U.S. Environmental Protection Agency recommended standard of 250 milligrams per liter. The chloride concentration of water pumped from Mokuhau 2, however, was 460 milligrams per liter in late 1996 when pumping was halted at this well. The midpoint of the transition zone, as measured at the Waiehu deep monitor well, rose by about 108 feet between 1985 and 1998.

  CONTENTS

• Abstract
• Introduction
• Purpose and Scope
• Well-Numbering System
• Previous Geohydrologic Studies
• Description of the Study Area
• Physical Setting
• Climate, Rainfall, and Fog Drip
• Irrigation Ditches
• Geology
• Hydrology
• Ground-Water Occurrence and Movement
• Dike-Impounded System
• Freshwater-Lens System
• Perched System
• Effect of Land-Use Change on Ground-Water Recharge
• Ground-Water Development
• Aquifer Response to Pumpage, Rainfall, and Land-Use Changes
• Water-Level Changes Since the Introduction of Pumping
• Water-Level Changes Relative to Rainfall
• Movement of the Freshwater/Saltwater Transition Zone
• Changes in the Chloride Concentration of Pumped Water
• Sustainable Yield
• Summary and Conclusions
• References Cited

The complete report is available as an Adobe Acrobat (.pdf) file (2,226 Kb).

Abstract from: Meyer, William, and Presley, T.K., 2001, The Response of the Iao Aquifer to Ground-Water Development, Rainfall, and Land-Use Practices Between 1940 and 1998, Island of Maui, Hawaii: U.S. Geological Survey Water-Resources Investigations Report 00-4223, 60 p.