During the past 25 years, our Nation has sought to improve its water quality; however, many water-quality issues remain unresolved. To address the need for consistent and scientifically sound information for managing the Nation's water resources, the U.S. Geological Survey began a full-scale National Water-Quality Asseswsment (NAWQA) Program in 1991. This program is unique compared with oher national water-quality assessment studies in that it integrates the monitoring of the quality of surface and ground waters with the study of aquatic ecosystems. The goals of the NAWQA Program are to (1) describe current water-quality conditions for a large part of the Nation's freshwater streams and aquifers, (2) describe how water quality is changing over time, and (3) improve our understanding of the primary natural and human factors affecting water quality.

Assessing the quality of water in every location of the Nation would not be practical; therefore, NAWQA Program studies are conducted within a set of areas called study units. These study units represent the diverse geography, water resources, and land and water uses of the Nation. The island of Oahu, Hawaii, is one such study unit designed to supplement water-quality information collected in other study units across the Nation while addressing issues relevant to the island of Oahu.