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Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

National Water-Quality Assessment Program ………………………………………………… iv What kind of water-quality information does the NAWQA Program provide? …………… v Introduction to this Report …………………………………………………………………… vi Summary of Major Findings ………………………………………………………………… Stream Highlights ……………………………………………………………………… GroundWater Highlights ……………………………………………………………… Introduction to the Oahu Study Unit ………………………………………………………… Land use is changing from agriculture to urban ………………………………………… Ground water provides public supplies, streams provide aquatic habitat and irrigation water ………………………………………………………………… Drinking-water aquifer is vulnerable to contamination ………………………………… Below-normal rainfall may have affected water quality ………………………………… Major Findings ……………………………………………………………………………… Ground Water …………………………………………………………………………… Organic compounds were detected in most wells, but few concentrations exceeded drinking-water standards ……………………………………… Nutrient concentrations were elevated in agricultural areas but did not exceed drinking-water standards ………………………………………………… Land use and aquifer vulnerability influence groundwater contamination ……… Mixtures of organic compounds were common in ground water ………………… Groundwater contamination in central Oahu reflects decades-old releases and former land use …………………………………………………………… Surface Water …………………………………………………………………………… Contaminants in stream water varied with land use, storms, and groundwater inflow ……………………………………………………………………… Excess nutrients may adversely affect stream and coastal ecosystems ………… Streambed Sediment and Fish Tissue …………………………………………………… Aquatic habitat is degraded by nonpoint-source pollution ………………………… Discontinued organochlorine pesticides persist in the environment ……………… Human activities elevate trace elements in stream sediments …………………… Stream Ecology ………………………………………………………………………… Urban alteration of stream habitat has adversely affected native aquatic species Benthic invertebrates reflect degraded stream quality …………………………… Most identified invertebrates were nonnative …………………………………… Study Unit Design …………………………………………………………………………… GroundWater Chemistry ……………………………………………………………… Stream Chemistry ……………………………………………………………………… Stream Ecology ………………………………………………………………………… References Cited ……………………………………………………………………………… Glossary ……………………………………………………………………………………… Appendix. Water Quality Data from the Island of Oahu, Hawaii, in a National Context ……… National Water-Quality Assessment Program The quality of the Nation's water resources is integrally linked to the long-term availability of water that is clean and safe for drinking and recreation and also suitable for industry, irrigation, and habitat for fish and wildlife. Recognizing the need for long-term, nationwide assessments of water resources, the U.S. Congress has appropriated funds since 1991 for the USGS to conduct the National Water-Quality Assessment (NAWQA) Program. Scientists in the NAWQA Program work with partners in government, research, and public interest groups to assess the spatial extent of water-quality conditions,...

Water-supply managers need adequate warning to protect water supplies if a contaminant is spilled in an upgradient tributary. The city of Lincoln draws water from alluvium associated with the Platte River near Ashland, eastern Nebraska. Using constant-rate injection methods and a conservative tracer, travel time and degree of mixing of contaminants in the Elkhorn and Platte Rivers were evaluated in 1995 and 1996. The results indicate that, for flows of 584 to 162 m 3

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