The NAWQA study design for ground water focuses on water-quality conditions in major aquifers with emphasis on recently recharged ground water associated with present and recent human activities. Study-unit surveys are used to assess the water quality of the major aquifer systems of each study unit. About 20 to 30 existing wells are randomly selected for sampling. Groundwater samples are analyzed for major ions, nutrients, pesticides, volatile organic compounds, and trace elements.

A study-unit survey (SUS) was conducted in the summer of 2000 to assess the quality of water from 30 drinking-water wells in the central Oahu groundwater flow system (see map below).

A special study (SPCG) was conducted in the summer of 2001 to supplement the study-unit survey by sampling 15 existing monitoring wells for young, newly recharged water from forested, agricultural, and urban areas of Oahu’s main drinking-water aquifer. The objective of this study was to assess the age and quality of ground water in the shallow irrigation-return layer of central Oahu. 

Chemicals analyzed and detected by Oahu groundwater sampling, 2001-2001