REGIONAL-SCALE GROUNDWATER VULNERABILITY ESTIMATES - IMPACT OF REDUCING DATA UNCERTAINTIES FOR ASSESSMENTS IN HAWAII

Nonpoint source ground-water contamination, resulting from regional scale applications of agrichemicals, is a major environmental issue. Several federal and state government funded modeling efforts were undertaken in the 1980s to assess ground-water vulnerability from past and current chemical use and to potentially aid in the regulation of new chemicals. This paper is concerned with the impact of data uncertainties in regional scale pesticide leaching assessments for the chemical diuron in the Pearl Harbor Basin on the Hawaiian island of Oahu. in the first part of the paper uncertainties in soil, recharge, and chemical data are artificially reduced to study the impact of reduced data uncertainties on ground-water vulnerability assessments made with simple mobility indices; the greatest improvements were realized for improvements in the chemical data. In the second part of the paper the impact of improvements to the Hawaii soil data, in the form of new soil organic carbon information, is characterized relative to changes in ground-water vulnerability assessments made with a simple index. The additional soil organic carbon data does not yield improvements to the original vulnerability assessment that would be considered justifiable. The best use of regional scale chemical leaching assessments based upon modeling approaches as simple as index methods is for guiding data collection strategies.