Application of a regional screening index for chemical leaching to groundwater vulnerability analysis in the national level

This chapter describes a regional screening index for use in Hawaii which has been recently updated to assess groundwater vulnerability to contamination by volatile organic compounds and pesticides. Specifically, this chapter will discuss two issues: 1) how we assess the accuracy of a new screening index compared to an analytical solution for the movement of contaminants and 2) how we extend the regional index scheme into a national-scale vulnerability assessment. We found that the screening index was able to be used as an initial diagnostic tool for groundwater vulnerability assessment as it consistently provided a conservative estimate of the vulnerability to protect public health. The results of the national-scale assessment also showed that the groundwater vulnerability to agricultural chemicals varied widely among the conterminous 48 states, which demonstrated the feasibility of the regional screening index to a large-scale vulnerability assessment. We present two examples to illustrate the regional and national levels of groundwater vulnerability assessment.