We have previously reported the revision of a GIS-based pesticide leaching tool in Hawaii that can begin to assess regional groundwater vulnerability to new agrochemicals such as volatile organic compounds (VOCs). The updated tool includes two additional terms in the screening indices to account for volatilization loss from soils, illustrating the leaching potential of the VOCs using three (chemical, soil, and recharge) benchmark properties which are widely available. In the present study, we will discuss the validation of our statewide assessment tool with its extended use of national-scale vulnerability assessment. The statewide tool was examined with two different types of analytical (STANMOD) and numerical models (HYDRUS) in a given set of local conditions. Extensive soil and recharge databases for the conterminous United States, along with national-level fertilizer and pesticide sale data, were compiled to assess groundwater vulnerability on a national scale. Tentative findings from our ongoing research showed that the statewide tool provides an acceptable level of prediction accuracy with other models at high convective velocities (e.g., more recharge). However, the result of national-scale vulnerability assessed by the state level tool was quite different from that of a hybrid model used by the USGS (combining statistical model and GIS, often referred as WARP), due mainly to low recharge rates in the mid-part of the continental US. Therefore, this study highlights the importance of determining accurate annual groundwater recharge amounts for assessing groundwater pollution potential, especially for national-scale vulnerability assessment. At the end of this study, an alternative screening tool using the Meta Model that reduces the dimensionality of input data in the numerical model with neural networks is briefly discussed.

Validation and extension of a regional groundwater vulnerability assessment tool in Hawaii for agrochemicals at a national scale

246th National Meeting (2013)

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