RECOGNIZING SHORTCOMINGS OF CRITICAL SITE CHARACTERIZATION DATA: INSIGHT FROM A STATEWIDE, MULTI-SITE, LEAKING UNDERGROUND STORAGE TANK (LUST) STUDY

The Arizona Groundwater Study was commissioned by the Arizona State Legislature to study leaking underground storage tank (LUST) impacts to groundwater resources in Arizona (http://www.eas.asu.edu/civil/Environmental/Groundwater.htm). The two-year study included: the review of 417 Arizona Department of Environmental Quality LUST facility files with compilation and analysis of relevant data; supplemental studies involving the collection and analysis of over 700 groundwater and 32 free-product samples, assessment of aquifer flow properties at 11 sites, over 300 groundwater level measurements and 175 monitoring well re-surveys, and additional field investigations at six LUST sites; and modeling to identify release scenarios that might endanger groundwater resources.

The LUST file review was the backbone of the study. Data compiled from 335 releases statewide facilitated the analysis of site characterization data, soil and groundwater contaminant concentrations and potential correlations, and relationships between site characteristics and groundwater impacts. Supplemental studies, designed to enhance the understanding of information gathered during the review process, focused on chemical and hydrogeologic characteristics of sites, field investigations to determine the integrity of conclusions drawn from file data analysis, and factors which could lead to erroneous flow direction interpretations. Significant findings which should challenge our traditional considerations of site characterization and screening for impact will be presented. These include: no correlation between soil and groundwater impacts; no correlation between depth-to-water and groundwater impact; significant variation in perceived flow direction over time at sites; and minimal to no downgradient groundwater monitoring of contaminant plumes at the majority of sites.