A graphical approach for determining dilution-attenuation factors: Basic theory and approach for submerged sources

The dilution attenuation factor (DAF) is a quantity used to relate the concentration of leachate leaving a source zone (e.g., landfill, impoundment, or contaminated soils) to its impact on down-gradient ground water quality. The DAF is of importance because it plays a key role in U.S. Environmental Protection Agency (EPA)'s methodologies for developing soil cleanup goals and for managing hazardous wastes. In this work, a simplistic graphically-based approach for determining site-specific and generic DAFs was developed. In this case the DAF is based on time- and vertically-averaged concentrations along the plume centerline, and the mathematical framework employs well-known analytical and semian-alytical solutions for dissolved contaminant transport. Finite sources with a range of decay characteristics are allowed for. One unique feature of this work is that the graphical approach allows for varying levels of site-specificity, and thus can be used when one has a little, or a lot, of site-specific information. The graphs visually indicate the sensitivity to various parameters, which is valuable information not easily gleaned from most numerical software simulators. This approach is, however, not applicable to very complex hydrogeologic settings (e.g., fractured geology), or to ground water flows that cannot be reasonably approximated as one dimensional.