| This document highlights the need to treat the discharge of groundwater to surface-water not as a two-dimensional area with static boundary conditions, but as three-dimensional volumes with dynamic transition zones. This ECO Update applies equally to recharge zones and can be used to evaluate advancing plumes that have not yet reached the transition zone. This document encourages project managers, ecological risk assessors, and hydrogeologists to expand their focus beyond shoreline wells and surface sediments and define and characterize the actual fate of contaminants as they move from a strictly ground-water environment (i.e., the commonly used 'upland monitoring well nearest the shoreline') through the transition zone and into a wholly surface-water environment. The approach is presented to help users identify and evaluate potential exposures and effects to relevant ecological receptors within the zone where ground-water and surface-water mix. The transition zone data collected for the ERA may also supplement data collected for the evaluation of potential human health risks associated with the discharge of contaminated ground-water. Should ground-water remediation be warranted (as a result of the risk assessment), the locational, geochemical, and biological aspects of the transition zone can be considered when identifying and evaluating remedial options. |