W6 AM Evaluation of Groundwater Communication with Surface Water and Contributions to Sediment Toxicity
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 324-326

(GRE-1117-807212) Framework for Incorporating Ground Water Communication with Surface Water Into Ecological Risk Assessments.

Greenberg, M^{1, 2}, Duncan, P¹, ¹ U.S. EPA² Wright State University, Dayton, OH, USA

ABSTRACT- The evaluation of the ground water-surface water communication in the context of site characterization and ecological risk assessment has recently emerged as a challenging issue in the management of contaminated sediments. The Ecological Risk Assessment (ERA) process requires evaluation of exposure and effects to characterize risk. However, without knowledge of the fate, transport and exposures from contaminated ground water within the transition zone (TZ) in the sediments between the ground and surface waters, this process is prone to uncertainty. Risks from contaminants in ground water can be evaluated using a flexible, cost-efficient, tiered approach that is consistent with the existing ERA process. First, the conceptual site model is extended to include consideration of the TZ during problem formulation. This is accomplished through: (1) review of the available chemistry data for the site; (2) addressing fate and transport to determine if there is ground water-surface water interaction and exchange at the site; and (3) selecting potential assessment and measurement endpoints for use in the ERA. The risks from contaminants in groundwater are determined through the following tiered process: (1) comparing existing well, piezometer, or interstitial water concentrations against appropriate screening values; (2) evaluating exposure point concentrations in the TZ; and (3) evaluating exposure and effects using organisms (e.g., toxicity testing in lab or field, community analysis) or models. This approach, which combines chemical, biological and hydrological measurements, provides a more accurate description of complete exposure pathways in aquatic systems containing contaminated groundwater discharges to a surface water body. It also provides a scientifically defensible approach to determine existing or potential adverse effects. This presentation will discuss case studies as well as a decision tree to demonstrate the application of the framework.

Key words: ground water discharge, ecological risk, decision tree, ground water surface water communication