Technical Evaluation of Natural Resources Damage Assessments (NRDA) of Groundwater Resources

To support a Natural Resource Damage Assessment (NRDA) for groundwater resources impacted by oil or hazardous substances, careful technical evaluation is required to define the nature and volume of the affected groundwater zone and the associated impact on the potential services provided by the affected aquifer and other interconnected water resources. Relative to the baseline beneficial use for which the groundwater resource was suitable prior to the impact, such loss of service may involve both: i) the loss of aquifer “storage,” i.e., the reduction in the volume of groundwater available for beneficial use, and ii) the potential loss in the “future yield” of the aquifer system, i.e., the reduction in the rate at which usable water can be produced due to the presence of the affected groundwater zone. Key technical considerations in this analysis include the actual and predicted water use activities, the nature and extent of the affected water zone, the hydrogeologic properties of the aquifer system and its interconnection with surface water resources, the ability for natural attenuation to restore lost beneficial use, the effectiveness of on-going remediation efforts, the applicability of ex-situ water treatment technologies to meet beneficial use criteria, and the relative contributions of different parties. Based on case studies of alleged damage claims, this paper provides practical guidelines for evaluation of losses in storage and potential future yield, considering each of these key factors and providing recommendations for appropriate use of tools such as Geographic Information Systems (GIS) and associated databases, groundwater data evaluation and interpolation methods, and groundwater fate-and-transport modeling.