Risk Evaluation of Discharge to Surface Water

SRS staff prepared a complex risk assessment for a site in which a catch basin served as a preferential pathway and discharged into a culvert, which then discharged into an adjacent stream.  Assessment of a recreational user of the stream and the stream itself was strategically evaluated in two parts.  One part was the direct discharge from the culvert and the other part was diffuse discharge of groundwater upstream of the culvert discharge point.  A site-specific surface water concentration was back-calculated for the recreational user under several scenarios (varying dermal exposure) in order to determine an acceptable surface water concentration that would be below an acceptable risk benchmark.