Stormwater and Aquatic Life: Making the Connection Between Impervious Cover and Aquatic Life Impairments for TMDL Development in Connecticut Streams

Stormwater can be a significant source of stressors to aquatic stream biota in many urban areas. The 2006 List of Connecticut Waterbodies Not Meeting Water Quality Standards has a total of 105 stream segments that do not meet aquatic life goals established in Connecticut's Water Quality Standards. At least 58% of these waterbodies have stressors related to urbanization as the suspected cause of the impairment (e.g.stormwater, habitat modifications, erosion, sedimentation etc.). Modeling stormwater impacts can be challenging due to their episodic nature. In many instances, surrogate measures of stormwater impacts may provide useful benchmarks when data are unavailable to support more complex stormwater models. The State of Connecticut, Department of Environmental Protection (DEP), has developed an Impervious Cover (IC) model applicable in situations where the most probable cause of the aquatic life support impairment is stormwater. An IC target of 12% was established for developing Total Maximum Daily Loads (TMDLs) based on correlating the percent IC upstream of macroinvertebrate monitoring locations with a final assessment of passing or failing Connecticut's aquatic life standards. Connecticut DEP has used the IC Model to develop a TMDL for a small stream in Eastern Connecticut and has engaged stakeholders to focus stormwater management efforts to restore aquatic life in the brook.