Prepared for Mystic River Watershed Association by Jeffrey D. Walker, PhD
Summary: Assisted the Mystic River Watershed Association (MyRWA) in the development of a new system for assigning an annual letter grade representing water quality conditions throughout the Mystic River Watershed. The new grading system provides separate grades for each tributary and mainstem based on a 3-year rolling window of indicator bacteria data. The grade is based on a weighted average of dry and wet weather compliance with water quality standards. The results show a wide variation in the compliance and resulting grades for different waterbodies throughout the Mystic River basin. Tributaries tend to have lower compliance than mainstem stations. This new methodology was adopted by the US EPA for assigning annual letter grades for the Mystic River.