WATER QUALITY AND FLOW PERFORMANCE-BASED ASSESSMENTS OF STORMWATER CONTROL STRATEGIES DURING COLD WEATHER MONTHS

Lack of widespread adoption of Low Impact Development (LID) designs in northern climates is in large part due to concerns about poor winter performance. An examination of six varied LID designs in contrast with conventional BMPs and manufactured systems between 2004 and 2006 illustrated that seasonal functionality was evident for many systems however the LID designs were consistently top performers. The designs were tested and monitored for cold climate performance including filter media frost penetration and resulting hydrographs, seasonal variations on contaminant removal efficiency, and attenuation of chloride pulses associated with melt events. LID systems evaluated include 2 types of bioretention systems, a surface sand filter, a gravel wetland, a tree filter, and porous asphalt. The LID performance data is contrasted with conventional structural BMPs (swales, retention ponds), and some select manufactured stormwater systems. Winter monitoring includes both rainfall runoff data and diurnal melt events. Contaminant event mean concentration (EMC), and performance efficiency were evaluated for storms with varying rainfall-runoff characteristics. Runoff constituent analyses included total suspended solids (TSS), total petroleum hydrocarbons-diesel range (TPH-D)), nitrate (NO3), and total zinc (Zn). Several water quality parameters (temperature, dissolved oxygen, pH, conductivity) were monitored as real-time data. Performance evaluations indicate that LID designs have a high level of functionality during winter months and that frozen filter media appears not be a concern. Trends in chloride attenuation are complex.