Ten years of MS4 monitoring: what have we learned?

Collecting stormwater samples representative of the Municipal Separate Storm Sewer System (MS4) is challenging and expensive. The intermittent nature of discharges, varying attributes of the drainage areas, diffuse nature of potential sources, and the large temporal and spatial distribution of implemented management practices make it difficult to identify specific sources and implement effective management actions through periodic sample collection from a few sites. For over ten years, Clean Water Services (CWS) has conducted stormwater monitoring at five locations for at least three representative storms to comply with the regulatory monitoring requirements issued to CWS in the National Pollutant Discharge Elimination System (NPDES) permit. Each location attempt to represent a single dominant landuse. The samples are analyzed for fifteen different water quality constituents to help characterize the runoff from the landuse contributing to the location. However, analysis of the current drainage areas of the sites has showed a lack of representation for the variability of the MS4 system. Analysis of the last ten years of data has likewise shown that an updated approach to MS4 monitoring and modeling is needed to better characterize the water quality of the urban stormwater, evaluate the effectiveness of the last few decades of MS4 management, and inform the future direction of our MS4 monitoring and adaptive management strategy to better protect water quality of urbans streams and rivers. This presentation will focus on the findings from this analysis and identify practicable solutions to address an adaptive approach to our MS4 monitoring, modeling, and management strategy.