Maryland’s Efforts on Consolidating, Analyzing, And Improving Stormwater Monitoring: Lessons Learned and Next Steps

More than 20 years of in-stream monitoring, including water chemistry, habitat, biological, and physical data, has been collected in Maryland since 1990 to fulfill the requirement of Phase I Municipal Separate Storm Sewer System (MS4) permits. We constructed a database and analyzed the data to better characterize stormwater discharges and evaluate watershed restoration progress. Nearly 97,500 records of chemical parameters and 2000 benthic and habitat monitoring results were included in the database, taken from around 5,000 sampling events at 79 monitoring locations. Initial analysis suggested that the concentrations of many pollutants decreased over time, but a more thorough analysis of three watersheds, selected based on monitoring length and data quality, suggested that no obvious trend over time for most pollutant concentrations. We also found that the current average method tends to underestimate concentrations compared with the flow-weighted concentration method, especially during big storm events. By working closely with academic institutions and other state and federal agencies, we organized several workshops and numerous in-person meetings to build consensus and improve collaboration among counties. During the process we learned the importance of 1) thinking about analysis when designing monitoring methods, 2) setting expectation upfront, 3) including a Quality Assurance Project Plan (QAPP) in the regulatory requirement; 4) incorporating flow data into analyses of; and 5) frequently communicate with local governments in the early permit writing stage. Therefore, we drafted MS4 Monitoring Guidelines for the coming renewal of MS4 permits based on the lesson learned, in which we emphasized the importance of developing and implementing QAPP, promoted the flow-weighted composite method of calculating concentrations, and increased requirements for probabilistic biological monitoring, turbidity monitoring, and conductivity monitoring. The next analysis effort will focus on 1) the effects of flow, land-use change and BMP implementation on pollutant concentrations and trends, and 2) how the current method used to evaluate concentrations may affect results. We also plan to initiate a Network of Control to coordinate current resources and efforts on long-term monitoring to better detect water quality changes, analyze the impact of major events, and evaluate restoration effects.