A Pragmatic Approach to Measuring Stormwater Program Effectiveness
Water quality sampling remains a common requirement in MS4 permits to assist stormwater managers in assessing the effectiveness of their overall program. Traditional monitoring approaches have several limitations that we believe can be overcome by creating experimental designs that address well-defined monitoring objectives. We present an innovative and practical approach to focused stormwater quality monitoring to definitively evaluate if urban stormwater runoff volumes and pollutant loads to receiving waters are decreasing over time. Our experimental design has three objectives: (1) generate results and provide information directly to stormwater managers on time scales relevant to them; (2) isolate the signal of management actions from hydrologic variability and other noise in measured datasets; and (3) be fiscally feasible for stormwater programs to implement consistently over a sustained time-period. We achieve these three objectives by monitoring water quality on a spatial scale relevant to municipal stormwater discharges and employing methods that cost-effectively capture, and thus remove, the noise inherent in water quality data to isolate the signal we care about – that due to stormwater program actions.
2NDNATURE is currently working with the City of Salinas to revise its stormwater monitoring program. Our experimental design is a holistic approach to data collection, management, analysis and reporting that is fiscally feasible and yields data to support informed programmatic decisions. While the ultimate motivation of MS4 permits is to protect receiving water beneficial uses, our ability to measure the response of the receiving water due to effective stormwater program actions will depend upon the geographic context and proportional contribution of the MS4 relative to other sources. In many instances, there are other contributing water quality impairments beyond the control of the MS4 stormwater manager. Monitoring at the discharge point of urban drainages to the receiving water is where we can most easily detect the signal of effective stormwater program actions.
Effective actions encouraged under integrated water management strategies (i.e., stormwater capture, recharge, retention, etc.) will result in measurable changes in the urban hydrograph. We employ cost-effective automated instruments to measure 10 min discharge the flashy discharge from an urban drainage. Coupled with relevant precipitation data, the stormwater hydrology data alone allows insightful trend analyses of the urban hydrograph changes (e.g., annual and event % runoff, peak rate, and total volume). The high-resolution hydrology also provides the foundational data needed to track changes in pollutant loading. Temporal hydrologic variability introduces profound noise in constituent concentrations obtained with grab samples. Automated samplers present the opportunity for flow-weighted composite sampling, but are costly to purchase, maintain and operate properly. The samplers also require expertise to manage, analyze and transform the data into reliable pollutant load values and extrapolate these data to unsampled flows. We employ low-cost passive sampling techniques to maximize the precision in the sample concentrations obtained, minimize the subjectivity in pollutant loading analyses, and easily extrapolate to unsampled flows for the year. A statistical correction of the hydrologic variability in the pollutant loads allows trend evaluations of the changes in the pollutant loading time-series due to management actions. Using this approach, we have reduced the annual cost of the City of Salinas Phase I monitoring program while obtaining data that is an easily communicable measure of the program’s performance and inform adaptive management.
Nicole leads the 2NDNATURE team of scientists, engineers and software developers to bring practical solutions to the field of integrated water management.