Green Infrastructure and Practical Accounting of Stormwater Pollutant Load Reductions
- Matthew Jones - Hazen and Sawyer
A variety of tools exist to estimate the performance of stormwater BMPs and their collective impact on receiving water quality; however, supporting documentation for these tools often note that BMP effectiveness estimates are broad representations, subject to variability, and based on limited data. This results in a situation where forecast water quality improvements may not be realized locally, impacting costs and planning strategies. Local monitoring of stormwater controls can address this uncertainty; however, detailed water quality monitoring can be costly and logistically challenging. Because the water quality benefits of green infrastructure are more associated with runoff retention than changes in pollutant concentrations, the performance of these controls can be more easily understood, repeatable, and more readily monitored using simplified approaches.
As part of an assessment of stormwater performance, more than 20 green infrastructure retrofits have been implemented and monitored for more than 2 years, forming a comprehensive area-wide performance evaluation. Utilizing robust and relatively inexpensive remote monitoring equipment, such as battery powered water level loggers, monitoring efforts at these locations have readily demonstrated substantial reductions in stormwater runoff volumes. Quantifying these runoff volume reductions provides an accounting framework for pollutant load reductions without costly water quality sampling. In addition to measurements of runoff volume reduction, limited water quality sampling has provided insight into the applicability of typical pollutant concentrations.
In total, pilot efforts have demonstrated how to overcome logistical and technical challenges associated with monitoring the performance of green infrastructure controls, valuable information regarding the performance of these controls, and how that monitored performance can be translated into accountable pollutant load reductions. Utilizing the information that results from such a green infrastructure monitoring initiative, stormwater planning efforts can be better informed, cost-effectiveness of implementation efforts can be optimized, and local water quality improvements can be directly accounted for.
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