A Design‐Build Treatment BMP to Address Turbidity and Metals in Industrial Stormwater Runoff
The industrial stormwater permitted site had been challenged in meeting turbidity, zinc, and copper permit benchmarks. In 2012, the site began to implement a more rigorous operational BMP program by sweeping more frequently and cleaning catch basins. The first treatment application included catch basin inserts and downspout filters with media to capture dissolved metals. The results of these treatments lowered the effluent values but not below the benchmark levels in the permit. Source evaluations and water quality characterization sampling was conducted to determine the sources of the contaminants, the percentage of dissolved metals, and the distribution of metals within sediment particles. The bench test showed that a combination of flocculation and filtration removed over 90% of the pollutants of concern. The question remained of how to implement BMPs on site that could provide both filtration of the solid material and pull the dissolved metals out of solution.
On the west side of the facility a swale had historically collected the site runoff prior to discharge. A design‐build approach was taken to enhance the performance of the existing bioswale utilizing the limited space available and a combination of proven technologies. Modifications to the existing infrastructure and equipment were designed using a combination of technologies and principles, including passive bio‐polymer flocculation, multi‐media filtration and adsorption, and low impact development. The system was designed to provide automated water quality monitoring and fail safe measures to prevent any potential non‐compliant discharge from occurring. Upon final completion, the system was designed to operate passively without reliance on pumps, filters or valves. The system was also designed to allow for future adaptation to other pollutants of concern that may require monitoring as a result of permit changes in the future.
The facility was able to implement an engineered solution through the design‐build process that resulted in a custom built system that utilized the natural and existing assets of the site. This provided significant economic benefits. Since installation, the system has achieved benchmarks demonstrating metals reduction over 95% and has provided an effective and efficient approach to address the compliance challenges of the site.