Maximum Extent Practical Stormwater Treatment Utilizing ASCE Water Quality Capture Volume Methodology

The development of a vault type stormwater treatment system that would achieve pollutant reduction to the Maximum Extent Practical (MEP) began in 1999. The Stormvault^TM Mitigation System has met that goal, utilizing the "Water Quality Capture Volume" (WQCV) sizing criteria as documented in "Urban Runoff Quality Management", WEF Manual of Practice No. 23 and ASCE Manual and Report on Engineering Practice No. 87. Third party monitoring of over 60 individual storm events confirms pollutant removal capabilities of Stormvault's ASCE sizing method. The tests document TSS pollutant discharge quality is superior to the listed removals comparable to traditional stormwater BMPs. The Mean WQCV is shown to be optimized to promote capture of approximately 86 percent of the average annual total suspended sediments in normal urban stormwater and detention time. The third party testing of the Stormvault^TM demonstrated that the ASCE "mean" WQCV criteria, utilizing the innovative patented baffle configuration, completely captures and treats up to 77% of the runoff hydrograph events for each design locale including the "first flush" of larger events. This ASCE mean event capture volume significantly reduces erosion and stream degradation from increased flows due to urbanization and helps restore pre-development runoff rates. Empirical calculations illustrate the Stormvault's ability to provide capture of TSS particles less than 70 microns in size and the retention of additional pollutants of concern such as heavy metals, nutrients and chemical oxygen demand.