1606 SE EVERETT MALL WAY ANTHEM SELF STORAGE 2025-07-25

I I Findings of Fact: • Influent TS S concentrations and particle size distributions were generally within the 1 range of what would be considered"typical" for western Washington (silt to silt loam). • Contech sampled thirty-two (32) storm events at two sites for storms from April 2003 to March 2004, of which Contech deemed twenty-two (22) as"qualified" and were therefore included in the data analysis set. • Statistical analysis of these 22 storm events verifies the data set's adequacy. • Analyzing all 22 qualifying events,the average influent and effluent concentrations and aggregate pollutant load reduction are 114 mg/L, 25 mg/L, and 82%, respectively. • Analyzing all 22 qualifying events based on the estimated average flow rate during the event(versus the measured peak flow rate), and more heavily weighting those events near the design rate(versus events either far above or well below the design rate) does not significantly affect the reported results. • For the 7 qualifying events with influent TS S concentrations greater than 100 mg/L, the average influent and effluent concentrations and aggregate pollutant load reduction are 241 mg/L, 34 mg/L, and 89%, respectively. If the 2 of 7 events that exceed the maximum 300 mg/L specified in Ecology's guidelines are excluded,the average influent and effluent concentrations and aggregate pollutant load reduction are 158 mg/L, 35 mg/L, and 78%, respectively. • For the 15 qualifying events with influent TSS concentrations less than 100 mg/L,the average influent and effluent concentrations and aggregate pollutant load reduction are 55 mg/L, 20 mg/L, and 61%,respectively. If the 6 of 15 events that fall below the minimum 33 mg/L TSS specified in Ecology's guidelines are excluded, the average influent and effluent concentrations and aggregate pollutant load reduction are 78 mg/L, 26 mg/L, and 67%,respectively. • For the 8 qualifying events with peak discharge exceeding design flow (ranging from 120 to 257%of the design rate), results ranged from 52%to 96%TSS removal,with an average of 72%. • Due to the characteristics of the hydrographs, the field results generally reflect flows below (ranging between 20 and 60 percent of)the tested facilities' design rate. During these sub-design flow rate periods, some of the cartridges operate at or near their individual full design flow rate(generally between 4 and 7.5 GPM for an 18" cartridge effective height)because their float valves have opened. Float valves remain closed on the remaining cartridges,which operate at their base "trickle"rate of 1 to 1.5 GPM. • Laboratory testing using U.S. Silica's Sil-Co-Sil 106 fine silica product showed an average 87% TSS removal for testing at 7.5 GPM per cartridge(100% design flow rate). • Other relevant testing at I-5 Lake Union, Greenville Yards (New Jersey), and Ski Run Marina(Lake Tahoe) facilities shows consistent TSS removals in the 75 to 85% range. Note that 1-5 Lake Union was operated at 50%, 100%, and 125%of design flow. I CONTECH-StormFilter®GULD Maintenance Update(November 2012) Page 16 I