Verdantas (formerly Alden Research Laboratory) conducted verification testing of two full-scale stormwater treatment units—the DM1200 and DM1200-OS (oil separator)—at its Holden, Massachusetts facility. These 4-ft diameter Diskman units were evaluated to determine their hydraulic and pollutant removal performance under controlled laboratory conditions. The only geometric difference between the two models was the weir height, which was reduced from 9 inches to 6 inches in the oil separator version to enhance oil capture capabilities.

Testing followed the Canadian ETV Program’s “Procedure for Laboratory Testing of Oil-Grit Separators (2014),” a rigorous protocol designed to assess stormwater treatment technologies. Verdantas focused on five key performance areas: hydraulic characteristics, sediment scour, sediment removal efficiency, light liquid re-entrainment, and particle size distribution. The test setup included a recirculating flow loop capable of delivering up to 10 cfs, with metered flow supplied by laboratory pumps and sediment injected upstream of the unit through a custom tee configuration. Background concentrations were minimized using inline filtration, and all sediment dosing and sampling followed the CETV protocol. All samples and collected sediment were processed in accordance with ASTM standards.

Hydraulic testing showed that both units maintained low head loss, with a maximum calculated unit loss of 0.11 meters. Sediment removal efficiency was evaluated across a wide range of surface loading rates (SLRs), from 40 to 1400 L/min/m², using silica-based sediment with a defined particle size distribution from 1 to 1000 microns. The DM1200 achieved removal efficiencies ranging from 29.7% to 67.7%, while the DM1200-OS ranged from 28.7% to 67.7%, demonstrating consistent performance across both models. Sediment scour testing on the DM1200 revealed minimal washout, with effluent concentrations ranging from 0 to 3.4 mg/L even at high flow rates.

A particularly noteworthy result came from the light-liquid re-entrainment testing of the DM1200-OS. Using plastic beads as a surrogate for oil, the unit retained 99.9% of the pre-loaded material across all tested flow conditions, confirming its effectiveness in capturing and holding hydrocarbons under dynamic flow scenarios.

Through this testing program, Verdantas provided validated performance data that supports the reliability and effectiveness of the Diskman stormwater treatment units and confirms compliance with CETV standards.