Roux Associates was commissioned to develop design plans and specifications for a Constructed Treatment Wetland (CTW) stormwater treatment system at a large railroad terminal in Norfolk, Virginia. The system was designed to treat contaminated stormwater runoff generated from maintenance and fuel handling areas on site. The design performance treatment objective was the reduction of total suspended solids, oil & grease, and selected metals to levels below the SPDES permit discharge standards established for the site. The final design consisted of a 3-acre subsurface-flow type CTW with a low visual impact and high geotechnical loading strength to meet the needs of a busy railyard facility.

The CTW treatment facility is sized to accommodate a minimum hydraulic loading rate of 85,000 gpd based on a three-day hydraulic retention time for removal of the constituents of concern. A total treatment capacity of up to 220,000 gpd is provided to accommodate first flush runoff from storms of up to 100-year return frequencies. Stormwater flows in excess of the design treatment capacity are be bypassed to an existing outfall.

The treatment system consists of multiple lined subsurface flow CTW cells arranged to accommodate both series and parallel flow configurations. Flow through the system is entirely passive with effluent released to a nearby river via a permitted outfall.