The Madrona Marsh Preserve is a former oil and gas recovery site, but after restoration and enhancement programs from both the City of Torrance and Modular Wetlands Systems, it is now a thriving healthy habitat.

To select an effective treatment method, the City of Torrance paired up with Modular Wetlands Systems (WetlandMod or MWS). The two entities joined efforts to brainstorm and design a feasible filtration system and decided on the WetlandMod, a self-contained treatment train including a pretreatment chamber and a horizontal flow biofiltration system (Fig. 3). The treatment train is built into a modular pre-cast concrete structure that incorporates capture, screening, hydrodynamic separation, advanced media filtration, and biofiltration. The biofiltration process replicates natural processes to remove a variety of pollutants from storm water runoff, including fine total suspended solids (TSS), bacteria, oils and grease, heavy metals, and harmful nutrients like nitrate and phosphorus. To adapt the system to the Madrona Marsh project site, the design team tweaked its original module to incorporate a much larger scale wetland bed to treat various flow volumes from the detention basin for use in the vernal marsh.Construction of the WetlandMod began in October 2011. This included dropping a 22’ precast box that houses a pretreatment chamber and media cartridges (Fig. 4). Contractors excavated a 107’ x 37’ x 3.7’ area for the filtration media bed. The clean soil from the excavation was used on site to restore access roads. The wetland media (lightweight ceramic sorptive media) filled the bed and wetland-specific vegetation was planted. Vetiver grass was chosen for its noninvasive yet vigorous root system, drought tolerance, and pollutant removal capabilities, including removal of dissolved nutrients and heavy metals.

– Full article featured in this issue of “Urban Coast” by Santa Monica Bay Restoration Foundation.

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