Oldcastle retention system sees green light from key agency

Oldcastle Infrastructure (formerly Oldcastle Precast, note companion item) recently announced that its BioMod System received Washington State Department of Ecology equivalency approval as a stormwater bioretention planter or planter box. By granting “functional equivalency,” the agency affirms that the BioMod Modular Bioretention System does not need to go through its Technology Assessment Protocol — Ecology (TAPE) program for approval, and may be designed using the same standards and criteria as any non-proprietary bioretention planter or planter box.


Oldcastle Infrastructure engineered the BioMod system recognizing stormwater management practitioners’ increasing use of soil- and vegetation-based methods, while ensuring hydraulic efficiency plus structural and consistent pollutant removal performance.

Project principals can work directly with Oldcastle Infrastructure to specify the system as a means of meeting Ecology or other agency requirements for bioretention in a complete and pre-assembled precast system. A conventional, vegetated package, BioMod comprises a series of modular precast concrete sections bearing layers of mulch, bioretention media, and drain rock. Standard components include both trench and end modules as well as modules for various inlet configurations, pretreatment, and high-flow bypass. Module count and diameter, as well as each system’s overall configuration, are determined on a site-specific basis. The BioMod system can also be configured as a stand-alone planter box consisting of a single concrete module.

Trench modules can be provided with open bottoms to promote infiltration on site or with closed bottoms and underdrains to connect to downstream storm lines. The BioMod system typically incorporates non-proprietary, low flow rate media with components and thicknesses specified per local regulations. It can harbor a wide variety of plants or trees appropriate to local conditions.

System approval in Washington state and other markets affords designers and engineers “a precast, prefabricated, modular option for stormwater bioretention. [They] can easily follow an agency’s standard bioretention guidance to design a BioMod system to meet the stormwater treatment requirements for their site,” says Oldcastle Regulatory Engineer Joanna Ogintz. “[We] can provide the most cost-effective, complete bioretention system available on the market.”