About Subsurface Gravel Wetland
General Information Performance Data Water Quality Treatment Process Design


click to enlarge


Back to List of Evaluated Treatments

Water Quality Treatment Process

1. Runoff flows into a forebay, which removes large objects and allows larger-sized sediment particles to settle.

2. Runoff exits the forebay through a perforated standpipe and flows into the vegetated treatment basins, where it is treated through a variety of physical, chemical, and biological processes.

3. Perforated riser pipes in the treatment basins conduct water to the subsurface gravel layer. There, biological treatment occurs through the uptake of pollutants by vegetation and microbial activity within the root system. Physical and chemical treatment—the trapping of contaminants—occurs on and within the gravel filter media and root mat. Other treatment processes include sedimentation, transformation through reduction/oxidation, and sorption with organic matter and mineral complexes.

4. Treated runoff exits to the surface via an outlet pipe that includes an elevated invert located eight inches below the wetland surface. This insures that the soil is nearly continuously saturated—a condition that promotes vegetation growth and water quality treatment.