Bioretention media modification for heavy metal removal in stormwater: A field study in North Carolina, USA

Stormwater runoff from highly developed catchments has been shown to have a negative impact on downstream water quality. This runoff can contain pollutants ranging from heavy metals, bacteria, and sediment to nutrients and organic compounds. Heavy metals in particular can pose a toxicological risk to flora and fauna in aquatic ecosystems, as well as threaten human health, especially near aquifers and surface water drinking sources. The Energy Independence and Security Act of 2007 recently set more stringent hydrologic and water quality improvement goals for, among other sites, military installations, which, due to their size and function, may be a potential source of heavy metal species in runoff. A two-part study is being performed on multiple bioretention cells at a battalion barracks / company operations facility campus on Fort Bragg, Army Installation in North Carolina.

1. Runoff flowing into existing bioretention inlet flumes was monitored for two months both from a personal vehicle parking lot and an operations facility to compare heavy metal concentrations between the two catchments. The heavy metals tested include: Aluminum (Al), Chromium (Cr), Copper (Cu), Iron (Fe), Manganese (Mn), Lead (Pb), Zinc (Zn), and Copper (Cu).
2. The bioretention cell belonging to the catchment showing the highest concentrations of heavy metals was then refurbished and amended with experimental proprietary media (AEWS Engineering), which is specifically  designed to adsorb and immobilize metal species. This bioretention cell and a control (no experimental media) in the same catchment type are being monitored for one year using a flow-paced composite sampling protocol at the inlets and outlets of both cells.

Specifically, proprietary media amendments were concentrated at key locations of potential
heavy metal exposure, namely the inlet areas and sections directly above the underdrain pipes.
Metal retention was also measured in the media and plant biomass using destructive laboratory
techniques to develop a metal mass balance over time.