Water Quality Improvement through Bioretention: Lead, Copper, and Zinc Removal

TLDR

Urban runoff is contaminated by lead, copper, zinc, and other heavy metals from automobile use, building weathering, and atmospheric deposition, and bioretention offers a low‑impact development solution to improve stormwater quality. Bioretention systems, composed of soil, sand, organic matter, and vegetation, were evaluated in pilot‑plant laboratory setups and two existing facilities to assess their capacity to remove low concentrations of lead, copper, and zinc from synthetic stormwater runoff. The studies showed near‑complete removal of these metals—effluent copper and lead below 5 μg/L and zinc below 25 μg/L—with minimal influence from runoff pH, duration, intensity, or pollutant levels, and no significant accumulation expected beyond 15 years.

Abstract

Intensive automobile use, weathering of building materials, and atmospheric deposition contribute lead, copper, zinc, and other heavy metals to urban and roadway runoff. Bioretention is a low‐impact‐development best management practice that has the potential to improve stormwater quality from developed areas. The practice represents a soil, sand, organic matter, and vegetation‐based storage and infiltration facility used in parking lots and on individual lots to treat runoff. Investigations using pilot‐plant laboratory bioretention systems and two existing bioretention facilities documented their effectiveness at removing low levels of lead, copper, and zinc from synthetic stormwater runoff. Removal rates of these metals (based on concentration and total mass) were excellent, reaching close to 100% for all metals under most conditions, with effluent copper and lead levels mostly less than 5 μg/L and zinc less than 25 μg/L. Somewhat less removal was noted for shallow bioretention depths. Runoff pH, duration, intensity, and pollutant concentrations were varied, and all had minimal effect on removal. The two field investigations generally supported the laboratory studies. Overall, excellent removal of dissolved heavy metals can be expected through bioretention infiltration. Although the accumulation of metals is a concern, buildup problems are not anticipated for more than 15 years because of the low metal concentrations expected in runoff.