This website is part of Dr. Allen Davis' Bioretention home page.

Summary: In 1996, a two-year study was initiated to quantify the effectiveness of bioretention in terms of pollutant removal efficiency. The study included laboratory column studies, box bioretention prototype studies, and field studies of existing bioretention facilities in Greenbelt, Maryland and Largo, Maryland. It was completed in 1999. Findings are summarized on the website. Two manuscripts have been published describing this work. One manuscript is cited separately on this page: "Water Quality Improvement Through Bioretention: Lead, Copper, and Zinc Removal." The other manuscript, not available online, is cited below.

Summary: The objectives of this study, conducted between August 2000 and March 2004, were to test the effectiveness of bioretention for treatment of urban storm water runoff by employing laboratory bioretention columns and on-site bioretention evaluations. 46 column studies and 8 on-site bioretention evaluations were used to investigate tradeoffs between infiltration rates and pollutant removals in the use of various media and media mixtures in bioretention. Findings are summarized on the website.

Partial abstract: The effectiveness of bioretention in treating repetitive inputs of runoff has not [previously] been investigated. In this study, a bioretention test column was set up and experiments proceeded once every week for a total of 12 tests. Through all twelve repetitions, the infiltration rate remained constant (0.35 cm/min). All twelve tests demonstrated excellent removal efficiency for TSS, oil/grease, and lead (>99%). For total phosphorus, the removal efficiency was about 47% for the first test, increasing to 68% by the twelfth test. For ammonium, the system removal efficiency ranged from 2.3% to 23%. Effluent nitrate concentration became higher than the influent concentration during the first 28 days and removal efficiency ranged from 9% to 20% afterward. Some degree of denitrification was apparently proceeding in the bioretention system. Overall, the top mulch layer filtered most of TSS in the runoff and prevented the bioretention media from clogging during 12 repetitions. Runoff quality was improved by the bioretention column.

This document is not available online. Dr. Allen Davis was the principal investigator.

Partial abstract: 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 the runoff.