Assessing the Water Quality Performance of Limestone Media in Bioretention and Sand Filter Basin Testbeds

Abstract

Low impact development (LID) practices are commonly used stormwater control measures (SCMs) designed to mimic the predevelopment hydrologic regime by restoring the natural water cycle and enhancing water quality. A full-scale LID testbed was designed and implemented to evaluate the performance of bioretention and sand filter basins under the same conditions. The LID testbed is composed of six parallel cells including (1) a regional standard bioretention soil mixture, (2) an innovative custom blend bioretention soil mixture with limestone sand, and (3) sand filter basins with limestone sand as filtration media. Each filtration media design was tested with and without an impermeable liner, to investigate the potential impacts of the direct infiltration on their water quality performance. The treatment performance was evaluated through series of water quality analyses comparing the event mean concentrations (EMCs) of the inlet and outlets. The results suggested enhanced pollutant removal efficiencies by use of limestone sand in the bioretention mixture as well as a standalone media within the sand filter basins, particularly for phosphorus. We observed 82%–93% and 97%–94% removal of dissolved and total phosphorus, respectively, and the regional bioretention soil mixture presented leaching of nutrients. No significant difference was observed between the water quality performance of sand filter and bioretention basins, or between lined and unlined systems.