Application of Expanded Shale as Filtration Media in Bioswales for Stormwater Treatment

Urbanization and the expansion of impervious surfaces have increased stormwater runoff volumes, altered runoff timing, and degraded water quality and aquatic ecosystems. Runoff from urban areas carries pollutants such as nitrogen, phosphorus, sediments, and heavy metals, which can adversely impact the physical characteristics of receiving waterbodies. Stormwater management programs aim to mitigate these effects using Best Management Practices (BMPs) to retain and treat stormwater on-site. However, in densely developed areas, space constraints and high costs often make traditional BMPs impractical. This study assessed the effectiveness of expanded shale, an engineered material, as a filtration medium in bioswales, a type of linear BMP commonly used in transportation infrastructure. Thirty scenarios were tested in a 15-ft long plexiglass flume using expanded shale mixed with sandy clay soil. The study evaluated the performance of expanded shale in removing total suspended solids (TSS) and turbidity. Results showed that expanded shale achieved sediment removal efficiencies ranging from 20% to 82% for TSS and -4% to 61% for turbidity under different conditions. Expanded shale outperformed conventional filtration materials such as sand and gravel, requiring less channel length. Remarkably, even in a small-scale laboratory setting, expanded shale met the sediment removal standard of 80%, demonstrating its potential as a highly effective filtration material alternative for urban stormwater management.