Evaluation of Transitional Performance of a Stormwater Infiltration Basin Managing Highway Runoff

Abstract

Infiltration basins are widely employed stormwater control measures (SCMs) to manage and treat urban stormwater runoff. However, these SCMs experience progressive failure and the environmental functionality of such `failed' infiltration basins in managing stormwater runoff is unknown. The purpose of this research study was to systematically quantify through field-scale research, the hydrologic and water quality performances of a failed infiltration basin facility managing highway runoff in Maryland, U.S.A. Stormwater runoff flows were continuously monitored and representative runoff samples were collected during storm events and for time periods between events over a three-year research period. Runoff samples were analyzed for a suite of pollutants including total suspended solids, nitrogen species, phosphorus, heavy metals, and chloride, that are of greatest concern in roadway runoff. The hydrologic and water quality performances were quantified using appropriate performance metrics and compared to established goals. The research study showed that the failed infiltration basin was naturally transforming into a wetland and/or wetpond-like practice and possessed both hydrologic management and water quality functions. The transforming infiltration basin effectively reduced the highway runoff flows by providing dynamic flow attenuation, and total volume and peak flow reductions. Water quality improvements were achieved through reductions in the mean pollutant concentrations and pollutant mass for all water quality parameters during both storm events and dry-weather periods. The discharge concentrations met the established water quality goals for all pollutants except total phosphorus. Comprehensive analysis of various pollutant species, coupled with hydrologic analysis and characterization of environmental conditions in the infiltration basin during different seasons and storm characteristics, showed that sedimentation, adsorption, and denitrification were the main mechanisms controlling water quality at the facility. The infiltration basin also provided ancillary benefits such as wildlife habitat, which added an overall ecological value to the facility. The transforming infiltration basins providing both hydrologic and water quality functions must be considered as functioning, innovative SCMs. Results and research information obtained from this study are applicable for assessing similar SCM facilities and improve understanding of SCM performances and designs. Ultimately, the knowledge obtained will lead to widespread and reliable implementation of SCMs for improved environmental quality.