HEAVY METAL CONTRIBUTION TO A RESERVOIR FROM STORMWATER PREVIOUSLY TREATED WITH BIOFILTRATION

City planners face the continuous challenge of providing efficient stormwater treatment and storage as impervious surfaces increase with rising development. Stormwater can contain various pollutants, including pesticides, fertilizers, salts, oils, and heavy metals. Biofiltration cells, less formally known as storm gardens, provide an effective option for filtration of stormwater. They have been shown to remove heavy metals and other harmful pollutants from water and mimic the natural hydrologic processes (e.g. infiltration, evapotranspiration) that were present before development. This study focuses on the ability of a specific storm garden to remove heavy metals from stormwater runoff in a suburban neighborhood in Spokane, Washington. After filtration, water is piped to a nearby pond located in an urban park. Potable water is also supplied to this pond year round to maintain water levels and may dilute metal concentrations in the stormwater. Water samples were collected from the pond and levels were tested for 22 metals, such as iron, lead, and arsenic. Alkalinity titrations were also performed on the samples. Concentrations of iron, lead, arsenic, as well as all other metals tested, were below both acute and chronic EPA standards for aquatic life and remained relatively constant over the winter sampling period. Results showed that the metal chemistry of the pond was not significantly affected by incoming stormwater. Further research is necessary to determine the efficiency of storm gardens and how they can improve stormwater quality before water is discharged into nearby waterways.