Investigating Remediation Strategies for Urban Stormwater Ponds Exporting Phosphorus

Recent research has demonstrated that urban stormwater ponds can experience internal phosphorus loading. As primary stormwater runoff treatment practices, the resulting poor water quality can be problematic for the lakes and other sensitive downstream ecosystems that the stormwater ponds are intended to protect. Many remediation strategies are available to pond managers combatting internal phosphorus loading, but effectiveness and cost-effectiveness are difficult to ascertain given the wide variability of stormwater ponds and the small amount of pond-specific management research when compared to lakes and reservoirs. We modeled four stormwater ponds in CE-QUAL-W2 and simulated six remediation scenarios: chemical treatment of sediments with either alum or elemental iron filings, outlet reorientation, mechanical mixing, reduced wind sheltering, watershed modifications to reduce volume and reduce concentration, and bathymetry modifications to enhance volume or surface area. We evaluated the effectiveness of each scenario both qualitatively and quantitatively, and we estimated the cost-effectiveness of each based on practitioner experience. Remediation recommendations for each stormwater pond will vary depending on its unique stresses, context, and performance goals, so we provide a comparison tool that can be used to examine options from multiple perspectives.