Stormwater Pond Management: Sizing Pretreatment for Cost Effective Maintenance and Evaluating Remediation Methods

Abstract 1 - Natarajan

As stormwater ponds age and accumulate phosphorus-rich sediments, their ability to retain phosphorus can decline. Reducing sediment phosphorus release from ponds is a major stormwater management challenge because phosphorus is the primary limiting nutrient that drives algal blooms and excessive floating vegetation. The Minnesota Stormwater Research Council funded a project to investigate the overall effectiveness and effectiveness over time of three promising pond remediation techniques: alum treatment, iron amendment of sediments, and enhanced watershed street sweeping. We collected water quality data and performed detailed sediment phosphorus chemistry analysis at several treated ponds over multiple years to determine the impact on sediment phosphorus release and assess the duration a given remediation technique would be effective. The study revealed variations in performance and longevity across the three methods, providing information that can help communities to select cost-effective maintenance strategies for reducing phosphorus export from ponds. 

Abstract 2 - Wilson

Passive stormwater treatment systems often have pretreatment requirements, but the sizing and comparisons between pretreatment options are not well described.  This paper provides a generalized methodology for practitioners for selection and sizing of pretreatment options that uses economic optimization. The pretreatment options included here are: forebays in wet pond systems, deep sump manholes, and shallow catch basin sumps.  Maintenance records from previous research on deep sumps, shallow catch basins, and pond clean-out activities were used to develop this methodology.  Some of the data from these records were then used to aid in the development of a pond sediment-settling model that predicted the effect a pond forebay on pond trapping efficiency.  This information was then included in a simple economic optimization, and presents a simple means to help practitioners choose the optimal size including economic considerations.  This method is shown for three watersheds representing residential watersheds in the Twin Cities Metropolitan Region in Minnesota.  While the development of the methodology to aid practitioners in the selection of appropriate pretreatment systems was the primary focus of the research, results from the data analyzed also point to an optimal pond forebay size for those watersheds modeled.  There appeared to be a similar trend across all systems modeled to have an optimal pretreatment of a forebay that is sized for about 8% of the treatment system wet surface area.