Finding the Elusive Sites for Hydrodynamic Separators Using Stormwater Master Plan Models

Due to the increasing cost of stormwater treatment, the City of Virginia Beach Department of Public Utilities (City) evaluated the requirements for developing a nutrient offset program. When a stormwater management facility (SWMF) can be incorporated into a site design, it typically comes at a significant cost. Creating regional SWMFs to offset the City’s facility specific nutrient removal requirements will help minimize costs associated with meeting the regulations and meet the stormwater treatment requirements.

The challenge often faced in building a nutrient credit lies in finding feasible sites that meet the multiple criteria for successful construction. The City proactively planned and projected the estimated nutrient offsets required for future improvements at the City sewer pump stations in all City watersheds over the next several years.

Working towards meeting this nutrient goal, the City adopted a tiered approach to find sites for stormwater treatment, with the first tier being looking for sites for hydrodynamic structures. These are manufactured treatment devices requiring smaller footprints and are quick to install if the right site is found. The 100-year simulation results from the calibrated stormwater master plan models were utilized to narrow down potential sites that are suitable for installation of hydrodynamic separators and meet the hydraulic requirements in accordance with the City’s Public Works design standards.

This presentation will walk through the site screening process in a single watershed evaluating potential sites for hydraulic feasibility, location on City owned property or within City right-of-way, treating flow from adequate drainage area and cost per pound of phosphorous removal combined with field investigations leading to selection of successful sites for installation. This approach eliminates hurdles during the design process and allows faster implementation of stormwater treatment projects. The presentation will also provide an overview of one site that was successfully selected and is currently under design.


Purpose: The purpose of this presentation is to provide an overview of the site selection process for stormwater treatment using available stormwater model results and evaluating main design criteria at the screening stage.