Nontraditional BMP in Narrow ROW


  • Public Utilities


  • Engineering
  • Roadways + Interchanges
  • Transportation
  • Water
  • Water Resources


  • Maryland Heights, Missouri

Essex Avenue is a residential street in Maryland Heights, Missouri. Prior to its reconstruction, Essex Avenue was an asphalt/chip-and-seal roadway with open drainage. The City reconstructed Essex Avenue (approximately 1,900 feet) to bring it to current City design standards, including concrete pavement, integral vertical curb and enclosed drainage.

Essex Avenue was one of the first roadway projects in St. Louis to satisfy the water quality stormwater requirements of the Metropolitan St. Louis Sewer District (MSD). These requirements center on the treatment of stormwater runoff before discharge into natural waters. Because this project was located in a developed residential area, space for traditional “Best Management Practices” (BMPs) such as rain gardens or detention ponds was unavailable.

HR Green solved this problem through the use of proprietary hydrodynamic separators (HDS). Each HDS is a rectangular concrete tank with three chambers. The first chamber swirls the water to separate suspended solids from the water. The second chamber collects floatables for removal. The flow controls in the final chamber ensure capture pollutants are not lost during large storm events. The treated water flows through an outlet pipe, back into the storm sewer system for eventual discharge downstream.

Because the HDS units are underground, they do not significantly affect the appearance of the landscape. Consequently, the Essex Avenue project was able to minimize environmental impacts, while also minimizing impacts to private property.


ACEC Missouri – Grand Award

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