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2009 Virginia Avenue

Hagerstown, Maryland

Owner:

AC&T 

Engineer:

Frederick, Seibert, & Associates

Contractor:

AC&T

Installation:

December 2014

Technical Description:

  • Stormwater Management StormFilter® 

In 2010 Maryland stormwater regulations that introduced the concept of Environmental Site Design (ESD). ESD tasks the engineer and the owner to look to the site first for cues in stormwater management. It requires the site be mapped for sensitive features worth protecting. Once the site has been mapped, the designer is meant to “fingerprint” site improvements that avoid impacting these features. Then, once the site has been laid out, the designer turns to more “structural” means of treating stormwater, both for quality and quantity.

This site development was for a largely impervious layout for the construction of a mini-warehouse storage facility that had very few (if any) natural features required to be mapped per the ordinance.  In order to meet the requirements of both water quality and quantity management using ESD, a large area of the site was dedicated to bio-retention ponds.  

The property owner asked engineer to take a second look at the proposed BMP. Upon further analysis, it became clear a structural solution to this problem was possible. Rather than installing the large bio-retention area, Contech recommended installing a StormFilter, a stormwater treatment system comprised of a concrete structure that houses rechargeable, media-filled cartridges that can treat stormwater to MDE standards.  A 8x11 vault with 22 Cartridges utilizing compost filter media was installed. 

Normally, these concrete vaults with filter cartridges are reserved for urban areas where water is stored in pipes upstream of the structure and slowly drawn through the filter media at a designed rate. In this case the structure was installed directly in the berm of the basin. The only difference is that the storage is taking place in a pond with a grass bottom. 

Runoff will enter the basin via direct sheet flow along the entire basin perimeter adjacent to the pavement. A stone trench at the edge of the pavement is used to settle fines and reduce flow velocity prior to flowing into the pond. There is no traditional underground storm drain other than the outlet pipe from the basin.  As water ponds up in the basin, runoff will drain into the StormFilter structure located in the berm via a small inlet orifice and trash-rack on the outside wall of the structure. Some evaporation of runoff in the basin will occur as it fills and slowly drains, which adds the benefit of at least some minimal volume/runoff reduction. Volume in excess of the ESDv will exit the basin through a new outlet control structure which provides overflow relief. 

Given the circumstances, this design makes sense. With an impervious lining, there is no opportunity for infiltration and recharge of groundwater and so the bio-retention pond is just a filter, discharging clean water at a certain rate. We replaced the bioretention structure with a concrete structure that has filter media inside of replaceable cartridges. At the end of the day, this solution offered all of the same stormwater management benefits for a similar cost and much less maintenance, which is exactly what the developer wanted.  

Technical Description:

  • Stormwater Management StormFilter® 

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