Prescription for Storm Water Management

Designing a storm water management system at a New Jersey pharmacy

Storm water management

Three storm water treatment devices were used at the Walgreens pharmacy. 

The redevelopment of Olden Avenue in Ewing, N.J., has resulted in a number of new businesses entering the area, including a new Walgreens pharmacy. The new store measures approximately 14,340 sq ft, and has a parking lot with 56 parking spaces.

Design Challenges

Designing a storm water management system for this site presented a number of challenges.

Because of invert constraints, it was necessary to tie the proposed storm water conveyance system to the existing infrastructure so the existing headwall at the discharge point could be left undisturbed. Also, because a portion of the site is within a floodplain, a net fill calculation with a New Jersey Department of Environmental Protection (NJDEP) Individual Permit was required.

In addition to township-level approval, the project had to be reviewed and approved by NJDEP and the Delaware & Raritan Canal Commission, each of which has stringent rules and regulations regarding storm water management and water quality for the development.

This filter was used in an area of the site with depth limitations, providing high-flow pretreatment and membrane filtration.

Technology Suite

Contech provided three treatment devices for the site: a CDS hydrodynamic separator, a peak diversion storm water management StormFilter, and a Jellyfish filter. Each system treats a different area of the site. Because a detention basin could not be used on the site, all units were sized per the peak runoff rate for a NJDEP water quality storm.

The hydrodynamic separator was used on a portion of the site that was previously developed and required 50% total suspended solids (TSS) removal. The hydrodynamic separator uses swirl concentration and continuous deflective separation to screen, separate and trap trash, debris, sediment and hydrocarbons from storm water runoff.

The two remaining areas needed to achieve 80% TSS removal per NJDEP regulations regarding major development of previous pervious land. Contech worked with the engineers to leverage the design advantages of the filters to develop the most economical design.

A peak diversion StormFilter was used in an area of the site with ample rim to invent elevation. The filter uses rechargeable, self-cleaning, media-filled cartridges to absorb and retain pollutants from storm water runoff. It provides offline bypass and treatment in one structure, eliminating the cost and installation of structures to bypass peak flows. The filter cartridges were filled with perlite, a form of expanded volcanic rock. The media’s porous, multi-cellular structure and rough edges make it effective for removing TSS, oil and grease.

A Jellyfish filter with a hatch was used in an area of the site that had depth limitations. The filter provides high-flow pretreatment and membrane filtration in a compact stand-alone system.

Contech provided sizing calculations as part of the application package. Also, budget costs were provided so the cost impact to the project was known ahead of time and would not become a surprise during the construction stage.

A field representative of the manufacturer was on site to guide and assist the contractor during installation, and all three systems were installed in one day.

“We were pleased with the technical support from Contech during the entire process, and happy with the fast turnaround time, mostly within 24 hours,” said John Zhang of Bohler Eng. 

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