Small Site Dictates Stormwater Treatment Solution in Mich. Redevelopment

June 28, 2002

In Ann Arbor, Michigan, stormwater typically drains into a network of more than 500 stormwater management systems (“county drains”) that are overseen by a Washtenaw County Drain Commission. These drains provide stormwater management, flood prevention and stream protection for urban and rural land in the county.

Ann Arbor, a densely populated university town of 180,000 (during the academic year), has been seeing an increase in urban redevelopment pressure in recent years as developable land has become scarce and land values have risen. The city of Ann Arbor has worked closely with the County Drain Commissioner’s office to use this redevelopment as an opportunity to improve the quality of stormwater flowing into the county drains.

Late last year, an Ann Arbor developer received a permit to build a new mini-storage facility on a site that had three exiting buildings. The site was on a congested four-lane road near the University of Michigan, one of the major routes into downtown Ann Arbor. According to general contractor Steven Lucchesi of Steven J. Lucchesi, Inc., the existing buildings on either side of the site would stay intact, but adding a new building to the site required that the overall systems serving the site, including water and sewer, be upgraded. The city’s stormwater ordinances require that stormwater runoff from any newly created impervious surface be captured and detained on site, and then treated prior to discharging into the city’s stormwater system.

“We were adding a 5,000 square foot building, which meant that there would be about 30,000 square feet of surface area runoff,” said Lucchesi. “In addition to a retention/detention system, the city asked us to install a swirl chamber to help clean the water before pumping it into the exiting sewers.”

 The ordinance requires that the treatment system remove 80% of Total Suspended Solids (TSS) or more, and that the system’s performance be verified by testing. The city also required that the system be accessible for maintenance and removal of trapped pollutants.

The site of the new building was a tight one, only 100 feet wide between the two existing buildings, and did not allow for a large excavation to install a stormwater treatment system.

Although another system had originally been specified, these site constraints caused the project engineer to change the specifications to a Vortechs System Model 1000, an oil and grit separator that treats a flow rate of up to 1.6 cfs. Manufactured by Vortechnics, Inc. of Portland, Maine, the Vortechs System uses a patented vortex process to remove 80 percent or more of Total Suspended Solids (TSS) including trash, oil, grit and hydrocarbons from stormwater runoff. The Washtenaw County Drain Commission allows the Vortechs System as an approved best management practice (BMP) for stormwater treatment, so the last minute change did not affect permitting or slow down the tight construction schedule.

To install the Vortechs System, Lucchesi needed to manipulate his machinery onto the site, excavate a hole, and set the precast unit in place. Because the system is horizontal in design and has a shallow profile, it required only a ten-foot deep hole on the site for installation. Other stormwater treatment systems can require depths of up to 18 feet to accommodate their vertical configuration.

“A Vortechnics sales engineer showed up the day of the installation, and really helped solve a few issues before they became problems,” he said.

“In Ann Arbor, we are installing more and more of these types of units. The city is requiring them on all new development, even if the site dumps into open detention areas,” said Lucchesi.

The process took about a day from start to finish, far less than he had anticipated.

For additional information, contact Vortechnics at 207-878-3662.

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