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In 2013, the owners of the restored Webster House, a popular downtown Kansas City, Mo., boutique shopping plaza and dining attraction built as the Webster School in 1885, developed a neighboring empty lot into a four-story commercial parking garage that required a strategic underground stormwater management solution. The 180-space garage also provides additional parking for the nearby Kauffman Center for Performing Arts. Retail shops are on the bottom floor of the $6 million project.

The underground stormwater detention unit had to be constructed to hold nearly 2,000 cubic feet of water in a system with a footprint smaller than 1,500 square feet. Putting it underground was necessary to control runoff and also practical because it made the best use of the available land. The system was built using more than 230 feet of large-diameter corrugated high-density polyethylene (HDPE) pipe in a rectangular configuration.

“Customized detention systems can be demanding due to the need for extremely accurate design documents,” said Daniel Currence, director of engineering, CPPA Division, Plastics Pipe Institute, Inc. (PPI). “Manufacturers’ application engineers can provide highly detailed, precise system drawings, which can be used by the engineer for submittal. For this system, for example, the Prinsco team provided the layout design for the system and for the fabricated components, which the contractor then used for installation. These design and construction documents ensured that the system not only met the needs of the project, but was built and installed correctly. Because of the very nature of HDPE pipe, the design can be customized to exacting requirements for a specific underground water management solution such as this one.”

The new parking garage, which opened in late 2014, is four stories tall and has 180 spaces to serve both the Kauffman Center and Webster House.

The system used 231 feet of 36-inch-diameter watertight Prinsco GOLDFLO HDPE pipe. Three cleanouts allow access for vacuum truck or waterjetting hoses to periodically clean the system. Two, 24-inch-diameter risers, which were fabricated at the Prinsco plant, provide for inspection, either by a crew or video camera. Two inline drains were also installed. The 17-foot-wide trench was excavated in the native clay soil to a depth of 5 feet, 5 inches. The system was backfilled with 1-inch-diameter clean aggregate before the final native soil fill was placed over the system.

“For this project, polyethylene pipe was a clear choice for a list of reasons including lightweight, ease of construction, readily available pipe segments and parts, longevity, ease of maintenance, and overall competitive cost,” said Kevin Pinkowski, project engineer, BHC RHODES Civil Engineering (Overland Park, Kan.). “The location of the installed system in a corner of the excavated site made the ease of handling and construction more prominent on the list of benefits.”

The garage was built by Kansas City general contractor McCownGordon Construction LLC and took about nine months. Helix Architecture + Design Inc. (Kansas City, Mo.) did the design, which utilized brick, glass, and metal to closely match buildings in this area known as the Crossroads.

Information provided by the Plastics Pipe Institute (plasticpipe.org), a trade association representing all segments of the plastic pipe industry.

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