DuroMaxx Meets Watertight Specifications at Transit Station


Courtesy of Contech Engineered Solutions LLC

Underground Stormwater Detention allows Sounder Puyallup Station Parking lot expansion

Puyallup, Washington - The number of commuters to the Sounder Puyallup, Washington, station exceeded parking capacity and Sound Transit decided to grade and pave an existing lot across from the Puyallup Fair & Events Center to accommodate the overflow. A new bus route was added to transport the Sounder riders to and from the station.

By partnering with the City of Puyallup and the Puyallup Fair and Events Center on this project, Sound Transit created an additional 219 permanent satellite park-and-ride spaces. The project also required the addition of drainage, new lighting and environmentally sustainable rain gardens to capture stormwater run-off from the lot's paved surfaces.

The rain garden system mimics natural hydrology by using a specially designed soil that allows maximum infiltration of stormwater while providing a nutrient-rich environment for plants. Stormwater that does not infiltrate the soil will be stored in a large detention system beneath the parking lot. Shrubs and other foliage native to the Pacific Northwest were also added to the gardens.

For the detention system, 60” diameter DuroMaxx® steel reinforced polyethylene (SRPE) pipe from CONTECH Construction Products, Inc. was used. The site featured a high groundwater table, requiring a high performance joint to prevent infiltration. DuroMaxx was the preferred choice because its 15 psi bell and spigot joints met the required watertight specifications. The 60” diameter also maximized savings on per gallon storage cost.

“We knew that the detention system for the parking lot would have minimal cover and heavy live loads, and would be installed in an area where the water table would be close to the top of the pipe for most of the year,” said Don Proctor, P.E., with Tetra Tech Inca Engineers. “We needed a reliable, large diameter pipe material that could meet the joint standards for sewer pipe. CONTECH’s DuroMaxx detention system exceeded all of our expectations due to the ease of construction. We were amazed at how quickly the system was assembled by the utility contractor.”

The DuroMaxx detention system was light weight, making it easily transported and assembled on site. Approximately 2,100 lf of DuroMaxx SRPE pipe was installed by Construct Company in just 4 days.

A hydrostatic test was required on this project. The manifold was filled to the risers and the water level was checked after 24 hours. A negligible amount of water was lost, likely due to evaporation. The water was kept in the manifold for a week after the test for ballast prior to paving.

The $2.8-million project was funded by a combination of federal and local grant monies and the expanded, upgraded parking lot was opened after four months of construction. 

Sound Transit

Tetra Tech Inca Engineers

Construct Company

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