WSU Puyallup LID Research Center Stormwater Retrofit Evaluation

(Puyallup, WA)  Landau Associates provided geotechnical engineering services for Washington State University’s Low-impact Development (LID) Stormwater Retrofit Evaluation project at the WSU Puyallup Research and Extension Center. Stormwater from impermeable areas at the site flowed into Woodland Creek, and eventually the Puyallup River, with no stormwater flow control or treatment. A series of LID stormwater flow control structures employing porous concrete and porous asphalt pavement, bioretention swales, and rain gardens were constructed at the site to help control site stormwater, demonstrate the technologies, and to educate the public about LID approaches.

Site subsurface soil and groundwater conditions were evaluated by advancing five geotechnical test pits within the footprint of the proposed pervious pavement and bioretention facilities. At two locations, the test pits were advanced until the site groundwater table was reached. At the other three locations, the test pits were advanced to near the bottom of the likely pervious pavement/bioinfiltration section. The design infiltration rate was estimated by completing a pilot infiltration test (PIT) at the base of each test pits. The PIT investigations were completed in general accordance with the procedure outlined in Appendix III-D of the 2005 Stormwater Management Manual for Western Washington published by the Washington State Department of Ecology. We provided recommendations for structural design of the porous pavement, including the thickness of asphalt, base coarse, and geosynthetic filter fabric.

Photos: Washington State University