Pervious concrete soaks up water, eliminating the need for conventional storm water detention systems.
Stratford Place
Location: Sultan, Snohomish County
Owner/developer: CMI Homebuilders
Project team: CMI Homebuilders, general contractor; Pervious Concrete Inc., concrete contractor; Smokey Point Concrete, ready-mix supplier
This 20-home development in Sultan is being hailed as possibly the first of its kind in the state to use pervious concrete storm water technology for all of its interior roadways, parking areas, sidewalks and driveways.
Photo courtesy CMI Homebuilders
Pervious concrete is a two-part system, consisting of the concrete pavement and a coarse gravel retention layer for storm water storage.
Using pervious concrete allows the development to exceed local storm water management regulations by eliminating untreated storm water and creating a zero runoff site. It also allows for direct recharge of rain water to ground water.
The developer saved about $260,000 by eliminating storm water catch basins, piping to detention areas and a detention vault. The system also allowed two more lots to be developed where the detention vault and associated structures would have been. Those lots are valued at $100,000 each.
Copyright ©2006 Seattle Daily Journal and DJC.COM.
Pioneering Pervious Pavement at Stratford Place
Task Force assists City of Sultan and Developer, Craig Morrison of CMI Inc.
Source: The Sustainable Development Taskforce of Snohomish County – Elements Newsletter – June 2006 Volume II Issue 5
https://www.snoedc.org/ssc/Newsletters/SDTF_June$2006.htm
City of Sultan, has pioneered pervious pavement in Snohomish County. This groundbreaking project paves the way for pervious pavement as a proven technology to provide an alternative to traditional stormwater management on public streets.
Only one other public road in Washington has been paved with pervious pavement, an engineered pavement product that allows stormwater to percolate through to recharge groundwater and keep stormwater on site.
The Stratford Place residential demonstration project included 32,000 sf (square feet) of previous pavement laid in place of concrete for one road, connecting driveways, and associated sidewalks on the 700 block of Fir Street. Builder / developer, Craig Morrison of CMI Inc. worked with the SDTF (Sustainable Development Task Force) members to pioneer the project. Morrison said it took three months to fully research the new paving alternative and to understand the engineering involved, including developing the right pavement mix, laying the materials, and how to incorporate pervious pavement into the stormwater management site plan. The builder worked with Bruce Chattin from Washington Aggregates & Concrete Association to learn about the technology and engineers at the City of Sultan to design the project.
Stratford Place was the last vacant parcel remaining in the area, so stormwater migrated to the site already, making stormwater management a crucial challenge. Morrison reports that although there was a significant learning curve involved with using pervious pavement, he plans to use this technology in future projects. In fact, he has formed a new company, Pervious Concrete, Inc., to provide expert design and installation services. The trick, he said, was “formulating the right mix and using the right equipment,” in which his new company has invested, and which offer greater efficiencies for laying pavement, compared to traditional flatwork methods.
CMI worked with Smokey Point Concrete to develop the mix, which includes fly ash, a waste by-product. Fly ash comes from coal-burning power plants and used to be dumped in landfills; but now, it serves as a superior substitute for Portland Cement in concrete mixes. The right mix is crucial to a successful pervious pavement project.
The next step was learning how to lay the material. Morrison reports that the “chance of failure can be high if (the pervious pavement) is not laid correctly.” He continues, “Hot sun and breezes can be unforgiving.” The traditional method to overcoming these obstacles in the field is to add water, but with pervious pavement, this strategy makes the pavement cream over, making it impervious. Here is where the months of research and the right equipment led to success. CMI learned how to work the material in changing temperature and weather conditions using a different approach to traditional flatwork (term used for laying concrete roads as opposed to foundations). Morrison said the pervious pavement comes out like “sticky pea gravel” and the trick is to use rakes to lay it in order to work with the short set time.
Once CMI figured out the intricacies of working with the new material, they were able to increase their efficiencies from laying 20 trucks of material per day up to an estimated 35 trucks per day. Traditional flat work lays 3 to 5 trucks per day, although traditional methods cannot be directly compared to pervious pavement efficiencies in terms of truckloads, since pervious pavement product needs to be thicker to meet the same performance goals of traditional concrete. Morrison does estimate that using pervious pavement yields a double increase in efficiency compared to traditional concrete, which takes a lot of work and time.
The Bottom Line
The proof is in the pudding. The proof here is that during the hard rains of November and December, “no water left the site,” according to Morrison and Rick Cisar, Sultan City Engineer. No traditional stormwater management system in this state can lay that claim, according to Morrison. Cisar was so impressed with the Stratford Place demonstration project that he is looking to try pervious pavement in a public street in town. He expects other projects to be in place sometime next year. He is particularly interested in a road section between wetlands and stream corridors. Cisar says pervious pavement resolves drainage problems, protects critical areas and stream corridors, and helps to protect adjacent properties from encroaching stormwater.
As for CMI builder Craig Morrison and his new company, Pervious Concrete Inc., pervious pavement “is golden.” Besides the stormwater benefits, using pervious pavement allowed Stratford Place to save two lots, which would have been lost with traditional methods for use as catch basins and vaults. Finally, the other winner with pervious pavement is the environment. Recharging groundwater through onsite percolation adds air to the water, which helps improve groundwater quality.
– Carol A. O’dahl
