In Bellingham, Wash., as in many communities across the country, the need to incorporate “green” and sustainable building methods is increasing rapidly. Often these projects utilize emerging technologies and construction practices that, without the economies of scale, can come at a cost premium.
Project engineers faced this challenge on the Matthei Place project, where 14 single-family attached homes with 21 parking places were to be constructed on a half block in Bellingham’s south side. The goal was to meet affordable housing requirements while also following green and sustainable design principles.
Following the construction of a new fire station on half a city block, the Bellingham City Council designated the remaining half of the block for affordable housing. The size of the site dedicated to the Matthei Place housing project was about 37,000 sq ft, and in order to meet the project needs—construct 14 units with parking and provide some open space—additional land was needed. On the fire station site, a 5,000-sq-ft storm water wet point provided storm water treatment and detention.
“At the level of density necessary to build this type of project, dedicating that much space to a detention pond is just not an efficient use of land,” said the project’s civil engineer, Chris Webb, P.E., of Chris Webb & Associates.
Webb and the owner approached the city of Bellingham with an offer: If they could provide the same storm water treatment and detention function afforded by the existing wet pond, would the city allow the land containing this pond to be added to the project? The city of Bellingham agreed to surplus the land for the storm water wet pond to the Matthei Place project if the solution also managed the fire station’s storm water flows.
LID Solution
Project engineers took a low-impact development (LID) approach to managing storm water. Chris Webb & Associates selected two storm water management StormFilter systems to provide the necessary treatment. The StormFilter, from CONTECH , is a passive media filtration system where siphon-actuated filter cartridges, which trap and adsorb pollutants, feature a surface cleaning system that prevents blinding and extends maintenance intervals. Utilizing the catch basin configuration offered small-scale decentralized treatment for the removal of fine sediment, nutrients and metals.
Following treatment, storm water flows into an onsite corrugated metal pipe (CMP) detention system, also from CONTECH . Flow from the homes’ roofs also is directed to the CMP detention system, which is about 250 ln ft of 60-in.-diameter pipe. There it commingles with the offsite flows and is detained prior to being released to the city’s storm water system.
The designers were also able to take full advantage of the infiltration capacity of the site’s sandy loam soils, and they installed a pervious concrete pavement system for all new parking areas. The new 12,000-sq-ft onsite parking lot did not require any additional treatment or flow control, as it was designed to directly infiltrate.
By using innovative technologies, project designers were able to meet storm water requirements as well as provide an affordable and sustainable development. Their solution incorporated LID principles and showed how to efficiently use land in a dense urban environment.