This project will involve the design and construction of porous bike lanes, sidewalk, and shared path, an LID stormwater treatment/retention facility, LED lighting, ADA facilities, and a warm mix asphalt overlay of 25th Street between Bill McDonald Parkway and Douglas Ave.
Actual Cost: $1,345,922.71 USD
Engineer's Estimate: $1,389,658.00 USD
Lowest Bidder: $1,235,413.76 USD
Length: 0.22 mi (0.44 lane miles)
Funders/Stakeholders: Local Transportation Benefit District
Owner: City of Bellingham, WA
Lead Design: Tuttle Engineering and Management
Design Support: Osborn Consulting, Rubenkonig Planning and Landscape Architecture
Contractor: Faber Construction
Functional Class: Collector
Greenroads Version: 1.5
This project improves bike, pedestrian, and transit facilities along existing roadways, provides stormwater detention and treatment, improves, and enhances safety.
A strong materials management strategy helped this project earn major points and substantially reduce their environmental impacts due to construction, earning more points for materials than any project to date.
The design team employed what is considered an approved "treatment trade" by the Washington Department of Ecology, where a stormwater BMP is designed to be bigger in order to accommodate an alternate or additional offsite area because site constraints (such as existing system capacity, right of way space, soil permeability, groundwater conditions, or topography to name a few) make it difficult and (sometimes) infeasible to meet minimum treatment or capacity requirements using low impact development (LID). This design approach is a creative way to meet compliance requirements for quantity of water managed and treatment goals, and ultimately satisfies state regulatory minimums for quality treatment and quantity. However, this approach does not meet Greenroads treatment performance requirements for the street itself, despite the giant stormwater basin that was installed with all good intentions and legally. Why?
It is an important lesson in the difference between "compliance" which is measured by permitting agencies, and often discounts existing conditions by allowing them to stay as-is, and "performance" which is measured by Greenroads Certification in the as-built condition and considers the whole project area (not just new or changed surfaces).
In the case of 25th Street, the site drainage pattern (you can see this in person and on the construction drawings) shows that a majority of the stormwater that falls on 25th Street and at the updated intersections drains into existing storm sewers and does not actually flow through and receive treatment in the huge basin that was installed. This means the project earns credit for EW-2 Runoff Flow Control, because the existing systems plus the new basin manage all of the expected volumes in some way. The volumes of water that do drain into the basin come from mostly uphill and the surrounding development areas on the north/high end of the project. The project was able to earn all 3 points for Runoff Flow Control due to the area of the basins that influenced the design being much larger than the project area itself, including three large subbasins in the surrounding watershed.
However, for runoff treatment, the volume of surface water that falls within the project area itself that flows into the new basin from within the project boundary is somewhere between 55-60% by volume, with the remainder flowing untreated into conventional storm systems at the south side of the project. All of the water that does flow into the basin is treated to an enhanced level (91% of 55-60% plus the run-on volumes from adjacent basins amounting to almost twice that of the project itself). Traditional stormwater systems do not provide pre-treatment only if they are not retrofit, therefore, EW-3 Runoff Quality was not earned, since the minimum treatment volume for EW-3 of 90% of on-site runoff was not met.
In case you are wondering, why is the infiltration basin so big? Two reasons it is such an impressive stormwater BMP:
A giant infiltration basin complete with concrete weirs was part of the stormwater management strategy for 25th Street.