The Town Center Regional Stormwater Facility project consisted of a large underground regional infiltration facility designed to promote downtown development by providing flow control and water quality treatment for future development. The facility was constructed beneath the parking lot for the City’s library and the adjacent police and fire department buildings. Construction required complete removal of the parking area to complete a 25-foot deep excavation. Careful planning allowed the library to remain open during construction and protected the existing structures throughout the excavation process. LID techniques used for this project included the use of infiltration into the native soil as well as the implementation of an amended soil layer for water quality treatment below the infiltration facility.
The result of the project is a new, more efficiently configured parking lot for the City as well as a new stormwater facility, which will allow full development of the downtown core without further stormwater mitigation. In total, approximately 13.1 acres area tributary to this new stormwater facility, including runoff from the City Hall site. Given the depth and large footprint of the stormwater facility, the existing sanitary sewer main within the parking lot had to be realigned around the stormwater facility. Perteet also prepared the entire specification package using WSDOT/APWA format and assisted with design support during construction. The project was delivered for $65,000 less than the design contract amount, while a creative stormwater solution for addressing the City’s needs brought in a winning bid of almost $1M less than the City had originally budgeted.