Commissioners will consider awarding a $3.28 million contract to Central Excavation during Tuesday’s meeting for the next phase of the 18th Street storm drain improvements.

The project is for work from 4th Avenue South to 8th Avenue South and 11th Avenue South to 15th Alley South, contingent on Montana Department of Environmental Quality concurrence.

Staff is recommending approval of the contract for what will be the final phase of the project to complete improvements to the south central Great Falls storm drainage basin.

This phase will upsize the storm drain pipe located along 17th and 18th Streets South between 4th Avenue South and Chowen Springs Park, according to the staff report. The project will also complete improvements along 19th and 20th Streets South between 11th Avenue South and 15th Alley South.

The project is scheduled for substantial completion in 230 calendar days.

This phase also includes removal and upsizing of the aging water main along 18th Street South that runs parallel to the storm drain work, according to the staff report.

There will be road closures during construction, but the improvements are expected to reduce stormwater impacts to cars and property during heavy rainfall, according to public works. Local access for churches, schools and residences will be provided during construction.

Thomas, Dean & Hoskins Engineering staff assisted city staff with design phase engineering and prepared plans and specifications, according to public works. City engineering staff will provide construction phase engineering services and project inspection.

This final phase will complete the upsizing of the existing storm drain pipe to large storm drain box culvert between 4th Avenue South and Chowen Springs Park and upsize connections between previously completed improvements in the south half of the basin between 11th Avenue South and 15th Alley South, according to the city.

Previous phases have included new upsized pipe on 18th Street South and 17th Street South between Central Avenue and 4th Avenue South and also between Chowen Springs Park and 11th Avenue South; new pipe and inlets along 23rd Street South and at 11th Alley South, as well as new storm drain pipe across the University of Providence to move water away from areas that experienced localized flooding during heavy rain events; an overflow channel on the west side of the intersection of 15th Avenue South and 23rd Street South, and an athletic field that also functions as a regional storm water pond during large events located on UP property; a shallow detention pond located at Chowen Springs Park; and 5) expansion of the Sand Hills Park detention pond.

During this phase, five blocks of larger concrete storm drain will be installed ranging in size from 10 foot by 3 foot box culvert to 59 inch by 36 inch arc pipe from north of the intersection of 17th Street South and 4th Avenue South to the northern half of Chowen Springs Park at 18th Street South; replacement and parallel storm drain pipe ranging in size between 48 inches and 24 inches will be installed from the intersection of 11th Avenue South and 19th Street South to 20th Street South and 15th Alley South; the water main along 18th Street South between 5th Alley South and Chowen Springs Park will be replaced and upsized; and other waterlines and sanitary sewers will be relocated at multiple locations to allow for the new large storm drain pipe. ADA accessible ramps and road resurfacing will also be included in this project.

The city received three bids for the project ranging from $3,283,284.00 to $3,525,141.00. Central Excavation, located in Great Falls, submitted the low bid.

The City has been approved for a State Revolving Fund Loan to cover the costs associated with this project. The City storm drain fund will repay the loan and the City water fund will pay for about $200,000 of the total project cost to cover the work associated with the water main replacement in 18th Street South, according to the staff report.