City completes major storm drain improvement project; commission to consider contract change, final payment

City Commissioners will consider a change order and final payment for the 18th Street storm drain improvements phase 2B during their Sept. 17 meeting.

Three bids were received for the project in March 2018 with bids ranging from $3.28 million to $3.5 million. Commissioners awarded the contract in March 2018 to Central Excavation, the low bidder.

The final project cost is $3.4 million, or $118,760.03 more than the amount originally awarded and approved. It’s a four percent increase over the initial contract and commissioners will have to approve the change.

The proposed change order accounts for the additional time, materials, labor and equipment that was needed to “complete additional work caused by unforeseen utility crossings, inadequate subgrade and additional roadway curb and surface work. Changes were agreed upon by both parties involved in the construction contract prior to work being completed,” according to the city staff report.

The 18th Street Storm Drain Improvement Project was initiated to increase capacity of the regional storm water system, according to public works. This was the final phase of the project and completed improvements to the south-central Great Falls storm drain system.

This phase significantly upsized the storm drain pipe located along 17th and 18th Streets South between 4th Avenue South and Chowen Springs Park, and also completed
improvements along 19th and 20th Streets South between 11th Avenue South and 15th Alley South, according to public works.

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

Thomas, Dean and Hoskins Engineering staff assisted city staff with design phase engineering and prepared plans and specifications. City engineering staff provided construction phase engineering services and project inspection. TD&H also assisted with construction phase engineering.

The full project was “designed to reduce the potential for flooding at the intersection of 15th Avenue South and 23rd Street South, and at 11th Avenue South and 11th Alley South between 18th and 19th Streets South.

In addition to Phase 2B, the following storm drain improvements have been constructed, according to public works:

  • 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 UGF to convey storm water away from areas that experienced localized flooding during heavy rainfall;
  • an overflow channel on the west side of the intersection of 15th Avenue South and 23rd Street South;
  • an athletic field that also functions as a regional storm water pond during large events located on University of Providence property;
  • a shallow detention pond located at Chowen Springs Park; and
  • expansion of the Sand Hills Park detention pond.

The most recent phase included the installation of 1,750 lineal feet of storm drain culvert ranging in size from 10 by 3 foot box culvert to 59 by 36 inch arch pipe; installation of 2,100 lineal feet of storm drain pipe ranging in size between 24 inches and 48 inches in diameter; replacement of 1,900 lineal feet of water main ranging in size between 6 and 16 inches in diameter along 18th Street South between 5th Alley South and Chowen Springs Park; miscellaneous waterlines and sanitary sewers relocations and replacements; and ADA accessible ramps and road resurfacing.

The project was substantially complete on June 19.

City staff verified that Central Excavation has completed all work and punch list items in accordance with the plans and contract. The two-year warranty period started the same time as substantial completion.

The city was approved for a State Revolving Fund Loan to cover the storm drain improvements costs associated with this project. The City Storm Drain fund will repay the loan. The increase in project cost due to the change order will be funded through the City Storm Drain and City Water Fund, according to public works.