City wrapping up $1.45 million sewer project on east side of Great Falls
A major city sewer project was completed in January and on Tuesday, staff is asking the City Commission to approve the final payment of $67,694.71 to Planned and Engineered Construction and $683.79 to the State Miscellaneous Tax Fund.
The North East Interceptor Rehabilitation project is a continuation of an ongoing program to rehabilitate sanitary sewer mains, using trenchless technologies to repair badly deteriorated mains.
This phase restored 10,225 linear feet of large diameter sewer main, equivalent of 25 city blocks. The rehabilitated main serves Malmstrom Air Force Base and residential areas on the east side of the City.
The contract for the project was awarded in February 2018 and a change order for repairs to the 10th Avenue Southwest segment was approved in October 2018.
The final project cost is $1.45 million and is $69,440 under the estimated cost since the city and contractors didn’t encounter as many problems with spot repairs, infiltration and main sizes and lengths as they planned for, according to the city staff report.
The project was funded by the city’s Sewer Collection Fund.
This project rehabilitated a large section of the North East Interceptor sewer main.
Due to the large volume and velocity of flows experienced in this main, routine inspection was difficult.
The east end of the main along 10th Avenue North from 38th Street to Malmstrom was lined during 2015-2016 to protect/arrest deterioration in the main and manholes caused by the presence of corrosive sewer gases as continuation of a previous project to rehabilitate the main and prevent further deterioration.
Although the sewer mains were functioning, the aged/corroded lines had developed pits, cracks, and holes. These defects can lead to raw sewage leaking into ground water and can also make routine maintenance difficult, according to Public Works.
In 2016, a section of the North East Interceptor sewer main near Columbia Grain collapsed, prompting further investigation of the entire North East Interceptor and the scope of rehabilitation was addressed in this most recent project which was substantially completed in mid-January, according to the city.
The recently completed project used cured-in-place-pipe to extend service life and alleviated corrosion and deterioration. Trenchless technology is a low-cost solution to the city that greatly reduces disruption and eliminates utility conflicts, according to the staff report.
This project rehabilitated 10,225 linear feet of 18-, 24-, and 30-inch diameter sewer mains along 12th Avenue North from 15th to 19th Street North. Beginning at 19th Street North, the main continues east on BNSF property paralleling River Drive North and then onto city property paralleling Eagle Falls Golf Course to 38th Street North. The 36-inch diameter main in 10th Avenue Southwest at 6th Street Southwest was also lined.
The contractor was required to keep the sewer mains functioning during the project by using bypass pumping and there was minimal impact to traffic since the majority of the main was located along non-residential city streets and BNSF property.
The utilities and engineering divisions of the city Public Works department conducted sewer main inspections that were used to identify and prioritize the mains that needed rehabilitation. City engineering staff designed the project and inspected construction, according to the staff report.