Corrosive Environment Forces Innovative Solutions In Denver

September 2009 Vol. 64 No. 9
A manhole after rehabilitation.

The Metro Wastewater Reclamation District (MWRD) of Denver, CO, successfully completed a significant manhole rehabilitation project on its South Thornton Interceptor this past summer.

The interceptor operates in one of the district's most challenging environments with levels of hydrogen sulfide gas in areas as high as 1,000 parts per million (ppm), significant flows and extensive concrete corrosion throughout the five-mile-long wastewater pipeline.

The project included rehabilitation of 49 manholes and was completed using an epoxy system to coat rebuilt base, benches and invert areas and the installation of fully structural composite manhole inserts.

Designed in house by the MWRD engineering department, the project was the culmination of research and efforts to find the most corrosion resistant, structural rehabilitation products and the best qualified contractor to install these products in the severe environment of the South Thornton Interceptor. Contractor on the project was Fisher Company Inc.

"We are very pleased with the outcome of this latest manhole rehabilitation effort," said Jeff Maier, P.E. , MWRD project manager and lead design engineer for the South Thornton Interceptor Manhole Remediation Project. "The South Thornton Interceptor has been challenging for us given its extremely corrosive environment and high flows. The contractor, Fisher Company, did an excellent job."

The same  manhole before rehabilitation.

Work on the project began in August 2008 and was completed in July 2009. The project included the use of innovative wastewater flow management techniques throughout the interceptor and in-pipe diameters ranging from 36 to 60 inches, carrying average daily flows of 6 to 14 million gallons per day (mgd), with peak flows exceeding 20 mgd.

Anything but ordinary
To completely and correctly rehabilitate the 49 manholes involved many challenges, starting in design and finishing with the successful installation of SewerShield epoxy and fully structural SewerShield corrosion resistant, composite manhole inserts.

"This was not your basic manhole rehabilitation project – it was much more extreme – and we did not use basic manhole rehabilitation products or processes," said Charlie S. Fisher, Fisher Company business development director. "The severely corrosive environment and dangerous hydrogen sulfide levels posed major obstacles in making sure this project was done well and in a safe manner."