Corrosive Environment Forces Innovative Solutions In Denver

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

Due to its limited grade and numerous force main connections throughout, the South Thornton Interceptor has significantly higher levels of hydrogen sulfide gas and consequently more severe corrosion than other interceptors in the Denver metro area. Levels of hydrogen sulfide gas in the Interceptor typically range from 50 parts per million (ppm) to 1,000 ppm, depending on the temperature, time of day and day of the week.

Structures ranged from six to 39 feet in depth with diameters from five to 8 feet. All were considered to be in poor condition prior to this project and a high priority need for rehabilitation.

The structures previously had been coated or lined with as many as three other rehabilitation/protective coating products that had all failed in the severe conditions. Maier said the failures of these previous rehabilitation efforts prompted MWRD to develop and implement a comprehensive, in house rehabilitation product evaluation/approval program to seek out quality products that could withstand severe wastewater conditions and identify applicator contractors that provide top quality workmanship. Maier said SewerShield and Fisher Company were found through this program. To date, he added, six rehabilitation product manufacturers and their respective applicators have been approved for use on MWRD projects.

The first challenge to getting the project under way was the bypass system to accommodate flow during construction.

"Bid documents for this project required complete bypass pumping," Fisher said. "However, Fisher Company was able to provide the client a substantial cost savings through use of alternate wastewater flow management methods, developing a wastewater flow management plan utilizing flow though plugs and piping to manage flows including those from numerous incoming force mains. Fisher Company project managers worked closely with Plug It Products on the development and design of plugs and fittings to meet the exact needs for this project and interceptor system."

Advantages
The advantages of Fisher Company's approach were realized almost immediately from both financially and operational standpoints.

"Because Fisher Company was thinking outside the box regarding flow management methods," said MWRD's Maier, "we were able to use a higher quality rehabilitation product that might have otherwise been too expensive, effectively utilizing the cost savings that would have instead been spent on unproductive bypass pumping. At Metro Wastewater, we encourage innovative thinking and creative problem solving to make the most of every rate payer dollar."