Skyrocketing H2S Levels Prompt Emergency Manhole Repairs

By Jeff Griffin, Senior Editor | May 2014, Vol. 69 No. 5
A fully deteriorated manhole at Moody Gardens, Galveston, TX.

Moody Gardens is a public, non-profit vacation and educational destination on Galveston Island, TX, utilizing nature to advance environmental research, conservation and rehabilitation, while providing interesting recreational opportunities.

Covering more than 240 acres, Moody Gardens includes nine interesting educational attractions, a hotel with restaurants and spa and a convention center, making it a popular attraction for Texas families, out-of-state tourists and organizations holding meetings and conventions.

In February 2014, a manhole in front of the hotel collapsed. Following emergency repairs, inspections of the sanitary sewer system serving the complex revealed serious environmental and health hazards.

“Tests revealed hydrogen sulfide (H2S) levels in the system were more than 600 parts per million (ppm), 600 times higher than the 100 ppm level OSHA says can be fatal,” said Eric Dupré, vice president of operations and technical advisor at Southern Trenchless Solutions, the contractor called in to rehabilitate the failing manholes.

Hydrogen sulfide is a powerful and deadly gas formed by decomposition of organic materials and is common in sewer systems. It emits a strong, unpleasant “rotten-egg” odor. Exposure to high levels is fatal – breathing the gas goes from the lungs into the bloodstream. H2S also is explosive, igniting from a spark or flame.

This reading shows an H2S level of 651.
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Dupré said Moody Gardens’ sewer system is connected to an 18-inch diameter city force main from across the bay which includes an industrial area containing a shrimp food processing plant. Effluent from the force main is discharged into Moody’s gravity flow system, passing through it to a downstream wastewater treatment plant.

Quick action

Due to the seriousness of the situation, Dupré said Moody Gardens decided to make repairs in hopes of preventing other failures. To heighten the concern further, Mardi Gras celebrations and spring break were only weeks away.

Mitchell Chuoke Plumbing of Galveston was the general contractor who brought Southern Trenchless into the project. Also involved was Gilbane Inc., which manages Moody Gardens’ infrastructure.

Southern Trenchless’ job was rehabilitation of eight manholes – seven with precast manhole replacements, the eighth with a 100 percent epoxy coating. The main itself was PVC pipe and did not require rehabilitation or replacement.