MANHOLE FOCUS NPS was contracted to begin the work of rehabilitating 28 manholes and a 17-ft deep lift station situated at the island’s marina in June 2007. During the summer months, it rains daily at a level of 1 to 2 in. over a short one- to twohour period in late afternoon. This rain pattern, coupled with high temperatures, hydrogen sulfide levels, humidity and tidal patterns, impact both underground structures and repair crews significantly. To overcome these challenges, crews were outfitted with protective gear and special cooler vests to combat the risks of heat stroke and dehydration.NPS performed any required pressure washing, injection grouting and sealing work for each structure during low tide.“By timing the work in this way, the grout and mortar has sufficient time to set before high tide occurs approximately six to eight hours later,” explains NPS business development manager Rodney Jones. “This scheduling also puts the crews in a timeframe to complete their work and avoid the daily summer rain patterns.” High water tables also need to be considered in project planning.The manholes to be rehabilitated ranged in depth from 3 to 17 ft. In some areas of Florida, groundwater levels are just 12 to 18 in. down from the ground surface.This factor contributes to high levels of inflow and infiltration (I/I), cracking and shifting of the structures in the ground. Cracks are to be expected and the NPS crews were trained and prepared to handle them. The lift station posed the biggest challenge.It was unusually deep for its location and numerous cracks had to be National Pipe Services crew performing the application of the Spraywall spray-applied polyurethane product. addressed before rehabilitation could begin.A large volume of De Neef grout was required along with special detailing. In addition, the lift station serviced an active line so bypass pumping was required for the duration of the rehabilitation process. To aid in the pre-spray cleaning process, NPS utilized combination trucks for initial cleaning and removal of any sediment and debris. Just like the manholes, the walls were then pressure washed and sealing mortar creaming was applied. After the initial cleaning, the crews found that intake and outake pipe connections to the lift station were seriously deteriorated and extensive grouting was used to re-establish structural integrity and support. Once all of the prep work was completed, the spray process began with the crews taking approximately one and a half days to finish applying a 1-in. thick application of the Spraywall product per the Manatee County specifications. At the conclusion of the project, it was determined that Long Boat Key had stopped approximately 15,000 to 20,000 gal per day of infiltration into its collection system. This reduction will not only save the community money in treatment expenses but also aids in the reduction of salinity levels of the wastewater in the sanitary collection system that Manatee County has been mandating. North, south, east, west, cold, hot, dry or wet, sprayapplied polyurethane technology is a technology worthy of consideration for sustainable and effective structural rehabilitation. With proper training, planning and execution, even the toughest environments can be conquered and old infrastructure can be returned to optimum performance and new assets given an extended lifespan. Suzan Marie Chin is the chief marketing officer and art director of Creative Raven, a marketing communications, design and production firm for those serving the water, wastewater and municipal infrastructure sectors. 28 TRENCHLESS TECHNOLOGY Circle 21 on reader service card. September 2007 www.trenchlessonline.com
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