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Efficient, Economical Grout Solution For Downers Grove
Reducing Sewer Line I/I With Grouting Allows Sanitary District To Avoid Major Expense
In addition, pre-grouting review of the televised lines revealed that 6,200 feet of 24-inch concrete pipe had extensive damage from hydrogen sulfide (H2S). It was agreed by all parties that these pipes would be removed from the project and bid as a separate project in which they would be rehabilitated with CIPP rather than grouted.
“These decisions underline an important aspect of the success of a project such as this,” points out John Manijak, project manager with NPR, who directed the grouting operation. “On any project, the engineer, contractor and owner must work as one team with the single goal of producing the best result. That means being committed to doing what is right for the success of the project rather than what is specified in the contract.”
Funding for the project was provided by the ARRA through the state of Illinois Environmental Protection Agency (EPA), and consisted of an interest-free loan that included 25 percent loan forgiveness. The approximate total cost of the project was $3 million. However, as the project progressed, changes that were made from the original project description lowered the cost. Manholes that the project had planned to seal with grout curtains turned out not to be viable candidates for the technology and were removed. With that “saved” funding, DGSD and the contractor identified two additional basins that could be treated with chemical grouting, bringing the total number of basins grouted to 17.
“Post-grouting flow-metering of the sealed basins showed varying levels of reduction in individual basins,” says Derek Wold, “but an overall reduction of I/I in the system of 21 percent. In addition to reducing the stress on the treatment system, these reduced flows also help extend the life of the pipes.”
Also, he points out, removal of roots and the use of additives to inhibit future intrusion reduces the workload of the DGSD’s maintenance crews, freeing them for other work.
Finally, as to the $3 million cost of the grouting project, by reducing the added flow of I/I water in the system, eliminates the need to construct additional pumping capacity, and larger or relief sewers that would otherwise be needed to handle peak flows that were threatening acceptable operation during large storm events. It is estimated that the cost of the grouting project, $220 per gallon per minute (GPM) of I/I eliminated, saved DGSD an estimated $2,050 per GPM that would be needed to construct those additional facilities. There are additional savings in costs of handling these excessive I/I flows at the treatment plant.