Featured Article: “‘Grout First,’ Right Answer to Solve Sullivan’s Island, S.C., I/I Issues”

The following article about Bio-Nomic’s involvement in an infiltration & inflow projects was initially posted at TrenchlessTechnology.com.

The year was 2004 and Greg Gress, manager of sewer and water for Sullivan’s Island, S.C., just completed the community’s CMOM self-assessment of its collection system. The 6-sq mile island located just north of Charleston hosts 80,000 ft of vitrified clay pipe (VCP) mainline sewers, 24,000 ft of 6-in. laterals (main to property line), 5,000 ft of force main, six pump stations and a wastewater treatment plant with a design flow of .570 MGD.

The condition assessment clearly indicated 90 percent of Sullivan’s Island problem was high infiltration and inflow (I/I) and 10 percent structural. Conventional wisdom suggests attacking structural issues first, but Gress thought otherwise and found an engineer who agreed with him.

James Shelton, vice president buried infrastructure for ARCADIS, sought to attack the problem at the source — excessive I/I — which was the underlying cause of the structural defects and here’s why:

• Destabilization of the pipe bedding
• Soil and sand reducing capacity
• SSOs from the collection system
• High flows at the WWTP
• Risk of effluent violations

Gress and Shelton weighed cost and technology alternatives for controlling I/I. Both had previous knowledge and experience with municipal grouting. Both attended grout schools to advance their understanding of methodology and supporting procedures. Their conviction for the low-cost, high-reward advantages of injection grouting led to a “grout first” approach with an innovative construction manager at risk (CMAR) delivery method.

The plan was to attack I/I holistically at all points where infiltration exacerbates system efficiencies and longevity. Credit to the foresight of Gress, he knew once the main’s, laterals and lateral connections were sealed, the groundwater table would rise and enter the system higher through the manholes.

To learn more about how Bio-Nomic got involved in the Sullivan Island infiltration & inflow project, read the full article.