The Town of Sullivan, a barrier island east of Charleston, South Carolina, owns and manages a municipal wastewater treatment plant and collection system that serves a population of 400, 000. Because the existing sewer pipelines were made of clay, 68% of the 585,000-gpd flow was attributable to infiltration and inflow (I&I). The wastewater system was subjected to frequent wet weather flows, which exceed three times the average flow, and rising sea levels are causing I&I flow to increase with each passing year. The island’s soils are sandy, and the groundwater table is high and Sullivan’s officials were growing increasingly concerned about the site conditions of the plant and pipelines. Because sewer line laterals also cross swales, the Sullivan Island project needed a programmatic approach that would minimize any potential need for regulatory action, reduce operating and long-term sustainability costs, and ultimately minimize impacts to the community.
Sullivan Island, which valued its long-standing and positive relationship with Arcadis as innovative thought leaders, reached out to Arcadis for direction on how best to achieve their goals. To fully understand Sullivan Island’s issues, Arcadis held numerous discussions with town officials, examining all available options in detail. Thorough and probing questions helped Arcadis arrive at an option that was both less costly and also more efficient. By inspecting the sewer lines with cameras and grouting where necessary, Arcadis could address the I&I issues without highly disruptive digging. Deploying multiple teams at various locations—and working with the town’s smaller in-house team—enabled Arcadis to accomplish the work quickly. The CMAR framework made it possible to shift the bulk of the project’s implementation risk to ARCADIS, allowing the Sullivan Island team to focus on its most pressing concerns: population impact, budget, and, ultimately, mitigation of I&I issues
The project was implemented under an accelerated schedule with guaranteed maximum price to achieve immediate flow reductions and reduce the sewer system’s overall operations costs. Beginning as the work was initiated, flow reduction benefits were evaluated, with operations reports showing that immediate impacts of lower than typical flow responses to the rainfall events were occurring.