Best Practices

Most municipalities can point to at least one chronic problem area within their sewer system — frustrating mazes of cracked or broken pipes, root intrusions, leaking laterals and illegal connections that consistently require repair. Typically, it can take several years to achieve significant infiltration and inflow (I/I) reductions in a problem-plagued system. But what happens when these problems need repair?

Under a traditional project delivery model, the municipality hires a company to categorize its entire collection system, determining existing problems and defining corrections. Then the owner bids the job out, often choosing another contractor to complete the work. Throughout this period, those sewer line problems can multiply. Environmental changes, such as the shifts between wet and dry periods, often mask some issues and reveal others. As work finally begins, the evaluation is quite likely outdated. Then, once the repair process is complete, still another contractor often evaluates the work.

But environmental management company Metcalf & Eddy (M&E) is changing that, pioneering an innovative model of sewer system rehabilitation based on design-build project delivery methods. Termed “assessment-and-rehabilitation” (A&R), this comprehensive new approach combines what traditionally have been several separate contracts into a single project. By generating a continuous flow of assessment, analysis, correction and feedback, the A&R team can potentially deliver faster, more efficient solutions in problem-plagued areas. In addition to speeding up the process and saving the client money, A&R lets the owner deal with a single point of responsibility for the entire project.

In a recent project in Georgia, for example, the municipality identified an area that it knew required considerable work. As soon as the A&R team began collecting data on I/I in the problem area, it determined necessary corrections. Within a few weeks, construction crews were in the field. Work continued with a constant flow of data collection, analysis and work order preparation. The team evaluated more than a half-million linear feet of sewer lines and more than 2,500 manholes in the first year of the project alone.

One great advantage to the A&R model is the ability to assess efficacy in real time. M&E installs flow monitors as part of its data collection process. Those flow monitors then determine exactly what progress the team is making in reducing I/I. Often, when data collection and repair work are not done at the same time or by the same contractor, actual reductions in I/I are not well quantified, and the repair contractor’s leakage estimates are inaccurate. Here, because flow monitors remain in place throughout the project, it is possible to quantify erroneous flow from the system.

The monitors are especially useful in situations such as Georgia’s current drought. In a drought, it can seem as though a significantly challenged sewer system is working just fine. While a number of methods exist to identify leakages and illegal connections that are not dependent on periods of high flow — such as closed-circuit television, manhole assessment, flow isolation and smoke testing — it is often difficult to determine repair effectiveness when little water moves through the system. When Georgia’s drought conditions end, it will be easy to quantify the level of I/I reductions.

Another significant advantage to the municipality in this kind of project delivery is the ability to control costs. As part of the bid process for the Georgia project, 800 to 900 very specific tasks were costed out. When the team finds a problem, they and the municipality both know exactly what the resulting work order will cost. This allows the owner to monitor the work and costs incurred in a much more detailed way than is usually possible.

A&R takes design-build project delivery to the next level. By single-sourcing the project, clients can get superior results faster and less expensively, just as in typical design-build projects. Extending the design-build model to the evaluation and repair of wastewater systems provides an innovative solution for problematic sewer systems and opens up the advantages of design-build for new project areas.