There probably isn’t a municipality in America whose public works department heads haven’t at one time asked themselves if it’s worth the cost to inspect sewer laterals before undertaking a complete rehabilitation of their wastewater conveyance infrastructure. At first guess, it seems almost a no-brainer that the time and expense of inspecting miles of pipeline and other underground assets that have seriously aged out would be far outweighed by the savings in simply instituting a top-to-bottom replacement effort of infrastructure of a certain age. It just stands to reason, doesn’t it? How much service life could that stuff have left in it, after all?
Well, two engineers took more than a passing interest in this very question, and performed an analysis of a sewer separation project completed by the Metropolitan Sewer District (MDC) in Hartford, Conn., not too long ago. George Pendleton, P.E., of Kleinfelder/ SEA Consultants (Rocky Hill, Conn.) and Jeffrey Griffiths of Hydromax USA (Newport News, Va.) presented their findings in a report titled “Are Sewer Lateral Inspections Cost Effective?” in March, 2012, at that year’s No-Dig show.
Background: Throughout the industry, the common conclusion is that private property I/I sources are significant. Many utilities are finding it cost-effective to address these problems and consequently reduce capital expenditures and operating costs. The report’s summary states that throughout the United States, authorities estimate up to 50% of a sanitary sewer collection system’s footage is comprised of public-private laterals.
Not surprisingly, this study found that inflow and infiltration (I/I) originates from a variety of sources within a collection system, many located on private property and/or not maintained by the local sewer authority. Based on surveys from many communities across the country, I/I derived from private sources ranges between 20% – 80% of total I/I (Private Property Virtual Library database).
The age-old question is: How do you cost-effectively address the problems? Do you simply broad-brush your approach, automatically rehabilitating 100% of the laterals in areas with significant I/I? Or are pre-rehab lateral inspections to determine actual need cost-effective?
Since 1929, the Metropolitan District (MDC) has managed the Hartford, Conn. region’s water and sewer systems, originally developed in the 1850s. The MDC set goals to replace laterals with poor performance based on
Recently, 1,160 laterals were inspected and coded, per NASSCO Lateral Assessment and Certification Program (LACP) parameters. In some cases, laterals could not be inspected due to lateral caps, large debris, rocks, defects, etc. After scoring and tallying all inspections, 646 laterals were identified as candidates for replacement.
However, the more important figure is the 514 laterals deemed in satisfactory operating condition, and not in current need of replacement. The cost to do the lateral inspections was an order of magnitude less than total rehabilitation.
Private source I/I reduction activities start with lateral inspections, which have proven to be a very cost-effective tool. The full report discusses lateral inspection techniques, presents data output, and demonstrates how data is used to support rehabilitation recommendations that provide clients with cost-desirable solutions.
This report—or excerpts from it—could be very convincing tools when planting seeds for new approaches next time you visit your municipal customers to generate a bit of new business. Who knows? Your fishing expedition could turn into some serious financial benefit for you and make you into a hero for your customer.