DC Water maintains critical water and sewer infrastructure in Washington, DC, essential services that come with a unique set of challenges and customer expectations—given that this is the nation’s capital. The water and sewer infrastructure is old, with a median pipe age of 77 and 85 years, respectively. Several critical water and sewer mains were placed in service before Abraham Lincoln began walking this fair city. DC Water maintains about 34 percent of a combined system where stormwater and sanitary flow are captured in the same pipe. Further, DC Water operates the largest advanced wastewater treatment plant in the world. This is an impressive operation. However, DC Water is confronted with a massive capital program totaling $3.8 billion over the next 10 years to comply with more stringent requirements of the Safe Drinking Water Act, the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program, the municipal separate storm sewer system (MS4) permit program, a consent decree and its aging infrastructure because of this operation. Many of the utility’s capital improvements are mandatory given the regulatory environment it operates in. Since the utility’s customers foot the bill, senior managers recognize the need to stretch every capital dollar. Managing asset life cycle costs becomes second nature at DC Water and a key decision point for many of its capital investments.
As an example, DC Water is responsible for maintaining the approximately 150,000 sewer laterals in public space. The utility replaces more than 400 sewer laterals per year at a cost of about $4.4 million. For decades, DC Water has employed the conventional open-cut construction method for lateral replacements, resulting in significant restoration costs and direct labor charges in addition to unavoidable customer inconveniences. The typical contractor installation takes four days to complete, and the average cost of a lateral replacement is $11,200, including restoration. The property owner remains responsible for the portion of the sewer lateral on private property.
As a strategic initiative, DC Water evaluated trenchless technologies to reduce the life cycle costs of the lateral inventory. It selected a cured-in-place pipe (CIPP) solution, deciding to use in-house crews over contractors to upgrade defective sewer laterals. CIPP can be used on approximately 80 percent of the lateral inventory. Typically, it can be installed in less than one day compared to the four days needed for the conventional method—resulting in only minor interference with utility customers’ daily routine. Work is completed with minimal surface excavation, providing a far safer environment for utility employees to work in. Here is how CIPP works.
A camera is sent through the lateral pipe to assess the material type and pipe condition. A decision is made onsite on whether the pipe condition is favorable for CIPP. The lateral is flushed, cleaned and cleared of all roots and other debris. A resin-soaked liner is then inserted into the damaged pipe using air pressure, followed by a bladder inflated with air to force the wet lining against the inside of the pipe. The resin cures in a few hours, leaving a smooth, seamless inner pipe wall, essentially a new pipe from the home to the main sewer connection with an expected useful life of 50 years.
CIPP eliminates infiltration and root intrusion and permanently seals open joints and holes in pipe walls. The CIPP process virtually eliminates road and pavement restorations associated with open-trench construction while also reducing the need for traffic control. Time spent on the job site is significantly reduced, often as high as 75 percent if crews do not have to install a clean-out, and the average cost of installation so far is about $3,900—or a $7,300 savings over the conventional open-cut method. Imagine spending 65 percent less to do more simply by working smarter. All investment decisions should be that easy.
Charles W. Kiely is the Assistant General Manager of Consumer Services and Operations for DC Water.