The Washington Suburban Sanitary Commission (WSSC) provides water and sewer service to 1.8 million residents in approximately 460,000 households and businesses in Prince George’s and Montgomery counties in Maryland. Established in 1918, WSSC is one of the largest water and wastewater utilities in the nation, with a network of about 5,600 miles of fresh water pipeline and over 5,400 miles of sewer pipeline. Unfortunately, over many years the maintenance and replacement of the piping systems was deferred.
Approximately 1,300 miles of the more than 5,600 water mains are more than 50 years old. Nearly 2,500 water mains are between 25 and 50 years old. Almost 1,800 miles of water main were installed in the last 25 years. The age of the piping reflects more the age of the buildout of the system than any maintenance and replacement, for decades the only pipe replacements were for failed piping. After decades of deferred maintenance water main breaks have grown in frequency to about 2,000 breaks a year. Though age is not the only factor that causes pipe failure, most of the system’s pipes were designed for an average lifespan of 70 years. Over the next 10 years WSSC projects they will have to replace over 2,000 miles of water pipe and similar amount or sewer pipes. WSSC estimates that water pipes cost about $1,600,000 per mile of pipe.
Now WSSC is introducing new pipes that feature a zinc-coating on the exterior, which protects against corrosion. This is an improvement on the previous industry standard of uncoated ductile iron pipes that are exposed to soil. The zinc coating increases the life of iron pipes. Charged zinc ions migrate to scratched areas naturally, so pipes are less susceptible to corrosion damage than those composed of other materials. Additionally, the new piping will also have a V-bio® enhanced polyethylene encasement wrap, which discourages the growth of harmful bacteria that can damage the pipe.
Traditional ductile iron pipe lasts about 50-75 years the new pipes have a projected lifespan of well over 100 years, based on experience in Europe. Zinc coating on ductile iron pipe has been in widespread use in Europe where the industry first began using zinc coatings in 1955. As a result of zinc's widespread use there, standards were both developed and widely adopted. The advances in zinc coatings over the past 60 years have resulted in a highly effective corrosion inhibiting pipe that is now also coated in a V-bio polywrap.
The wrap protects the iron from a fresh supply of oxygen, thus halting or greatly inhibiting the corrosion. The patented V-Bio prevents microbiological cells from forming that would attack the iron and deplete the zinc. It is believed that the use of V-Bio with the presence of zinc as an anode to iron will further slow the process, though field tests in the United States have so far been about 10 years. The new pipe costs slightly more than the older style pipes, but since installation is the bulk of the cost the total price per mile is estimated to increase to $1,620,000 from $1,600,000. A reasonable cost for what WSSC hopes will be decades of additional service.
Though recently, WSSC has been replacing about 55-60 miles of water mains per year that has not been enough to keep up with the aging system that suffers from decades of deferred maintenance and some problematic piping. That rate of pipe replacement would replace the water system in 101 years, but much of the system has already exceeded their design life and some pipes in the WSSC system have not been lasting as long as originally projected.
Most of WSSC was installed after World War II in the booms of the 20th and 21st centuries. Post-World War II pipes tend to have an average life in the real world of 50-105 years depending on many factors (AWWA). To extend the life of the ductile pipes they were mortar-lined. These linings were meant to prevent corrosion and increase pipe longevity. In the 1970’ steel reinforced concrete pipe with a promised life of 100 years began to be used for the giant water mains by WSSC. Unfortunately, these concrete trunk lines began to fail catastrophically decades before their promised 100-year life expectancy.
WSSC has 350 miles of steel reinforced concrete pipe. WSSC ‘s supplier, Interpace, may have produced inferior pipe- the company was successfully sued by WSSC and others and is now out of business. Nine of the WSSC’s concrete mains have blown apart since 1996. After a particularly spectacular blowout 2008 and to prevent future catastrophe, WSSC installed a sensor system along all the concrete mains that cost more than $21 million to alert WSSC of an impending failure, but unfortunately the replacement program became an emergency replacement program responding to sensors and smaller breaks. Now the new program hopes to improve this situation, but with 1,300 miles of piping over 50 years old it is likely that the number of water main breaks will get worse before it gets better. Remember most pipes break in the winter months, so be prepared for emergencies and store an adequate emergency supply of water in your home- 10 gallons per person should be a three day supply.