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Five Questions: Old water pipes and your health

For all the excitement over high-tech drugs and surgical procedures, clean drinking water is one of the top life-saving health advances of the modern age.

A PGW worker wades in receding water after a water-main burst June 14 at 52d Street and Wyalusing Avenue.
A PGW worker wades in receding water after a water-main burst June 14 at 52d Street and Wyalusing Avenue.Read moreTOM GRALISH / Staff Photographer

For all the excitement over high-tech drugs and surgical procedures, clean drinking water is one of the top life-saving health advances of the modern age.

Yet billions do not have access to it. According to a June report by the World Health Organization, at least 1.8 billion people still drink water contaminated with feces.

Philadelphia was one of the first cities in the U.S. to have a public drinking water supply provided by the government. It was begun in 1801 after a series of yellow fever epidemics killed thousands of people. Some pipes that date back nearly that far remain in use today.

When two water mains burst this summer, inundating streets and basements and forcing evacuations, the age of pipes became a hot topic.

Here to tell us more about the city's drinking water pipes is Christopher Crockett, deputy commissioner of planning and environmental services at the Water Department.

1 How much pipe is under the city, and how old is it?

We have 3,047 miles of pipes, basically the distance from Philadelphia to the West Coast. Most of the pipes are four to 12 inches in diameter, but the main lines are 16 to 132 inches. We're talking big enough to drive a car through.

Our records show we have some pipes dating back to the period of 1820-1830. About 25 miles of pipe is pre-Civil War.

2 How many miles do you replace every year, and how much does it cost?

Our program calls for replacing 28 miles a year. That costs us about $44 million, roughly $1.5 million a mile. Last year, we replaced 35 miles. A good rule of thumb is to replace about 1 percent of your system per year.

3 How do you decide which pipes to replace?

In the 1980s, we did a study of our pipe system with the Army Corps of Engineers and really started getting a feel for which pipes to replace. We came up with a simple point system: Each segment of pipe was given a score based on its age and the number of breaks that had occurred on that pipe during its life. After that, we saw a significant downward trend of breakages. Now, with new technologies, we have a screening tool to look at all the pipe in the city, and, with the data from 100 years, calculate the probability of failure. We know that certain types of pipes in certain types of conditions from certain decades have a higher likelihood of failure than other pipes. It's not always the oldest pipe.

The second piece of scoring is to look at the consequence of failure. If a pipe breaks, do we shut down a hospital, do we shut down a school? Is there some other major negative impact on the community?

We combine those two things, and that allows us to rank pipes, to look at what 100 miles of pipe we need to replace over the next five years.

4 Is there any cause of breakage that is more prevalent than others?

Every time a pipe breaks, we do a forensic analysis, like CSI. In Philadelphia, the cause is rarely corrosion, because we have sacrificial anodes (highly active metals used to prevent a less-active material surface from corroding) and cathodes that protect the pipe.

Though a pipe break appears sudden, the conditions that lead up to it often are things that happen over 20, 30, 40, 50 years. Some of the pipes were laid along old stream beds that have been filled in. That soil is less stable and can shift, putting stress on the pipe. During temperature changes, not only does the pipe expand and contract, but the soil around it is also expanding and contracting. Those two things alone can cause a break.

Or the stress could cause a leak. It might be so small we can't even detect it. But over decades, that leak causes dirt underneath pipe to wash away. The pipe starts to act as a beam holding up the street. Eventually, the pipe gets stressed to the point where it breaks.

Nearby construction can create vibration or a void. Contractors routinely hit our pipes.

5 When a pipe breaks, doesn't bacteria get in there?

People get mad when they see water coming out of a pipe. But we have to keep the water flowing until we know we can isolate the break so dirty water doesn't get sucked back into a pipe and get into people's houses.

When we repair or replace a pipe, we have a protocol. We flush it out, put chlorine in it, and, basically, sanitize it. We let water with chlorine in it sit for a day or so, and then test it for bacteria. If we don't find any, and if we have the right chlorine level, we put that pipe back into service. If anything is not right, the pipe has to go through the whole process again. It's very simple, but very critical.