To find out what happens in these pipes, I talked to Raleigh's dean of pipage, sewer collection superintendent Hunter "Gene" Stanley. "We're not like New York City," Stanley says right off. "Some of those you can drive a truck through." New York has a combined sewer system that has to be prepared to move the billions of gallons of water that a major storm could dump on the city, not just the comparative trickle of sewage the city generates daily. Combined systems manage overflows with relatively simple mechanical junctions called regulators: basically weir dams in pipes or junction boxes. A weir is nothing more than a low barrier for steering water. When flow is routine, the dam routes it through pipes to the treatment plant; during large rain events, the flow of mixed stormwater and wastewater rises high, overtops the weirs, and flows directly through outfalls to rivers or lakes. Such an event is called a CSO, or combined sewage overflow. New York dumps about 40 billion gallons of CSOs into its rivers and harbors every year.
But before you draw too much comfort from Raleigh's system having to convey only sewage (the plant treats about 45 million gallons per day that are generated by the 400,000 or so customers connected to the system; it's rated for 60 million gallons, and it's being expanded to 75), consider this: The increase in flow caused by nothing more than rainfall and street flow coming in through manhole vents in low-lying areas can nearly double the flow to the treatment plant. Really? "Oh yeah, oh yeah," Stanley says. "A thousand gallons a day [per manhole] if it rains all day." Add in leaky joints, cracks, and holes made by thirsty tree roots, and you can have significant water infiltration during rainstorms. Though catching and correcting the breaks and overflows are an unavoidable part of his job, Stanley stays focused on preventive maintenance.
Stanley grew up in rural North Carolina and has called his preventive maintenance management "an ol' country boy work system"--he copies pages from the map book of his system and gives them to his crews. When the crew has flushed and inspected every line on the map, it comes back. The department logs its maintenance in feet per day, and it likes to reach 300,000 feet per month if it can, meaning that every pipe in the system gets a look-see once every few years. GIS keeps the maps updated, of course, but Stanley's system has been working since they were using nothing more than blueprints and as-built surveys; finding that what's an 8-inch pipe on the map is really a 6-inch is just part of keeping on top of things. That's why you carry different-size saw blades in your truck.
Stanley says a sewer is a simple thing: The pipe needs to drop about half a foot per 100 feet of length, a slope of 0.5 percent, which is fast enough to keep everything moving, but not so fast that the liquid races away from the solids. Bigger pipes--30 inches or larger--can slope even less. But they all must flow downhill, powered by gravity, which is why sewer pipes so commonly crisscross the stormwater drainages: Raleigh Public Utilities Department director Dale Crisp calls all the sewers that run in a particular drainage a "sewershed," which for a while became my favorite new word.
Of course, if wastewater pipes followed only natural gullies, the mains would eventually have to parallel the river, and for many reasons, from aesthetics to the catastrophic results of a spill, nobody wants that. The system generally moves downhill, but pipes sometimes need to cross rises. So the city has more than 100 lift stations, where the contents of pipes are pumped to join other flows or where wastewater from lowlying areas collects in sumps. When the water gets high enough, it trips a float valve and a pump clicks on and lifts it up a hill--kind of like your toilet, only this float valve starts the flush instead of stopping it. I visited one lift station, a 10- by 20-foot rectangle of electrical boxes that look like a central air-conditioning system behind chain-link fences between two houses, controlling an underground sump; even when it's pumping, if you were more than 10 feet away you wouldn't hear it. The station has a backup pump and a generator to power it, plus a little antenna to send information back and forth to the supervisory control and data acquisition (SCADA) system at the treatment plant; that's plenty of equipment, but just the same, if you weren't looking for it you wouldn't know it was there. A much larger station sits on the trunk line, giving a lift to pretty much all of Raleigh's waste on its way to the plant. It's underneath a highway on-ramp, and though some people suggested I could find it by following my nose, it didn't smell when I went out to visit it.