By Amy Silverman
By Olivia LaVecchia
By Monica Alonzo and Stephen Lemons
By Chris Parker
By Michael Lacey
By Weston Phippen
The U.S. Environmental Protection Agency has estimated that U.S. sewer systems need $390 billion in improvements. In Arizona, the American Society of Civil Engineers has set the price tag at $6.2 billion.
The cost of waiting can be high, in terms of both dollars and health. Cities that have delayed repairs are facing multibillion-dollar fixes and big fines from the federal government. Without repairs and adequate maintenance, sewers can overflow, spewing disease-causing pathogens and heavy metals into streets and buildings.
To be sure, Phoenix isn't alone in its sewer woes, and problems elsewhere in the nation are far worse. But Phoenix stands at a crossroads. With more than 4,300 miles of pipe in the ground, ours is one of the largest sewer systems in the nation. If we don't take care of it now, the frayed edges will soon turn into major rips.
So far, the city has taken a calculated risk, triaging repairs and betting that the system won't crumble.
Think about that the next time you flush.
When a survey crew stuck a camera down the sewer pipe alongside an I-17 frontage road near the Durango Curve a few years ago, the experts were stunned. A 30-foot segment of the pipe was nearly gone. At 36 inches in diameter, this pipe was a big one, a critical segment of the system -- pipes that large are capable of handling nearly 30 million gallons of sewage each day, or 857,000 flushes.
Although sewage was still flowing through the void and onward to the treatment plant, a water line above the collapsed pipe was held up only by soil above where the pipe had been. Had that soil broken loose and cascaded downward into space, the resulting sinkhole could easily have been large enough to hold several SUVs, especially if the water line also broke and added to the torrent eroding away the earth.
The city had encountered that danger in January 2001, when an even larger 54-inch pipe two stories below the ground collapsed and created a massive sinkhole beneath a vacant lot near 22nd Avenue and Lower Buckeye Road. The hole quickly grew as sewage gushed from the line that conveyed several million gallons a day, threatening streets, railroad tracks and utility lines. Pumping frantically and working in the wee hours, when sewage flow is lowest, crews shored up the sides of the pit, stopping its expansion and containing the sewage spill to the immediate area.
Ten months later, a city work crew found a hole in a 54-incher at the wastewater treatment plant on 23rd Avenue, dug a little more, and discovered that the entire top of the pipe, concrete more than five inches thick, had corroded away on a 50-foot segment. Tens of thousands of gallons of raw sewage -- no one is quite sure how much -- overflowed the repair trench one night after a worker mistakenly allowed it into the pipe. The spill was large enough that the city told the Arizona Department of Environmental Quality that a monitoring well should be drilled to make sure pollutants didn't reach groundwater.
Right under the nose of the city's Water Services Department, one of the biggest pipes in the city had dissolved. It shouldn't have been a surprise.
For nearly a decade, the water department had known that more than 40 miles of concrete sewer pipe were melting away. Ranging in diameter from 24 to 90 inches (sewer connections to houses are four inches in diameter), the lines are among the most important segments in Phoenix's sprawling wastewater system, the arteries that carry our toilet flushes on the last part of their journey to a treatment plant. Considered state-of-the-art when they were installed in the 1960s and 1970s, the lines turned into one of the most expensive headaches in the city's underground world.
Concrete, it turns out, is a terrible material for transporting sewage, especially in a city like Phoenix. High temperatures prompt bacteria to produce astonishing amounts of hydrogen sulfide, which turns into sulfuric acid powerful enough to dissolve concrete. Worsening an already bad situation, sewage rushing through the pipes erodes acid-weakened material, causing deep grooves to develop on sidewalls of pipes where wastewater rises and falls each day, depending on when people are eating, taking showers or sleeping. Below the waterline, millions of pebbles bounce along, chipping away the bottom. And sewage became more potent as water reclamation projects siphoned off liquid, leaving solids behind.
The forces of chemistry and physics became clear during 1992 inspections of half the city's concrete sewer pipe. Rather than fix the pipes, the city monitored, lowering cameras into sewers and waiting until 1998 to survey the whole network. The idea was to wait as long as possible before replacing or lining the pipes, a task that would cost well over $100 million. The city was betting that it could detect imminent disaster on a case-by-case basis and fix the deteriorating pipes over time. The stakes were huge, considering many of the pipes crossed freeways and rail lines that could be shut down if the pipes failed.
But the most recent surveys showed corrosion was an exponential equation. Even as the sinkhole on Lower Buckeye opened up, videotapes of the city's lines were showing that pipes that had looked okay five years earlier needed immediate replacement.