Columbia's sewer system isn't supposed to break down and spill wastewater.
It happens for a simple reason: the system is wearing out.
About two-thirds of the system is more than 50 years old, city officials estimate. In the past 15 years, city crews have found collapsed sewer pipes and leaky manholes that allow sewer spills.
Even some concrete pipes, thought to be state-of-the-art when installed in the 1970s, are deteriorating from exposure to sewer gases. The older clay pipes actually stand up better to sewer gases, but the joints don't always stay sealed.
One of the biggest sewer pipes in town, a 48-to-60-inch line between Elmwood Avenue and Blossom Street, has partially collapsed and is awaiting nearly $10 million worth of improvements.
The city's problems aren't unique.
Many of the country's 16,000 wastewater treatment systems are in poor condition because governments have not invested enough in maintenance and upgrades, according to a 2009 study by the American Society of Civil Engineers. Sewer spills caused by blocked or broken pipes release up to 10 billion gallons of sewage each year across the country, the report said.
In Columbia, pumps that push wastewater uphill to the city's treatment plant are overwhelmed if too much rain-fed stormwater washes into sewer pipes.
That inability to move all the extra water through the pipes causes sewage to back up and spill from manholes or battered wastewater lines.
While the main problem is with old sewer lines, overtaxed pump stations and leaky manholes, the city's sewer plant near the Congaree River at Interstate 77 also faces challenges.
If too much stormwater washes into the city's sewer plant, it can makes treating the sewage more difficult. Treated wastewater goes into the Congaree.