Should the town of Cary -- or any other town -- be allowed to dump partially treated sewage into a river after heavy rainfalls?
Utilities officials in Cary, Durham and Greensboro support a proposed U.S. Environmental Protection Agency policy that would allow sewage plants to release a mixture of fully treated and partly treated sewage during peak flows. The practice is called blending.
Some plant operators say the change would give them more flexibility to protect their plants, help ensure that all sewage gets some treatment, and prevent overflows of raw sewage. State water quality officials oppose blending, and the city of Raleigh said it wouldn't do it. Environmentalists say it encourages plants to skip treatment steps more routinely and release more disease-causing organisms into the water.
"Obviously, from our standpoint and most cities' that have plants in North Carolina, the issue is the extreme weather conditions," said Rob Bonne, Cary's public utilities director. He wrote to the EPA last year supporting the change, which is now in the final stages of review. "You are protecting the river or stream that you are discharging into from a catastrophic failure of the treatment plant."
State officials say state policy doesn't allow skipping any treatment step but makes allowances case by case for releases during wet weather.
"Certainly under very extreme circumstances, such as hurricanes, blending is an inevitability," said Mark McIntire, a state regulator. "However, in these situations, it is the division's experience that entire facilities are inundated. As such, blending is a force of nature rather than a mode of operation."
Bypassing one stage
The EPA first announced the idea a year ago and is reviewing a final policy. The change has been sought by the association that lobbies on behalf of municipal sewage plant operators who face the prospect of spending millions of dollars to repair cracked underground sewage lines that fill up with groundwater during wet weather.
Plants typically treat sewage in several stages. First, raw sewage passes through screens to filter out large solids such as sticks and litter, then moves to settling tanks to allow other solids to sink to the bottom. The partly treated sewage then undergoes a second round of treatment in aeration basins, where microorganisms eat the dangerous viruses and parasites in organic waste. Some plants also treat sewage with disinfectant to kill pathogens before piping it into a creek or river.
The EPA proposal would allow plant operators to skip the second step when the volume of sewage exceeds the capacity of microorganisms to consume the waste. Some of the partly treated sewage would be diverted around the second treatment step and mixed with fully treated sewage before release.
"There are times when that is necessary," said Terry Rolan, water management director for the city of Durham. "It is sometimes practical to not put all the flow through those units and save the system so it operates the next day when the flow drops back down."
Plant operators say blending for a day during peak flows can prevent problems that can shut down a plant for days. A surge of stormwater can act like a tidal wave, washing most of the living microorganisms out of the basins that are critical to biological treatment. That can render a plant ineffective for days or weeks.
During wet weather, the city of Greensboro has used blending for decades at its smaller sewage plant, which discharges into North Buffalo Creek, which eventually flows into the Cape Fear River. A valve automatically diverts flow around the secondary treatment once the plant reaches capacity.
"It's a ho-hum thing for us," said Martie Groome, who oversees compliance for Greensboro's sewage plants. "We've been doing this for years. If we still have to meet our limits, we don't see it as a big deal."
Blended sewage, under the EPA proposal, still would have to meet plants' regular discharge limits. Typically, those are based on average concentration levels.
McIntire, the state regulator, said it would be impossible to know whether the wastewater being released during blending complied with permitted discharge limits until after the fact -- when the treated sewage was already in the river.
"How will a facility know if it's in compliance when it takes five days to get some of the test results?" McIntire asked. "I'd be real surprised if we'd ever approve blending as EPA defines it."
McIntire said that state law does not allow plants to skip the biological treatment and that a well-run sewage plant should not need to resort to blending. Treatment plant operators are required to report unexpected releases of sewage. State regulators review those releases case by case.
The city of Raleigh added 30 million gallons of storage capacity after a series of discharges of partly treated sewage into the Neuse River after heavy rains.
T.J. Lynch, superintendent for Raleigh's sewage plant, said the city would not adopt the blending policy. "You are guessing as to what your pollutant levels are," he said. "I don't want to take that risk."
Jim Swartzenberg, an oyster farmer and president of the N.C. Shellfish Growers, said sewage blending could lead to coastal shellfishing waters' being closed for longer periods after heavy rains.
"I'm against it," Swartzenberg said of the EPA proposal. "It recognizes there is a problem out there. It just says we'll legalize it, not fix it."
Staff writer Wade Rawlins can be reached at 829-4528 or email@example.com.