Cost to separate sewers extreme

City Councilman Mike Haire’s question flowed out of a discussion on the city’s ongoing cooperation with other local agencies to clean up water discharged from storm sewers into area streams:

What happens if environmental authorities eventually compel municipalities like Altoona to separate their “combined” sewers, which carry both sanitary and storm effluent?

“It would be astronomical,” Councilman Bruce Kelley replied. “It would make the unfunded pension liability look minuscule.”

That unfunded pension liability, an earlier topic of discussion at the same meeting on Wednesday, is about $25 million.

Actually, Mark Glenn, the consulting engineer for the Altoona Water Authority, estimated in a long-range capital study in 2008 that separating the sewers would cost $65 million.

A combined system that serves the center city area includes a combined sewer overflow facility for each of the outfalls that carry effluent to the city’s two sewer plants.

The tanks – which the authority empties after storms – capture the “first flush” of heavy runoff and the pollutants and litter it carries, while preventing the rush of water from overwhelming the sewer plants.

But the runoff can be great enough to exceed even the recently expanded treatment capacity of those plants, in which case the excess is diverted directly to streams.

That excess includes sanitary waste – although it’s highly diluted.

Moreover, the combined sewer setup requires the plants to treat the storm runoff that they can handle – which is an unnecessary expense.

Combined sewer systems don’t get built anymore, and people have been talking for a long time about undoing the ones that exist in older cities, Public Works Director Dave Diedrich said.

There’s no indication such a mandate is imminent, Diedrich said.

But it is “unreasonable to assume that no action will be required in the next 25 years,” Glenn wrote in 2008.

Separating the sewers would require placing additional and smaller sanitary lines parallel to the large combined sewer lines, then repairing the combined sewer lines, which would continue to carry storm runoff, Glenn said then.

Separating the sewers would need to be a project that is done “one piece at a time,” Kelley said.