The Altoona Water Authority is working on a plan outlining a test protocol to demonstrate the effectiveness of two facilities that are designed to prevent contamination of streams from the city’s “combined” sewer system after heavy rains.

The plan is a requirement for the authority to renew its National Pollutant Discharge Elimination System permit from the state Department of Environmental Protection for its combined sewer overflow systems.

Once DEP approves, the authority will need to conduct tests to show — officials hope — that the combined sewer overflow systems prevent measurable problematic contamination in the Little Juniata and Frankstown Branch of the Juniata rivers.

The combined systems, which serve the central part of the city and a bit of Logan Township, take in both sanitary sewer effluent from toilets, tubs and sinks and storm runoff from streets.

Such systems are common in older cities. But they’re less than ideal, because sewer authorities have to pay for processing nominally clean storm runoff along with sanitary effluent. In addition, when storm runoff exceeds the capacity of the sewer plants, the sanitary effluent that happens to be in the overflow enters streams without being treated.

Overflow systems are designed to prevent or minimize that discharge of sanitary effluent by diverting the “first flush” following storms into large tanks.

After those tanks fill up, the remainder of the storm surge goes into the streams, although the oil residue and litter from the first flush remains in the tanks — whose contents are pumped out after the storm subsides for treatment in the sewer plants.

The current permits for both the authority overflows, one at Tuckahoe Park and the other behind Peoples Natural Gas on Bellwood Avenue, are expired — one in 2012 and the other in 2013, reflecting the state’s general backlog on combined sewer overflow permitting, according to Todd Musser, the authority’s environmental services manager.

For the new permit, DEP will require a long-term plan that shows how the authority is improving the streams into which the overflows discharge, a kind of document the authority has never provided before, Musser said.

Despite the absence of such a document, improvements by the authority to the overflows — and the treatment plants — have improved those streams, as demonstrated by the likelihood that DEP will upgrade the Little Juniata River between the Easterly Sewer Treatment Plant and Bellwood to a high-quality cold-water trout fishery, Glenn said.

Actual testing for contaminants like E. coli and fecal coliform will take place next year during a four- or five-month period, according to Mark Glenn of Gwin Dobson & Foreman, the authority’s consulting engineer.

That testing would need to take place following storms and could require workers going out at any hour of any day, said authority General Manger Mark Perry.

Mirror Staff Writer William Kibler is at 949-7038.