If the city of McCall chooses to re-introduce its treated wastewater to the North Fork of the Payette River, then the state will require an offsetting amount of phosphorus be removed from other sources.
In the mid-1990s, the city built its current treatment system that stopped putting treated sewage into the North Fork. The Idaho Department of Environmental Quality urged the removal because phosphorus in the effluent encouraged algae growth downstream in Lake Cascade.
The city's wastewater treatment plant currently uses land application as a method of discharging its treated effluent. The city contracts with agricultural landowners south of the city- to apply treated effluent with water as a source of irrigation using the city's J-Ditch pipeline.
In the' winter, the effluent is stored in the city's giant J Ditch pond.
Both the Idaho Department of Environmental Quality and the U.S. Environmental Protection Agency will have to approve McCall's plan to cut down phosphorus in the water to be put into the river.
"We are open to that discussion," said Craig Shepard, regional manager of water quality for DEQ.
Idaho currently has a phosphorus-trading program on the lower Boise River, but no one has ever used the program, Shepard said.
Currently, there is no language in the plan that governs Lake Cascade that would allow a trading program, he said.
However, Shepard said that language to allow a trading program for Lake Cascade would be an easy fix.
In a trading program, the city would pay agricultural producers to reduce the amount of phosphorus that enters the watershed from their farms.
"Historically it is cheaper to get phosphorus out of ag sources than it is to build wastewater treatment facilities," Shepard said.
Storm water targeted
The city is already investigating phosphorus offsets, which could include better ways to handle storm water drainage, which contains phosphorus.
How much phosphorus is contained in storm water would have to be determined in order for the DEQ to be able to credit the city accurately for phosphorus it removes from the watershed.
"They (the city's engineer) are going to have to figure that out," Shepard said.
The city could build storm water retention basins, use grease, and sand traps and other technologies to reduce the amount of phosphorus entering the watershed via storm water.
The city can also reduce phosphorus by paving gravel streets in McCall, Shepard said.
If the city chooses the surface water discharge route, it will still be required to treat its waste water at a higher level than it currently does to remove more phosphorus before it can discharge into the river, Shepard said.
Rapid infiltration in seepage basins, the other option the city is considering, could also eventually leak phosphorus into the river, Shepard said.
"I'm not a geologist, but it is a different calculation," he said. "The soil will hold a certain amount of phosphorus for a certain amount of years."
