Filling basins that allow highly treated wastewater to seep into the ground could be the answer to McCall's growing pains.
The city of McCall is down to two options on how to solve its wastewater capacity problems spurred by rapid growth in the city.
A public meeting and hearing on the options are set for Tuesday night at McCall City Hall.
Of the two remaining options the city council is considering, rapid infiltration costs $5 million more than the option that would have the city discharge highly treated wastewater into the North Fork of the Payette River.
However, rapid infiltration may not have as many regulatory obstacles to overcome, according to the city's engineer.
The acquisition of land is the reason McCall's rapid infiltration option costs about $5 million more than discharging treated wastewater into the North Fork of the Payette River, city engineer Betsy Roberts said.
In the rapid infiltration option, the city would still need to build a new wastewater treatment facility that can treat wastewater to a higher degree than the city's current plant.
Instead of then discharging the wastewater directly into the river, the city would pump the wastewater through a pipeline to rapid infiltration basins to allow the wastewater to seep into the ground.
The estimated cost of this option is $75.8 million, about $5.6 million more than the river discharge option. However, the option may be more palatable to the Idaho Department of Environmental Quality and the U.S. Environmental Protection Agency, the two regulatory agencies who will decide if McCall's plan is a workable solution.
41 acres needed for basin
Rapid infiltration basins would be constructed cm I I acres of land the city would have to purchase.
The basins would be constructed in areas where the soil is conducive to absorbing the wastewater quickly.
Two basins would be built in the first phase, which is estimated to cost $53.1 million, Roberts said.
The basins would be rotated. After filling one basin, the wastewater would be rerouted to a second basin. Once the first basin allows the wastewater to seep into the ground it would then be ready again to be filled.
The wastewater would also have to be treated to a higher degree than it is now, Roberts said.
The new plant would use the existing aeration lagoons to modify the flow to minimize the effects of peak flow periods related to heavy rain events, Roberts said.
Fine screens and vortex grit removal devices would also be a part of the plant to filter out sand and gravel.
A pump station would also have to be constructed in the plant. Four aeration basins with
a membrane bioreactor, which would use biological organisms that eat nitrogen and phosphorus, would be built.
Nitrogen and phosphorus are two chemicals that can saturate a watershed and lead to deadly consequences for fish in Lake Cascade and the North Fork of the Payette River.
High amounts of phosphorus caused the city to abandon its practice of discharging its treated wastewater into the North Fork in the 1990s.
The move forced the city to dispose of its waste water through the J-Ditch pipeline that irrigates ranch land south of the city in the summer months.
During the winter, the city stores the wastewater from McCall and from the Payette Lakes Recreational Water and Sewer District in a large storage pond.
The new plant would also use chemical additives to disinfect the wastewater before it is finally pumped through a pipeline to the seepage basins.
