One of the items Kenai Peninsula Borough officials hope to have state lawmakers include in the state’s capital budget is infrastructure needed to create a long term solution for treatment and disposal of landfill fluids, also known as leachate.
In its draft capital funding priorities list to be considered by the Kenai Peninsula Borough Assembly at its Jan. 8 meeting, borough administration requested $3.4 million for a leachate thermal evaporation unit. The unit would be the least expensive and most effective process to allow the borough solid waste department to deal with the leachate that can no longer be treated in the way it has been for the last several years.
Jack Maryott, borough solid waste director, said the borough has had to treat leachate since changing environmental regulations required landfills to install liners beneath waste masses. As a result of the liner at the Central Peninsula Landfill, precipitation percolates through the garbage, is collected at the bottom, pumped out and managed. It is not considered a hazardous material, he said.
A permit the borough previously obtained allows landfill managers to recirculate that leachate back into the waste, which has numerous benefits, Maryott said. Although the landfill, at any given time, may have millions of gallons of leachate circulating through it, spikes in leachate that can’t be handled on site need to be disposed of properly. Spikes are caused by heavy rainfall, large snowfalls, spring breakup and are also influenced by the amount of waste contained in the cell.
Maryott said the borough previously sent that excess leachate to Kenai’s wastewater treatment facility for several years, but the city recently notified the borough that option was no longer on the table.
Kenai City Manager Rick Koch said the city’s treatment facility was being adversely affected by the borough’s leachate.
“The composition of that leachate is different than it used to be,” he said. “I don’t know what it is, but we immediately see the effect in the plant. It’s a significant effect. It took us almost three months to recover from the last time we took it.”
Koch said the city would have liked to help the borough.
“They got a problem and unfortunately with these sorts of things there are no cheap solutions to any of this stuff,” he said.
A borough-commissioned leachate management study generated five options to deal with the liquids, including the evaporation unit, pre-treatment and shipment to Kenai’s treatment plant, pre-treatment and then discharge into an engineered wetland, full treatment and discharge into the Kenai River or hauling it to the waste water utility in Anchorage.
While the evaporation unit was determined to be the most logical, the borough is also working on a temporary discharge permit with the municipality of Anchorage to have a backup option available, Maryott said.
Maryott said it is common practice in the state for landfill leachate to be treated at municipal wastewater treatment plants. The borough didn’t think the leachate would upset Kenai treatment facilities when the option was first examined, but knew it needed a long-term solution, Maryott said. The borough shipped 700,000 gallons of leachate to the Kenai facility in 2008, but that number dropped to 200,000 in 2010 and 98,000 in 2012, he said.
“When you have these big surges, you want to get rid of the excess and that’s what’s been going to the city of Kenai,” he said. “The amount that we are managing versus the amount that we’ve actually shipped off is not even close.”
One of the “big benefits” of being able to recirculate the leachate through the waste mass is that the process aides in stabilizing the waste quicker, Maryott said.
“By reinjecting the leachate back into the waste mass, what that does is the waste breaks down and decomposes faster, you end up getting more air space and one of the primary benefits in theory is you stabilize the waste mass sooner,” he said.
Once the waste settles and adds “air space” the borough can come back into that cell and add more waste.
However, each time the leachate circulates through the landfill’s waste mass, less and less is absorbed. Eventually the cell will reach “field capacity,” and will no longer hold any more fluids.
The borough, Maryott said, has a sizeable effort to mitigate leachate production, mainly by covering portions of the landfill not in use with plastic. Precipitation that doesn’t mingle with the garbage can be treated as storm water runoff, he said.
Another benefit of the leachate circulation process has to do with the gas normally produced at a landfill. Regular processes that generate gas through the decomposition of waste are expedited through leachate recirculation because it increases the speed at which waste breaks down.
“You don’t generate an aggregate more total gas, it just comes faster,” Maryott said.
Eventually, enough gas is produced at the landfill that it needs to be managed, which is where the thermal evaporation unit comes back into play, he said.
While the thermal evaporator is the cheapest option for leachate, the unit has a high energy cost.
If installed, the unit would require natural gas from the market to operate initially. But Maryott hopes gas the landfill produces will be sufficient to offset that fuel cost in the future.
The evaporation unit, he said, runs at a low temperature and releases only water vapor into the air leaving trace amounts of leachate residuals that are then put back in the landfill. Eventually, as each of the landfill’s cells are closed and capped they will be drained of their excess leachate.
The unit will also allow the borough to not get caught up in any changing environmental regulations tied to Cook Inlet, as that is where most municipal water ends up after treatment. Additionally, the borough will not have to adjust how they handle the leachate based on how its composition may change in the future. Other treatment methods might require process adjustments to match the leachate’s makeup.
“It will be strictly under our management,” Maryott said. “Total control with no outside influences.”
Brian Smith can be reached at firstname.lastname@example.org.