Public comment is currently being accepted on a proposed permit to allow the Nikiski Combined Cycle Plant to discharge treated process wastewater in Cook Inlet.
The Alaska Department of Environmental Conservation is currently weighing the request from Alaska Electric and Energy Cooperative Inc., a subsidiary of Homer Electric Association, to discharge into the inlet a maximum of 50,400 gallons of wastewater per day containing reverse osmosis reject water, carbon filter back washes and wash down water.
"These waste streams are co-mingled and treated and then discharged through an outfall into Cook Inlet under a wastewater discharge permit," said Wade Strickland, acting wastewater discharge authorization program manager.
Strickland said the 50,400 gallons per day limit is a comparatively low volume of water discharge compared to other active permits. Strickland also said the concentration of pollutants from the discharge would be relatively low, as well.
"The projected concentrations of the pollutants that will be discharged are not much higher than our applicable water quality standards, which are found in regulation that are protective of aquatic life in the receiving water in Cook Inlet," he said.
The Nikiski Combined Cycle Plant is part of HEA's Independent Light project. Its main component is a new steam turbine that will be fueled by steam produced from exhaust heat coming off the existing natural gas turbine. The project would allow the Nikiski Generation Plant to nearly double in generation power, from 40 megawatts to as much as 77 megawatts, HEA wrote in a press release.
HEA spokesman Joe Gallagher said in an email the average discharge will be intermittent and be about 10 gallons per minute with a maximum of about 35 gallons per minute.
"A form of chlorine is added to the water treatment system to prevent algal and biological growth, consequently there is some residual chlorine in the water discharge, much like there is municipal drinking water systems," Gallagher wrote.
Strickland said the permit would be for up to five years. The DEC has tentatively determined to issue a permit for the project.
Gallagher said well water will be purified to reduce nitrogen oxide emissions of the existing combustion turbine, and for use in the heat recovery boiler to generate steam to drive the turbine.
Strickland said reverse osmosis process usually starts with a "raw source water," in this case well water located near the project site.
"Then they will take that, run it through some processes to really make sure that the water is ultra-clean essentially," he said.
The waste from that is the reverse osmosis water, which is further treated by a settling process. Disposal of any sludge from that water would require a solid waste permit, Strickland said.
Depending on what is naturally occurring in the source water will usually be what's in the reject, slightly concentrated and so in this case there is some arsenic and potentially some copper," he said.
Strickland also said the processes detailed in the application "should not result in the discharge of benzene."
"There is the potential for oil and grease, but not necessarily specifically the hydrocarbon benzene in the discharge," he said.
The DEC has also proposed a circular mixing zone with a radius of eight meters, or 27 feet, for the disposal site.
"A mixing zone is basically an area in the receiving water that allows for initial dilution of the wastewater stream where water quality criteria can be exceeded, but at all points outside of the mixing zone, the water quality standards for that receiving water have to be met," Strickland said.
Deadline for public comment on the project is 5 p.m. on April 25. No public meeting is planned, Strickland said, but if there is significant public interest, the DEC would host one on request.
"The thing to note about this discharge is that it hasn't occurred yet, so ... during this permit cycle we'll learn more about the characteristics of the waste stream to further refine the permit during the next permit cycle," he said.
Gallagher said the project has been through extensive review and scrutiny by numerous permitting agencies as well as a National Environmental Policy Act environmental assessment by two cooperating federal agencies -- the U.S. Army Corps of Engineers and U.S. Department of Agriculture Rural Utilities Service.
"The environmental assessment process involved federal, state, and local resource managers to ensure any and all concerns were adequately addressed," he said.
Brian Smith can be reached at firstname.lastname@example.org.