"We have one liner on the base in the landfill, and capping on the top. The void space in between is what we can sell for people to put rubbish in."
Until November 2017, leachate from the landfill was treated and discharged into Tutaenui Stream. Since then a full treatment system has been installed on the landfill site.
As waste in the landfill decomposes, water is released and is added to by rainfall percolating through it. This leachate is all collected and treated to "a fairly high standard" that removes organics and nitrogen.
Since August 2018, the treated leachate has been added to Whanganui's wastewater treatment plant.
Members of the public seldom get to see the landfill or the leachate treatment in operation, Mullinger said, but district mayors have been impressed with it.
"Everyone is staggered, because it isn't like what they can recall from 30 years ago."
Mullinger is originally from the food industry, and said he was there to make a difference and was part of the community too.
"We just sit there in the background and we don't make trouble, and if there are issues we deal to them."