A family member did not want to comment this week.
Last year, Horizons Regional Council issued an abatement notice to HDC to cease causing objectionable odour beyond the landfill boundary and fined it $1000.
Last week, Horizons regulatory manager Greg Bevin said the abatement notice was still in place but the landfill was compliant because there had been no recent verified odour complaints.
Malcolm Hadlum, from the Neighbourhood Liaison Group, an Environment Court created landfill watchdog, said it appeared HDC purchased the property to stop odour complaints.
"Because of its location, the landfill will always leak gas and leachate," he said.
A Tonkin and Taylor landfill report this year gave HDC three options, including one to close the landfill in 2019, Mr Hadlum said.
"All things considered: financially, environmentally, culturally and morally, this option is the logical choice. The sooner it closes the better," he said.
He said NLG had argued for almost 20 years that the landfill would be a massive burden for future generations because it was in an aquifer in porous sand country.
The HDC paper said because of odour complaints, purchasing the property was prudent to "annex the landfill".
It would allow officers to gain a better understanding of issues affecting surrounding properties.
HDC inferred that buying the property was a cost-effective way to manage odour issues. It said the long-term cost of managing complaints, including costs associated with its resource consent review, exceeded the property's purchase cost.
Horizon's next compliance assessment of the landfill is scheduled for later this month.