"But when it dries out in summer, the balls pop up and get picked up."
Mr Faesenkloet said the site's uses were limited by a problem starting in the 1940s when people were able to tip anything they wanted.
"We don't know what toxic material is down there .
"The ground is still sinking, continually moving."
He said it could be 60 to 100 years before the landfill's production of methane gas settled down but the range did not need a gas monitor, because it was in the open air.
"But the great thing is that the site works favourably in all areas," said Mr Faesenkloet.
"It's a good revenue earner for the council and it gets more use than any golf course on the North Shore -- literally millions of balls are hit here a year."
The reserve, between the Akoranga Bus Station and Fred Thomas Drive, is one of three urban coastal closed landfills which have high priority for repairs to their clay cap.
The others are Ngataringa Bay Park, in Devonport, and Waikowhai Park, Mt Roskill, on the Manukau Harbour.
The manager of the council's closed landfills and contaminated land response team, James Corbett, said the sites needed to be investigated, remedial works designed and resource consents obtained.
Work on the first site to get consents was planned to begin in the 2016 earthworks season.
Mr Corbett said costs would depend on how much work was needed to give adequate capping for contaminated waste and also trapping the water running off the landfill.
Fifty out of a total of 194 closed landfills under council management had been identified as needing active monitoring based on health and environmental risks.
Several were in a long process to prepare them for safe public use.
"About 80 per cent of what we manage are used for playing fields and recreation and most people would not know they are on a closed landfill."
North Shore ward councillor Chris Darby welcomed investigations at Ngataringa Bay and Barrys Point to allay concerns at the risks of environmental damage and mounting costs of remedial work.
Mr Darby said he hoped investigations would show how the public might safely use reserve land on closed landfills that are now in strategic locations.
"There are severe limitations on what can be put there.
"There is very costly compliance for the Lake House Arts Centre at Barrys Point, with hundreds of thousands of dollars spent on gas monitoring equipment.
"It is important to find out whether gas has reduced over 20 years."
Puketapapa Local Board deputy chairman Harry Doig said the old Waikowhai landfill had caused problems with leachate seeping from it and hard pieces of rubbish piercing the cap at a playground.
The leachate was tested and found not to be a health hazard, said Mr Doig.
"But the worry is the uncertainty over what's down there and the drilling to be done will gauge the extent of the material."
The board plan says it will cost $4.3 million for an investigation, remediation and stabilisation of slopes, improved capping and management of leachate release to walkways and beaches.
"The actual remedial work might not be as dramatic as that but we would encourage anything to stop the Manukau Harbour being polluted."
Auckland's landfill legacy:
• 194 Auckland Council-owned sites
• 50 sites actively monitored for health and environmental risk
• 44 sites have resource consents for discharge of contaminants
• 80 per cent of sites are used for recreation sports fields
• 3 urban sites due for investigation and remedial works
