Next month, the chief executives (CEs) of Otago's five territorial local authorities (TLAs) will discuss a proposal to standardise record-keeping and reporting of potentially contaminated land.
The plan, if adopted, could see hundreds and possibly thousands of landowners being notified of potential historic contamination on their properties.
TLAs are responsible for identifying contaminated land within their patch. Otago's TLAs are Dunedin City Council, Central Otago District Council, Clutha District Council, Queenstown-Lakes District Council and Waitaki District Council. The Ministry for the Environment's Hazardous Activities and Industries List (Hail) specifies 53 industrial and rural uses, such as petrol stations, gasworks, orchards, sheep dips, engineering workshops, timber plants and mining, which can cause contamination.
Otago Regional Council keeps a Hail master list for the province.
Sites on the list have been ranked by level of risk. Among those ranked a high risk are the former Dunedin Gasworks, the one-time Blue Mountain Lumber site in Tapanui, the erstwhile Odlins Timber Treatment Plant in Ranfurly, and an old gasworks near Oamaru's northern foreshore.
But the master list is incomplete and the communication between the regional and territorial authorities is imperfect, Jeff Donaldson, who is ORC's director of environmental monitoring, says.
''This is where we are wanting all the CEs of the region to start thinking along the same lines,'' Mr Donaldson says.
''So we can ensure the database is up to date ... So that everybody is doing the same thing.''
The ORC Hail list itemises 950 parcels of land. But the total number of potentially contaminated sites is probably in the thousands, Simon Beardmore, who is ORC's senior environmental officer, says.
A lot of the information that would help identify those sites is buried in the TLA's historic records of building and resource consents.
In May, ORC's Canterbury equivalent, Ecan, sent letters to the owners of 11,000 Christchurch properties that may have contaminated soil.
Mr Donaldson hopes something similar will happen in Otago.
''We need another month to confirm whether the TLAs are on board with this, but I'm pretty sure they will be,'' he said.
''The proposed plan is, once the list has been updated, if we have the support of TLAs, then landowners on the list will be notified by either the ORC or their TLA.''
Mr Beardmore says it is likely only a small fraction of those sites would turn out to be contaminated if they were investigated.
