Quite a bit more of that kind of thing expected with the increase in extreme weather events from climate change. In Westland alone there are another 12 at-risk old landfill sites. It's estimated that the cost of preventing further spills from the one already-open landfill alone is ~2.3M. In an economically depressed region like Westland it won't be funded, and they're far from the only region in NZ that's facing this problem. Just the first to have experienced a spill event.

Unfortunately the purely-for-profit structure of these long-term ventures can mean that there is no money to cover the cleanup if things go really wrong, depending on who owns the site. I think you need to look at some sort of cleanup fund in escrow as a precondition for building sites like this, which should incentivize improvements in safety measures too.