"There were three rounds of widespread sampling of groundwater and bore work, and there were external things like contractors and lab testing [lab testing alone cost $100,000].
"The costs are about where we thought they would be - the work has been expensive but no one else in the region had the capacity or capability to do it," Mr Maxwell said.
He said the regional council was the only agency to have the expertise to gather the information, and that the results fed into the government inquiry.
"Although we didn't end up prosecuting [Hastings District Council], this information will be critical for the inquiry," he said.
He added that there were no guarantees any money could be recouped from the court costs, which earlier last year the regional council said it was told could be possible if there was a successful prosecution.
A substantial investment had also gone into the inquiry, which resumes this Monday.
To date it had cost $637, 310 with the possibility of increasing further while the inquiry was ongoing.
The lion's share of that expense came from Chen Palmer law firm legal fees, that as of this week stood at $413,867.
Group manager strategic development James Palmer said the whole process had been "resource hungry" .
He said Chen Palmer was engaged as legal counsel because it was a public law firm, and the issues were not quarantined to the Resource Management Act.
They also included health, local government authority and inquiries act issues, he said.
"We have no in-house experts for inquiries of this nature - it's standard practice to outsource.
"It's not just legal advice that has resulted in legal fees - it also includes servicing the inquiry in its totality from day one. There's a team of people at Chen Palmer who have been having almost hourly interactions with the inquiry's counsel and other legal representatives.
"It was always going to be necessary to have legal counsel for the inquiry and needed a team of people. I think the costs for the other core participants will be similar if not greater."
Councillor Fenton Wilson challenged the Hastings District Council to release the numbers on what it had spent on the investigation and inquiry to date.
Hawke's Bay Today put that question to Hastings mayor Lawrence Yule on Tuesday.
He said they would need a couple of days to compile the costs, and that some of the expense may be covered by insurance.