The site, situated on the south side of Gargan Rd, near the corner of Wintrebre Lane and Belk Rd, is owned by TBE 3 Ltd and is part of the Tauranga Business Estate subdivision.
Drains on the site, which was formerly farmland, flow west and form a tributary stream that flows into Wairoa River about 1.4km away.
In 2017, TBE 2 Ltd obtained resource consent from the council to convert about 9ha of the 350ha site into industrial use subject to a raft of conditions.
This included sediment and erosion controls being installed before construction works started and the primary sediment retention pond being built near two farm drains.
Construction of that work, undertaken by A & R Earthworks Ltd, began in early January 2018.
During an inspection that month, the council found earthworks involving almost 7.5 ha had been done prior to the pond being finished.
The pond was also not built in accordance with the consented plan, the council said.
On April 29, 2018, the council received a complaint from the member of the public that sediment was leaking from the site.
Two council officers visited and found a large amount of sediment-laden water flowing through a breached part of the wall of the sediment pond.
The officers tracked the flow overland and noted there was "very discoloured" water downstream of the discharge point.
They took samples of the contaminated stormwater the next day from two places downstream where a tributary stream flows in the Wairoa River. Suspended solid levels in the samples were high, the summary of facts said.
Council officers noted discoloured water near the site again on May 13 and tracked it back to an issue at the pond, and again three days later.
The regional council said it was likely that the discharges negatively impacted the quality of the stream habitat including rocks and cobbles, and plant beds that are part of the food chain for indigenous fish.
The council had earlier taken enforcement action against the same defendants, which included abatement notices for contaminant discharges.
The council's lawyer Adam Hopkinson told Judge Melinda Dickey that this offending could be characterised as "reckless".
He also said Bryce Donne, the company director for both defendants, deserved credit for showing "exemplary remorse" including a "very heartfelt" apology to the council.
He said Donne had offered to pay the council's full legal costs of $118,728 and to donate $50,000 for a restorative enhancement programme in the region.
Hopkinson said Donne had cooperated with the investigation and, unlike some defendants, made no attempt to shift the blame on to anyone else.
The defendants' lawyer Mark Beech argued his clients' culpability was not as high as Hopkinson had submitted.
Beech said it was water saturation in the pond walls that ultimately led to the failure, which was not picked up earlier even by geotechnical engineers.
He said the defendants took extensive steps to try to remedy the failure, including paying $80,000 to mitigate the effects, he said.
Beech urged Judge Melinda Dickey to also take into account that his clients had gone well beyond what was expected of them in trying to make amends.
Judge Dickey reserved her sentencing decision.
