Members of the council response team have been at the scene since Monday, at first putting up an exclusion zone while risk to the environment was investigated.
"Due to the location of the incident, and extremely steep bank that drops off from the road edge, this was a complex investigation," Mr Mellor said.
Until the investigation was complete he could not estimate the total amount of chemicals spilled.
According to information provided by the council, ferric chloride was primarily used for metal etching and effluent treatment.
It was classified as a dangerous good and people dealing with it required protective gloves, clothing, face and eye protection. It could contaminate sewers or waterways but the regional council confirmed there was no running water beneath the crash site.
Mr Mellor said regional council staff would remain on site until all of the drums had been safely removed and the road and site had been cleared of any contamination material.
Fire Service north communications shift manager Scott Osmond said fire crews from Rotorua were still recovering the drums yesterdayafternoon and had yet to bring up the truck and trailer from the bank.
Fire crews were there to assist regional council staff in securing the drums of hazardous chemicals.
A crane was on site to pull up the truck and trailer.
The driver, a 63-year-old man from Rotorua, died in the crash. He was yet to be named by the police.
Diversions remained in place at the north end of Pyes Pa Rd near Te Matai Rd and the south end of Pyes Pa Rd near Dudley Rd.