BlueScope Steel reported 32 incidents where it breached its pollution licence in 2011-12, including exceeding limits for mercury and cyanide in discharges into Port Kembla harbour.
The state's environmental watchdog said that while the discharge incidents were "relatively minor", just exceeding pollution conditions, BlueScope had been ordered to investigate the causes.
"Subsequent monitoring by BlueScope demonstrated compliance with licence requirements," a spokeswoman said.
Twelve of the incidents occurred in hot metal areas like the blast furnace and coke ovens, including a gas blast that rocked the No 4 coke battery in October last year.
A NSW Environment Protection Authority investigation into the blast found there was no harm to health or to the environment, but the explosion still amounted to a breach of licence conditions.
In response to the 32 incidents the EPA issued two fines totalling $3000, seven formal warnings, launched or modified six pollution reduction programs, and altered licence conditions.
The fines were in relation to a systems failure in basic oxygen steelmaking in February that led to undetected emissions.
None of the incidents caused significant off-site impacts, the EPA spokeswoman said.
The regulator continued to meet with BlueScope to "further reduce possible environmental impacts from the site", she said.
BlueScope's decision last year to shut down the No 6 blast furnace and halve production at Port Kembla also led to cuts in pollution levels.
General manager steelmaking John Nowlan said there had been a 40 per cent reduction in greenhouse gas emissions.
"Those rare occasions where we do not meet our licence requirements are typically related to process disturbances, where emissions only slightly exceed extremely low limits and do not pose a risk of material harm to the environment or to human health," he said.
"To put these licence non-compliances into context we have hundreds of individual licence requirements and analyse thousands of individual monitoring samples each year.
"Over the last five years, the number of environmental non-compliances across the company has successfully been reduced by more than 50 per cent.
In relation to the breach involving cyanide in the harbour, he said the concentration was "four times lower than water you could drink for five days and stay below the World Health Organisation recommended safe levels".
The company met its strict licence conditions in "almost all instances" and had invested more than $500 million on improvements in the past decade, he said.