chromium from its ammonium nitrate plant near Stockton that affected 70 households; the second one was the release of arsenic into the Hunter River at Newcastle; the third was of mercury vapours from its Botany site; the fourth was a leak of ammonia from its site at Kooragang; the fifth was an ammonium nitrate leak of at its Kooragang Island plant, only a day after being allowed to reopen; and the sixth incident was a sulphuric acid leak of approximately at its Port Kembla site. The fourth leak triggered a public forum and NSW Government investigation into the leaks, and the temporary shut down of the Kooragang Island plant. Hexavalent chromium leak, 2011 Orica's Kooragang Island chemical plant released hexavalent chromium into the atmosphere on 8 August 2011. The known carcinogen was released between 6 and 6:30pm and the spill continued for approximately 20 minutes. An estimated of hexavalent chromium was discharged from the Orica plant, with another over the suburb of Stockton. Approximately 20 workers at the plant were exposed as well as 70 nearby homes in Stockton. Orica failed to notify government authorities until 16 hours after the incident and residents were not formally notified for three days. Under a Prevention Notice issued on 11 August 2011, the NSW Office of Environment and Heritage (OEH) closed the ammonia plant at Kooragang Island. The hexavalent chromium leak was the subject of a New South Wales Parliament Upper House inquiry that was concluded in February 2012. Hunter River arsenic leak, 2011 Effluent containing high levels of arsenic leaked into the Hunter River from the Kooragang Island chemical plant on 19 August 2011 at 3pm. Arsenic had not been used on the site since 1993, however during a cleanup of a hexavalent chromium spill on the site the week prior, old deposits of arsenic leaked into a storage pond and drained into the Hunter River. It was estimated the arsenic concentration was 0.067 milligrams per litre, exceeding licence limits. Barry O'Farrell, the NSW Premier, said "two spills in a fortnight raise reasonable concerns about systemic failures in the way in which this company is operating its facilities." O'Farrell continued, "I've had a gutful of families being distressed, by potential threats to their safety and threats to their local environment." Ammonia leak, 2011 On 9 November 2011 more than of ammonia was initially suspected of venting to the atmosphere from the Kooragang