DSTP proper technology - PNG national court

The National Government said that deep sea tailings placement (DSTP) presents a viable alternative for PNG mines as compared with traditional land based tailing storage method and that the Government is applying good resources in managing its impact.
During his opening remark at the PNG Mining & Petroleum Environment Seminar in Port Moresby from July 19 to 20, Minister for Environment & Conservation Benny Allen said that high risks for land based tailing storage practices in PNG are often associated with characteristically high rainfall and geologically active surface formations. 
On DSTP, Mr Allen explained that it refers to the tailings passes down a deep sea pipeline that discharges well below the maximum depth of the marine mixing zone, which is generally about 100 meters depth. 
"Water below this depth generally remains effectively cut off from the upper waters by the strong temperature and salinity gradients that extend down through the first hundred meters or so of the water column," Mr Allen said.
Mr Allen said effectively, discharge below 100 meters below the maximum depth of mixing zone will generally be trapped there by the layer of warmer waters above. 
He reiterated that by way of precautionary measure in dealing with environment risk, his department applied a substantial safety margin to the depth of all operational DSTP outfalls in the country between 130 and 150 metres well below the mixing zone.
He used Ramu NiCo's DSTP system as an example. According to Mr Allen, the Ramu DSTP outfall is discharging at 150 metres into Basamuk Canyon, adding much safety margin. 
"At this depth movement of the tailings into the upper mixed waters is considered most unlikely and the tailings will be confined to this area as they slowly decompose over the coming decades," he said.
He said the National Government with MRA commissioned the Scottish Association of Marine Science (SAMS) which conducted comprehensive oceanographic surveys of three DSTP locations in PNG between 2007 and 2009 that assessed the environmental risks and impacts DSTP posed and prepared a comprehensive set of Environmental Guidelines for DSTP in PNG.
"These guidelines are being applied to DSTP systems in PNG, including the recently completed Ramu Nickel Mine in Madang Province," Mr Allen said.
Misima is the first PNG mine practicing DSTP. DSTP is currently used at Lihir and Simberi Island mines.