The establishment of a $300 million cement plant near Oamaru was its most viable option, Holcim told an Environment Court hearing at Oamaru District Court today.
That was due to the inefficiency of Holcim's Cape Foulwind plant, near Westport, the company said.
The Weston plant - near Oamaru - would use cleaner, dry coal burning technology which would emit less carbon dioxide, sulphur dioxide and nitrogen per tonne of cement compared with Westport, which uses wet coal burning technology, Holcim lead project engineer Stuart Ward said.
"It goes without saying you end up producing less CO2."
However, as the Weston plant would produce up about 880,000 tonnes of cement a year, he conceded the total carbon footprint of Weston would be greater than that of Westport, which produces about 500,000 tonnes a year.
Mr Ward said Holcim had considered 18 sites in New Zealand, with Weston being the most suitable option.
Building a new dry technology site in Westport would be infeasible, he said.
The Weston plant, if constructed, would be about 1km long and have an estimated stack height of 104m.
Mr Ward said the size of the plant had been chosen to supply current needs and to allow for expected market growth in New Zealand into at least the 2030s.
The significant advantages of Weston included the large deposit of high-grade easily quarried limestone near the plant site, he said.
Most of the cement would be transported to Timaru via rail and then shipped around New Zealand aboard a specialised vessel.
Landscape architect Allan Rackham was the fourth of the 15 witnesses Holcim will call to the stand during the hearing.
Mr Rackham said the visual effect on the area would be relatively minor compared with the other sites that were considered.
"Its effects are surprisingly low in reference to a development of this size."
He said while the Whitstone Escarpment would obscure the view of the quarry the smoke stack would be visible from most sites within a 3km radius.
Suggestions Holcim was trying to buy the support of the community and Ngai Tahu were firmly rejected.
The suggestions were "offensive", Holcim Capital Projects manager Ken Cowie said.
The accusations were put up by counsel for the Waitaha Taiwhenua o Waitaki Trust Board regarding the proposed establishment of the plant.
Counsel Joan Forrett implied Holcim's proposal to form and fund a community trust was a way of earning support.
Trust spokesperson Stephen Bray later told The Oamaru Mail that the Waitaha people felt "disenfranchised from the whole proceedings".
The Waitaha tribe were the first occupiers of the land before being absorbed by Ngai Tahu.
