The anticipated cost to build a controversial water-supply project in northern Colorado has increased 15% from 2006 estimates, to $490 million, project officials say. That total is up sharply from the original $350-million estimate at the project’s 2003 inception.

The Northern Colorado Water Conservancy is coordinating the Northern Integrated Supply Project, or NISP, for 11 funding cities and four water districts in Weld and Larimer counties. At completion, NISP will supply 40,000 acre-ft of water per year to area residents.

Additional capacity is critical: A recent water study says that, by 2050, Colorado’s population will double, and 80% of the state’s new residents will live on the east side of the Rocky Mountains. A majority will occupy the South Platte River Basin, the area served by the NISP project. The growth will require an additional 830,000 to 1.7 million acre-ft of water to meet municipal and industrial needs.

The project includes extensive pipeline construction and two new reservoirs: the 170,000-acre-ft Glade Reservoir northwest of Fort Collins and the 40,000-acre-ft Galeton Reservoir east of Greeley.

NISP officials said the new, $490-million price tag includes expanded storage of up to 45,600 acre-ft in Galeton Reservoir and more capacity for pump stations and pipelines, plus inflation costs for construction materials.

The project has been hit by additional environmental studies and permitting delays. The Army Corps of Engineers completed a draft environmental impact statement (EIS) two years ago but then added a supplemental EIS after critics raised concerns about water quality, hydrology and riparian corridor issues.

The supplemental EIS should be complete early next year, with a record of decision expected in 2012.