The Southwest Corridor light rail project is now expected to cost $2 billion — $341 million more than the prior estimate, the Metropolitan Council said Monday.

Most of the additional cost was attributed to ground conditions along the route and soil contamination in St. Louis Park and Hopkins.

"The additional costs for the Southwest LRT Project pose significant challenges for our funding partners and taxpayers," Met Council Chair Adam Duininck said in a statement on the new cost estimate. "I will be talking to our funding partners, local communities and legislative leaders to determine the future of this project — all options are on the table."

The Met Council said that additional testing and engineering work filled in planning for the project, from a 1 percent level of detail to a 30 percent level of detail. Those new details include:

• 80 percent increase in retaining walls identified, as well as bridges and connecting roads.

• Redesign to accommodate poor ground conditions along the length of the corridor.

• Redesign to accommodate wetlands, flood plains and drainage areas, primarily in Eden Prairie.

• Acquire 137 acres of property, up by 11 acres from 126.

• Redesign to address rail safety requirements, including five gated LRT crossings and five shared freight rail and LRT crossings.

A map of the proposed Southwest light rail route. Courtesy of Metropolitan Council

Gov. Mark Dayton said he was "shocked and appalled" to learn of the big jump in the line's expected cost.

"The continuing escalation of the costs to design and build this line raise serious questions about its viability and affordability," Dayton said in a statement, adding the Met Council board "should quickly review other options for providing much-needed public transit to this region of the metro area."

Duininck said he has asked planners to look for cost savings on the project to reduce the increase.

Trains are now expected to start rolling on the Minneapolis-to-Eden Prairie line by 2020 instead of 2019.

The ballooning costs are the latest in a series of obstacles for the project, which had an estimated price tag of $1.25 billion just two years ago. Since then, it has faced a series of delays due to opposition from Minneapolis residents concerned it would harm nearby lakes and a popular recreation trail.

The city and the Metropolitan Council eventually agreed to bury the trains in a $130 million dollar tunnel as they pass between Cedar Lake and Lake of the Isles. The Met Council struck a separate deal with the Minneapolis Park Board, which was concerned that the trains would detract from the scenic channel of waters between two lakes.

In addition to the problems raised by the latest cost estimates, the project also faces two lawsuits — one from a group of Minneapolis residents, and another from the owner of a Minnetonka apartment complex.

The new details and cost estimates are scheduled to be included in a Supplemental Draft Environmental Impact Statement, originally scheduled for January of 2014, now expected in May.

The Met Council has already spent $59 million on project planning.

Light rail is still the best option to meet transit needs in the southwest metro, but the project's expenses need to be reduced, Hennepin County Commissioner Peter McLaughlin said.

McLaughlin supports the southwest light rail project but acknowledged the jump in expected cost is a "huge setback. We're going to have to find ways to make the thing work."