Adding toll lanes to Interstate 270 and Maryland’s part of the Capital Beltway would require moving 70 miles of large water and sewer pipes at a cost of up to $2 billion, according to a new estimate.

That analysis, by the Washington Suburban Sanitary Commission (WSSC Water), is far higher than the $900 million in pipe relocation costs estimated by the Maryland Department of Transportation (MDOT).

An MDOT spokeswoman said the state included pipe-related costs in its estimate that building toll lanes on both highways would cost more than $9 billion to $11 billion. However, she said she could not confirm how much the state allotted.

It remains unclear if the potential expense of relocating the pipes leaves the overall project cost projection too low.

Montgomery County Council member Tom Hucker (D-District 5) said he’s concerned residents and businesses in Montgomery and Prince George’s counties could get stuck paying for the pipes via higher rates on their WSSC Water bills for decades to come, even if they never benefit from the toll lanes.

WSSC Water estimates that relocating its huge mains — some are up to eight feet in diameter — would cost between $1.3 billion and $2 billion depending on the construction method used, according to a utility report to both county councils.

A 1958 memorandum of understanding designates who pays to move pipes for road widening projects — the utility or the Maryland State Highway Administration — depending on whether each stretch of land first had pipes or a road. If one agency or the other had “prior claim” to the land, the other one pays, according to the agreement.

Even so, WSSC Water spokesman Chuck Brown said the utility and state typically split the costs. One problem, he said, is that the agreement does not address highway projects built as a public-private partnership, as the state plans for the toll lanes.

“We don’t want our customers to bear the financial burden of this project to relocate any pipes at all,” Brown said. “It’s just too massive.”

The utility said the state hadn’t included in its estimate $280 million that would be necessary to move the 5.3-mile bi-county water tunnel, a steel pipe seven feet in diameter that opened in 2015 adjacent to the Beltway after six years of construction.

Maryland Gov. Larry Hogan (R) has advocated for the toll lanes as a way to relieve the stifling traffic congestion that officials say threatens the economic growth and quality of life in the state’s Washington suburbs.

Maryland highway officials have said they plan to add up to four toll lanes — two in each direction — to both highways and the American Legion Bridge. They have said they hope to award the first contract to a team of private companies in 2021.

MDOT spokeswoman Erin Henson said in an email that it’s too early to determine the costs of relocating utilities because the state hasn’t completed a federally required environmental review of the project.

She said the state’s recent solicitation to the private sector seeking companies to compete for the public-private partnerships “specifically incentivizes the developer to work with the community to reduce impacts to the community or utilities from this critical project that is focused on reducing congestion for residents that navigate the I-270 and I-495 corridors every day.”

In its report to the two county councils, WSSC Water said paying off the debt to move the pipes would cause customers’ water and sewer rates to swell by 277 percent over the next four decades. That would translate to the typical household paying an additional $2,253 over that time, WSSC Water said.

Hucker said the utility should have told the state’s Board of Public Works about the pipe-related costs before the panel approved the toll lane project as a public-private partnership in January. That approval allowed the state to begin soliciting teams of companies to build the lanes and finance their construction in exchange for keeping most of the toll revenue long-term.

“It’s highly disappointing that we’re finding out about this at the 11th hour, when the [first contract] solicitation is about to go out,” Hucker said.

He said he hopes state lawmakers will introduce legislation during the final weeks of the General Assembly session to require the state’s private partners to pay for the pipe relocation costs as part of the overall construction.

WSSC Water said it based its projections on the design option that would widen the highways the most.