The alternative routes for Enbridge’s proposed pipeline across northern Minnesota hardly seem like alternatives given the way the regulatory process has shaken out.

When big energy projects like oil pipelines and power lines are proposed in Minnesota, it’s common for regulators to lay out several choices. But the five alternatives to Enbridge’s Line 3 replacement proposal look more like an intellectual exercise than ­plausible pipeline routes.

The reality on the ground essentially rules out most of them, even though some have favorable environmental ­attributes.

The controversial Line 3 replacement, which would deliver Canadian oil across Minnesota to Superior, Wis., is in its last regulatory lap, with key decisions at hand in the next six months. At stake is a $2.6 billion pipeline project that’s generated much opposition from environmentalists and American Indian tribes.

The Minnesota Public Utilities Commission (PUC) on Dec. 7 rejected the state’s Environmental Impact Statement (EIS) for Line 3, though on narrow grounds. Essentially, the PUC told the EIS’ author — the Minnesota Department of Commerce — to fix three things within 60 days.

The EIS is a key tool that the PUC will use when it decides next spring whether a new Line 3 is needed, and if so, which route it will take.

In the EIS, the Commerce Department evaluated potential environmental impacts of Enbridge’s preferred pipeline route, as well as five alternative paths for Line 3. The 2,000-page EIS made no conclusions. Examining alternatives is common in environmental reviews.

The 1960s-vintage Line 3 is one of six Enbridge pipelines that cross Minnesota. Line 3 is corroding and operates at only 51 percent of capacity for safety reasons.

Enbridge says a new Line 3 would be a major safety upgrade — and it would restore the full flow of oil to that route. The new Line 3, as Enbridge sees it, would run parallel to the company’s current pipeline corridor to Clearbrook, Minn., where it would then jog south to Park Rapids before heading east to Superior.

It would follow an existing oil pipeline to Park Rapids. But after that, the new Line 3 would create a corridor that exposes a new area of lakes, wild rice waters and wildlife habitat to possible environmental degradation.

“If you open a new corridor, you introduce risk that previously wasn’t there,” PUC Commissioner Dan Lipschultz noted at a recent PUC meeting.

Two alternatives to Enbridge’s proposed route — dubbed “RA-07” and “RA-08” by regulators — largely follow the current Enbridge pipeline corridor all the way across Minnesota.

The Minnesota Pollution Control Agency (MPCA), in comments filed recently with the PUC, concluded that the RA-07 route “offers the greatest potential to minimize adverse effects to surface water and groundwater resources.”

The MPCA also concluded that RA-07 “shows relatively low erodibility, while (Enbridge’s preferred route) includes areas of high or very high erodibility.” High erodibility can lead to “a greater likelihood that pipe can become exposed or undermined” during construction or thereafter, the MPCA said.

The state Department of Natural Resources, also in comments recently filed with the PUC, determined that RA-07 “does the best job at minimizing potential impacts to state managed natural resources.”

Neither department made an actual recommendation for any pipeline route.

Enbridge says it studied using Line 3’s current route. The idea was partly rejected because of “congestion” in the pipeline corridor, said Barry Simonson, Enbridge’s Line 3 replacement project director. Towns have increasingly grown around the corridor, he said, and construction would be tricky with so many adjacent pipelines.

There’s another big reason: Enbridge’s current Line 3 runs through two American Indian reservations: Leech Lake and Fond du Lac. The latter is against any new oil pipeline, according to PUC filings, while the former has been even more explicit.

“I think it has been clear since early on in this proceeding that the Leech Lake band had made it quite clear they will not allow a project to go through their reservation boundaries,” Bill Grant, a Commerce Department official, said at a recent PUC meeting. Two Line 3 alternative routes — RA-07 and RA-08 — do just that.

Another route alternative, the northerly “RA-06,” wouldn’t cross the Leech Lake reservation, but it would go through Fond du Lac. Plus, it’s a big loser on another front: It crosses a lot of terrain that hasn’t been disturbed by oil pipelines. “It’s a greenfield route and very remote,” said Enbridge’s Simonson.

Then there’s a pipeline alternative known as “SA-04,” which was proposed by Friends of the Headwaters, an environmental group opposing Enbridge’s new Line 3 route.

SA-04 follows an existing natural gas pipeline route. It would start in northeastern North Dakota, run to the South Dakota border, and then head southeast through Minnesota and Iowa until ending near Enbridge facilities in the Chicago area.

In other words, it would bypass Enbridge’s Upper Midwest system, which links its Superior terminal — via more pipelines — to the Chicago region, Detroit, Sarnia, Ontario and the U.S. Gulf Coast.

“If the agencies [the Commerce Department and the PUC] look at this narrowly, then it’s about what Enbridge says and that is to deliver oil to Superior, Wisconsin,” said Scott Strand, an attorney representing Friends of the Headwaters. “If your premise is to get oil to Superior, you limit the alternatives.”

Unlike the other Line 3 alternatives, SA-04 would avoid lake country altogether and travel mostly through agricultural land. The MPCA found that SA-04 offers lower potential environmental effects on water resources than Enbridge’s preferred route. SA-04 has low erodibility, too.

But SA-04 is considerably longer than Enbridge’s proposed pipeline path, thus a bigger potential hazard. It also would require regulatory approval in several other states. And, SA-04 is not formally a “route alternative” in the Minnesota Line 3 proceeding; it’s a “system alternative.”

That sounds like bureaucratic mumbo-jumbo, but it means that the PUC can’t actually choose SA-04 as a pipeline route if it approves Line 3. The PUC can only deny Enbridge’s proposal for a pipeline altogether, and then tell the company to come back with a proposal that looks like SA-04. That’s highly unlikely.

Enbridge “has made it clear and on the record before the EIS [was completed] that it would not build system alternative SA-04,” the Commerce Department’s Grant told the PUC.

Enbridge’s Simonson told the Star Tribune that any new pipeline must run through its existing Upper Midwest customer network via its Clearbrook and Superior terminals.

So, that leaves one other possible Line 3 route, so-called “RA-03.” While this route would avoid more lake and wilderness areas than most other alternatives — including Enbridge’s preferred route — it’s longer and still runs near the Mississippi River headwaters, a big problem with environmentalists.

Plus, Enbridge’s proposed Line 3 route has been subject to actual engineering studies. “That has not occurred on the other route alternatives,” Grant told the PUC.