It’s stinky, it’s smelly, and it has city and state officials simultaneously crinkling their noses and scratching their heads.

The mysterious pungent odor emanating from Skater’s Cabin near the entrance to the Mendenhall Lake Campground has returned for a second winter in a row, prompting rallying cries from city and state officials to locate its source and cause before its wafts away like last year.

“This was a particularly challenging problem to pinpoint last year because there were three separate theories for the source, and since the problem was intermittent, identifying the cause was elusive,” City and Borough of Juneau Assembly Member Ruth Danner said in an email.

Tongass National Forest officials, the Alaska Department of Environmental Conservation and the city have teamed up to investigate the cause of the unpalatable stench, which ranges in description as “the rotten egg smell,” “decomposing skunk cabbage,” and “organic material decay.”

Danner called for a continuation of last year’s investigation after receiving “a great deal of correspondence” on the matter beginning in mid-October. The area near Skater’s Cabin, which is often frequented by dog-walkers and hikers, sees many Nordic skiers during the winter months and has a high concentration of recreational users, some of whom have called to complain, said Ed Grossman, Tongass National Forest Recreation Program Manager for the Ranger District.

“At the start and end of their trips, they’re getting this blast of odiferous unpleasant smell,” he said, adding that the subdivision of houses nearby gets a noseful each time the wind blows.

Complainants and officials were originally worried it was a health and safety concern, and one of the three theories that developed was that the smell was coming from a nearby city sewage pumping station.

In February of 2010, DEC staff tested the water in the road ditch for fecal coliform bacteria, pH levels and sulfate and found there were no violations of water quality standards, eliminating theory No. 1 and reassuring the public that the smell was not generated from a toxic source.

“I know it’s irritating and such, but from my results last year, there wasn’t a permit violation,” Brock Tabor, a member of DEC’s Division of Water Nonpoint Source Water Pollution Control team said by phone recently.

Guy Archibald, the clean water coordinator for the Southeast Alaska Conservation Council and former environmental chemist, also tested the water in the area when residents had asked him in April of 2010.

“My first thought was this was a septic issue,” Archibald said.

He took samples from the water downstream of the sewer lift system as well as water coming out of a discharge pipe in a gravel pit, and tested for enterococci bacteria, an indicator of human waste contamination. Nothing.

“That’s the only parameter I tested for, and the amounts were pretty small,” he said. “So I couldn’t come to much of a conclusion at all (that was the source of the smell) based on that.”

Two theories remain: it could be caused from outflow of the adjacent privately-owned gravel pit and tree stump dump caused by a pond barrier failur, or by decaying organic matter possibly combined with the weather.

The DEC says though the smell is coming from the gravel pit, there’s no link establishing that the smell is caused by the outflow of the pit, and said that has been largely inconclusive from the testing they’ve done.

“All I know is that we haven’t been able to verify that the source is the gravel pit based on sampling,” said DEC Compliance Manage for the Division of Water Chris Foley. “... As far as we can tell, it’s a naturally occurring phenomenon that for some reason is strong out by Montana Creek.”

Archibald and Tabor explain that the smell is probably a result of a chemical compound reaction. In the winter, once the ground starts to freeze, the ground water can have elevated levels of sulfate if it doesn’t have a chance to breathe. Sulfur reducing bacteria prefer to get their oxygen based energy source from the reduction of nitrate. “When available nitrogen levels drop, bacteria turn to sulfate reduction producing H2S (hydrogen sulfide), and hence, the smell,” Archibald said in an email.

Tabor says the smell is actually not unique to this particular spot, it’s been reported in various places in the valley. Because groundwater in Alaska is highly mineralized since it comes from deep inside the earth, when the water comes to the surface it often has a scent to it.

“I’ve definitely concluded it’s not an issue with the gravel pit,” Tabor said, noting he hasn’t been out there this year. “It would be a nonpoint source, I think it’s coming from a natural source. ... Based on the testing I’ve done, it appears to be natural.”

He says nonpoint sources are difficult to quantify and qualify, but they are a potential pollutant, for example, sediment on the roadway being washed into a stream.

Grossman says officials are working hard to determine planning from here, and asks for patience as they work to figure out the cause of the smell and how to curb it. But one thing’s for sure, he said, it’s a something that won’t be ignored.

“We’re hopeful, yes, that we can get what we need before it disappears on us again,” he said. “It’s too smelly to ignore for the moment.”

• Contact reporter Emily Russo Miller at 523-2263 or at emily.miller@juneauempire.com.