Officials long concerned over a potential cyanide plume in downtown Traverse City’s Warehouse District breathed a sign of relief Wednesday after learning the contamination appears to have been mostly eliminated, saving millions of dollars in anticipated clean-up costs.

Dirk Mammen of Environmental Consulting and Technology (ECT) presented the findings of an environmental study Wednesday to the Grand Traverse Brownfield Redevelopment Authority (BRA) that used samples from 17 monitoring wells in and around the Warehouse District to measure potential contamination. A combined $600,000 grant and loan from the State Land Bank helped pay for the project, which was designed to determine how much cyanide still exists in the district.

The BRA first discovered an underground cyanide plume in the area in 2010. The plume’s full extent didn’t become known, however, until the construction of Hotel Indigo in 2013, when developers encountered dangerously high levels of pollution in the soil and groundwater. The ensuing massive clean-up effort pushed environmental clean-up costs to $5 million and delayed the hotel’s opening by several months.

With concerns mounting over the possibility of remaining cyanide migrating to Grand Traverse Bay – and neighboring developments including Patti Mercer’s Grandview Place and Thom Darga’s Warehouse Flats set to come online – officials set out to formally measure how much pollution still existed in the area. Mammen told BRA board members his firm “started out (the project) wondering how many millions of dollars it might take to clean this up” – but came away with good news.

“We non-detected cyanide in all 17 wells but one, and that one is still lower than even the most restrictive clean-up criteria,” Mammen says.

Cyanide is measured in two ways: “available,” which is the most crucial measurement used to determine risk if there is direct contact with water, humans or animals, and “total,” which can include many forms of cyanide, including those that are stable and essentially harmless to humans. Federal regulations state the highest level of available cyanide that’s permitted in drinking water is 200 parts per billion. Among seventeen Warehouse District samples – all of which were taken this month – only one site registered any available cyanide whatsoever. That well, located at the intersection of Garland and Hall streets, only registered 3 parts per billion.

A handful of well sites exceeded the total cyanide standard for industrial clean-up, or 300 parts per billion. Those wells were located at the Hall/Garland street intersection and across the street near the West End beach parking lot. The results indicate water treatment could be needed if there was development in those areas. However, the levels are nowhere near those discovered at Hotel Indigo.

“We thought after this effort we were going to design some type of system (to clean up the cyanide) and move forward, but at this stage, with this data…we’re just not seeing anything that we can go in there and pump and treat for a whole lot of money,” Mammen says, calling the project results “very positive and optimistic news.”

Mammen says Hotel Indigo’s monumental clean-up effort – which required the removal of 20,000 tons of soil and the treatment of over 20 million gallons of groundwater during a three-month dewatering process – likely helped eradicate the plume for the entire district. “I think (that project) may well have impacted this to a far greater level than many of us expected,” he says. “It probably influenced the whole area…it made it easier for everyone else (who’s developing). I’m hopeful that maybe it took a whole lot nervousness out of that area.”

The fact no cyanide was uncovered during the reconstruction of Garland Street last year is further evidence the plume has likely been remediated, Mammen said.

Mammen explained to BRA board members that the plume likely originated because of a coal gasification facility that existed from 1901 to 1945 on the now-vacant Hall Street property between the Candle Factory and Bay Area Transportation Authority (BATA). Now private property, that lot was not included in ECT’s well testing and will need to be monitored carefully if future development occurs on the site, Mammen says. But as with other facilities of its kind in the past, the gas plant appears not to have stored its cyanide directly on-site but instead on adjacent property – likely the site of Hotel Indigo.

While the study’s preliminary findings mean good news for both local officials and developers in the Warehouse District, Mammen said the area will still need to be monitored going forward. Citing the potential for seasonal fluctuations in measurement data, ECT will likely recommend quarterly well testing over the next year to ensure the findings are consistent. Developments like Mercer’s that require digging and disturbing the soil in the future could potentially release cyanide, though Mammen doubts contamination levels like those at Hotel Indigo will be found again. He explains the study results mean that the Warehouse District doesn’t require immediate clean-up or intervention, but that future developments may still need to test and treat their groundwater.

“We don’t have any risk factors that require any active remediation, but we still need due care,” he says.