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Alton gas project worries geologist

Annabelle Thiebaux protests at the entrance of a work site in 2016 near the Shubenacadie River in Fort Ellis, where AltaGas has proposed to build undergound gas storage caverns.
Annabelle Thiebaux protests at the entrance of a work site in 2016 near the Shubenacadie River in Fort Ellis, where AltaGas has proposed to build undergound gas storage caverns.

ALTON, N.S. – A retired geologist says the massive undergound gas storage caverns planned for the Brentwood area won’t be able to stand the pressure.

“It’s very likely, not just possible,” Robert Grantham, who lives in nearby Stewiacke, said of the potential for failure of the proposed storage units that are to be created by flushing out underground salt beds.

Grantham points to a similar underground hydrocarbon storage plan that went awry in Cape Breton in the mid-1970s. A cavern flushed out of the salt bed in Richmond County, about 10 kilometres from Port Hawkesbury, was eventually deemed to be too far from the northeastern United States market that it would serve to make it economically viable. Grantham said the real problem was that the underground facility simply could not withstand pressure testing.

He said the project proposed by Alton Natural Gas LP, a subsidiary of AltaGas, will suffer the same fate. The company plans to flush out two underground storage caverns, each about the size of a 25-storey office building and capable of storing four billion to six billion cubic feet of natural gas. Nearly 10,000 cubic metres of water would be pumped daily from the Shubenacadie River system to the well bores at Brentwood Road. The residue brine would be pumped back to the estuary for release into the river system, a gradual discharge of 1.3 million cubic metres of salt over a two- to three-year period.

“My biggest fear in this whole Alton project is that if they dissolve all this salt and pump it into the Shubenacadie and the caverns do fail the pressure test, there is a tremendous problem that they’ve created in the Shubenacadie and Stewiacke rivers, and it’s not appropriate.”

Mi’kmaq and non-native residents have long protested the project, saying the discharge of salt will destroy the river system and kill off fish and plant species. The company counters that the gradual discharge of salt into the tidal river system will not be enough to significantly alter the salinity levels.

Grantham, a longtime mining company geologist and a former resident expert at the Nova Scotia Museum of Natural History in Halifax, said the problem with the Brentwood caverns, like the issue in Cape Breton four decades ago, is the continuity of salt.

“It’s a situation that the structure that they are drilling into, if it doesn’t have continuity in salt, if there isn’t continuous salt, then there is a risk of leakage.

“It’s also a faulted area from hundreds of millions years ago. That creates fractures. Salt is a very mobile mineral. It’s what is referred to as ductile, it can be shaped and moved by pressure from overlying rock. I just don’t think that it will survive the pressure tests.”

Grantham said the theory is to drill holes to try to find a continuous band of salt that contains no linkages of dolomite, which is similar in composition to limestone.

Limestone or dolomite would interrupt the continuity and give way to leaks, he said.

The project is on hold while the Sipekne’katik Band, many of whom live in Indian Brook near the Shubenacadie and Stewiacke rivers, and the company pore over an impact-benefits proposal regarding the project. Chief Mike Sack said last week that the band referendum on an impact agreement will be held in the coming weeks.

– By Francis Campbell/The Chronicle Herald


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