Natural gas traffic stopped temporarily today on the Alliance Pipeline to Chicago from northern British Columbia and Alberta after a processing plant mistakenly let a poison impurity briefly flow into the export conduit (see related story).

Alliance said the halt would continue until the contamination — hydrogen-sulphide, which occurs naturally in many Alberta and BC wells — is removed from its pipe. The cleanup is being done by flaring off the bad gas, called “sour gas” in the industry, at an isolated compressor station in rural Saskatchewan.

Controls on the burning keep the poison out of the atmosphere, and the operation poses no threat to human health or the natural environment, Alliance said.

The volume of gas that has to be flared and the amount of time that will be needed to do the cleanup were not known. The mishap temporarily stops flows of about 1.6 Bcf/d of liquids-rich gas.

Keyera Corp., a Calgary-based midstream services specialist, disclosed that a “brief operational upset” at its Simonette sour-gas plant in northwestern Alberta put the sour gas into the Alliance line.

Both companies apologized for the disruption and vowed to restore service as soon as safely possible. Gas producers Seven Generations Energy Ltd. and NuVista Energy Ltd. warned their shareholders to expect an interruption of their output.