According to the source, the plant was ordered closed but was back in operation again within a day or two.
The plant is the sole supplier of fly ash to the Muskrat Falls project. The operation is housed in an old hangar near the Goose Bay Airport. The building is reportedly in poor condition and, according to the former worker, unsuitable for its current use given the toxic nature of fly ash.
Fly ash is used in conjunction with (or as a partial replacement for) Portland cement to improve a particular property of concrete (e.g. to slow hardening) or to restrict a specific chemical reaction. It is a by-product of pulverized coal and this source believes that, based upon product data sheets, the ash contains a high percentage of silica.