BRIEF-British Columbia responds to Imperial Metals spill
TORONTO Aug 5 (Reuters) - Imperial Metals Corp
* Mount Polley tailings pond released estimated 10 million cubic meters of water, 4.5 million cubic meters fine sand
* BC energy and mines minister says "this is a serious incident that should not have happened"
* BC energy and mines minister says impact on watershed is unknown, ministry is conducting water tests Further company coverage: (Reporting by Allison Martell)
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