An N.W.T. diamond mine "misunderstood" its reporting requirements earlier this year when it failed to flag a massive groundwater spill, according to the territorial government.  A broken pipeline leaked 450,000 cubic metres of groundwater — enough to fill 180 Olympic-sized swimming pools — and was first spotted at the Diavik mine on Feb. 7, the N.W.T.'s lands department (now the Department of Environment and Climate Change) said in March.