translate English to French: Annually averaged levels of arsenic recorded in downtown Yellowknife fell substantially after the overhaul of arsenic control equipment at the Giant Yellowknife mine in the mid-1970s.
Les concentrations annuelles moyennes d'arsenic enregistrÃ©es au centre-ville de Yellowknife ont diminuÃ© de faÃ§on apprÃ©ciable aprÃ¨s la rÃ©vision du matÃ©riel de rÃ©duction des Ã©missions d'arsenic Ã la mine Giant, au milieu des annÃ©es 1970.