▁waste ▁came ▁into ▁force . ▁ ▁At ▁the ▁end ▁of ▁ 1 9 8 6 , ▁the ▁T rel le borg ▁industrial ▁con gl omer ate ▁acquired ▁a ▁cont rolling ▁interest ▁in ▁Bol iden . ▁The ▁same ▁year ▁also ▁saw ▁Bol iden ▁ac quire ▁the ▁Spanish ▁company , ▁Ap ir sa ▁S . L ., ▁which ▁extracted ▁z inc ▁from ▁the ▁A zn al c ó ll ar ▁open ▁pit ▁mine , ▁ 4 5   km ▁west ▁of ▁Se ville . ▁T rel le borg ▁launched ▁a ▁major ▁rest ruct uring ▁of ▁the ▁Bol iden ▁Group ▁in ▁ 1 9 9 6 , ▁and ▁the ▁new ▁company , ▁Bol iden ▁Limited , ▁was ▁formed ▁in ▁Toronto . ▁Two ▁years ▁later , ▁Bol iden ▁Ltd . ▁bought ▁the ▁Canadian ▁company ▁West min . ▁ ▁On ▁ 2 5 ▁April ▁ 1 9 9 8 , ▁the ▁tail ings ▁dam ▁at ▁Ap ir sa ' s ▁Los ▁Fra iles ▁mine ▁burst ▁and ▁ 4 . 5 ▁million ▁cub ic ▁metres ▁of ▁tail ings ▁sand ▁dra ined ▁out ▁into ▁the ▁nearby ▁Gu ad iam ar ▁river , ▁near ▁Do ñ ana ▁National ▁Park , ▁causing ▁the ▁worst ▁environmental ▁accident ▁in ▁Spain ▁so ▁far . ▁ ▁Ext ensive ▁investig ations ▁revealed ▁defect s ▁in ▁both ▁the ▁dam ' s ▁original ▁construction ▁and ▁in ▁subsequent ▁construction ▁projects . ▁ ▁The ▁company ▁react ed ▁quickly ▁to ▁the ▁situation ▁and ▁immediately ▁began ▁a ▁compreh ensive ▁programme ▁of ▁re clam ation ▁work . ▁In ▁ 2 0 0 6 ,