Complex sentence: Each year dozens of tons of unexploded shells are recovered and, according to the Sécurité Civile agency in charge, at the current rate no fewer than 700 more years will be needed to completely clean the area.
Split into simpler sentences: Each year dozens of tons of unexploded shells are recovered. According to the Sécurité Civile agency in charge, at the current rate no fewer than 700 more years will be needed to completely clean the area.