It could be a very happy New Year for some City Hall employees — from the mayor to department heads — as a new study recommends a bump in salary ranges. Department heads could see a 15 percent hike. Here’s a sampling of how the ranges could change:CORPORATE COUNSEL AND CFOOld range: $115,000 to $165,000Proposed range: $132,250 to $189,750DPW CHIEF AND HEAD OF I.T.Old range: $110,000 to $155,000Proposed range: $126,500 to $178,250