Re: historic - historical
Historic is IMPORTANT in history. An historic event, an historic day, an historic castle. (Yes, I write "an" because I say 'istoric. Both are okay.)
Historical simply means that it was in the past. This site's historical use for debris disposal has created groundwater contamination. The historical data shows that incidents of bee stings is the greatest in May.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.