Good rule of thumb - don't lie on applications or background checks. It never ends well.
More to the point, you need to disclose that you were part of a PTI program, and that you successfully completed that program. The issue isn't so much that you had an alcohol-related issue in the past, it's that you took responsibility for it and have made better choices since that time.
In the meantime, you should hire an SC attorney to expunge that arrest.
The foregoing is not legal advice, and nothing in the foregoing shall be deemed to create an attorney client relationship. If you feel you need to speak with an attorney regarding your issue, it is recommended that you contact an attorney with expertise in your area of inquiry. The information related above is purely for informational purposes, and should not be acted upon without speaking with qualified counsel familiar with you specific situation and the laws related thereto.