If you have an attorney for the case for which you received ARD, you should contact them to discuss what may lead to an ARD revocation in that county. In Centre County, you could be convicted of the Underage offense, and you would generally not be revoked from participation in ARD. However, in other counties, you may be revoked even if you are not convicted. You should contact an attorney in the county in which the ARD is pending to find out the parameters of the probation department and DA's office for ARD revocations. Every county is different.
With regard to the Underage suspension, it depends upon what charges you had with your first case. If your DUI case for which you received ARD also had an Underage Drinking charge, then you should have received two 90 days suspensions, one for the DUI and one for the Underage. Your post states that you only incurred a 90 day suspension, which most likely was linked to the DUI, which means that you probably were not charged with an Underage as part of the DUI case. Some cops do charge an Underage along with the DUI, others do not. PennDOT handles the duration of suspension issues, and PennDOT bases everything on records. If your new Underage is the first on PennDOT's records, then you will receive a 90 day suspension. If this is the 2nd Underage on PennDOT's records, then your suspension will be 1 year. Note that the record of the DUI on PennDOT's records does not count as a first offense of Underage Drinking. A DUI and an Underage Drinking suspension on your PennDOT records are different.
You should talk to a lawyer in the area about your Underage case. If you are found not guilty, then there is no suspension at all.
Jason S. Dunkle, Esquire
D & H Law Group, P.C.
State College, PA 16801
I would contact the attorney who represented you in your DUI. Each County in PA handles things differently. It is not a guaruntee that they will revoke your ARD but once again it is critical that you speak with an attorney about this as soon as possible and handle it accordingly.
You should contact the attorney that represented you in the DUI ARD. As my colleagues have stated, each county in PA has it's own unique rules. Some counties will allow you to have multiple ARD's for different offenses simultaneously, while others won't allow it.