OWI's tend to be hard to keep off anyone's record.  The arrest is likely to stick, but he can do some things to  minimize the effect with a dismissal or reduced sentence.  Considering you son's age, if he hasn't had any major criminal history, he will have a better shot at a reduced sentence.  Much will depend on the prosecutor and the programs offered in your jurisdition.  More are offering divert programs for youthful offenders which allow them complete a rehab program in exchange for a reduced sentence or a dismissal.  You may want to find an attorney that regularly handles cases in the court where your son's case is pending.  They will usually know if there are any specialized divert programs available that you son would qualify for.