It depends on how the case is resolved. If the person is convicted, WA law requires an evaluation for treatment. The evaluation can recommend anything from a one day alcohol / drug information school, up to two years of treatment.
Different types of resolutions (diversion, deferred prosecution) have different treatment requirements.
If you are convicted of a DUI, or a DUI related offense in Washington state, the court will order you to obtain an assessment to determine if you need any sort of alcohol treatment. The amount of treatment, or rehab, will be based upon that assessment. Some people are ordered to do a one day class called Alcohol Drug Information School (ADIS). Others are ordered to attend treatment of some sort for up to two years.