I was told alcohol can be detected for up to 30 days after consumption. Is this true with mouth swab or urine tests?

You might be confused between Alcohol and ETG. Alcohol disappears quickly. Metabolites-ETG- remain but they are removed by your body and little if any is detectable after 80 hours. 30 days would be impossible based on current detection methods.

In a healthy person its impossible to detect alcohol use 30 days after the last use. As was stated 80 hrs is the accepted limit for alcohol consumption. However Unhealthy people with kidney disease for example, can give a positive for alcohol, and some medications or products containing forms of alcohol can also trigger a positive test result.