I would try and sort it out with you friends client DontRemember as presumably it is not the client accusing you but one of the drinking contractors.
Maybe you will have to be wary about accepting this work in the future - I don't know legally where you would stand but as supervisor you probably do have some form of responsibility at least I think that would be the case in the UK and I don't suppose the US is that different.
Hope things get sorted out OK and congratulations on 40 days sober