Alcohol is water soluble & is gone from the system within 72 hours of consumption.
THC is fat soluble & remains in the system up to thirty days. Testing positive means a set threshold has been exceeded.
This was the Army standard our drug boards used.
Sometimes thresholds for things are more about detectability than impairment.
Anyone who seriously believes that someone smoking a joint a week ago is as relevant to discussion of ‘problems’ and solutions probably thinks that ‘Reefer Madness’ is a documentary .