Any company that drug tests for pot should also be testing for booze. It has been proved many times that booze poses a bigger problem then pot does in and out of the work place. I have never understood why companies would not hire a pot head, but would hire an alcoholic.
When companies test for pot they are trying to find out if an employee or potential employee is able to function on the job. It should not be about legality or illegality. And that is why the test should also include the effects of alcohol. If one is under the influence of either of these one simply should not be working, especially at any sort of potentially dangerous job.
Pot SHOULD never be used (the legality is a separate matter), but alcohol is perfectly fine in small amounts. Just because you have alcohol, it doesn't make you an alcoholic. However, if you have pot in your system frequently enough that you tested positive, then you are probably addicted and might not be able to function as well as is needed.