So many clueless people here...
First of all, we have to clarify, again: Marijuana smoke CANNOT damage your building. It is not possible. There is no such thing as marijuana smoke "remediation". If it is your opinion that it damages people, great. If it is your opinion that it should be illegal, great. Does not change the fact that it CANNOT damage a building, even if you sit in there puffing away 24/7. It is not tobacco, every substance creates a different kind of smoke. Every house is going to have a different kind of smell left by the previous tenant even if they never smoke. People stink. This is why houses need to be cleaned. Just because it vaguely smells like pot the day they leave, does not mean it will smell like that tomorrow. Open the friggin window!
Some of you are trying to compare this to candles. How many have a "no candles" policy in the lease and enforce actually it? This is a good comparison, because marijuana smoke will make a house smell the same way a scented candle does - for a few hours and then you never know it happened.
It sounds like what this is coming down to is "he didn't follow the rules, get 'em!!!" and you just want to be the alpha male for no reason. You enjoy the power of being a landlord or you would not have asked this question. Just because you think you are the boss does not mean evictions are any better for you than they are for the tenant. The truth is, it will cost you money. And in Newberg, Oregon (I lived there for 30 years BTW) almost every tenant is going to smoke pot. I betcha $20 mom tokes too. It sounds like the OP really needs to take a toke...
IF he was causing damage I would evict them in a heartbeat. IF the neighbor was complaining I would evict them in a heartbeat. Just because he didn't follow the letter of a stupid rule? Quit trying to be a dictator. No tenant will ever like you. This is like a cop pulling you over for going 60mph in a 55mph zone. If that cop gives you a ticket for that he is an *** on a power trip, and it will likely be thrown out in court.
Have you even bothered to simply ask this kid, "hey, I see where you are smoking, could you please go do that over there?" This kind of nonsense is why people tend to hate landlords even if they have never met them. Nit picking is not a smart business move.