How much would drinking once a week effect athletic performance?

I'm currently a college distance runner. In high school I didn't drink an ounce of alcohol however, once i got to college I might of started some bad habits. I usually have some alcohol once a week every Saturday night or so after a track/XC meet. Never to the point I black out though and usually never to the point of throwing up (minus one time). Could once a week effect how i do in practice and at meets?