It's been a while so

crimson - chat her up some then at the end of one of your visits when the convo stops on high note ask her out. Get an idea of what she likes and schedule. Be specific not 'hey you want to go out sometime?' but 'Hey I got a great idea lets go get some dinner at X(place) on X(day time). It would be a lot of fun.' Or something similar to that.

I would be a bit more casual about it. Some girls can be turned off by such a blunt approach. Maybe talk to her a couple more times and then just talk about movies, games, or whatever and throw out "we should go see this upcoming movie sometime" or "hey, we should get together and play some games sometime" or something along those lines. If she's interested in such a meet-up, she'll give you her contact info. Do you work as this gas station too, or is this just a place you semi-frequent? I've never been a big proponent of asking out co-workers cause of drama and work strife it can cause if things go south.