hair follicle test, where is it done?

hey guys.
i recently got a call about a possible job offer... and they need to do a drug test.
i have been worried like crazy for the past 2 days.
i smoked like 1-2 blunts a day until 2 days ago when i got the call.

problem is i have no idea what kind of test they are going to do so i wanted to prepare for both urine and hair tests.

so where do they take the hair sample? do they do it at job site or send me to a lab like they do for the urine tests?

btw anyone kno what test method bechtel uses? lol