can you get a charge for failing a drug test if you aren't on probation or anything like that?

If it's "active" in your system then you can be charged with being under the influence of a controlled substance. But, if it is no longer having an effect on you, and is merely "residual" traces in the bloodstream, you're not going to get charged.

Of course, your scenario really begs the question: Why are you being tested to begin with? Police don't do blood tests without good reason . . . either indicators the person is currently under the influence, they're on probation, there's a court order, etc. So, having residual narcotics in your system may get you in trouble depending on the underlying cause of the testing.

Legally you can't be charged with possession because you have THC in your bloodstream. However, if you have THC in your bloodstream the police can plant the evidence on you and the failed blood test will be used to support the charge. Most judges or juries nowadays would accept the evidence -even if it is fabricated- in light of the blood test; this is especially true in a heavily Republican southern state like VA. Anytime you have a chemical in your bloodstream you set yourself up to become a target of corrupt police officers.

You can be in violation if it's in your system, but the charge would just be violation of probation. You can only be charged for possession if you are literally in possession of a drug.

if you fail a drug test, say at work, i don't think that is enough evidence to create a criminal case against you.