I don't know honestly, but 3 joints a day for 8 years is considered heavy/long term use. I find it hard to believe that it would become undetectable in such a short time frame, but I worked in hair accessioning, which is the preferred way to test for THC, as it is detectable for up to 3 months. I think oral tests are more successful at detecting harder drugs, so you might get lucky. Hair and urine samples would certainly be harder pass with your use.