I am trying to sample an (obscure, delicate) source for (engineering, compliance, litigation) purposes and was wondering what method I should use?

We are more than happy to help you with comparing methodologies if you contact us, however, we strongly recommend that you first contact the governing agency ultimately responsible for the site. If there is no agency, the most legally defensible data will use 40 CFR 60 or other US EPA sanctioned methods. The more you deviate from the method, the less legally defensible it becomes.