The exploration and production exclusion, and its edges
Wastes uniquely associated with the exploration, development and production of crude oil and natural gas are excluded from federal hazardous waste regulation. Drilling fluids, produced water and many associated residues fall under it. That exclusion is wide, and it is also narrower than it is usually treated: it turns on the waste being uniquely associated with primary field operations, so unused chemicals, service-company wastes, painting and maintenance residues, solvents, and material from activities that are not primary field operations are generally outside it. Exempt is also not the same as unregulated — state programs, surface discharge rules and NORM requirements still apply. The useful question on a lease is therefore not "is this hazardous" but "is this exempt, and who says so", and getting it wrong in the generous direction is the more expensive error.