@blatham,
We will have to wait to see what he does while in office. As far as I am aware the new designee has no issues with the CERCLA and RCRA laws that govern nearly all environmental rules and clean-up standards in the country. He has however contested EPA's very recent (last two years) claims that the Clean Air act empowers them to regulate the CO2 that animals, humans and heat engines exhale and the methane in animal farts; and that the Clean Water Act empowers them to regulate (permanently) any standing water , anywhere - even a transient puddle that appears in a farmers field or on an industrial site. Both involve very obvious stretches beyond the original intent of the laws in question, but the EPA has asserted that it (somehow) has the authority to interpret them as they see fit. Whether the new Administrator and/or Trump amends these provisions or not they will likely see numerous challenges in Federal Disdtrict Courts and eventually the Supreme Court. I have no opinion of the likely odds in the case of either law..
Apart from that, I see no issues involving how things have been done for the past 25 years, excepting only the determination of maximum allowable standards (concentrations) in air, soil and water for some new emerging contaminants. Lately EPA has taken to establishing concentration standards/allowable limits (in some cases parts per trillion) far below the ability of any known technique to measure. That creates rather obvious problems for enforcement and compliance which, in it supreme wisdon, EPA has not yet deigned to address. That may be an issue too.
As an operating entity EPA is wasteful and generally populated with people unskilled in what they do, and not particularly energetic in either working or learning. Bureaucrats to the core.