Some state bureaucratic ass-hats tried the same thing on me a few years ago.
Luckily, I had homesteaded my property and therefore was protected from having to do any “improvements” as long as my existing septic system was functional and stable.
Some of my friends were not so lucky. They had to install a new aerobic system for $6K out of their own pocket due to these new “Environmental Regulations” passed in Austin.
Environmental tyranny at it’s finest.
Listen folks, tyranny exist everywhere and in many forms, even in the great State of Texas!
The only advice I can give you is to Know the Law because tyrants feed on two things: IGNORANCE OF THE LAW and FEAR!