Also, some US states are encountering issues with bio contamination in their aquifers and as water issues become more prevalent (perennial droughts in some states shrinking aquifers making them less resilient to contamination; perennial flooding in others moving the water tables closer to septic tanks and making them more prone to contamination), the requirements to isolate septic tanks from local ecologies will only grow (ie, increasingly more counties will require to close them, watertight protect them, require them to be regularly pumped moving forward, and/or replace them with a connection to nearby sewage systems).
Yes the ground water level, soil permutability, distance to water sources etc. has a lot of implications on what sceptic system you can implement and I would bet that many tanks are put in without much regulation or oversight.
Other areas like those in which ground temperatures drop below freezing for long period of time might also require tight tanks and constant pumping since the cold may stop the reaction in the tank so it would surprise me if tanks in places like say N. Dakota would be pumped year before winter to prevent them from freezing shut and overflowing.
