What you don’t read about are accounts of the failures of on-site systems. While it is true that any mechanical system, including public sewer systems, can fail, the fact is that most of the severe problems that plagued some municipal sewer systems have been addressed by modern Environmental Protect Agency and Pennsylvania Department of Environmental Protection (PA DEP) regulations and enforcement.
Unlike individual on-site systems, the operation of public sewer systems is monitored by the PA DEP. While it is always possible to find examples to the contrary, the fact is that public sewer systems are better for the environment because their operation is monitored for proper performance and they are generally kept in a good state of repair. There is no such monitoring of on-site systems.