Septic systems fail for a variety of reasons. The one on the left is part of a community system that presumably as installed in the 1930's. While the system was not designed to meet current performance standards, it became useless as a wastewater system when it was physically damaged as a result of nearby construction.
The photo on the right shows effluent above the level of the tank which is indicative of a failed absorption field or a crushed or clogged effluent line between the tank the distribution box. The absorption field was completely clogged and sewage was backing up into the house.
Here are a couple of more failures. On the left you can see trenching designed to provide hydraulic relief in a soil with a water table near the surface. Sometimes it's possible to "add water to water" and make it appear that a system in a soil with a high water table is working. Sometimes disposal is possible in this situation but treatment of the effluent usually isn't possible. In this instance, the effluent simply leached into the trench and flowed to the road ditch.
The photo on the right is another drainfield failure and an example of differing priorities.