How does a leach field become saturated

When groundwater levels rise after a period of heavy rains, or if you have heavy clay soils, the leachfield may become saturated and cause wastewater to backup into the septic tank (causing sluggish or noisy drains) or rise to the surface of the ground (creating a damp spot or puddle). Some of these symptoms may occur intermittently, usually after a heavy rain, and close attention to water use is needed in order to identify a problem.
If the level stays high for more than a few days, the leachfield may be saturated and on the verge of failing. Pump the tank to prevent surfacing effluent and talk with a septic pumper or contractor to determine if the leachfield should be repaired.
Hope this answers your question. Tom