A typical septic tank system consists of a holding, or septic, tank, that collects household waste and water, and a leach bed through which excess water drains. The solid waste remains in the tank, and gradually sinks to the bottom, while the waste water seeps slowly through a network of perforated drainage field pipes set into shallow trenches lined with gravel or crushed rock. When water usage in the home is high, the soil under and around the field line pipes becomes saturated with waste water that builds up toward the surface of the soil to within the reach of the lawn grass roots and rhizomes.
Grass Color Significance
Household waste water is rich in many of the nutrients that plants and lawn grasses, such as Kentucky bluegrass (Poa pratensis) use. Kentucky bluegrass grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. When grass growing over saturated field lines turns bright green, it may indicate stress in the system, as the water has nowhere else to go but up, toward the surface, where it is easily accessible by grass plant roots in large quantities. In a septic system that's working correctly, waste water is filtered out into the surrounding soil. Brown grass over field lines indicates that the system is functioning as it should, and that the waste water is draining properly.