Seepage Pit (Drywell)
A seepage pit is an older design that includes a deep, underground chamber for dispersing septic tank effluent into the soil, used when space is limited or soil conditions are unsuitable for a traditional leach field. It consists of a vertically excavated pit, often lined with unmortared blocks or other porous materials, and surrounded by gravel to facilitate the gradual infiltration of partially treated wastewater from the septic tank. Seepage pits are distinct from cesspools, which historically served as both the septic tank and the dispersal system.
How a Seepage Pit Works
- Receives Effluent: Partially treated wastewater from a septic tank flows into the seepage pit.
- Porous Walls: The walls of the pit are designed to be porous, allowing the effluent to seep out.
- Gravel and Soil Filtration: The pit is filled with gravel and surrounded by a layer of gravel, which helps distribute the effluent and filters it before it enters the surrounding soil.
- Soil Absorption: Microorganisms in the soil digest organic matter, and the remaining water slowly absorbs into the ground.
Seepage pits are not as effective as newer soil dispersal or drainfield systems and therefore pose greater contamination risk to groundwater.
Signs of a Failing Seepage Pit
- Slow drainage from the pit
- Sewage backups into the residence
- Pooling of wastewater on the surface of the property
- Foul odors near the pit area
