There are two main types of seepage pits, drywells and cesspools. These systems are no longer permitted to be built and are generally older systems. Unless specifically stated the term seepage pit will be used to describe both systems.
A drywell has a septic tank between the house and the pit. This type of pit is designed to handle black water from the septic tank. A cesspool has no septic tank and functions as both the drainfield and septic tank.
Water absorption in a seepage pit is more important through the bottom than the sidewalls. The driving force to absorb water through the sidewalls drops quickly as the distance from the pit increases. The bottom of the pit is the most important component for the absorption of water.
Because of the bottom of the pit is generally a small surface area, it tends to become hydraulically overloaded quickly. This causes the rate of water absorption to slow until the pit fills with water and needs to be pumped. Since the ground surrounding the pit has become saturated, there is generally a large backflow of water into the pit when it is pumped. This backflow can decrease the ability of the pit to recover after a pumping because it quickly fills up again.
A seepage pit should be pumped and cleaned whenever the water level at the beginning of a day is less than at least one days usage of water. That is the remaining capacity of the pit is not sufficient to hold a days addition of water.
Cesspools probably should be pumped and cleaned at least once a year in order to prolong their life. This entails the removal of all sludge and scum along with some cleaning of the bottom.
Since the bottom of seepage pits are anaerobic, the buildup of sulfides occurs quickly and contributes to the decrease in absorption capacity and the rate of water absorption. Septic-Scrub can help restore this.
The best way to treat seepage pits is to have the pit pumped and add the Septic-Scrub while the pit is essentially empty. A typical residential system needs to start with at least four bottles. More may be required if the water levels cannot be maintained at a level sufficient for at least one days addition of water. Remember that after a pit is pumped, water from the surrounding ground may flow back into the pit faster that the ability of the pit to absorb water. If this happens, determine if this is a temporary condition or if the treatment was not sufficient to restore the water absorption rate. If this happens, additional Septic-Scrub may be needed. This is true for both seepage pits and cesspools.
Monitoring seepage pits is important in order to keep them working and extend their useful lives. A riser added to the top of the pit can help make this process easy. If these is not ready access to the pit, consider this addition to your system. A fishing float hung into the pit can also help monitor the water levels and the changes in the water levels easier.