In the November Agricultural Engineering Newsletter we discussed the issue of septic drain field failures. The term "failure" is usually used to refer to systems that are no longer accepting as much wastewater as generated. The symptom of failure is either very slow plumbing in the home, untreated effluent coming to the surface in the yard or both. As indicated in the November article, the problem is very important to determine why the system failed before taking corrective measures. If the cause of failure is not determined and dealt with it may persist and result in premature failure of the repaired or replaced system.

The normal solution to a failed drain field is to replace the drain field with a new system following the current code of the local health jurisdiction. If the failed system was installed within the last ten years or so there is probably a designated location for a replacement system on the lot that will show in the original installation permit on record with the health department. If a designated replacement sight exists, it should be used. Before beginning any replacement process it is necessary to contact the local health department and have them assist in determining what needs to be done as well as to issue a replacement system permit.

If a replacement system is installed, every possible effort should be taken to avoid any damage to the existing system. A diverter valve should be installed so that in the future the effluent can be switched back to the original system. Over time it will be rejuvenated through biological action. After about two years the old system will be nearly as good as new and alternating between the two systems on a one- to two-year frequency can greatly prolong the life of the replacement system.

If there is not room for a complete replacement system, other options may be used. One may add to the existing system in such a way that water will overflow and go into the new trenches only when the existing system is completely filled water will overflow. Chances are, if the system is not in extremely bad shape, existing trenches will continue to take a significant amount of wastewater. Only if the excess is diverted to the new trenches will they retain the ability to dispose of wastewater at relatively high rates.

Another option, and one that has been proven to be very effective by research in Wisconsin, is to add an aerobic treatment unit or a sand filter between the septic tank and the existing drain field. It has been shown that providing the added treatment and converting the effluent going to the soil system from anaerobic septic tank effluent to aerobic effluent from a sand filter or aerobic treatment unit can cause the clogging in the soil system to be decomposed. The installation process involves pumping the septic tank, pumping all the water out of the drain field, adding the aerobic treatment unit and putting the unit back and into use. Over 90% of systems corrected in this manner have operated without additional symptoms of failure. The other 10% required some addition to the size of the soil absorption area. In most cases this was because the system was too small to start with.

Other processes exist for treating failed drainfields. These include the use of enzyme products, dried bacteria and physically opening soil pores by air blasting to lift and fracture the soil which also opens the clogging mat. We do not have data on the performance of these processes and cannot recommend either for or against their use.