In the February Newsletter we discussed dealing with drainfield failures and indicated that the next subject would be repairing failed systems. Before a failed system is repaired the cause of failure should be determined and eliminated unless it is failure due to old age. See the February Newsletter for this discussion.

The most common approach to system repair is to install a completely new soil absorption system in an isolated area so the old system is not disturbed in the process. A diversion valve should be installed so that in the future it will be possible to direct the flow from the septic tank to either of the soil absorption systems. After the failed system is replaced and the flow diverted from it, it will slowly rejuvenate itself and be available for use in the future. The rejuvenation process takes at least two years and involves naturally occurring organisms which decompose the clogging mat that has formed and return the absorptive system to near original capacity. The rejuvenation process can be accelerated if a septic tank pumper opens the field and removes all the ponded wastewater that he can possibly pump out.

After a replacement system has been installed, a homeowner should plan to switch back to the old system after about two years and then switch back and forth between the two systems about annually. This will result in a continuous use and rejuvenation cycle for both drainfields and should prevent future failures. It is a good idea to install an observation tube in each drainfield so that it is possible to monitor the amount of wastewater that ponds. That can be a guide to the frequency of alternating between the two fields. (We'll deal with observation tubes next month)

If the old system is a trench system with at least six feet of undisturbed soil between the trenches, it is possible to install replacement trenches between the old trenches if an adequate area for a new system does not exist in a separate location. However, the plumbing for the new and old system must be entirety separate so that when one is in operation the other has the opportunity to completely dry out.

In very sandy soils, it is possible to completely excavate the old system and install a new system in the site of the old one, but this eliminates the opportunity to have alternating fields. This would be a last resort if there is no space available.

Another repair process that has proved very effective, based upon research at the University of Wisconsin, is to improve the wastewater treatment prior to soil disposal by adding an aerobic treatment unit or sand filter between the septic tank and the soil absorption system (SAS). This might be done where there is no space to install a replacement system or where it is difficult or undesirable to do the excavation work to install a new SAS. By providing enhanced treatment and discharging an aerobic effluent rather than anaerobic effluent to the soil, aerobic organisms are enhanced in the SAS and they decompose the clogging mat. Research has shown that if the septic tank and the drainfield are pumped out as completely as possible when the aerobic unit is installed, the system can be put back into use and expected to function. The original drainfield must be of adequate size for the amount of wastewater being generated based on current specifications.

The Wisconsin research showed a success rate of about 95% in rejuvenating systems by this method. This process might also be attractive if the system needing repair is located in an area that is sensitive to pollution from septic systems. Much cleaner effluent is discharged to the soil.