Last month we addressed abandoning sewage treatment tanks and other pretreatment devices such as ATUs and media filters. This month we turn to properly abandoning the soil treatment area.

Often when an onsite system is replaced, the old soil treatment area is left intact. This is an acceptable practice recognized in most state and local codes. If there are inspection ports, or risers over drop or distribution boxes, these should be removed and disposed of. If effluent was surfacing over the area, it can be treated with hydrated lime and allowed to dry, with some topsoil added and vegetation reestablished. In all cases, the vegetative cover should be maintained over the area.

Remember that when a system is abandoned or removed, measures must be taken to protect the installer, homeowner and others from any current safety or health hazards or those that could arise in the future. Every year we read about someone being hurt or killed by falling into abandoned parts of onsite systems that were not properly abandoned or removed. Often these are old cesspools or seepage pits, but not always; they can be holes left due to improper filling of tank or trench cavities. It is probably a good practice on the part of the installer to go over the property with the homeowner to see if there are other older systems or other parts of the system that should be addressed.

In many cases, the soil treatment part of the system must be removed because the homeowner desires to use that area of the lot for another purpose. Mounds or at-grade systems are other situations where the system must be replaced. Here, part of the replacement process means removal of the system and rebuilding from the ground up at the same location.

Whenever soil treatment and dispersal systems are removed, contaminated materials from the system must be properly handled to prevent human contact. Contaminated materials include the distribution or drop boxes, the distribution media, rock chambers, etc., any distribution piping, and soil or sand within 3 feet of the bottom of the system.

When the tank or tanks are pumped, the distribution or drop boxes should also be pumped. This material should be treated like septage and disposed of in accordance with federal and state requirements. Our state requires an agreement between the sewage receiving facility and the service provider to ensure proper disposal practices. If the waste is land-applied offsite, it must be handled according to the federal 503 regulations and meet any additional state and local requirements.

When a system is taken out of service and the tanks are pumped, allow sufficient time for the soil treatment area to dry out. If the system is being rebuilt on the current site, this may not be feasible, but as much of the liquid should be removed as possible. Before any other construction activities take place, it is important to allow the soil surface to completely dry out where the mound or at-grade will be replaced. Additional surface preparation may be required to ensure the area for the replacement system is ready when the new system
is installed.

Your state may have specific handling and storage requirements if the plan is to use or spread the excavated soil and sand on the site and lawn area. The installer is responsible for knowing these rules. In Minnesota, if the material is going to be spread or used on site it must be stockpiled on site in a location meeting all the soil and setback requirements for a soil treatment area. So there must be three feet of soil to any limiting layer, lake, stream or building, and other setback requirements must be met and maintained.

The material should then be covered with 6 inches of uncontaminated soil and erosion control measures should be taken to prevent runoff. After a year, all of the material can be spread on site, topped with 6 inches of topsoil and the vegetative cover established. After one year the material can also be used to fill holes or voids where the sewage tanks were abandoned. This is not a common practice, however, due to length of time you have to wait and because most of the material would not meet the requirements of clean sand or other granular materials used to fill the tanks.

All of the piping should be removed, along with the trench media and any geotextile fabric used in covering the system. The material should be dried thoroughly and taken to a mixed municipal solid waste landfill. Whether additional fill is hauled in or the materials excavated are used to fill and grade across the site, a good vegetative cover of some type should be established.

When a system is abandoned, there is usually a requirement to inform the local government when the work is completed. Sometimes this is a part of the permit for the replacement system; sometimes a special form and permit are required. As in the other cases, it is the installer’s responsibility to know these rules and discuss the abandonment with the proper local authorities before proceeding.