Landscaping Part II – Tanks, Pretreatment Units and Architectural Features

Landscaping Part II – Tanks, Pretreatment Units and Architectural Features

Driving any vehicle over a soil treatment area should be avoided due to soil compaction, which can cause a lack of oxygen transfer to the system and increase frost depth in cold climates.

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What property owners do around their tanks and pretreatment units and over their soil treatment area can greatly impact the accessibility and longevity of the system.  

Vegetation around tanks and pretreatment units

Pretreatment occurs in septic tanks and pretreatment units prior to final treatment in the soil. Typical pretreatment units include septic or pump tanks, aerobic units, and media filters. These pretreatment systems typically have manholes and accesses at grade for operation and  maintenance and should all remain at grade. The finished grade around these access points should slope away from the pretreatment unit for drainage and not allow soil or other debris to enter the system when opened. This typically means they will stick up a minimum of a few inches above grade. 

It is best to not bury the lids with soil or mulch. If the visibility of the lids is of concern decorative lids are available. The lids must be secured to prevent access, as hazardous conditions exist in these tanks. The frequency of access to these tanks and pretreatment units varies from every six months to several years, but access is mandatory and becomes must more difficult when buried.   

Vegetation should be kept short over the pretreatment to allow easy access. Perennials can be planted around septic and pump tanks as well as pretreatment units. Anything with a woody structure should be avoided included vines, bushes or trees close to all pretreatment units as it’s possible that these roots may damage components. In general turf grass is recommended.

Architectural features                                                                                           

Architectural features like retaining walls, stone walkways, ponds, decks, patios or fire pits are items to avoid over your septic system. These heavy architectural features can create problems including lack of maintenance access, septic tank leaks and pipe ruptures. In addition, remind homeowners that swimming pools, sports courts, storage sheds, swing sets and sand boxes should not be placed over any part of your septic system due to soil compaction. These features may get damaged if repairs are needed to the septic system.  

Decorative items including art or benches are possible but homeowners must remember that it’s possible to smell odors from a septic system near the tanks or pretreatment unit. In cold climates, a thick vegetative cover across the area is wise to help insulate the pretreatment units and help hold snowfall. 

Fencing and gate placement can affect septic pumper truck access. The hoses on the service truck are heavy and going over fences can cause damage. For tank cleaning, access within 50 feet of the truck is best. 

Animal, human and vehicle traffic

Animal traffic over your pretreatment units and soil treatment area can cause damage to the system. Grazing animals eat away protective vegetation over the drainfield and expose components of the septic system. In areas with a lot of wildlife, grazing should be prevented by fencing or landscaping features around the septic tank system to keep animals out. Animal repellents can also be used that will discourage animal traffic by giving off unpleasant noises or smells. The other concern with animal traffic, particularly livestock, is the compacting of the soil. All livestock should be kept off the septic systems.

It is also not advised to create walkways or high traffic paths over the soil treatment area due to soil compaction, which can cause a lack of oxygen transfer to the system and increase frost depth in cold climates. There should never be a temporary or permanent driveway over a septic system and all vehicular traffic or parking should be kept off the septic system.

About the author

Sara Heger, Ph.D., is a researcher and educator in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota, where she also earned her degrees in agricultural and biosystems engineering and water resource science. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is the President-Elect of the National Onsite Wastewater Recycling Association and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system design, installation, maintenance and operation by sending an email to


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