System Site Plans: Site Review of Topography and Existing Conditions

Many site features can impact the constructability of an onsite system, so it’s important that the design matches the site

System Site Plans: Site Review of Topography and Existing Conditions

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The second major step in the planning process for an onsite system is to conduct a site review after the design has been reviewed. This allows for a comparison of what is on paper to what is on the property. It is possible that the design plan may not show constraints such as trees or recent site improvements. The design needs to match the site characteristics in the most elemental features like property lines, relative topography and features shown on the plan. 

Topography evaluation

A topographical evaluation should be done as part of the site review. Although topography is considered in the design plan review process, a visit to the site can provide a different perspective. The topography within the soil treatment area is an important aspect to consider. If the access or construction area gathers surface runoff, provisions for weather needs to be made so that construction is not scheduled on a rainy day. Steep slopes may hinder construction or limit the type of equipment that can be used on the site. The installer needs to be familiar with the equipment that can be used on steep slopes and the proper techniques for using such equipment in these areas.


The installer should keep in mind potential drainage issues as the site review is being conducted. Drainage for the site may involve the construction of swales or berms to direct surface water away from foundations and the onsite wastewater treatment system as called for in the design/plan. If the foundation needs subsurface drainage or if there is a curtain wall drain system existing or planned for the site, the installer should be aware that certain jurisdictions limit the location of these in relation to the onsite system. The location of where the subsurface drain daylights directly impacts the functionality of the onsite wastewater treatment components. These drains should discharge where the impacts to the onsite system and to neighboring lots are minimized.

Drinking water

If present, the drinking water supply line location should be identified. There are typically setback requirements to drinking water supply lines imposed by the authorizing jurisdiction. The drinking water transport line is also usually subject to setback requirements. The design plan should show the existing or proposed drinking water transport line, source of the water (private well or municipal grid), and the setbacks to any onsite wastewater treatment system. The drinking water source may be already in the ground (as a drilled well) or may be awaiting hook-up (pressure line from municipal source or well). The site review should identify the drinking water source for the planning stages and job staging steps. 

Existing improvements

While at the site, identify constraints to the construction of the onsite system that are related to existing improvements that need to be preserved. These constraints might be structures, driveways, trees or special landscape units. These constraints might place a burden on the type of equipment that can be used, hinder accessibility to the construction site, or require protection during construction. 

Vegetation/obstruction management

The vegetation at the site should be carefully observed and documented, particularly in areas that affect the installation process. Thick underbrush may hinder a thorough site review and may have to be dealt with before any visit to the site can begin. Some vegetation might have to remain intact as required by some jurisdictions, especially within buffer areas close to the edge of water, wetlands or areas where erosion protection is important. Removal of vegetation might also require the addition of erosion management measures such as hay bales or silt fencing to prevent fines from migrating outside of the disturbed areas. Other obstructions may include boulders or other natural features that impede the access for necessary machinery. These obstructions should be addressed during the site review and possibly in conjunction with the homeowner interview.  

Often, the need for landscaping and or tree removal may not be clear until the site review is conducted. This can seriously affect the system constructability and/or installation cost. When landscaping or trees need to be removed, the installer has the option of subcontracting those services to a qualified landscaper. Some jurisdictions require trees and some woody perennials to be located at a certain setback from the soil treatment area or other onsite system components. When removing tree stumps and roots that are close or in the area of the soil treatment area, the backfill used to fill the resulting hole may be required to have certain characteristics, depending on the jurisdiction. The installation cost may be impacted depending on the availability of the required backfill. Stump removal may be required under some jurisdictions. Tree stump removal may cause severe damage to the soil treatment area, depending on the size and type of tree. For example, some upland pine trees have a rugged root system that typically has a large deep taproot; even young pine trees develop this taproot. Some other trees develop surface roots that may be removed without disrupting the soil at the depth of some soil treatment areas. Some smaller trees in this category may not need to have the stump removed. 

If the plan does not match the site in any aspect or is missing information, the installer should contact the designer so the discrepancies can be resolved. Depending on the number of designs that an installer may bid on, the installer may choose not to do a thorough site review before bidding a job. If this is the approach the designer chooses to take, he or she should be sure to conduct the site review before finalizing a contract for the job as details frequently come to light during a site review that dramatically impact the cost of the installation. 

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 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

This article is part of a series on site planning:


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