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Do not drive over Septic System Components
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- Is it ok to have septic piping or a septic tank under a driveway or parking area?
- Can we drive over septic piping or tanks?
- Can we drive over the drainfield?
- Can we build, pave, or put astroturf over a septic drainfield?
Here we discuss the problems that occur if septic components are located under a drive or parking area. Our page to photo shows a big effort underway to pull a dump truck out of a seepage pit. Luckily no one was injured but the cost of extracting the truck and repairing the septic system was significant. Readers should also see SEPTIC & CESSPOOL SAFETY.
Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are welcome and are listed at "References." This is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
Do not drive over the septic tank, septic piping, or septic drainfield.
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Unless special provisions have been made such as protection of sewer piping and septic tanks from damage, vehicle-rated septic tank covers, or similar steps, do not drive vehicles over septic system piping or septic tanks. Driving over septic tanks, septic piping, or drainfields risks costly damage to the septic system and may also be dangerous. The bulldozer in our photo (left) was called to help remove a truck which drove over septic system components leading to a surprise collapse. A property owner may not immediately recognize a septic system problem when piping has been run below a driveway, as crushing and blockage of the line may not happen until a heavy vehicle enters the driveway (such as the loaded septic pumping truck arriving to pump the septic tank). Or a septic line may be broken, permitting soil or roots to enter to complete the clogging process. |
How do we run a sewer line under a driveway to get to the septic tank?
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If a septic line must be run under a driveway, for example to pass from a building to the septic tank, the line must be protected by choice of materials (schedule 40), or placed in a covered and protected trench at adequate depth (such as with concrete covers over the trench) to avoid damage to the piping. Our photo (left) shows a new sewer line being installed down a hillside, connecting a house to its septic tank. The original terra-cotta sewer line lasted for decades until the building owner (DF) hired a landscaping company to mow the lawn. The fourth time that a heavy lawn mower drove over the original sewer line it was crushed and broken, leading to a costly sewer line replacement job. The new sewer line was bedded in sand and protected from damage. If a sewer line is run below a drive or parking area without proper choice of materials, protective measures, etc. it is an improper installation likely to fail. |
Can a septic tank be located safely below a drive or parking area?
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If a septic tank is to be located below a drive or parking area, it too must be properly designed and protected from collapse. The tank must be constructed of proper materials and provided with a cover rated to withstand the weight of heavy vehicles. If the septic tank is steel, site-built, home-made, or even pre-cast concrete but lacking a cover rated to withstand vehicle traffic, driving over the tank risks collapse and even a potential fatality. Our photo (left) shows a rusted-through collapsing steel septic tank cover that nearly led to a fatality to a home inspector. |
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Home made or "site built" septic tanks often have a cover made of wood or other flimsy materials, and depending on the tank construction (dry-laid concrete blocks or stones) the sides may also be likely to collapse if exposed to the weight of even a small vehicle. The site-built septic tank shown in our photo (left) was collapsing as well as impacted with solids. Driving even a lawn mower over this tank was likely to lead to a catastrophe. |
Can a septic drainfield be located below a parking area, pavement, driveways, patios, decks, or other structures?
A septic drainfield should not ever be located below a driveway or parking area.
Driving or parking on a drainfield will prevent proper drainfield operation due to soil compaction and also due to loss of proper evaporation of moisture through the surface, as well as almost certainly leading to crushed broken piping. In sum, ddriving over the leach field in any vehicle larger than a child's bicycle is a bad idea. Heavy vehicles may actually crush buried leach field lines, or they may compress the soils around the leach field, either of which leads to failure. Driving on or parking on leach fields will destroy them.
Paving over a drainfield, or installing patio stones or astroturf or any other material that blocks proper soil transpiration interrupts the evaporation of moisture from the drainfield, interfering with its ability to dispose of effluent. Furthermore covering a drainfield may result in inadequate soil oxygen, thus inadequate bacterial action, thus inadequate treatment of septic effluent, thus leading to ground water and possibly local well contamination.
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Our photo shows what happened when a swimming pool was constructed over the edge of a septic drainfield in Poughkeepsie, NY. The gray water shown leaked from the drainfield onto the pool perimeter when the homeowners did their laundry. |
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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
- Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
- Thanks to J. D. Fuller, an ASHI member and professional home inspector in Texas for suggesting clarifications on this information.
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More Information on Building Diagnostic Inspections and Repairs
- ...
- The Septic System Information Website home page for this topic
- Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
- The Home Buyer's Guide to Septic Systems
- Septic Tank Pumping Guide: When, Why, How to pump the septic tank
- Home & Outdoor Living Water Requirements
- Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
- How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
- Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
- Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
- Ten Steps to Keeping a Septic System Working, suggestions from the U.S. EPA, edits and additions by DJF
- What is a Septic System An Engineer's View & Septic System FAQ's
- Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
- Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
- Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
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