Septic system collapse and truck rescue (C) Daniel Friedman

Do not drive over Septic System Components

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?
Questions & Answers about drainfield damage due to vehicle or equipment traffic
References

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This article explains the problems that occur if septic components are located under a drive or parking area. We explain why you should not drive cars, construction equipment, or other heavy machinery over the septic drainfield and in some cases also not over the septic tank. 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.

Do not drive over the septic tank, septic piping, or septic drainfield.

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.

Watch out: as we report at SEPTIC TANK ACCIDENT REPORTS, driving over and damaging a septic tank cover or lid can result in a later cave-in, fall-in, or extremely serious hazards. While it is possible to purchase septic tank covers that are rated for withstanding heavy loads, even vehicles, as-installed residential septic tank covers are not normally capable of withstanding such traffic.

How do we run a sewer line under a driveway to get to the septic tank?

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. Also see CLOGGED DRAIN DIAGNOSIS & REPAIR.

Can a septic tank be located safely below a drive or parking area?

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.

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, driving 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.

Building any structure over a drainfield risks damage to the drainfield from:

Vehicle traffic during construction
Broken drainfield pipes due to excavation for piers, footings, or other structural supports
Covering the soil, blocking transpiration and oxygen
And construction over the drainfield may make it impossible to later repair it when needed.

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.

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.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to J. D. Fuller, an ASHI member and professional home inspector in Texas for suggesting clarifications on this information.

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
Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include

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.)

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Inspecting Septic Systems: Online Book, Inspection, Test, Diagnosis, Repair, & Maintenance: our Online Septic Book: Septic Testing, Loading & Dye Tests, Septic Tank Pumping, Clearances, details of onsite waste disposal system inspection, testing, repair procedures.

Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389 (2006). Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going for homeowners but is a text I recommend for professionals--DF.
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP; Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP; Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.


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