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.
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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.
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.
Also see SEPTIC & CESSPOOL SAFETY.
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?
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.See SEPTIC TANK DESIGN STRENGTH SPECS for details about the strength requirements for safe septic tanks, cesspools and drywells.
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.
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.
Generalizing the Reasons to Keep Equipment, Grazing Animals, Paving, Coverings and What Have-You Off of Septic Drainfields
Reader Question: I would like to put a skating rink in my yard over the septic field (mid-Dec. to mid-March, i.e. northern Illinois) because it is the flattest part of my yard. I read everywhere on the internet and your site that one shouldn't put "anything" on top of a drainage field, at least the channels where the pipes ("tiles") are buried.
Photo at left: a NiceRink™ ice skating rink installed in a level area, photo used with permission. [Click to enlarge any image]
My question is exactly how a skating rink can damage field. Has research been done on this specific situation? Is the problem of a skating rink perceived or real? I haven't read of a failure due to a skating rink, though skating rink are relatively rare. I thought about the various issues: weight and permeability. Are there others?[... content and detail moved to ICE SKATING OVER SEPTIC]
Reply: worries arise if building a skating rink atop a septic drainfield
Regarding your assertion and question
Of course not. The number of possible SNAFUs humans can come up with is near infinite. We are not likely to find a study of skating rinks over septic drainfields because of their rarity. And some reasons for their rarity may be founded in common sense: the various objections to placing anything over a drainfield or soakaway bed can be generalized so that a requirement that experts explicitly address everything imaginable that one could place and should not place in that location is, with respect, well I'll leave out the adjective.
The reasons to stay off of a drainfield, including keeping equipment from driving over the septic fields in just about all regards are outlined at SEPTIC FIELD FAILURE CAUSES
Details of the pros, cons, & warnings about building a temporary ice rink over septic fields are found at ICE SKATING OVER SEPTIC
I have an extra large cesspit serving 2 properties on my land (19m x 4m) and is a pit only no outlet . Its brick built and was installed early 70’s, it has 2 chambers running back to back, and has a concrete cover on it which spans the whole length and width of the tank having 2 cast iron lids for emptying in the middle.
Question is – I inherited this with house from my Grandfather who used to drive over it with a small vehicle to get to his garage when the pit was still under a lawned area.
Could you please advise if you would consider that this was the type of cess that was constructed for driving over, and would still be ok??? - L.H. 3/25/2014
Reply: warnings about driving over the cesspool
Watch out: driving over a cesspool risks sudden collapse and even a possible death or injury.
We moved the full text of this question and its answer to SEPTIC TANK DESIGN STRENGTH SPECS
Continue reading at ICE SKATING OVER SEPTIC or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: best materials for a walkway over a septic field
(Sept 27, 2012) Clark said:
(Dec 11, 2012) beth said:
Reply: in the U.K. see Section H2 of the Building Regulations about pathways over septic fields. In the U.S. minimize the surface blockage and weight.
Beth, in my opinion a walk across the septic field should cover so little area as not to interfere with field function. I'd use dry laid slate if not for the worry of trip hazards for your occupants.
But I have a secondary worry. Make sure that during construction heavy equipment is kept away from the fields to avoid damage. As some readers comment (below) "you can't construct a 'path' over a septic tank drainfield. But "path" in the U.K. can have a very different meaning than in the U.S. or Canada. In the U.K. there are old right-of-way common access pathways across otherwise private land. These paths can have significant usage - which is why one would not route an access path across a septic leachfield or soakbed. But on private property where there is limited access the issues are less severe and walking across a working drainfield should not harm it.
(Jan 9, 2013) Maureen Webb said:
A path "constructed" over a drainfield, especially if it means carrying equipment or traffic that compacts soil, would, I agree, be a bad idea.
On the other hand, for a properly built and working drainfield, a human (not livestock) just walking over the field, will be harmless.
(Dec 22, 2012) Great page said:
(Mar 27, 2013) Bill said:
Reply: neighbour dug up part of our septic system which is on their land
What a mess. Your septic system is almost surely illegal right - in all of the local sanitary codes I've seen you are not allowed to dispose of your septage nor septic effluent off of your property (onto a neighbor.)
You will want to relocate your septic tank and other components to be completely on your property as well as far enough from property boundaries and other site features to be code compliant.
Question: rock garden over leach field
(Mar 25, 2014) Tricia Williams said:
Yes and no. Yes if you're talking about light-weight stuff and no use of heavy equipment to set it in place and no deep-rooting plants.
Please see PLANTS & TREES OVER SEPTIC SYSTEMS at
Question: sports area over the septic soakbeds?
June 30, 2014) Alison said:
In my OPINION, normal human foot traffic over a working (not leaking, not unsanitary) septic drainfield should not damage it.
BUT the construction of a play area over a septic field by using equipment that might compress or disturb soil or break a buried pipe risks costly damage
AND adding topsoil can seriously interfere with proper drainfield operation by reducing the oxygen level in the soil below, thus reducing the level of aerobic bacterial treatment, thus leading to discharge of contaminants to the environment. Adding topsoil also can reduce the disposal of water in the effluent dispersal system via evaporation.
Question: ok to put up a post-supported structure over the septic fields?
(July 21, 2014) Steve said:
(July 23, 2014) DanJoeFriedman (mod) said:
I would not build a structure over a drainfield. What happens when you need to repair or replace the fields? And what are the chances that we an build a structure without ever driving machinery close-by, ruining the fields?
Question: drove the moving van over the septic area ... it was only there for a short time. Is there damage?
(Sept 18, 2014) Ann said:
good question, Ann,
If your system has a distribution box, open the box and see if there are signs of backup or failure to accept effluent in one or more of the lines.
Beyond that, I don't know a good answer. In my OPINION if there is no sign of blockage such as a sewage backup, new odors, or wet areas developing in the drainfield or near it, then it's not worth digging up the spot to see what happened.
If you do find signs of a backup at the D-box or on the ground surface or in the septic tank and were looking for a broken crushed drainfield line, then I'd dig and look at just where the van drove over the field trenches.
Question: build a small Tee-Box on the septic fields at a golf course
(Oct 21, 2014) Mike Allara said:
(Oct 21, 2014) DanJoeFriedman (mod) said:
If you mean a rain shelter or larger structure, it'd be smart to keep such structures away from the fields. For that matter, we might worry about field compression and damage if people are driving golf carts over it too.
If you mean the distribution box, the size needed is determined by the number of connections the box must feed. Or you could daisy-chain several.
Question: Nina's contractor leaves a mess
24 Feb 2015 Nina said:
He also put the lines in our driveway! He is supposed to be a professional
Our septic tank guy left the drain lines on top of ground! Is this acceptable?
He also put the drain lines in our driveway!
Nina I don't have a clear picture of what the heck is going on but it sounds as if a septic field installation is unfinished.
Certainly we wouldn't put a drainfield under a driveway, but pipes (rated to withstand the weight of traffic) might have to cross a driveway to carry effluent to a drainfield or septic tank.
Question: picnicing over the drainfield: dirt, mulch, rocks or what?
24 Feb 2015 karen said:
What we want to avoid over a leach field are plants that might send down deep roots that invade the system and clog it, and of course we don't want to drive equipment over the field while delivering anything heavy as that too can damage the fields. Your citation that there are trees over the septic fields is itself a worry.
a complete guide is at PLANTS & TREES OVER SEPTIC SYSTEMS
If you were to replace a small area of grass with stone, say around a picnic table itself I doubt that'd have a measurable impact on the septic system. But if you were to add gravel over large areas, while transpiration (evaporation) of effluent may continue, you're losing the benefits of moisture movement that is achieved by the grass that was there - a result is a wetter lleachfield and a shorter life.
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