FAQs on Building, Driving, or Paving Over the Septic Tank or Fields

Q&A about Driving over a Septic Leach Field

Also see DRIVE OVER a SEPTIC TANK or DRAINFIELD WITHOUT DAMAGE Q&A

Is it ok to drive a bucket truck on planks over the drainfield?

Would it be Ok to drive a bucket truck on to the lawn on planks for a short period of time, just long enough to pressure wash the peak of the house, let it dry and paint it? (July 20, 2015) Marg

Reply: use thick heavy planks + plywood or check the truck route

Marg

If the weight of the truck is sufficient to compress soil or worse to break a buried line, that takes only seconds. So "a short period of time" won't avoid trouble.

IF and I do mean IF your contractor can put down enough heavy 4x8 sheets of plywood to distribute the weight over a larger area than would be done by planks you might get away with it. Use 4x8 foot plywood of 5/8 or better 3/4" thickness.

Planks are more doubtful.

OR you can make sure that the route of the truck is not over piping or soakaway bed trenches.

What's the maximum allowable weight to drive over the septic soakaway bed?

Tell me the maximum weight over weeping bed - On 2016-05-17 by Anonymous

by (mod) - depends on soil conditions and traffic volume

Anon: there is no precise answer to maximum weight over a soakaway bed because bed design, soil properties, depth of the buried pipes, soil moisture and other factors may vary widely.

But generally considered "safe" are riding lawn tractors in the 500-700 pound range.

A 2000 pound lawn tractor is pushing your luck.

A VW Beetle weighs about 3000 and a Toyota FJ Cruiser about 4000 pounds. Certainly those would be considered "cars" that ought to stay off of a drainfield.

If you see that a vehicle leaves ruts or depressions in the soil over which it is driving that's a warning that the combination of weight and soil conditions is risking damage to the drainfield both by breaking or crushing pipes and by compressing the soil.

My opinion is that regular and varying passage over whole area of the fields by a heavy motor might be considerably worse than a single trip as one trip may break a pipe but won't compress the entire soil area.

How much weight can septic system piping withstand without damage?

What is the maximum weight piping can withstand before a field is compromised? And once compromised how long do property owners have to rectify the situation? On 2019-10-07 by Terry

Reply by (mod) -

Terry

Weight limits for traffic or vehicles moving over septic tanks and septic drainfields

Thanks for an excellent question of how much weight a septic system can withstand - and one that stumps me. I don't think there can be a reasonable single "right answer" to how much weight can a drainfield withstand before there is damage because the variables are missing:

- what are the soil properties: density, current moisture level, gravel content above, around, and below the piping?

- what is the depth of the piping and how were trenches constructed?

- how much traffic is moving over the field?

- how is the traffic weight distributed? Tires vs wide tread equipment vs equipment driving over heavy plywood sheets?

- where on the field does the traffic flow: over all of it, over an edge, parallel to drainfield trenches or across them

Examples:

a 10 ton dump truck driving across the head (where pipes enter) of a rectangular drainfield comprised of soft soil during wet weather with pipes 12" below the surface using older orangeburg or clay or thin PVC piping is likely to crush pipes and collapse trenches

Driving over or making a parking area over a conventional fiberglass or steel or even most residential concrete septic tanks risks collapsing the tank unless the tank is specifically constructed and designed to withstand vehicle traffic.

a conventional walk-behind power-driven residential grade lawnmower weighing just a hundred pounds or so used for mowing the surface is not likely to damage the fields

recurrent driving over a drainfield by automobiles or farm tractors risks compressing the soil and interfering with transpiration and absorption of effluent even if pipes are not broken.

I've done stupid or mean things in my life of which I am deeply ashamed. But I'm not fool enough to claim that anyone can give you a simple "right answer".

I can give a qualitative answer:

ANY kind of traffic over a septic drainfield or soakaway or leach field that is heavy enough to compress the soil is damaging the field and reducing its life; still-heavier weights may actually crush septic piping causing immediate failure.

ANY kind of vehicles driving over a septic tank heavier than a golf cart or residential lawnmower risk collapsing or damaging the septic tank unless it is rated and designed to withstand such traffic.

Also see SEPTIC TANK DESIGN STRENGTH SPECS

Also see DRIVING or PARKING OVER SEPTIC

Septic failure after I drove over septic with a Kubota BX that weighs around 1300 pounds?

I have a Kubota BX that weighs around 1300 pounds. I didnt think about it at the time. What are my chances.

My tank worked fine all summer. Last winter however someting froze. I'm not sure the two are connected. On 2016-10-28 by Jim

Can a 2000 pound lawn tractor drive over weeping tiles - On 2016-05-17 by Anonymous

by (mod) - If your tractor never leaves depressions or ruts on the ground surface it may be OK

Fair questions, Jim and anonymous.

A lot depends on soil conditions and depth and type of piping and installation details. If your tractor never leaves depressions or ruts on the ground surface over the drainfield I don't think it's likely to be the culprit.

by Jim

Thanks for your comments. I really appreciate it. jim

Is it safe to drive over a drainfield where pipes are 3 feet underground?

If septic laterals are at least 3 feet underground, and have been there for 17 years, is it safe to drive a car over them? On 2016-07-21 by Mary Skarzenski

by (mod) - probably not but here are the considerations and a suggestion for protecting the fields from damage

Great question, Mary. Not one that someone could possibly answer for certain by mere e-text: variables that affect the risk include:

- soil properties, density

- soil moisture levels

- pipe material

- existing pipe condition

- weight of the vehicle.

If you're facing a simple one-time crossing event, consider laying down pieces of plywood to distribute vehicle weight.

Is it ok to park a boat over the septic field?

Okay, nothing over the septic field. What about storing a boat? (Oct 1, 2015) Anonymous

Reply: That's OK provided you don't drive over the field and your boat isn't heavy

Anon: a boat supported on a dolly, if it is not heavy enough to crush soils or drainfield trenches, would not be likely to be a problem, but driving onto the fields to park or remove the boat could damage the fields.

Paving or Gravel Over a Septic Drainfield FAQs

To zero-scape our yard with Egg Rock - ok to put it over the septic field?

I live in South Florida with very sandy soil. My Wife and I want to zero scape our yard with Egg rock. We have a 22' X 25' drain field in the area we we want to place the rock. Any ideas about placing about 2" of rock over the field.

Details: I would like to place an inch or two of egg rock over my drain field, will this hurt the drain field in any way? This is sandy soil,in full sun most of the year, and there will only be wheel barrow traffic on it until the rock is spread.

This is about 500 sf of drain field, 22x25. Installed in 2013. Thanks David (Oct 3, 2014) Davis

Reply: a thin layer of loose rock won't stop evaporation/transpiration but will prevent grass growth that can help with effluent dispersal

Davis

Watch out: What I'd be nervous about is driving equipment over the septic field, destroying it.

Driving equipment over the field to place rock risks damaging it. But gentle hand work as described should not.

Watch out: removing grass covering also reduces the soil transpiration and moisture uptake rate so might reduce the fields ability to dispose of effluent.

Click the Egg Rock photo (Lowes) above to see a related guide: Native Garden Guide for Homeowners, from the US Department of Interior.

Davis added:

No driving of equipment over the field, just a wheel barrow. Will placing about 1 1/2 to 2" of egg rock compromise the field in any way?

There is currently no grass over the field, just sand. I think we will plant a garden of some sort over the field. Flowers and such, nothing edible . Again thank you for your help.

Moderator reply

Sounds as if you're ok. An authoritative answer would, of course, come from the design engineer to designed the specific septic system in question as s/he would know the details.

Be sure to see PLANTS & TREES OVER SEPTIC SYSTEMS

Can I build a rock garden over the leach field

Can I place a rock garden over part of my leach field? I want to put it right in the center and then plant bermuda grass over the rest of the field, around the rock garden. (Mar 25, 2014) Tricia Williams

Reply: You're reducing the capacity of your septic drainfield

Tricia

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.

But even then, Watch out: rocks means no grass which means you're givin gup the grass covering. That reduces the soil transpiration and moisture uptake rate so probably reduces the fields' ability to dispose of septic effluent.

No otherwise.

Please see PLANTS & TREES OVER SEPTIC SYSTEMS

I paved over the leachfield - soakbed - is that OK?

I had my 900 gallons septic tank pumped two years ago. Prior to that I pumped it three years earlier and after three years it clogged up. I uncovered it closest to the house today to see how it is doing and it appears to pretty full. Is that normal? The scum is about 4" below the inlet "T".

When I flushed the toilet and watch the water entering the septic tank it was coming out of the top of the "T" instead of the bottom. Is that normal?

There are only two of us living in the house full time a only a few times a years do we have company and heavy use on the tank. I did pave over my leach field and plant plants over another section of it. Did I compromise the leach field by doing so? I have friends two doors away that pump their tank about every fifteen years.

Your advice will be greatly appreciated. Thanks 9 Jan 2015 Anonymous said:

Reply: No, paving over the drainfield is a serious error

Anon

Keep in mind that while pumping the septic tank on schedule can help preserve the life of the drainfield, once the fields are in failure, pumping doesn't fix anything

Waste coming out of the top of a tee suggests that either the tee bottom was blocked or the drainfield is saturated. Try clearing the tee bottom and checking the thickness of the floating scum and settled sludge layers.

You don't ruin a leach field with a small single event of sending it solids but yes, in general that's indeed a way to speed leachfield demise.

Tank pumping frequency is given and explained

at

SEPTIC TANK PUMPING SCHEDULE

Watch out: paving over a septic drainfield is likely to destroy it, first by damage during the driving of paving vehicles over the field and second because the pavement prevents part of the field's functioning that requires transpiration or evaporation of a portion of the septic effluent and third because the cutoff of oxygen from the soil will halt operation of and kill off the required septic digesting bacteria needed for proper effluent treatment.

See DRIVING or PARKING OVER SEPTIC 

Buying a house where they paved over the drainfield with asphalt

All reports state no driving/parking on the drain field area. I am looking at buying a house and the driveway covers the edge of the drain field. Our best guess is the driveway was originally gravel and therefore an acceptable material.

Then someone upgraded to an asphalt drive without realizing the drain field was there.

Are there any solutions? What if it only covers a small portion (and how could we find that out?). If it is unsafe, how can it be fixed ? On 2016-06-24 by Melissa

by (mod) - Any kind of driveway over the septic - is trouble

Even if the drive was gravel, if it passes over the soil abaorption area, or worse, over piping, the weight of vehicles compresses soil and may break pipes - ruining the fields; remember that it's not just light-weight cars but heavy trucks that may pull into a drive from time to time.

If the drive was on the very edge of the fields it might make little difference; you need to know where & what components and pipes are located, the overall field design and layout.

Have the septic system inspected and tested; if it's not in failure I doubt that it's cost-justified to excavate, move, adjust soil etc.

Driveways or Roads Over a Septic Leachfield FAQs

Septic drainfield placed under the driveway by builder is failing and expensive to repair

Jim,

I have a two year old expensive custom home. The septic drain field was placed under the drive by the contractor who built the home. It was then paved over. It is now failing. I am facing a large unexpected expense.

Your explanation is clear. I am now looking for references (code, rules, formal guidance) that say this should not be done. Can you help?

Next, best route to extend drain field is from end away from septic tank. I think it is sufficiently protected to prevent crushing. Is using the existing drainfield pipe a performance issue? On 2016-11-01 by Charlie

Reply by (mod)

Aw geez, Charlie. One more real-world case illustrating that "expensive homes" are not necessarily built by a builder with any more sense than less costly homes.

In my experience, no competent, honest building code inspector would approve such a design. You will want to check with your local plumbing or building or health department - whomever approves septic designs where you live, to obtain a copy of the local septic code

Typically local codes (modeled on Shasta CA septic regulations as an example www.co.shasta.ca.us/docs/Resource_Management/ehd-forms/Septic.pdf?sfvrsn=0 ) state something like this:

"The site of the leach field and 100 percent of the replacement area shall not be covered by asphalt, concrete, or other impervious material or [sic should be nor] subject to vehicular traffic or other activity which would adversely affect the soil or leach lines". [Op. cit.]

I use this citation because you don't say where you live.

What does your local building department say? Did they approve this septic system as built? Can you get a copy of the septic plan as approved?

The issue isn't just crushing pipes it's that there is no aeration, no oxygen, and no transpiration. So the drainfield won't work to treat effluent even if it does seem to dispose of it.

I agree that extending the drainfield into an open area makes sense. If I were building it I'd ask my local plumbing or building inspector if they'll approve an extension without making me chop up the drive to replace the perforated piping;

if the inspector says no, then I'd look into a plumbing contractor who has the equipment to re-line or seal a perf pipe line to get thee effluent to the new destination. If you can achieve that by gravity flow you're in good shape. if not there's the added work to install a pumping chamber and effluent pump to a new drainfield in a suitable location.

(Or move the drive if that's feasible).

Please see SEPTIC & DESIGN CODES & SPECIFICATIONS U.S.A. for links to septic code sources for various U.S. and other communities.

by Charlie

Thanks for your suggestions. I live in rural New Mexico sorry. In many ways its still the wild west

Walkways Over the Septic Drainfield Area FAQs

Is it OK to build a walkway over septic?

Can I create a walkway (patio stones/interlock) over a tile bed (in Ontario Canada)

The walkway would only be from 4 to 6 feet wide and would cross the tile bed (July 15, 2015) Dave

Reply:

Dave:

You've probably read that in general we don't want to cover the absorption bed and we don't want to compress soils nor drive over it.

I don't know the total size of your particular tile bed but I speculate that the area that is covered and thus lost to transpiration / evaporation by simply hand-laying interlocking pavers to walk over the area would not be significant and so may be just fine. MAYBE.

If you are going to drive equipment over the "walkway" then I'd vote against it. If you are simply going to have people and maybe pets walking on it that's likely to be ok.

Dave said:

Thank you for your info. A little more info on the possible project.

The walkway would only be for people and pets to access the home(looking to relocate entry door to home) also I was thinking that I could use a combination of flagstone and clear stone to create the walkway. Would that be acceptable?

Would that affect the tile bed, especially in the winter (we get temperatures as low as -40 Celsius)

Reply: flagstones forming a simple, narrow walking path over a septic are probably perfectly ok

The weight of flagstones and people walking a narrow path across a septic field shouldn't harm it;

What are the best materials for making a walkway over a septic field

I am hoping to drive a 2220kg Thomas loader over a septic system for the removal of tree brush. We plan on laying down thick plastic pads to disperse the weight of the loader. What is your opinion on the risk of this action? - (Sept 27, 2012) Clark

I'm designing landscape for nursing home. is there any type of material that can be used for a walkway so that it can cross a leaching field? (Dec 11, 2012) beth

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:
In the UK, you cannot construct a path over a septic tank drainfield - Section H2 of the Building Regulations.

Reply:

Maureen:

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.

Sports or Play Area Over the Septic Drainfield FAQs

Can we build a sports area over the septic soakbeds?

We want to create a sports area for the grandkids when they visit and the flattest and most unused area of our property is over the septic field.

Could we add more topsoil, turf it and then use it for games such as badminton, croquet, bocce, horseshoes and golf putting?

Obviously we would not dig any holes within the field itself and use would be infrequent. June 30, 2014) Alison

Reply: human foot traffic is OK, heavy equipment, paving, digging, etc. are not; do not add topsoil

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.

Watch out: if the septic field fails such that sewage effluent is present on the ground surface, the area is not healthy for sports or play use.

Watch out: if the septic "drainfield" is wet by an aerobic septic effluent spray system it should not be used as a play area as there may be health risks from pathogens in sewage effluent.

Is it ok to put up a post-supported structure over the septic fields?

Could I erect a building on posts above our field bed knowing exactly where the lines are and placing the posts to avoid them? <p>&nbsp;</p>

Reply: warnings about hitting a pipe or driving equipment over the septic soakaway

You might be OK with the posts if you stop there.

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?

Can I build a small Tee-Box on the septic fields at a golf course

Can I build a small tee box on my septic field at my golf course? the field is reasonable large and I would not look to add anything bigger than 4 x 5 with some elevation. (Oct 21, 2014) Mike Allara

Reply:

A tee-box indeed sounds like a golfing system component. If you mean a tiny receptacle to accept golf tees, just put a birdhouse-sized box on a little post and don't drive the post into a drainfield trency.

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.

Installing Mulch or Bark Chips Over the Septic Leach Field FAQs

For picnicing over the drainfield can we put down dirt, mulch, rocks or what?

We have grass and couple of picnic tables over our leach field but we would like to put some more dirt or some mulch because the roots from trees and the fact that grass doesnt grow too well from limited sunlight in this area.

We were thinking of putting mulch, small stones or rubber mulch down which is easy to walk on. What material is okay to put down over a leach field ? 24 Feb 2015 karen

Reply by (mod):

Karen,

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 comment 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.

Watch out: if the septic field fails OR if it uses an aerobic effluent spray dispersal system such that sewage effluent is present on the ground surface, the area is not healthy for picnicing, sports nor play use.

Signs of Drainfield Damage from Driving Over It FAQs

How soon will we see signs of damage from driving over the septic system or drainfield

Someone just drove over our septic area about 4 feet from the riser. How soon should we notice a problem in the house (gurgling drains,etc.) if damage to the line was done? (Apr 7, 2015) Ruth

Reply: within a day or a week at most

I can't say, Ruth as we don't know enough about your septic system piping layout.

If an exit line between septic tank and drainfield were totally blocked and if the septic tank has no leaks, you'd notice backing up drains as soon as you've run enough wastewater to fill the septic tank that last few inches to its lid and to fill the piping between tank and house - normally within a day.

But a cracked or partly crushed line could still be damaged but take months to show up as a problem since it can take time for soil or roots to fill in the damaged piping.

LInes buried very deeply are less likely to have been damaged by a drive-over.

Since you know exactly where the line was driven-over, you have the option of digging to look.

I just ran a large mini excavator across a drain field perpendicular to pipes

I just ran a large mini excavator across a drain field perpendicular to pipes .

The machine had tracks not tires and the tracks are at least 8 foot long .

Since it had tracks it didn't sink into areas where pipes were ( I could see where soil was lower where the pipes were buried) I'm worried that damage may have occurred, how do I tell if it was damaged ? Only crossed it once. (Sept 25, 2015) David N

Reply:

David,

All the worrying is my profession I have to admit that not every possible catastrophe is going to happen. Your septic fields may be okay. It depends on

• The weight of the machine
• The properties of the soil
• The depth of the drainfield piping and contstruction of the trenches

If there is a distribution box upstream from the leach field lines that you crossed you can open that box to watch for signs of an effluent backup.

To go further would require excavation either at the end of the leach line or in the area where you drive across it before digging up such lines to look for damage I would watch the d'box as I said and I would watch for effluent break out or back up anywhere in the system.

if you don't see those problems then I think the further excavation is probably not justified. Do keep us posted on what you see.

Electric company drove their truck over our septic drainfield - one pipe is dented - is this a problem?

My leach bed was drove on by a electric company truck. I dug down to the plastic leach bed things. One section is dented down 4 inches or so. Will this cause me problems with my leach bed? On 2019-05-17 by Samadhi On 2019-05-05 by Brian

Reply by (mod) - will a dented or crushed leachfield pipe cause me trouble

Brian:

The risks include blockage of part of the septic drainfield, thus reducing its capacity to handle effluent in volume and shortening its life, and also possibly further line collapse and blockage. Also the soil itself is compacted by driving over the fields.

Details are at DRIVING OVER SEPTIC SYSTEMS

Movers drove their van over the septic drainfield and we see ruts: was it damaged?

We jusr purchased our first home with a septic bed. The inspector said our bed was great and advised us to never drive over it. On moving day it is obvious that the previous owners used a truck right over the bed to move.

There are many heavy tire marks over it. How can I tell if this damaged the tiles? On 2017-12-03 by Angelina

Reply by (mod) -

The fact that you already see tire ruts where those fellows drove across the drainfield means that there's indeed a risk of compressed soil and possibly a broken pipe.

A sewer line inspection camera can scope the pipes to see if one was crushed, but that won't address the problem of compacted soils.

Watch out: You might find the effects of drainfield damage subtle and delayed, ranging from a shorter life and reduced drainfield capacity due to soil compaction, to an actual drain line damage or collapse.

The latter shows up as a sewage backup or slow drains, or is revealed by having a plumber scan the drain interior using a sewer inspection camera

Can I repair damage caused by driving a truck over the drainfield

I've driven truck and damaged septic field.can it be repaired? On 2017-04-15 by Joe

by (mod)

Yes of course, by excavating and repairing the points at which drainfield lines were crossed.

There are more than one kind of possible septic drainfield damage from vehicle traffic:

• Broken or crushed drainfield piping - find by scoping the lines with a sewer line camera
• Crushed or compressed soils that might reduce the ability of the drainfield soil to handle septic effluent
• Creating ruts that direct surface runoff onto rather than away from the drainfield