This article explains the types of gardens or other plants that should or should not be planted over or near septic fields or other septic system components.

The page top photo shows the author inspecting the juxtaposition of field crops to a septic absorption field in Germany in 1968.

Planting Fruit, Vegetable, or Ornamental Gardens Near or Over Septic Systems

This is a guide for homeowners who are planting trees, shrubs, gardens, ground cover, or other plants near a septic system and who need to know that can be planted near or over septic system components like the septic tank, distribution box, and drain field or soil absorption system.

Planting the wrong things or in the wrong places can lead to the need for expensive septic system repairs.

Planting trees, shrubs, and even some ground covers over septic system components are causes of septic system failure in the drain field, leach field, seepage bed, or similar components.

Photo: giant trees & shrubs dwarf walkers in this Costa Rican jungle where very wet soils can make septic system absorption design difficult.

Planting fruit trees, or vegetables (or anything else edible) over the septic drainfield might produce food that is unsafe to eat:

see SEWAGE CONTAMINANTS in FRUIT / VEGETABLES for details.

Also see SEWAGE PATHOGENS in SEPTIC SLUDGE

and also SEWAGE NITROGEN CONTAMINANTS.

Is it Safe to Eat Food Grown Near the Septic System?

I am trying to determine if it is safe to eat the lemons and tangelos [planted or grown] near the septic system of our home.- K.P.

The short answer is it's better to keep fruits and vegetables away from septic systems, especially septic drainfields but above-ground crops such as fruit trees are less likely to be contaminated.

Watch out: gardening or planting anything but basic grass type groundcover over septic drainfields risks damage to the septic system by soil compression, damage to pipes, root invasion of pipes - all problems that can lead to costly septic system repairs.

Details and report of a study documenting bacterial hazards in fruits and vegetables actually watered with septic effluent [a more stringent test case] are

at SEWAGE CONTAMINANTS in FRUIT / VEGETABLES.

Watch out: do not plant a raised-bed garden over the septic drainfield. Constructing a "raised bed" garden which requires the addition of soil above surrounding ground levels can damage the system or can reduce soil transpiration thus preventing the drainfield from functioning properly.

Watch out: do not plant root crops over a drainfield. They may be contaminated with sewage bacteria.

Watch out: even above ground edible plants such as leafy vegetables or lettuce may become contaminated by sewage splash-up onto the plants during watering or rainfall.

Planting a fruit or vegetable garden over or near septic system components raises some important questions:

• Will there be pathogenic or chemical contamination of the soil (bacteria, viruses, cleaners) below the garden?
• Will septic system pathogens enter in or contaminate fruits or vegetables planted over or near the septic system?
• Will chemicals or salts passing through the septic system harm nearby plants?
• Will the garden planting itself harm the septic system in some way?

The effectiveness with which the soil biomat is treating pathogens in septic effluent, the ability of the soil to filter effluent, the chemicals or salts entering the septic system, and the type of plants placed over or near the system are some of the factors that lead to answers to these questions. [The photograph above shows our vegetable garden gone wild in Costa Rica.]

• Septic effluent contains chemicals and pathogens which are potentially unhealthy
  
  or harmful to people, animals, or plants.
  
  If a septic absorption system's biomat is functioning successfully, the level of these pathogens is reduced by up to 45% for conventional septic systems, up to 70% for advanced treatment systems, and for more advanced (and rarely found) systems it is possible to treat effluent to a level of sanitation similar to that of typical surrounding surface water before effluent leaves the drainfield.
  
  So there is a reasonable chance that food-plants located over or close to a septic drainfield contain harmful levels of bacteria or other contaminants.
  
  See SEWAGE CONTAMINANTS in FRUIT / VEGETABLES. The "safe" distances between edible crops and septic components depend on
  • The level of treatment of septic effluent achieved by the onsite septic or wastewater treatment system
  • The soil type (see below)
  • The crop type (see below)
  • Possibly seasonal or other changes in surrounding surface runoff and groundwater, independent of the individual septic system but affecting its performance and thus its level of treatment of the sewage
• Soil types
  
  affect how the septic system behaves and how it affects nearby plants of any kind. Clay soils release cleared effluent in perhaps a few inches but then clay doesn't perc well and is bad in general for a septic location. Sandy soils permit much greater travel of effluent and pathogens, certainly several feet.
  
  These "close" distances do not even consider what happens when the drainfield is not working well or is in failure. In that case pathogens may be released to the general environment and might travel any distance from the septic field.
• Root crops
  
  such as carrots or potatoes which develop in the soil are likely to pick up pathogens from effluent in the soil over, next to, or downhill from drainfield trenches or galleys.
• Leafy crops
  
  such as lettuce or perhaps broccoli which develop above the ground but close to it may be contaminated by pathogens that splash up from the soil surface during watering or during rainfall.
• Above ground crops that grow on a raised vine
  
  such as cucumbers, tomatoes, or peppers may fare better if they must be planted over or close to septic system components, since they are higher up and less likely to be contaminated by soil splash-up.
• Salts and the septic system:
  
  Homes whose water supply is "hard" and which employ a salt-based water softener system are more likely to be passing high levels of salt into the septic drainfield. Not only does this salt risk harming the drainfield operation (mineral clogging or damage to the biomat) but such salts may also damage some plants that grow nearby.
• Chemicals and the septic system:
  
  At this website we've advised strongly against use of "magic bullet" chemical or other septic treatments as some of them are toxic and environmental contaminants. Some of these may also contaminate your garden.
  
  See ROOT KILLERS in SEWER LINES or SEPTIC PIPES.
• Gardening
  
  activities such as walking or digging into the first few inches of soil over a drainfield are not likely to damage it.
  
  Watch out: driving equipment such as a plow or roto tiller over a drainfield can compress soil below or damage piping and drainfield trenches
  
  Not "functioning properly" here means that the drainfield stops successfully treating the pathogens that flow into it. It stops working and begins discharging unsanitary effluent into the environment, and into your garden.

Research: Septic Contamiants in Gardens Over or Near Septic Systems

• Day, Susan D., and Ellen Silva, PLANTING ON YOUR SEPTIC DRAINFIELD [PDF] Virginia Cooperative Extension, Pub. 426-617, retrieved 2019/08/27 original source: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/426/426-617/426-617_pdf.pdf
• Gantzer C, Gillerman L, Kuznetsov M, Oron G. Adsorption and survival of fecal coliforms, somatic coliphages and F-specific RNA phages in soil irrigated with wastewater. Wat Sci Technol. 2001;43(12):117–24.
• U.S. EPA, PROPER LANDSCAPING ON & AROUND YOUR SEPTIC SYSTEM [PDF] (2015) U.S. Environmental Protection Agency, retrieved 2022/04/25 original source: https://www.epa.gov/sites/default/files/2015-06/documents/septicsmart-week-landscaping-final.pdf
• Manios T, Moraitaki G, Mantzavinos D. Survival of total coliforms in lawn irrigated with secondary wastewater and chlorinated effluent in the Mediterranean region. Wat Environ Res. 2006;78(3):330–4.
• Rahube, T. O., Marti, R., Scott, A., Tien, Y. C., Murray, R., Sabourin, L., Zhang, Y., Duenk, P., Lapen, D. R., & Topp, E. (2014). Impact of fertilizing with raw or anaerobically digested sewage sludge on the abundance of antibiotic-resistant coliforms, antibiotic resistance genes, and pathogenic bacteria in soil and on vegetables at harvest. [PDF] Applied and environmental microbiology, 80(22), 6898–6907. https://doi.org/10.1128/AEM.02389-14
  
  Abstract:
  The consumption of crops fertilized with human waste represents a potential route of exposure to antibiotic-resistant fecal bacteria. The present study evaluated the abundance of bacteria and antibiotic resistance genes by using both culture-dependent and molecular methods. Various vegetables (lettuce, carrots, radish, and tomatoes) were sown into field plots fertilized inorganically or with class B biosolids or untreated municipal sewage sludge and harvested when of marketable quality.
  
  Analysis of viable pathogenic bacteria or antibiotic-resistant coliform bacteria by plate counts did not reveal significant treatment effects of fertilization with class B biosolids or untreated sewage sludge on the vegetables. Numerous targeted genes associated with antibiotic resistance and mobile genetic elements were detected by PCR in soil and on vegetables at harvest from plots that received no organic amendment.
  
  However, in the season of application, vegetables harvested from plots treated with either material carried gene targets not detected in the absence of amendment. Several gene targets evaluated by using quantitative PCR (qPCR) were considerably more abundant on vegetables harvested from sewage sludge-treated plots than on vegetables from control plots in the season of application, whereas vegetables harvested the following year revealed no treatment effect.
  
  Overall, the results of the present study suggest that producing vegetable crops in ground fertilized with human waste without appropriate delay or pretreatment will result in an additional burden of antibiotic resistance genes on harvested crops. Managing human exposure to antibiotic resistance genes carried in human waste must be undertaken through judicious agricultural practice.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

How long before we can you ground for planting a vegetable garden?

We are terminating our septic for city sewer. How long before we can you ground for planting a vegetable garden? Safety wise for uncontaminated food. On 2014-06-16 by Lisa K.

by (mod) -

That's a great question, Lisa and I don't know a firm answer because there are so many variables including:

- the degree of sewage effluent water that actually was in the soil that will be in contact with plant roots
- the soil properties
- the soil moisture level
- the health of aerobic and anaerobic bacteria in the soil
- the type of crops intended for planting and their root depth

We looked at this question some time ago in assessing how long it would take for raw sewage in a latrine pit or outhouse pit to break down if the pit were abandoned and covered - that represents the most extreme or difficult case - far more difficult than the situation you describe. In that case the answer could be a decade or more.

In the case of a septic system that was not sending effluent to the surface, my in-expert OPINION is I'd wait a year or more before planting root crops (potatoes) or low crops that might be contaminated by rain splash-up. Taller crops that produce edibles high enough above ground to avoid those risks, and fruit trees, are safe for planting sooner.

 

Is a Vegetable garden being planted in front of a sewer - health hazard?

Hi, we have neighbors planting a vegetable garden on the city owned green strip of grass between sidewalk and gutter It is directly in front of a sewer.

This is also a daycare center. Is this safe for eating? My husband says its very dangerous. I've recvd no response from the city. Thank you. On 2017-08-15 by Eileen Dargon

by (mod) - safety of a municipal vegetable garden near a public sewer

Eileen,

I'm not sure about the safety or danger of the garden you describe.

A city sewer line ought to be a water-tight buried pipe, and thus not leaking sewage contaminantes into nearby soils or gardens,

Watch out: however because who knows what contaminants fall into the garden from the street itself: diesel oil, road salt, road dirt and debris, splash-up from street drainage.

Not to mention peoples dogs and cats using the area as a toilet. Some of these risks can be reduced by fencing, though for a narrow garden space the result may be untenable.

Does your city (what city is this?) permit residents to farm the grass strip you describe?

Let's both do some further research.

Planting a garden over septic drainage rock paths

I am trying to plan a flower/vegetable garden(farm) in an area that has septic drainage(leach drainage) with rock paths with no pipes under that area of wanting to plant a farm.

I’m guessing we should get the soil tested, septic system effluent effectiveness tested, etc.

What else should I consider ?

The septic drainage rock paths are seen in the picture -1, 2, and 3 drainage path. On 2022-09-25 by DenverJohnny

Reply by InspectApedia (Editor)

@DenverJohnny,

There are bacterial and other pathogenic hazards that might be present and may be a real concern when growing vegetables where there is sewage effluent nearby - especially at the surface where it can contaminate edibles as both a dust or a liquid.

Even if properly specified tests found no unusual hazards, in my OPINION, I'd want to know a bit more about the septic system and its history, condition, maintenance, and the soil properties, drainage, etc. before investing in a garden whose produce might later have to be tossed-out.

by DenverJohnny

@InspectApedia (Editor), thanks !! I can find out all the details of the septic system since the property is in the family. What types of things should I find out about the septic system ? I want to make sure the area is okay for growing vegetables. Thanks

by InspectApedia (Editor)

@DenverJohnny,

• Location of the septic components: tank, drainfield, piping: driving equipment over those components can cause costly damage
• Maintenance and repair history
• Depth of components
• Signs of failure
• Boundaries outside of which you'll want to keep your plantings
  

by DenverJohnny

@InspectApedia (Editor), so the area doesn’t have any components, just rock drainage paths (see in the image), so I’m assuming I would have to just test the soil for bacteria/pathogens, check the drainage efficiency, and the boundaries where I should plant according to the tests?

by InspectApedia-911 (mod) - avoid growing edibles over a septic field

@DenverJohnny,

Sorry but we're getting over my head here. I simply don't understand enough about the property. My basic point is that we prefer to avoid growing edibles over a septic field.

How long should the septic fields remain unused before planting a vegetable garden?

I am a member of our Town's conservation Board and we would like to plant a community vegetable garden in a space where there must be septic fields. The community house predates the board of health and the town has no record of where the fields are since the building is circa 1919.

The town is putting in sewer lines and by next year the septic system will be off line. Currently the building gets infrequent use.

We would like to know how long the fields should be remain unused in order for the soil above them to be safe for planting edibles. Thanks so much for any info you can provide. On 2022-06-20 by Janeen Sudaka-Karlsson

Reply by InspectApedia (mod) -

@Janeen Sudaka-Karlsson,

As we replied to another reader (Lisa K.) just above on this page,

"...there are so many variables to consider including:

- the degree of sewage effluent water that actually was in the soil that will be in contact with plant roots
- the soil properties
- the soil moisture level
- the health of aerobic and anaerobic bacteria in the soil
- the type of crops intended for planting and their root depth

In the case of a septic system that was not sending effluent to the surface, my inexpert OPINION is

I'd wait a year or more before planting root crops (potatoes) or low crops that might be contaminated by rain splash-up. Taller crops that produce edibles high enough above ground to avoid those risks, and fruit trees, are safe for planting sooner."

Will putting raised bed gardens over the septic cause a problem?

Will putting a couple of raised gardens (using landscaping material on the bottoms of them to prevent rooting) on the leachfield be a problem seeing that there will be plenty of uncovered area for evaporation? - On 2016-04-28 by Bill -

Reply by (mod) - Yes: don't put raised bed gardens on top of the leachfield

Good question, Bill.

I am not an authority - those are your local code officials.

OPINION

But I think that the original, approved design of any septic system includes the layout and overall size of the drainfield or absorption system.

When you cover part of that area with anything - even simplhy 1 to 3 more feet of soil to build your raised bed garden - that reduces the transpiration rate (movement of effluent moisture into the air above the fields) you are reducing the field's effluent handling volume and thus its effectiveness.

Actually *measuring* the amount of that impact is difficult, as we don't know the proportions of moisture disposal into air vs. into the ground below. I think that's why people don't try to figure it out, they simply apply "safe" rules.

You could probably install raised gardens, prevent root intrusion, reduce the efficiency or effectiveness of the drainfield, and see no effect for years. But the ultimate costs could be earlier field failure and costly replacement, or a shift in effluent disposal balance that inadvertently contaminates groundwater in your area.

OK to plant Flowers with shallow roots won't harm a drainfield

I would like to plant annual flower beds over a leach field. No digging, but shaping beds in rows (essentially, flower farming) with 6 inches of new soil. OOn 2021-10-21 by Kosodate

y danjoefriedman (mod) -

@Kosodate,

Flowers with shallow roots won't harm a drainfield, but I'd be careful about adding fill; burying a drainfield can interfere with its proper operation.

f I move plants out of the leachfield are they edible?

Will plants moved from a leach field to a safe field be edible ? On 2021-05-21 by Mark I

by danjoefriedman (mod) - sewage contamination of edible roots

@Mark,

Answer to your question is, unfortunately, it depends.

Edible root plants that may have absorbed contaminants from soil may need considerable time in a clean field to be rid of those contaminants.

But all of this is theoretical, and if you'll forgive me a bit of arm waving, since we have nothing specific such as what the plants are, what kind of edible or fruit structure is used, whether the edible part of the plant that was on a septic field is above or below ground, what are the conditions of the septic field or suck away bed itself, including soil-moisture levels and sewage contaminant levels, and a host of other questions.

In my opinion the greatest risk of sewage contaminants on edible plants nearby is from rain splash up of sewage bacteria on the soil surface.

The question of sewage contamination of edible roots from other plants is as I've outlined more complex.

It would be helpful to actually have a sample of one of your plants tested for sewage pathogens.

If the edible part of the plant is a root,, have the root tested.

If the edible plant of a plant on the septic field is above-ground, have that part tested.

Let me know what you find, as that would be immensely helpful to other readers as a case providing actual objective data instead of only relying on Theory.

Ok to plant vegetables over abandoned septic drainfield if we wait?

We had an old septic system, with lateral lines, replaced with a complete new system in a different place. If we let the old lateral line field sit for 1 year can we plant a vegetable garden on top? We would till the soil twice and add a bunch of top soil.

It might be important to know the lateral lines where not functioning properly in the first place, which is why we had the system replaced. On 2020-07-19 by Jennifer

Answer by (mod) -

Jennifer

You ask a perfectly reasonable question but not one I can answer with certainty, as I have no information about factors that would make the vegetable garden definitely safe or definitely unsafe.

In general soil bacteria break down sewage;

Adding topsoil and plowing the future garden are good ideas. It might be most effective to do that ASAP, then wait a year. By giving the garden soil more oxygen (by plowing) you help put the aerobic bacteria to work breaking down pathogens.

If there was actual sewage on the area surface, it might be useful to have a representative soil sample tested for level of e-coli bacteria. Do this at the end of your year wait. Don't expect zero bacteria, but do expect little or no e-coli.

As you'll read in this article series, the principal garden sewage pathogen risks that we've found and documented were from raw sewage on or splashing-up onto crops close to the ground.

Do keep me posted, especially with what you find a year from now.

Daniel

Will planting ANY TREE / SHRUB over or near a drain field cause the tree/shrub to die or not do well ?

I plan to plant a Southern Magnolia near the septic tank drain field (not exactly sure of the boundaries of the drain field). Two Questions:

1. Is planting this magnolia potentially hazardous to the drain field?

2. Will planting ANY TREE / SHRUB over or near a drain field cause the tree/shrub to die or not do well ? - On 2020-05-03 by Ronald E. Rogers

Answer by (mod) -

Ronald

Thank you for helpful question. N

The problem is not usually that the tree plant or shrub near the septic dies but rather that the nutrients in a septic effluent are so delicious to the tree planter shrub that it grows like crazy and sends roots that invade and damage septic system.

That's why you will see in this article series that plants with deep or aggressive roots are Best Kept away from the septic drain field.

Safe to eat Lychees from a Lychee tree jplanted over the old drainfield?

I moved into a house that has a large mature approx 15ft -20ft lychee tree right on the edge of the drain field. The drain field was replaced and is new as of 4 nonths ago. My question is when the lychee tree fruits are they safe to eat?

The roots didn’t seem to bother the old system. It was simply old and was time to replace

Tamara On 2020-04-21 by Tamara

Answer by (mod) -

Tamara,

Usually fruits above the height of splash-up of pathogens from the soil during rain or watering will be ok

Can I line our rock bed garden bottom with plastic and put it over the septic field

We just moved into a new house and there is a rock garden bed near the septic tank. I'm not sure exactly how deep the septic tank is.

My question is, if I line the bottom and edges of the garden with the plastic tarp material that you use for a greenhouse, and put new dirt in it, would it still be safe to grow vegetables there? The garden is not moveable and it is not on top of the septic tank, just near it. Thank you. On 2020-01-16 by LeeAnn

by (mod) - NO - you block the septic field's evaporation / transpiration

Thanks for the septic and garden bed question, LeeAnn.

There are two different things to avoid:

1. over the septic tank itself, what you propose won't hurt the tank, but what the heck: when you need to pump the septic tank - as must be done periodically to avoid ruining the septic drainfield - you will have to cut through or dig up or remove the rock garden to give access to the tank in one or more places.

So it's a bad location to start and it risks sewage contamination from spills during pumping.

You could build an access well or install septic tank risers that poke through your garden and come to the surface above it to give septic maintenance access but take care not to spill sewage into your veggies during pumping.

2. Over the drainfield: You never want to put down plastic over the septic soakaway drainfield itself.

That interferes with transpiration - basically disposal of some of the sewage effluent by evaporation, and it starves soil bacteria of oxygen, thus preventing sanitary processing of the sewage effluent and thus contaminating the environment around your home.

Will vegetable garden roots block pipes in a drainfield that's 12 feet deep below?

I plan to build a septic system with a drain field which will be approximately 12 feet below ground level. Is this distance great enough to allow for root vegetables, such as potatoes and other non tree type vegetables to be grown safely? We have limited gardening space.

tjd15sep@yahoo.com Thank you On 2020-01-16 by LeeAnn

Answer by (mod) -

Tim I'm doubtful that any vegetable roots extend down to the depth you describe for your drainfield, but, then,

Watch out: my OPINION is that a drainfield that's 12 feet below the soil top also will not work to treat effluent successfully, as there will be too little oxygen.

Can I water my vegetable garden with my aerobic spray head sprinklers?

I have an aerobic system and was wondering if a vegetable garden could be planted near the sprinklers to aid in watering it On 2017-04-05 by Towreaper

by (mod) - Bad idea: spraying sewage effluent onto your vegetables above ground

If You'll be spraying sewage effluent onto your vegetables above ground - that's not something I'd recommend.

Can you define "close" to a septic drain field as you refer to it?

I read your article on growing vegetables on a property with a septic tank and drain field. Can you define "close" to a septic drain field as you refer to it?

That is, roughly how many feet away from the drain field, pipes, etc.should in-ground gardening be to be assured that even root vegetables would not absorb waste, assuming the system is functioning correctly? If raised beds are installed, how many feet away from the drain filed to assure no absorption of contaminants?

How far to avoid reducing the effectiveness of the field by covering ground it with the raised beds? Thank you so much for your help. On 2016-08-04 by Kay

by (mod) - keep far enough away that septic / sewage effluent isn't in your food

Kay I'm a little scared to give a definite answer since defining "close" , well, as my guru Mark Cramer (Tampa FL) says " .. it depends"

Depends on:

Soil slope: crops downslope from a drainfield are more at risk of sewage contamination from surface runoff and ground-water

Soil properties: how quickly and easily does water move from one location to another under ground - flow rates, porosity, soil composition

Type of food being grown: above-ground crops are less at risk for bacterial contamination through ground water but might be contaminated by rain splash-up if surface runoff is contaminated

So if you are confident that your crops aren't being drained-into by sewage effluent nor being contaminated by sewage splash-up during rain, you're in at least a defensible position. Whether that's ten feet or 50 feet I can't know for your particular site. If never the less you twist my arm and demand a number I'll make one up: keep the food crops at least as far from the septic fields as you'll keep your drinking water well.

Search InspectApedia.com for SEPTIC CLEARANCE DISTANCES to see a full table of those numbers.

I would NOT install raised bed gardens over a septic field in any event as adding soil cover beyond the original design depth will reduce transpiration and risks damaging the drainfield or shortening its life.

 

When we stop using a septic leachfield do we have to have the soil removed as toxic material?

My understanding is that when a leach field is taken out of service, the dirt/sand/gravel is considered toxic and must be disposed of accordingly if removed.

How long does it take for it to lose it's toxicity and can be considered safe? On 2018-06-12 by John

Answer by (mod) - No, not normally

John,

In my experience your understanding is not correct. There's no regulation, color, or guideline that I have been able to find that suggests that when a leach field or drain field is abandoned that the soil has to be removed from the site.

Length of time for soil bacteria to completely process the remaining biomat pathogens could be anywhere from 3 to 20 years depending on the soil properties, moisture levels, and the biomat thickness and chemistry.

That does not mean at the site should be considered toxic. In fact if there's no sewage on the surface there's no reason to be concerned with normal use of such a property.

by John

Thanks for the info - I was not thinking that the soil had to be removed, but if it is, I have been told it is considered toxic.

I am interested in re-using the land in a manner that requires some excavation and so my concern is for the safety of doing so. It has not been an active leach field for 20 years so it sounds like I should be OK - does that sound right?

Answer by (mod) -

I'd review this question with your local health officials. I'd expect they'd be ok with a bit of soil mixing on the existing property - at most you might need to top it with clean fill.

Research on Septic Drainfield / Soakaway / Leachfield Soil Toxicity

• Amador, Jose A., and Janet A. Atoyan. "Structure and composition of leachfield bacterial communities: Role of soil texture, depth and septic tank effluent inputs." Water 4, no. 3 (2012): 707-719.
  
  Abstract:
  
  Although groundwater quality depends on microbial processes in the soil treatment area (STA) of onsite wastewater treatment systems (OWTS), our understanding of the development of these microbial communities is limited. We examined the bacterial communities of sand, sandy loam, and clay STAs at different depths in response to septic tank effluent (STE) addition using mesocosms.
  
  Terminal restriction fragment length polymorphism (TRFLP) analysis was used to compare the bacterial community structure and composition of STE, native soil prior to STE addition (UNX) and soil exposed to STE (EXP). Principal component analysis separated communities with depth in sand but not in sandy loam or clay.
  
  Indices of richness, diversity, and evenness followed the order: sandy loam > sand > clay. Analysis of TRF peaks indicated that STE contributed least to the composition of STA bacterial communities (5–%16%), followed by UNX soil (18–%48%), with the highest proportion of the community made up of TRFs not detected previously in either UNX or STE (50–%82%) for all three soils.
  
  Soil type and depth can have a marked effect on the structure and composition of STA bacterial communities, and on the relative contribution of native soil and STE to these communities.
• Beal, C. D., E. A. Gardner, and N. W. Menzies. "Process, performance, and pollution potential: A review of septic tank–soil absorption systems." Soil Research 43, no. 7 (2005): 781-802.
  
  Abstract Except:

  On-site wastewater treatment and dispersal systems (OWTS) are used in non-sewered populated areas in Australia to treat and dispose of household wastewater.
  
  The most common OWTS in Australia is the septic tank–soil absorption system (SAS)—which relies on the soil to treat and disperse effluent.
  
  The mechanisms governing purification and hydraulic performance of a SAS are complex and have been shown to be highly influenced by the biological zone (biomat) which develops on the soil surface within the trench or bed. Studies suggest that removal mechanisms in the biomat zone, primarily adsorption and filtering, are important processes in the overall purification abilities of a SAS.
  
  There is growing concern that poorly functioning OWTS are impacting upon the environment, although to date, only a few investigations have been able to demonstrate pollution of waterways by on-site systems.

  In this paper we review some key hydrological and biogeochemical mechanisms in SAS, and the processes leading to hydraulic failure.
  
  The nutrient and pathogen removal efficiencies in soil absorption systems are also reviewed, and a critical discussion of the evidence of failure and environmental and public health impacts arising from SAS operation is presented. ...

• Field, Jason Paul. "Comparative Effectiveness of Conventional Trenches and Seepage Pits for Treatment of Septic Tank Effluent." (2003). University of Arizona A Thesis Submitted to the Faculty of the DEPARTMENT OF SOIL, WATER AND ENVIRONMENTAL SCIENCE
• Reneau Jr, R. B. Changes in concentrations of selected chemical pollutants in wet, tile‐drained soil systems as influenced by disposal of septic tank effluents. Vol. 8, no. 2. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 1979.
  
  Abstract
  
  

  Changes in P, MBAS, NH4, NO3, NO2, Cl, pH, and Eh from septic effluent disposal were monitored in shallow ground waters between septic effluent disposal fields and an agricultural tile drainage system in an area composed of Typic and Aeric Ochraquults.

  As effluent moved through the soil system toward the agricultural tile, P and MBAS decreased logarithmically with distance.
  
  As much as 87% of the observed variation could be attributed to distance for both P and MBAS. Phosphorus and MBAS in ground waters intercepted by the tile drainage system at two of the sites had been reduced to acceptable levels. At location 1 (Typic Ochraquult), P and MBAS moved further (12 m) than might be predicted and were present in ground waters intercepted by the agricultural tile.
  
  These concentrations of P and MBAS in waters intercepted by the tile at location 1 resulted from rapid movement of effluent via saturated flow through the larger soil pores and from an inadequate soil volume for effluent purification.

  The concentrations of inorganic nitrogenous components in relation to the disposal area were similar at all three locations. The NH4-N concentration was highest adjacent to the drainfield (20–30 µg/ml) and decreased logarithmically with distance.
  
  A maximum of 83% of the observed decrease in NH4 could be attributed to distance. The NO3 concentration increased to a maximum at approximately 5 m and then decreased with increased distance. This was substantiated by the NO3/Cl ratios which indicated that NH4 was nitrified and the NO3 produced was subsequently denitrified to a large degree.
  
  The NO3 accumulation was seasonal with the highest concentrations present during periods of rising water tables.

 

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