How Long Does Sewage Contamination Last

How Long Does Sewage Contamination Last

how long does sewage contamination last

Virtually all of the research on the survival of these bacteria has focused on water, soil, manure, and sewage sludge. On the other hand, the indoor environmental investigator needs to know how long the bacteria survive as a sewage spill or flood dries, and how to document that the environment has been sufficiently cleaned.

Bacterial decay (death) rates are generally measured in log reductions in culturable organisms. Note that there may be viable organisms remaining that are not culturable but could indicate a continuing risk of exposure. A logarithmic decline in a bacterial population means that a large percentage of the bacteria die quickly, and the rate of death slows as time passes.

A quick survey of the literature revealed the following estimates of survival time for some important bacteria:

How long does sewage contamination last?
Bacteria NomenclatureAffected SubstrateSewage Contamination Surviving Period
E. coliWaterUp to 103 days
EnterococcusDry SurfacesUp to 27 hours
Staphylococcus aureusHospital dry surfaceBetween 10 and 12 days
E. coliLettuceUp to 28 days
E. coliSoilUp to 70 days
E. coli H37SoilUp to 17 weeks

Analysis About The Determination Of How Long Does Sewage Contamination Last

The fact that all of these times are indicated with “greater than” means that residual organisms were present at the end of each of these experiments. To clarify what logarithmic decay means, let’s assume you have a sewage spill with 1,000,000 bacteria/100ml and a decay rate of 1 log/day. (This is an artificially high rate for convenience). After one day you will have 100,000 bacteria/100ml, and it will take 5 additional days to reach 1 bacterium/100ml. For a small spill (e.g., 30 liters), you will have a total of 30,000,000 total bacteria after one day, and 3,000 at day five.

This assumes, of course, that the rate of decay remains constant over the time of measurement and you don’t do anything to artificially reduce the population. In the case of indoor sewage spills, the natural decay rate would tend to increase because of the reduction in the amount of liquid remaining (as it evaporates), and because the air and surface temperature to which the spilled sewage is exposed is likely to be higher than that in the original source. Both increasing temperature and drying tend to increase the decay rate.

Let’s say that the decay rate in the spilled sewage increases gradually over 24 hours to 2 logs/day. Thus, by the end of the second day in the example above you will have 1000 bacteria/100ml, and by day 3 you may be down to less than 10 bacteria/100ml. Of course these changes are dependent in part on ambient relative humidity and both ambient and surface temperatures.

Now, let’s assume you are on-site within 1 hour after the spill. You are faced with slightly less than 300,000,000 bacteria. You get right to work removing the water and the solids and are able to effect a 99.9% reduction by the end of the day. You have removed 3 logs of bacteria and are now down to about 30,000 bacteria assuming natural decay continued.

The good news is, if you used detergent and bleach (1/2 c/gallon of water), you have killed at least 3 logs more, bring you down to 30 bacteria, which in my opinion is an acceptable number. Unfortunately, these 30 bacteria will not be grouped in one little spot so that you can collect them and “prove” that only 30 are left. Depending on the size of the area affected, you would have to take many samples to document efficacy. I don’t think the effort and cost is worth it.

Documentation on how to clean sewage spills indoors is available in many places. The procedure explained at is good, although I would use a more concentrated bleach solution. Another good procedure can be found at Washington State Department of Health’s “Cleaning up a sewage spill.”

An important thing to remember is that once the spill has happened, the bacteria are not confined to the actual wet places. They could also be on higher surfaces. It is important to clean all surfaces that might be touched by the occupants in the near future.

How Long Does Sewage Contamination Last In The Case Of Floodwater?

Floodwater can overflow from wastewater treatment plants, sewer lift stations, sewer collection systems (e.g., manholes and sewer mains), and individual or community septic systems into human use spaces like ball fields, playgrounds, and residential yards. These floodwaters may spread bacteria, viruses, protozoa, and other microbial contaminants that can cause illnesses ranging from mild stomach upset to serious diseases such as dysentery, infectious hepatitis, and severe gastroenteritis (1). Typically, it takes 2–3 months for enteric bacteria to significantly reduce in soil, with certain exceptions. But due to different microbial responses to the environment, providing universal guidance is difficult.


Sanitary sewer overflows can be caused by too much precipitation infiltrating leaky sewer pipes, inadequate system capacity to handle newly-developed residential or commercial areas, blocked or broken pipes, or improperly designed and installed sewer systems.

Sewage backups not only present unpleasant odor problems, they may cause property damage and present unhealthy living conditions. Untreated sewage contains disease-causing organisms such as bacteria, viruses and parasites.

Contact with contaminated water can cause skin infections and rashes, and if ingested accidentally via improperly cleaned hands or food preparation surfaces, these contaminants can cause nausea, abdominal pain, vomiting and diarrhea.

Respiratory infections and allergic reactions may also result from inhaling associated airborne microorganisms.

The drying out process can take several weeks in an enclosed area such as a basement or crawl space, and growth of microorganisms will continue as long as the humidity remains high. If the damaged area is not cleaned and dried out properly, a musty odor, signifying the continued growth of microorganisms, can remain long after the sewage overflow.

Contaminated materials outside the home If there is a broken sewer line outside the home or in a
crawl space under the home, the first step is to put on protective clothing such as waterproof boots, gloves, eye protection and clothes that are either washable or disposable. A dust mask should be worn when cleaning to avoid breathing airborne microorganisms.

Plastic ground liners, surface contamination, and heavily contaminated soil should be removed from the impacted area if possible. The remaining contaminated soil should be treated in place with a liberal application of garden lime to reduce odor and enhance degradation of the organic matter.

If the contaminated area is in the open, it should either be covered with clean dirt or temporarily fenced off to prevent accidental contact with the lime and any remaining contamination. After a day or two, mix the lime in with a rake and use a sprinkler or hose to water the lime and any remaining residues into the soil.

Let the area dry in the sun if possible before allowing access.

Excavated soils may be remediated onsite by treatment with garden lime and should be turned over frequently to provide oxygen to the naturally occurring microbes in the soil that degrade the organic material. If onsite treatment is not possible, or if it can’t be accomplished without creating a nuisance condition, contaminated soils and other materials removed from the impacted area may be disposed of at any landfill willing to accept them.

Contaminated materials in the home

When sewers back up into homes, the damaged area
must be thoroughly cleaned and disinfected to reduce the
risk of disease. Again, the first step is to put on
protective clothing as noted previously. The humidity in
the damaged area should be lowered by opening up the
house and removing standing wastewater with a mop,
wet vac, or squeegee. Interior closets and cabinet doors
should be opened to allow circulation. Fans,
dehumidifiers, and window air conditioners can be used
to circulate the air, but whole house air conditioners or
furnace blowers should be used only if the air ducts were
not impacted by standing wastewater. Moisture
absorbing products can be purchased in home
repair/lumber stores and should be placed in enclosed
areas where air can’t move through.
The contents of the damaged area should be sorted to
separate salvageable furnishings from unusable debris.
Hire a professional cleaning company to steam clean and
disinfect salvageable furnishings. Materials that were
exposed to the wastewater that cannot be thoroughly
steam cleaned or disinfected should be disposed of. All
potentially contaminated food items, cosmetics, stuffed
animals, and baby toys should be discarded.
Contaminated mattresses, pillows, foam rubber items,
upholstered couches and chairs, books, and most paper
products should generally be discarded because they
soak up contamination and are difficult to disinfect. If
the furnishings are of particular value, a cost estimate
from a professional cleaner can help determine if they
are worth saving.

Soiled clothing and small throw rugs should be
thoroughly washed in warm or hot water, with bleach if
possible. Larger rugs and those with foam backing may
have to be discarded, as may wall to wall carpeting.
After getting wet, wall to wall carpeting usually will not
return to its former size and has to be thrown away. If
only a portion of the carpeting is damaged, it may be
adequately cleaned by a professional carpet cleaner. The
foam padding will likely have to be replaced, however.
Discarded items should be sealed in heavy plastic
garbage bags before disposal. Your trash collection
company should be contacted about removing furniture
and bulky furnishings, or these items can be taken
directly to a landfill by the homeowner.
Minimal Damage
If there is minimal damage to the home and the overflow
can be cleaned up promptly, then the damaged area may
simply need to be cleaned and disinfected. This involves
thoroughly washing and disinfecting the walls, floors,
closets, and other washable contents of the damaged
area. In most cases, common household cleaning
products and disinfectants will do the job if used
correctly. Disinfectants and sanitizers often contain
toxic substances, so be sure to read and follow all label
instructions carefully. Be careful about mixing
household cleaners and disinfectants together, since
some can produce harmful vapors. For example, mixing
bleach and ammonia forms the toxic gases chloramine
and ammonium chloride. Fresh air should always be
provided by opening windows and doors and using fans
to circulate air both during and after the use of
disinfecting, cleaning, and sanitizing products.
A mixture of one-quarter cup chlorine bleach in 1 gallon
of water is an effective and readily available cleaning
solution. This solution should be kept in contact with
the item to be cleaned for at least one minute. After an
item is cleaned in such a manner, it should be rinsed
well, and gone over again with mild soap and water and
thoroughly rinsed again. Since most fabrics can’t be
cleaned with bleach without fading, they may instead be
cleaned with a quaternary ammonia product such as
Extensive Damage
If damage was extensive or the overflow could not be
cleaned up promptly, removal and replacement of
damaged wallboard and wall insulation should be
considered to avoid indoor air quality problems later.
Wallboard acts like a sponge, drawing
moisture up
above water level. It becomes very fragile if it stays wet for long and will fall apart when bumped. Even if the
area is dried out, contaminants may have gotten up
behind the drywall and dried inside. Microorganisms
can penetrate deep into soaked porous materials such as
wood, insulation and drywall and continue to damage
these materials long after the overflow event is over.
Even after everything has dried out, microorganisms can
later be released into the air and trigger allergic reactions
when inhaled.
Wooden wall studs and sills probably won’t need to be
replaced if they are thoroughly cleaned, disinfected and
allowed to dry properly. Since the studs and sills will be
covered by new wallboard and painted, they will be
removed from direct human contact.
If the walls are paneled, the bottom of each panel should
be carefully pried away from the wall. A block or
something similar should be used to hold the paneling
bottom away from the wall sill so that the area between
wall studs can drain and dry out. The paneling may have
to be completely removed in order to take out any wet
insulation or extensive contamination behind it. Once
disinfected and dried out, the paneling can often be
nailed back into place.
Wastewater won’t damage concrete like it will wood or
wallboard, but it will still soak in to some extent.
Concrete walls and floors should be washed thoroughly
and allowed to dry out.

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