A Citizen’s Guide to

Bioremediation

What Is Bioremediation?

Bioremediation is the use of microbes to clean up 

contaminated soil and groundwater. Microbes are very 

small organisms, such as bacteria, that live naturally 

in the environment. Bioremediation stimulates the 

growth of certain microbes that use contaminants as 

a source of food and energy. Contaminants treated 

using bioremediation include oil and other petroleum 

products, solvents, and pesticides.

How Does It Work?

Some types of microbes eat and digest contaminants, 

usually changing them into small amounts of water and 

harmless gases like carbon dioxide and ethene. If soil and 

groundwater do not have enough of the right microbes, 

they can be added in a process called “bioaugmentation.” 

For bioremediation to be effective, the right temperature, nutrients, and food also must be present. Proper 

conditions allow the right microbes to grow and 

multiply—and eat more contaminants. If conditions are 

not right, microbes grow too slowly or die, and contaminants are not cleaned up. Conditions may be improved 

by adding “amendments.” Amendments range from 

household items like molasses and vegetable oil, to air 

and chemicals that produce oxygen. Amendments are 

often pumped underground through wells to treat soil 

and groundwater in situ (in place).

The conditions necessary for bioremediation in soil 

cannot always be achieved in situ, however. At some 

sites, the climate may be too cold for microbes to be 

active, or the soil might be too dense to allow amendments to spread evenly underground. At such sites, 

EPA might dig up the soil to clean it “ex situ” (above 

ground) on a pad or in tanks. The soil may then be 

heated, stirred, or mixed with amendments to improve 

conditions.

Sometimes mixing soil 

can cause contaminants to evaporate 

before the microbes can 

eat them. To prevent the 

vapors from contaminating the air, the soil 

can be mixed inside a 

special tank or building 

where vapors from 

chemicals that evaporate may be collected 

and treated.

To clean up contaminated groundwater in situ, wells 

are drilled to pump some of the groundwater into 

above ground tanks. Here, the water is mixed with 

amendments before it is pumped back into the ground. 

The groundwater enriched with amendments allows 

microbes to bioremediate the rest of the contaminated 

groundwater underground. Groundwater also can be 

pumped into a “bioreactor” for ex situ treatment. Bioreactors are tanks in which groundwater is mixed with 

microbes and amendments for treatment. Depending 

on the site, the treated water may be pumped back 

to the ground or discharged to surface water or to a 

municipal wastewater system.

How Long Will It Take?

It may take a few months or even several years for 

microbes to clean up a site, depending on several factors. 

For example, bioremediation will take longer where:

• Contaminant concentrations are high, or contami- nants are trapped in hard-to-reach areas, like rock

fractures and dense soil.

• The contaminated area is large or deep.

Is Oxygen 

Always Needed?

Some contaminants can 

only be bioremediated in an 

aerobic environment─one 

that contains oxygen. Others 

can only be bioremediated 

in an anaerobic environment 

without oxygen. Anaerobic microbes do not need 

oxygen to grow.

Microbe takes in oil, oxygen, and nutrients and releases 

gases and water.
United States Office of Solid Waste and EPA 542-F-12-003

Environmental Protection Emergency Response September 2012

Agency (5102G) www.epa.gov/superfund/sites

www.cluin.org

NOTE: This fact sheet is intended solely as general information to the public. It is not intended, nor can it be relied upon, to create any 

rights enforceable by any party in litigation with the United States, or to endorse the use of products or services provided by specific 

vendors. The Agency also reserves the right to change this fact sheet at any time without public notice.

Example

Bioremediation is cleaning 

up groundwater contaminated with dry cleaning 

solvent at the Iceland Coin 

Laundry Superfund site in 

New Jersey. To improve the 

conditions at the site for 

bioremediation, amendments 

were added. A solution of 

vegetable oil and baking 

soda was injected into the 

groundwater in an area of 

particularly high contaminant concentrations. Bacteria 

also were added to increase 

the existing population of 

microbes. The treatment 

area is about 1800 feet long, 

500 feet wide and extends 

40 feet below ground.

Preliminary testing of the 

groundwater has shown that 

bioremediation is working 

and contaminant concentrations are decreasing. The 

objective is to continue to 

reduce the concentration 

of contaminants from 10 or 

more parts per billion to less 

than 1 part per billion.

For More Information

For more information about 

this and other technologies 

in the Citizen’s Guide Series, 

visit:

www.cluin.org/remediation

www.cluin.org/products/

citguide

www.cluin.org/bioreactor 

www.cluin.org/

bioremediation

• Conditions such as temperature, nutrients, and microbe population must

be modified.

• Cleanup occurs ex situ.

Is Bioremediation Safe?

Bioremediation relies on microbes that live naturally in soil and groundwater. 

These microbes pose no threat to people at the site or in the community. Microbes 

added to the site for bioaugmentation typically die off once contamination and the 

conditions needed for bioremediation are gone. The chemicals added to stimulate bioremediation are safe. For example, the nutrients added to make microbes 

grow are commonly used on lawns and gardens, and only enough nutrients to 

promote bioremediation are added. To ensure that the treatment is working and to 

measure progress, samples of soil and groundwater are tested regularly.

How Might It Affect Me?

Bioremediation often occurs underground and does not cause much disruption to the site or surrounding community. Contaminated soil and groundwater stay onsite, reducing truck traffic, compared with some other cleanup 

methods. However, area residents and businesses may hear the operation of 

pumps, mixers, and other construction equipment used to add amendments 

or improve site conditions to begin the bioremediation process. Excavation 

and pumping also will occur for ex situ bioremediation. (See a Citizen’s Guide 

to Excavation of Contaminated Soil [EPA 542-F-12-007].)

Why Use Bioremediation? 

Bioremediation has the advantage of using natural processes to clean up sites. 

Because it may not require as much equipment, labor, or energy as some 

cleanup methods, it can be cheaper. Another advantage is that contaminated 

soil and groundwater are treated onsite without having to dig, pump, and transport them elsewhere 

for treatment. Because 

microbes change the 

harmful chemicals into 

small amounts of water 

and gases, few if any 

waste byproducts are 

created.

Bioremediation has 

successfully cleaned 

up many polluted sites 

and has been selected 

or is being used at over 

100 Superfund sites 

across the country.

Injection of vegetable oil underground to improve conditions for 

bioremediation.