How Long Does Soil Remediation Take?

Soil remediation is the process of removing or replacing the soil to get rid of contamination. Soil contamination occurs when toxins get mixed with the natural compounds of the soil.

Many times, these chemicals come from industrial activity or hazardous waste such as heavy metals and/or pesticides. However, contamination can come from many places including:

Livestock manure runoff
Farming chemicals
Failure of a septic system
Improper waste disposal
Failing underground oil tanks
Nearby industrial activity

If toxins are present in the soil, you must be proactive with soil remediation to eliminate the contaminants and restore the safety of your land.

Some common soil remediation strategies include bioremediation, soil washing, and thermal desorption. The effectiveness of these options depends on the specific type of contamination in your soil as well as how extensive it is.

These soil remediation technologies can be used to separate out the chemicals, but sometimes it may be necessary to remove the contaminated soil and replace it with clean fill.

How Long Does Soil Remediation Take?

Excavating contaminated soil can take one day or several years. The actual time it takes to excavate the contaminated soil depends on several factors including:

Large contamination area
Depth of contamination
Contamination below the water table

Time by Type of Soil Remediation

Each type of soil remediation strategy takes a different amount of time. However, in all strategies, one of the primary factors is how much soil is contaminated.

Bioremediation

Bioremediation occurs by stimulating the growth of certain microbes to use contaminants, such as oil, as a source of food and energy. As a byproduct, the microbes release water, carbon dioxide, and other non-harmful amino acids. The microbes secrete enzymes similar to the way the human body makes saliva and stomach bile. The enzymes break down the contaminants into smaller pieces. Then, the microbes can consume the broken-down contaminants.

Ideal environmental conditions are necessary to start the bioremediation process including a balance of temperature, surface pH, available moisture, and other factors. In the right environment, with ample food supply, the microbes reproduce. More microbes can then further aid in the removal of additional contaminants. The cycle repeats until the food source is depleted.

Due to the need to maintain environmental conditions, it can take weeks, or even months for microbes to clean up a site. The primary consideration is the number of contaminants present in comparison to the number of microbes present.

Soil Washing

Soil washing is a remediation strategy that removes contaminants by washing the soil with a liquid (often a chemical additive), scrubbing the soil, and then separating the clean soils from contaminated soil and wash water.

The concept of soil washing is based on the idea that contaminants will bind with fine-grained soils like silt and clay. These—in turn—are prone to bind with coarse-grained soils like sand and gravel. The main goal of soil washing is to separate the contaminated fine-grained soils and wash water from the cleaned coarse-grained soils.

The contaminated soils and wash water can be treated or disposed of. The washed soils may be reused as a backfill at the site if all contaminants have been successfully removed. Soil washing can be broken into six steps:

Pretreatment
Separation
Coarse-grained treatment
Fine-grained treatment
Process water treatment
Residuals management

Soil washing is a very fast method. The process can be run at a very high rate of around 100 cubic yards per day. Soil washing is often also used in conjunction with another remediation method because it can concentrate the contaminants down into a smaller volume of soil which can be easily treated by another strategy.

Thermal Desorption

Thermal desorption removes organic contaminants (including volatile organic compounds and some semi-volatile organic compounds) from soil by heating it in a machine called a thermal desorber to evaporate the contaminants. Semi-volatile organic compounds require higher heat than volatile organic compounds. The contaminants are evaporated separated from the solid material.

Thermal desorption may take a few weeks to a few years. Cleanup time will depend on several factors, including:

The contaminated area is large or deep.
The desorber is off-site.
A lot of debris must be crushed or removed.
The desorber is small.
Contaminant concentrations are high.
The soil contains a lot of dust, clay, or organic material.

Most thermal desorbers can clean over 25 tons of contaminated soil per hour.

Benefits of Faster vs. Slower Soil Remediation Methods

Bioremediation is the slowest method while thermal desorption and soil washing are much faster.

One difference in the strategies is how the contaminants are disposed of. With soil washing the contaminated soil and wash water must be processed.

The wash water must be treated in order to be reused in the soil washing process or to be disposed of in sewers. Disposing requirements are stringent, so recycling the water back into the system is the preferred choice as long as it does not interfere with the washing process.

Contaminated fine-grained soils may be disposed of in a landfill. If they are still considered contaminated, they may require further treatment before disposal.

When it comes to thermal desorption, gas collection equipment captures the contaminated vapors. The vapors often require further treatment, like removing dust particles. The remaining organic vapors are usually destroyed using a thermal oxidizer.

The thermal oxidizer heats the vapors to high enough temperatures to convert them to carbon dioxide and water vapor. At sites with high concentrations of organic vapors, the vapors may be cooled and condensed back to a liquid form. The liquid chemicals may be recycled or incinerated. If the concentrations of contaminants are low enough, and dust is not an issue, the vapors can be released without treatment into the atmosphere.

While bioremediation takes much longer, once the process is complete, the microbe population will naturally decline. The microbes also do not create any residual waste that needs to be processed or treated. The carbon dioxide, water, and other amino acids they produce absorb naturally into the environment without any negative impact.