When nature and human activities clash, it’s practically inevitable that pollution and toxins contaminate our soil, sediment, groundwater, and surface water. Sadly, soil contamination has serious, long-term effects on property and eco-systems, even resulting in massive animal die-offs.
What Is Contaminated Soil?
Contaminated soil is defined by significant harm to the health of living organisms or interference with ecological systems, which usually involves significant pollution to either the soil itself or nearby water.
Environmental contaminants are not only harmful to nature, but they can also negatively impact human health. In fact, people can get permanently ill from soil contamination.
One high-profile example of environmental contamination that made people sick involved Erin Brockovich, who helped build a case against the Pacific Gas and Electric Company in 1993. PG&E had allegedly allowed hexavalent chromium to contaminate the drinking water in Hinkley, California.
The case was settled in 1996, resulting in the largest settlement ever paid in a direct-action lawsuit in the United States. The incident was the focus of the 2000 film “Erin Brockovich,” starring Julia Roberts.
Given how devastating the effects of environmental contamination can be, remedial action is often necessary to address contaminated soil and water. That’s why numerous regulatory requirements have been legislated over the years, helping maintain standards by which government agencies and environmental remediation services must abide.
What Is Soil Remediation?
Soil remediation is a term applied to various processes used to decontaminate the soil. The goal is to treat contaminated soil by removing and converting pollutants into less harmful products.
Some of the pollutants that soil remediation addresses include:
- Heavy metals
- Petroleum and fuel residues
Removing these pollutants from the soil prevents them from seeping into the groundwater, surface water, agricultural crops, and wild flora. In cases where they’ve already affected water sources, additional land remediation techniques are required.
Types of Soil Remediation
There are four main techniques used for soil remediation, each of which takes a distinct approach to removing pollutants. These techniques are:
- Thermal Soil Remediation
- Air Sparging
It’s important to choose the right soil remediation technique for each situation, as each method has an indicated best use.
Thermal Soil Remediation
Thermal soil remediation is an in-situ technique that involves heating contaminated material in a Primary Treatment Unit (PTU) to the point where hydrocarbon impurities and water evaporate. Polluted materials are typically treated at temperatures ranging from 650 to 900 degrees. Think of the PTU as a massive oven that bakes the soil.
Once heated, the materials are transferred from the PTU into a cooling unit such as an auger or mixer. At this point, water is added for additional cooling and dust control. Once cooled, the material is moved from the cooling unit via a conveyor system and is then tested and recycled.
Thermal soil remediation is best used for soil that has been polluted by either contaminated water or hydrocarbon compounds like petroleum products. Since thermal remediation methods are performed without excavating the contaminated zone, they are great for hard-to-access locations such as between buildings and around buried utilities.
Another soil remediation method is called air sparging, which involves injecting large amounts of air into a contaminated soil stratum to force organic vapors outwards where they can be treated by carbon filtering. Unlike other methods, air sparging has to be applied directly to the soil instead of being used on extracted soil in a treatment unit.
Air sparging is commonly used for removing hydrocarbon pollutants, but it’s best used in cases where the soil can’t be removed from the site.
Encapsulation is an interesting remediation soil technique because it separates contaminates instead of filtering them. Essentially, encapsulation ensures that the pollutants can’t spread any further than they already have, so it acts similar to a medical quarantine.
The contaminant source is covered with layers of lime, concrete, clay caps, or synthetic textiles that limit precipitation’s infiltration, thereby preventing the leaching and migration of contaminants away from the isolated zone. The process isolates the polluted soil and prevents it from coming into contact with the surrounding soil.
Unfortunately, although the technique is effective, it doesn’t treat and recycle the soil to be used in cultivation. Instead, encapsulated soil will never be used to grow anything ever again, which makes encapsulation a sort of “last resort” technique.
Bioremediation is a soil remediation technique that uses a biological mechanism rather than mechanical means. The contaminated soil is treated at the site with aerobic and anaerobic bacteria that have been engineered specifically to consume and break down pollutants. Once the contaminate has been taken care of, the microbes die off.
While bioremediation is the most natural technique of soil remediation, it’s most successful when the soil maintains a temperature of 70 degrees with sporadic rainfall to optimize the moisture levels. As such, bioremediation isn’t always possible, especially in extreme climates. In colder climates, the soil must be covered and insulated prior to the bioremediation.
NJDEP Soil Remediation Standards
In 2017, the New Jersey Department of Environmental Protection (NJDEP) updated the residential and non-residential soil remediation standards for 19 contaminants listed in the United States Environmental Protection Agency Integrated Risk Information System database. The updates reflected recent revisions made to existing toxicity data.
Overall, the standards to remediate soil increased (became less stringent) for 11 contaminants and decreased (became more stringent) for six contaminants. One contaminant will no longer be regulated and one remained unchanged.
Of the six contaminants for which the standards become more stringent, three stood out as having their remediation standards decrease by an order of magnitude:
Thallium is the contaminant no longer being regulated by NJDEP soil remediation standards.
How Much Does Soil Remediation Cost?
Historically, soil contamination has had far-reaching economic impacts, but remedial action aims to minimize those adverse effects. Soil remediation costs vary depending on the technique, but the NJDEP has released an estimated soil remediation cost per acre-foot that can provide a glimpse into the economic impacts.
For example, consolidating and covering on-site soil with roads or other structures costs around $1000 to $2000 per acre-foot. Blending contaminated soil with clean soil can cost up to $15,000, while treating soil with innovative treatment technologies can range from $50,000 to $100,000 per acre-foot.
Remediating soil isn’t necessarily easy or cheap, but remediated soil prevents long-term, detrimental effects on our ecosystem. Taking responsibility for man-made contaminants goes a long way toward ensuring a healthy planet for future generations.