Soil can become contaminated in many ways. In order to decontaminate it properly, you must know what the primary contaminant is. Some of the most common contaminants are oil, pesticides and herbicides, and mercury. In order to decontaminate soil, it will usually need to be removed from the ground.
- Petroleum contamination is a very common problem. Before the U.S. government began regulating the disposal and storage of oil, many tanks were buried in the ground with no safeguards in place. These tanks sometimes leaked oil and gas into the surrounding soil, and potentially, into groundwater sources. There are two effective ways to treat soil that has been contaminated with petroleum. The first is incineration. This process cooks the soil at very high temperatures, usually at least 2000 degrees. It destroys all contaminants in the soil, but unfortunately, it also destroys the soil.
Much soil that is contaminated can be reclaimed and reused, so a process called thermal soil remediation has been developed. This cooks the soil at temperatures between 350 and 700 degrees Fahrenheit. These temperatures are high enough to vaporize any petroleum contaminants in the soil, but not high enough to destroy the soil. The vaporized contaminants are collected by a mechanism called a baghouse, which works much like a filter in a furnace. Any harmful chemicals within the contaminants collected by the baghouse are destroyed by an afterburner. This process needs to be completed by a company which specializes in thermal soil remediation. After the process is complete, soil can often be put back in place and used.
- Another effective treatment for petroleum-contaminated soil is soil washing. In this process, soil is removed and washed with a solution typically containing mild solvents. The soil is then agitated very rapidly. This separates the larger, contaminated particles from the non-contaminated soil. These particles are then collected and destroyed, while the healthy soil is returned to the ground.
- For soil that has been contaminated by herbicides and pesticides, a process called iron remediation is effective. The contaminated soil is removed from the site and mixed with iron and water. It is then returned to the site and covered with plastic sheeting. Iron helps accelerate the chemical degradation process. This method is generally less expensive than thermal remediation.
- All soil has some mercury present in it. However, if higher-than-normal levels of mercury are present, it can be harmful to even touch the soil, as mercury can be absorbed through the skin. A new, environmentally-friendly way of treating mercury contamination is by a process called phytoremediation. Phytoremediation uses plants to decontaminate the soil. Genetically-altered strains of poplar and cottonwood trees are capable of absorbing mercury from the soil, converting it to a safer form and releasing it into the air. This process doesn't require removing the soil from the site, although it is slower than either thermal remediation or iron remediation.
- If your soil has been contaminated in only a very small area with a small amount of harmful chemicals, you can apply an absorbent, such as activated charcoal, to contain the chemical. This method is useful when you spill a chemical on the ground, and are aware of it immediately. Charcoal will absorb much of the chemical, and it can then be discarded. Be sure to dispose of the used charcoal in an environmentally-responsible way.
Soil decontamination, or remediation, is a process that should only be undertaken by a company which specializes in eliminating chemicals from the ground. If you suspect soil contamination, have a professional soil test taken. If in doubt, contact your town's building inspector. He should be able to provide you with local resources for soil testing and decontamination, if necessary.