Technologies of Soil Remediation There are a variety of methods used to remediate properties. The method(s) chosen depend on the level of contamination, state laws, the depth of the contamination, the ground water table and if the ground water is contaminated, the type of contaminant, and time line required for the remediation. Following are common methods of treatment: No Treat m en t : In some cases, it can be decided to simply not treat a situation. Close monitoring may merit that it is not necessary. Dig and Hau l: In some cases, the contaminated soil is simply dug out and hauled to another location where it may or may not be treated. Soil Vapor E xt ra ct io n (SVE ): In essence, this method uses air flow through soil to strip VOC’s and other contaminants generally above the ground water table. SVE is applied when the contamination is above the water table and when the contaminant can be volatized and extracted from the ground water using VOC’s. The zone above the water table is known as the vadose zone. A basic SVE system is shown below following:
Mult iph ase E xt ra ct ion (MP E): MPE is a modification of SVE that is performed below the ground water table and extracts both ground water and vapors for treatment. It is a generic term involving several subcatagories namely DPE and TPE. In the case of MPE the pollution region is basically dewatered, or in otherwords the local ground water table is lowered in order to allow air and vapors to flow through this region. Two Phase Ext ract ion (TP E): TPE uses an extraction well below the water table. Ground water is removed simply by using the turbulence and velocity of the vapor stream in the same well to carry the contaminated water together with the air/vapor stream into a separation vessel. The water is pumped away from the separation vessel using a liquid pump, and the air stream is pumped away by a vacuum pump. Ground water may be hauled away and treated or treated and returned to the earth. The vapor stream is treated by on site treatment equipment such as carbon beds or thermal oxidizers. TPE is also frequently referred to as DPE. The following diagram shows a typical TPE system:
Typical TPE system. Dua l Phase Ext ract ion (DPE): DPE uses an extraction well below the water table and a submersible pump at the bottom of the well. Ground water is removed through a separate pipe inside the well by the submersible pump. The air and vapor stream is pumped through a vapor/water separator by a vacuum pump and ultimate pass through the vacuum pump. The separated water is periodically drained from the separator. Ground water may be hauled away and treated or treated and returned to the earth. The vapor stream is treated by on site treatment equipment such as carbon beds or thermal oxidizers. The following diagram shows a typical DPE system:
Typical DPE system.
DPE systems are subcategorized into two further groups: Low Vacuu m DPE (LVDPE ): In cases where air and vapor flow can be induced using a lower vacuum level, LVDPE is used. These cases are basically sands and silty sands. High Vacuu m DPE (HVDP E): In cases where higher vacuum levels are required to induce air flow, HVDPE is used. These cases are basically sandy silts and clays. Air Sparging: This method injects uncontaminated air below the ground water table to volatize contaminants and improve air and vapor flow into the vadose zone. This method is generally used with SVE which eventually draws in the contaminants and pumps the vapors into air pollution control equipment. Following is a diagram depicting a basic DPE system:
Typical air sparging/SVE system Bio re me d ia t ion : This method injects air/oxygen into the earth to feed VOC eating organisms. These organisms are naturally living in the ground. There are two basic types of bioremediation as follows: Bio ve n t in g: Injecting air above the ground water table. Biosparging: Injecting air below the ground water table. Remed ia t io n Equ ip me nt : Remediation equipment are usually prepackaged on skids, houses, and portable trailers, and hauled to the contamination site. They often include vacuum blowers or vacuum pumps, air sparging pumps, separation vessels, liquid pumps, filters, and air treating equipment such as carbon beds or thermal oxidizers. Following are diagrams and pictures of typical remediation skid and portable packages: