In Situ Technologies

Currently, most remediation projects are carried out using ex situ technologies, both in the U.S. and in Europe. However, there is an increasing trend toward the application of in situ technologies because of their considerable advantages over ex situ techniques, such as less disturbance of the site, lower treatment costs, and so on. 

It is an in situ technology and can even be applied below existing buildings, roads, and so on, thus causing minor disturbance to ongoing site operations. 

For practitioners of in situ technologies, note that U.S. EPA has issued a policy statement that reinjection of contaminated groundwater is allowed under Resource Conservation and Recovery Act (RCRA)35 36 as long as certain conditions are met. This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to reinjection. Treatment may be by a pump-and-treat system or by the addition of amendments meant to facilitate subsurface treatment. Also, the treatment must be intended to substantially reduce hazardous constituents in the groundwater (either before or after reinjection) the cleanup must be protective of human health and the environment and the injection must be part of a response action intended to clean up the environment.37... 

Naval Facilities Engineering Service Center, Chemical Oxidation, In-Situ Technology Web Page. Available atportal.navfac.navy.mil, 2006. 

On the basis of the feasibility studies, an in situ technology was applied for the biological remediation of TNT and its transformation products. Microbiological transformation of TNT in the soil was stimulated by the addition of a carbon source and iron particles. The amount of additive was 51/m molasses and 5kg/m iron particles. Thus for the treatment of the whole 2,000m site, there was a requirement for lOm molasses and lOt iron. The addition of molasses and a subsequent mechanical tillage to a... 

In-situ Technology. The initial major objective of AOSTRA then was to develop a new in-situ technology or speed up existing in-situ technologies for each of the four major deposits. A call for proposals resulted in response of 21 major applications and from these an in-situ program was established which included four tests in three of the four major deposits. They include ... 

The Aerobic Biotreatment System (ABS) is an in situ technology that treats soils, sludge, and sediments contaminated with petroleum hydrocarbons, polyaromatic hydrocarbons (PAHs),... 

Bioslurping is a commercially available, in situ technology that combines vacuum-enhanced free-product recovery with bioventing of subsurface soils to simultaneously remediate petroleum-hydrocarbon-contaminated groundwater and soils. Vacuum-enhanced recovery utilizes negative pressure to create a partial vacuum that extracts free product and water from the subsurface. Bioventing is forced aeration to accelerate in situ bioremediation of hydrocarbons and non-aqueous-phase liquids (NAPLs). 

Technology expected to treat contaminants more rapidly than other in situ technologies, leading to more rapid site closure and reduction in liability. 

Cosolvent flushing is an in situ technology that enhances the remediation of contaminated soils and groundwater by injecting water and a cosolvent such as alcohol (e.g., ethanol, methanol, and isopropyl) into a contaminated area. Research has shown that an organic cosolvent can also accelerate the movement of metals through a soil matrix. The alcohol causes both an increase in aqueous contaminant solubility and lowering of non-aqueous-phase liquid (NAPL)-water interfacial tension. 

Electrokinetic soil treatment is a commercially available in situ technology for the removal of metals and organic compounds. The application of direct current (DC) in a porous medium leads to two transport mechanisms electromigration and electro-osmosis. The combination of these two transport phenomena results in the movement of contaminant ions toward either the cathode or anode. Nonionic contaminants are transported by electro-osmosis alone. 

Grid injection is a commercially available, in situ technology for the treatment of soils contaminated with organic compounds. The technology injects steam to vaporize volatiles and drive out nonvolatiles in a fashion similar to steam stripping. 

Reclaim is a passive, in situ technology that uses a hydrophobic porous polymer to attract, adsorb, and concentrate petroleum hydrocarbons and volatile organic compounds (VOCs) from soils and/or groundwater. Reclaim is considered a passive treatment technology because it requires no mechanical equipment remediation consists of placing polymer-filled canisters in recovery wells and allowing the containers to attract and adsorb organic contaminants. Reclaim canisters are then recycled and contaminants recovered for analysis and/or disposal. This polymer extracts contaminants whether they are in liquid phase, vapor phase or dissolved phase in water. 

The two-zone plume interception treatment technology is designed to treat chlorinated and nonchlorinated organic compounds in groundwater using a sequence of anaerobic and aerobic conditions. The in situ technology has been applied to aquifers contaminated with benzene, toluene, ethylbenzene, and xylenes (BTEX) petroleum products hydrocarbons coal tar wastes and industrial feedstock chemicals. The technology does not treat metals. 

The HRUBOUT process may also be applied as an in situ technology for excavated soils (see Hrubetz Environmental Services, Inc., HRUBOUT Process, In Situ, T0379). 

The steam-enhanced recovery process (SERF) is an in situ technology designed to remove and treat volatile and semivolatile organic compounds (VOCs and SVOCs) in contaminated soils by using steam injection and vacuum extraction. The technology is based on the idea that added heat (thermal enhancement) increases the volatility and mobility of SVOCs and VOCs and thus facilitates the extraction of soil contaminants. The process works by injecting high-quality steam... 

The lET barrier system is a patented, commercially available in situ technology for the diversion and collection of contaminated groundwater or the confinement of contaminated soil. The lET barrier can be constructed as a boom around a portion of the contaminated area or as a bottomless tank. Barriers consist of a high-density polyethylene (HDPE) liner or thick steel sheet pile with a patented locking mechanism. Collection reservoirs are installed adjacent to the barrier and can be used to treat contaminants in place or to pump contaminated groundwater to the surface for treatment. 

The Biodrain system is a patented, commercially available, in situ technology for the collection and treatment of biodegradable contaminants in soil and groundwater. The Biodrain system... 

Some caution may be needed when evaluating in situ technologies for the remediation of sediments. In situ treatment of sediments may be less cost-effective than ex situ methods because the treatment level for in situ methods is not uniform and in some cases project goals cannot be met throughout the site (D20043R, p. 6). 

Metal-based permeable reactive barriers (metal-based PRBs) are an emerging class of in situ technologies for the treatment of groundwater contaminated with volatile organic compounds... 

TERRA-PURE is an in situ technology that ntihzes a flushing system for extraction of contaminants from soil. According to the vendor, it is applicable to organic and inorganic contaminants present at relatively high concentrations and to non-aqueous-phase liquids. 

Can be used to enhance the performance of several in situ technologies, including bioremediation, in situ chemical oxidation, in situ thermal treatments, and in situ solidification. 

The soil-cement mixing wall (SMW) is an in situ technology for the fixation, stabilization, and solidification of soils contaminated with metals and semivolatile organic compounds. SMW can be used to treat soils contaminated with pesticides, polychlorinated biphenyls (PCBs), phenols, and poly aromatic hydrocarbons (PAHs) to depths of up to 100 ft. The technology uses hollow-stem augers to inject solidification/stabilization agents and blend them with the soil. 

In situ technologies are typically less disruptive and expensive than ex situ technologies. 

Steam injection and vacuum extraction (SIVE) is a patented, commercially available in situ technology. SIVE has been used to remove non-aqueous-phase liquids (NAPLs), diesel fuel, jet fuel, semivolatile and volatile organic compounds (SVOCs and VOCs), chlorinated solvents, acetone, and benzene, toluene, ethyl benzene, and xylenes (BTEX) from soil and ground-water. 

The Trench Bio-Sparge (TBS) system is an in situ technology for the treatment of groundwater contaminated with organic compounds. The system employs diversion walls to direct the contaminant plume to a subsurface trench reactor, where treatment is achieved by physical and/or biological means. The technology has been field tested at the pilot scale but is not yet commercially available. 

The pneumatic soil fracturing (PSF) technology is a commercially available, in situ technology that increases the airflow in low-permeability soils, such as clay, thus increasing the amount of volatile organic compounds (VOCs) withdrawn by vacuum extraction. Additional flow paths are created by injecting compressed air into soil, creating fractures around the injection point. 

---