Following are the various environmental remediation technologies employed by TERRY. Experience shows that often the use of multiple remedial technologies in a “treatment train” approach will reduce the time required to switch between remedial processes, thereby increasing the overall efficiency.
Bioslurping – Use of vacuum-enhanced pumping to recover light, non-aqueous phase liquid (LNAPL) and initiate vadose zone remediation through bioventing. In bioventing, air is drawn through the impacted vadose zone via extraction wells equipped with low vacuums to promote biodegradation of organic compounds.
Bioremediation – Enhanced microbial degradation of organic constituents by which complex organic compounds are broken down to simpler, usually less toxic compounds through aerobic or anaerobic processes. Often incorporates either augmentation of current microbial populations or supplementation of nutrients to enhance existing populations.
Air Sparging – Injection of gas (usually air or oxygen) under pressure into wells installed within the saturated zone to volatilize contaminants dissolved in groundwater, present as non-aqueous phase liquid, or adsorbed to the soil matrix. Volatilized contaminants migrate upward and are removed upon reaching the vadose zone, typically through soil vapor extraction. Most applicable for volatile organic contaminants in relatively moderate to high permeability geologic materials.
Blast-Enhanced Fracturing – A technique used at sites with fractured bedrock formations to improve the rate and predictability of recovery of contaminated groundwater by creating “fracture trenches” or highly fractured areas through detonation of explosives in boreholes (shotholes). Blast-enhanced fracturing is distinguished from hydraulic or pneumatic fracturing in that the latter technologies do not involve explosives, are generally conducted in the overburden, and are performed within individual boreholes.
Directional Wells – Encompasses horizontal wells. Trenched or directly drilled wells installed at any non-vertical inclination for purposes of ground-water monitoring or remediation. Especially useful when contaminant plume covers a large area and has linear geometry, or when surface obstructions are present. This technology can be used in the application of various remediation techniques such as ground-water and/or non-aqueous phase liquid extraction, air sparging, soil vapor extraction, in situ bioremediation, in situ flushing, permeable reactive barriers, hydraulic and pneumatic fracturing, etc.
Ground-Water Recirculation Wells – Encompasses in situvacuum, vapor, or air stripping, in-well vapor stripping, in-well aeration, and vertical circulation wells. Creation of ground-water circulation “cell” through injection of air or inert gas into a zone of contaminated ground-water through center of double cased stripping well which is designed with upper and lower double screened intervals. Injection of air creates “airlift pumping system” due to density gradient, causing ground-water with entrained air bubbles to rise and partition volatile contaminants from dissolved to vapor phase. Water exits upper screen beneath a divider, where vapors are drawn off through annular spaces between well casings by vacuum pump, and ground-water re-enters the contaminated zone, where it is again drawn into the stripping well. In this manner, ground-water is re-circulated through the stripping well until remediation goals are met. Several commercial types of in-well vapor stripping exist which strive to make the general process most efficient, or to use the process to enhance bioremediation or metals fixation by taking advantage of the circulation cell development. Most applicable to volatile organic contaminants; modifications of the basic remedial process are proposed for application to semi-volatile organic compounds, pesticides and inorganics. May be used in unconfined or confined aquifers; process has been applied to geologic materials of wide ranging permeability.
Hydraulic and Pneumatic Fracturing – Techniques to create enhanced fracture networks to increase soil permeability to liquids and vapors and accelerate contaminant removal. Especially useful for vapor extraction, biodegradation and thermal treatments. Hydraulic fracturing involves injection of high pressure water into the bottom of a borehole to cut a notch; a slurry of water, sand and thick gel is pumped at high pressure into the borehole to propagate the fracture from the initial notch. The gel biodegrades, leaving a highly permeable sand-filled lens that may be up to 60 feet in diameter. Pneumatic fracturing involves injection of highly pressurized air into consolidated sediments to extend existing fractures and create a secondary fracture network. Most applicable for unconsolidated sediments or bedrock.
In Situ Flushing – Also known as injection/recirculation or in situ soil washing. General injection or infiltration of a solution into a zone of contaminated soil/groundwater, followed by downgradient extraction of groundwater and elutriate (flushing solution mixed with the contaminants) and above ground treatment and/or re-injection. Solutions may consist of surfactants, cosolvents, acids, bases, solvents, or plain water. Any variety of configurations of injection wells, directional wells, trenches, infiltration galleries and extraction wells or collection trenches may be used to contact the flushing solution with the contaminated zone. Excellent understanding of the hydrogeologic regime for potential projects is essential; best applied to moderate to high permeability soils. May be used for variety of organic contaminants, including non-aqueous phase liquid; may have application to some inorganic contaminants.
In Situ Stabilization/Solidification – Also known as in situ fixation, or immobilization. Process of alteration of organic or inorganic contaminants to innocuous and/or immobile state by injection or infiltration of stabilizing agents into a zone of contaminated soil/groundwater. Contaminants are physically bound or enclosed within a stabilized mass (solidification), or their mobility is reduced through chemical reaction (stabilization). Excellent understanding of the hydrogeologic regime for potential projects is essential; best applied to moderate to high permeability soils; may be used for variety of organic and inorganic contaminants.
Permeable Reactive Barriers – Encompasses passive barriers, passive treatment walls, treatment walls, or trenches. An in-ground trench is backfilled with reactive media to provide passive treatment of contaminated ground-water passing through the trench. Treatment wall is placed at strategic location to intercept the contaminant plume and backfilled with media such as zero-valent iron, microorganisms, zeolite, activated carbon, peat, bentonite, limestone, saw dust, or other. The treatment processes which occur within the treatment wall are typically contaminant degradation, sorption or precipitation. Applicable to wide range of organic and inorganic contaminants; choice of media for treatment wall is based on specific contaminant. Hydrogeologic setting is critical to application; geologic materials must be relatively conductive and a relatively shallow aquitard must be present to provide a “basement” to the system. Ground-water flow should have a high degree of preference, and ground-water quality must support the desired reaction without imposing additional loading of the reactive media or creating undesirable by-products.
Thermal Enhancements – Use of steam, heated water, or radio frequency (RF) or electrical resistance (alternating current or AC) heating to alter temperature-dependent properties of contaminants in situ to facilitate their mobilization, solubilization, and removal. Volatile and semi-volatile organic contaminants may be vaporized; vaporized components then rise to the vadose zone where they are removed by vacuum extraction and treated. Steam best applied to moderate to high permeability geologic materials; RF and AC heating may be applied to low permeability, clay-rich geologic materials as the clay will preferentially capture the RF or AC energy. Excellent understanding of hydrogeologic conditions essential for all applications. May be used for variety of organic contaminants and non-aqueous phase liquid; may have application to some inorganic contaminants.
Treatment Train – the sequential use of unique remediation technologies to treat the same volume of contaminated soil or groundwater.
Intrinsic Bioremediation – Natural, non-enhanced microbial degradation of organic constituents by which complex organic compounds are broken down to simpler, usually less toxic compounds through aerobic or anaerobic processes. For environmental application, documentation that current biodegradation rates are sufficient to control or degrade a contaminant plume or zone without creation of unacceptable risk to human health or the environment must be demonstrated.
Monitored Natural Attenuation – Encompasses intrinsic bioremediation. Reliance on a variety of physical, chemical, or biological processes (within the context of a carefully controlled and monitored site cleanup approach) that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater.
Phytoremediation – The general use of plants to remediate environmental media in situ. Includes rhizofiltration (absorption, concentration, and precipitation of heavy metals by plant roots), phytoextraction (extraction and accumulation of contaminants in harvestable plant tissues such as roots and shoots), phytotransformation (degradation of complex organic molecules to simple molecules which are incorporated into plant tissues), phytostimulation or plant-assisted bioremediation (stimulation of microbial and fungal degradation by release of exudates/enzymes into the root zone), and phytostabilization (absorption and precipitation of contaminants, principally metals, by plants). May or may not involve periodic harvesting of plants, depending upon method utilized. Applicable to a wide range of organic and inorganic contaminants; most appropriate for sites where large volumes of ground-water with relatively low concentrations of contaminants must be remediated to strict standards. Most effective where ground-water is within ten feet of the ground surface, and soil contamination is within three feet of the ground surface.
Treatment Train – the sequential use of unique remediation technologies to treat the same volume of contaminated soil or groundwater.