Environmental Remediation Glossary

Definitions for key terms used in in situ remediation, environmental drilling, and groundwater treatment — from IET's expert team with 28+ years of field experience.

A

Activated Persulfate: A chemical oxidation process in which persulfate (S₂O₈²⁻) is activated by a catalyst — most commonly ferric iron (Fe³⁺) — to generate highly reactive sulfate radicals (SO₄•⁻ at 2.60V) and ferrate (Fe⁶⁺ at 2.20V). IET holds U.S. patents on ferric iron-activated persulfate technology (US Patent No. 9,126,245), which simultaneously provides chemical oxidation and sustained secondary bioremediation lasting 2+ years.; See also:ISCO Services IET Patents
Aerobic Bioremediation: A biological treatment process in which naturally occurring or introduced microorganisms degrade organic contaminants using oxygen as the terminal electron acceptor. Aerobic biodegradation is highly effective for petroleum hydrocarbons (BTEX, TPH) but is not effective for chlorinated solvents, which require anaerobic conditions for reductive dechlorination.; See also:Bioremediation
Anaerobic Bioremediation: Biological degradation of contaminants under oxygen-depleted (anaerobic) conditions. This is the primary mechanism for reductive dechlorination of chlorinated solvents such as PCE and TCE. Microorganisms use halogenated compounds as electron acceptors, sequentially removing chlorine atoms. IET stimulates anaerobic conditions through electron donor injection.; See also:Bioremediation
Aquifer: A subsurface geological formation of permeable rock, sediment, or soil that stores and transmits groundwater. Contamination of aquifers by chlorinated solvents, petroleum, and other chemicals is the primary driver of environmental remediation projects. Aquifer characteristics — permeability, porosity, depth, flow direction — govern remediation technology selection.
Attenuation: The natural or engineered reduction of contaminant concentration in soil or groundwater over time and distance from a source. Mechanisms include dilution, dispersion, sorption, volatilization, and biodegradation. Monitored Natural Attenuation (MNA) is sometimes used as a stand-alone remedy or as a component of active remediation programs.
Aluminum: A metal that occurs naturally in some rocks and enters groundwater through drainage from mines. Aluminum is not a primary health concern at typical concentrations, but it precipitates out of water after treatment, which can increase turbidity and cause discolored water. Aluminum is not destroyed or removed by in situ treatment; where it is a concern, it is managed by pH adjustment and precipitation in water treatment.
Antimony: A metal that enters the environment from natural weathering, industrial production, municipal waste disposal, and the manufacture of flame retardants, ceramics, glass, batteries, fireworks, and explosives. Lifetime exposure at high levels has decreased longevity and altered blood levels of glucose and cholesterol in laboratory animals. Antimony is immobilized in situ under ISCR, where zero-valent iron and its corrosion products remove it by adsorption and precipitation.; See also:ISCR Services Heavy Metals Treatment
Arsenic: A naturally occurring element that also enters groundwater from industrial activity, pesticides, and the smelting of copper, lead, and zinc ore. Arsenic causes acute and chronic toxicity, liver and kidney damage, and decreased blood hemoglobin, and is classified as a human carcinogen. IET manages arsenic in groundwater with in situ chemical reduction (ISCR), which converts mobile arsenic to less soluble forms.; See also:Heavy Metals Treatment ISCR Services

B

Benzene: A volatile aromatic hydrocarbon (C₆H₆) and known human carcinogen commonly found at petroleum release sites including gas stations, refineries, and underground storage tank (UST) sites. Benzene has the lowest MCL (maximum contaminant level) of the BTEX compounds (5 µg/L). IET remediates benzene using ISCO, enhanced bioremediation, and combined approaches.; See also:Petroleum Treatment
Bioaugmentation: The injection of specialized microbial cultures into contaminated groundwater to supplement or introduce populations capable of degrading specific contaminants. Commonly used when native dechlorinating bacteria (such as Dehalococcoides) are absent or insufficient to drive complete reductive dechlorination of TCE/PCE to ethene. IET uses bioaugmentation as part of enhanced ERD programs.; See also:Bioremediation
Bioremediation: The use of living microorganisms to degrade hazardous contaminants in soil and groundwater to less toxic or non-toxic forms. Enhanced bioremediation involves adding nutrients, electron donors, or specialized bacteria to accelerate natural degradation processes. IET specializes in enhanced reductive dechlorination (ERD) for chlorinated solvents and aerobic/anaerobic approaches for petroleum.; See also:Bioremediation Services
Biostimulation: The addition of nutrients, electron donors, or other amendments to stimulate the growth and activity of indigenous microorganisms capable of degrading contaminants. Distinguished from bioaugmentation in that no external microbes are added — existing populations are stimulated. Common amendments include vegetable oil emulsions, lactate, and molasses for anaerobic dechlorination.; See also:Bioremediation
BTEX: An acronym for Benzene, Toluene, Ethylbenzene, and Xylene — a group of volatile aromatic hydrocarbons commonly found in gasoline and crude oil. BTEX compounds are primary contaminants of concern at petroleum release sites. Benzene is classified as a human carcinogen. IET treats BTEX contamination using ISCO (ferric iron-activated persulfate), enhanced bioremediation, and combined approaches.; See also:Petroleum Treatment
Barium: A metal that occurs naturally in some limestones, sandstones, and soils, particularly in the eastern United States. At elevated concentrations barium can cause a variety of cardiac, gastrointestinal, and neuromuscular effects and is associated with hypertension and cardiotoxicity in animals. Barium does not respond to oxidation or reduction, so it is treated by promoting precipitation as sparingly soluble barium sulfate or by sorption-based stabilization rather than by in situ destruction.; See also:Heavy Metals Treatment
Beryllium: Occurs naturally in soils, groundwater, and surface water, and is widely used in electrical industry equipment and components, nuclear power, and the space industry. Beryllium enters the environment from mining operations, processing plants, and improper waste disposal. It causes acute and chronic toxicity and can damage the lungs and bones, and is considered a possible carcinogen. Beryllium is not destroyed in situ; it is stabilized by precipitation and by sorption onto iron oxides under controlled pH conditions.; See also:Heavy Metals Treatment

C

Chemical Oxidation: See In Situ Chemical Oxidation (ISCO).; See also:Chemical Oxidation
Chlorinated Solvents: Organic compounds containing chlorine atoms, widely used as industrial degreasers and dry cleaning agents. Common examples include PCE (perchloroethylene/tetrachloroethene), TCE (trichloroethylene), 1,1,1-TCA, and DCE (dichloroethene). These compounds are persistent groundwater contaminants that form DNAPLs. They are degraded by reductive dechlorination (anaerobic) or chemical oxidation (ISCO).; See also:Chlorinated Solvents Treatment
Cone Penetration Test (CPT): A geotechnical investigation method in which a cone-tipped probe is pushed into the subsurface at a constant rate to measure soil resistance and friction. CPT provides continuous stratigraphic profiles without soil sample retrieval, enabling rapid site characterization. IET uses CPT with Membrane Interface Probe (MIP) logging for simultaneous contaminant screening.; See also:Geoprobe Services
Contaminant Rebound: The return of contaminant concentrations to pre-treatment levels after an active remediation program ends. Rebound commonly occurs after ISCO when oxidants are exhausted and contaminants continue to dissolve from NAPL, sorbed phases, or back-diffuse from low-permeability zones. IET's patented ferric iron-activated persulfate technology specifically addresses rebound by sustaining secondary bioremediation for 2+ years post-injection.; See also:ISCO Services
Creosote: A complex mixture of PAHs, phenols, and heterocyclic compounds produced from coal tar distillation, historically used as a wood preservative for utility poles and railroad ties. Creosote is a dense, viscous DNAPL contaminant that is particularly persistent in the subsurface. IET specializes in creosote site remediation using ISGS (In Situ Geochemical Stabilization) and EZVI technologies.; See also:NAPL Treatment ISGS
Cadmium: Found in low concentrations in rocks, coal, and petroleum, and dissolved into groundwater and surface water by acidic waters. Industrial discharge, mining waste, metal plating, water pipes, batteries, paints and pigments, plastic stabilizers, and landfill leachate are common sources. Cadmium replaces zinc biochemically and can cause high blood pressure, liver and kidney damage, and anemia, and it is toxic to aquatic biota. IET addresses cadmium through in situ chemical reduction, where zero-valent iron and its corrosion products reduce mobility by adsorption and precipitation.; See also:ISCR Services Heavy Metals Treatment
Chloride: A common groundwater ion often associated with saltwater intrusion, mineral dissolution, and industrial or domestic waste, and with elevated sodium where concentrations are high. High chloride levels deteriorate plumbing, water heaters, and municipal water-works equipment, and taste becomes noticeable above the secondary maximum contaminant level. Chloride cannot be destroyed in situ; it is managed through source control and removed from extracted water by reverse osmosis or ion exchange.
Chromium: A metal that enters groundwater from runoff and leaching at old mining operations, fossil-fuel combustion, cement-plant emissions, mineral leaching, and waste incineration, and is used in metal plating and as a cooling-tower water additive. Trivalent chromium (Cr III) is a nutritionally essential element, while hexavalent chromium (Cr VI) is far more toxic, causing liver and kidney damage, internal hemorrhaging, respiratory damage, dermatitis, and skin ulcers at high concentrations. IET treats Cr(VI) with in situ chemical reduction using zero-valent iron, converting it to immobile Cr(III).; See also:ISCR Services Heavy Metals Treatment
Copper: Enters the environment from metal plating, industrial and domestic waste, mining, and mineral leaching. Copper is an essential trace element, but high doses can cause stomach and intestinal distress, liver and kidney damage, and anemia, and it imparts an adverse taste and significant staining to clothing and fixtures. It is toxic to plants and algae at moderate levels. Copper is immobilized in situ under ISCR, where zero-valent iron and iron corrosion products adsorb and precipitate it out of groundwater.; See also:ISCR Services Heavy Metals Treatment
Cyanide: Often used in electroplating, steel processing, plastics, synthetic fabrics, and fertilizer production, and released through improper waste disposal. Cyanide poisoning results in damage to the spleen, brain, and liver. Free cyanide is destroyed by chemical oxidation, including catalyzed hydrogen peroxide and alkaline chlorination, and can be degraded biologically under engineered aerobic conditions.; See also:ISCO Services Bioremediation

D

1,4-Dioxane: A synthetic cyclic ether (C₄H₈O₂) used historically as a stabilizer for 1,1,1-trichloroethane (TCA) and as a solvent in paints, dyes, and varnishes, which makes it a frequent co-contaminant at chlorinated solvent and dry cleaner sites. 1,4-Dioxane is fully miscible with water, does not sorb to soil, and therefore travels farther and faster than the solvent plume it accompanies. It is classified as likely to be carcinogenic to humans, has no federal MCL, and is regulated by several states at concentrations in the low microgram-per-liter range. Because it resists air stripping, carbon adsorption, and reductive dechlorination, IET treats 1,4-dioxane in situ with activated persulfate in the ISCO program designed for the accompanying chlorinated solvents, and with aerobic cometabolic bioremediation, delivering the amendments across the full depth of the dioxane-bearing interval.; See also:Chlorinated Solvents Treatment ISCO Services Bioremediation
DCA (Dichloroethane): Dichloroethane (C₂H₄Cl₂), a chlorinated solvent that exists as two isomers of concern in groundwater. 1,1-DCA is a component of 1,1,1-trichloroethane (TCA) formulations and the first degradation product of TCA, so it is typically found alongside 1,4-dioxane and TCA at solvent release and dry cleaner sites. 1,2-DCA (ethylene dichloride, EDC) was used as a lead scavenger in leaded gasoline and as a feedstock for vinyl chloride production, and is classified as a probable human carcinogen with a federal MCL of 5 µg/L. Neither isomer degrades readily on its own: 1,1-DCA dechlorinates slowly to chloroethane, while 1,2-DCA resists reductive dechlorination and is destroyed mainly by oxidation or by dichloroelimination to ethene under strongly reducing conditions. IET treats DCA with activated persulfate ISCO, enhanced reductive dechlorination where the site geochemistry supports it, and aerobic cometabolic bioremediation for the 1,2-DCA fraction.; See also:ISCO Services Chlorinated Solvents Treatment Bioremediation
DCE (Dichloroethene): A chlorinated solvent that is a degradation daughter product of TCE and PCE during reductive dechlorination. The cis-1,2-DCE isomer is the most commonly observed intermediate. Complete dechlorination continues from DCE to vinyl chloride (VC) and ultimately to non-toxic ethene. DCE "stall" — where dechlorination halts at DCE — is a common site challenge IET addresses through bioaugmentation and geochemical optimization.; See also:Bioremediation
Dehalococcoides (DHC): A genus of anaerobic bacteria that are the primary organisms responsible for complete reductive dechlorination of chlorinated ethenes (PCE → TCE → DCE → VC → ethene). Dehalococcoides require hydrogen as an electron donor and are uniquely capable of dechlorinating vinyl chloride to harmless ethene. IET uses molecular tools to confirm DHC presence and determine if bioaugmentation is needed.; See also:Bioremediation
Direct Push Technology (DPT): A drilling method in which small-diameter sampling tools or probes are advanced into unconsolidated soils by applying hydraulic pushing force, without rotating or removing cuttings. DPT using Geoprobe® or AMS equipment is faster, cheaper, and generates less waste than conventional drilling. IET uses DPT for soil/groundwater sampling, plume delineation, and injection point installation for ISCO and bioremediation programs.; See also:Geoprobe Services Direct Push Drilling
DNAPL: Dense Non-Aqueous Phase Liquid — a contaminant that is denser than water and does not mix with it, causing it to sink through the water table and accumulate in zones of low permeability. Common DNAPLs include chlorinated solvents (PCE, TCE), coal tar, and creosote. DNAPLs are highly persistent subsurface contaminant sources and require specialized treatment technologies such as EZVI, ISGS, or aggressive ISCO.; See also:NAPL Treatment EZVI Technology
Dissolved Solids: A measure of the dissolved salts and minerals in water. They occur naturally but also enter the environment from man-made sources such as landfill leachate, feedlots, and sewage, and the measurement can include some dissolved organic compounds. High concentrations influence the general acceptability of water, may indicate the presence of substances outside the Safe Drinking Water Act, and shorten the life of hot water heaters. Dissolved solids are not destroyed in situ; they are managed by source control and removed from extracted water by reverse osmosis, ion exchange, or precipitation softening.

E

Electron Donor: A substance that provides electrons in a chemical or biological reaction. In enhanced reductive dechlorination (ERD), organic compounds such as vegetable oil, lactate, or molasses serve as electron donors, providing hydrogen that Dehalococcoides bacteria use to sequentially remove chlorine atoms from PCE/TCE. Selecting the appropriate electron donor type (fast-release vs. slow-release) is critical to ERD program design.; See also:Bioremediation ISCR Services
Enhanced Reductive Dechlorination (ERD): An enhanced bioremediation approach in which fermentable organic substrates (electron donors) are injected into anaerobic groundwater to stimulate reductive dechlorination of chlorinated solvents. ERD drives the sequential degradation PCE → TCE → cis-DCE → vinyl chloride → ethene. IET designs and implements ERD programs using controlled-release substrates and bioaugmentation.; See also:Bioremediation ISCR Services
EZVI (Emulsified Zero Valent Iron): A NASA-patented remediation technology (U.S. Patent No. 6,312,194) consisting of nanoscale zero-valent iron particles suspended in a vegetable oil-water emulsion. The lipophilic outer membrane allows EZVI to mix directly with DNAPL chlorinated solvents, enabling abiotic reductive dechlorination at the source. IET is licensed to apply EZVI and has completed 50+ DNAPL source zone applications nationwide.; See also:EZVI Technology

F

Fenton's Reaction: A chemical process in which hydrogen peroxide (H₂O₂) reacts with ferrous iron (Fe²⁺) to generate highly reactive hydroxyl radicals (OH• at 2.80V) that destroy organic contaminants. Modified Fenton's reagent (also called catalyzed hydrogen peroxide or CHP) is used in ISCO for rapid treatment of petroleum hydrocarbons and some chlorinated solvents. IET practices Fenton-based ISCO as one of several oxidation approaches.; See also:ISCO Services
Ferrate (Fe⁶⁺): A supercharged iron species with an oxidation potential of 2.20V generated when persulfate is activated by ferric iron. Ferrate functions as both an oxidant and a coagulant, directly destroying organic contaminants while simultaneously improving aquifer geochemistry. Ferrate generation is a key feature of IET's patented ferric iron-activated persulfate technology, providing a multi-mechanism oxidation system.; See also:ISCO Services
Fluoride: Occurs naturally in groundwater and is added to many municipal water supplies, and is also widely used in industry. Fluoride decreases the incidence of tooth decay, but high levels can stain or mottle teeth, and very high levels cause a crippling bone disorder from calcification of the bones and joints. Fluoride is treated by precipitation and coagulation with alum or lime, or by sorption onto activated alumina, rather than by in situ destruction.
Free Product: Contaminant present in the subsurface as a separate, non-aqueous phase liquid (NAPL) — either floating on the water table (LNAPL) or sinking below it (DNAPL). Free product recovery typically requires specialized extraction techniques before dissolved-phase treatment can be effective. IET uses ISGS and EZVI to address free product that cannot be practically recovered.; See also:NAPL Treatment EZVI Technology ISGS Technology

G

Geoprobe®: A brand name for direct push drilling equipment manufactured by Geoprobe Systems®. Geoprobe rigs are widely used in environmental drilling for soil/groundwater sampling, monitoring well installation, and remediation injection point installation. IET operates one of the largest fleets of Geoprobe equipment in the eastern United States, with multiple models including the 6610DT, 7822DT, and 8040DT.; See also:Geoprobe Services
Groundwater: Subsurface water occupying the saturated zone below the water table. Groundwater is the primary pathway for contaminant migration from release sites to drinking water wells and surface water receptors. Most IET remediation projects target groundwater contamination by chlorinated solvents, petroleum, or heavy metals.

H

Hardness: The result of metallic ions dissolved in the water, reported as a concentration of calcium carbonate derived from dissolved limestone or from discharges from operating or abandoned mines. Hard water decreases the lather formation of soap and, at high levels, increases scale formation in hot water heaters and low-pressure boilers. Hardness is managed by water softening, most commonly lime softening or ion-exchange softening, rather than by in situ treatment.
Hexavalent Chromium (Cr VI): A highly toxic, mobile form of the heavy metal chromium found in groundwater at electroplating facilities, tanneries, and sites where chromate compounds were used. Cr(VI) is a human carcinogen regulated at extremely low levels (0.1 µg/L in some states). IET uses ISCR with zero-valent iron to permanently reduce Cr(VI) to the immobile, non-toxic Cr(III) form.; See also:ISCR Services Heavy Metals Treatment
Hollow-Stem Auger: A conventional drilling method in which a helical steel auger with a hollow center is rotated into the ground, allowing soil samples and monitoring wells to be installed through the hollow stem. HSA drilling is commonly used for environmental site investigations and permanent monitoring well installation in unconsolidated soils.; See also:Environmental Drilling
Hydraulic Profiling Tool (HPT): A direct push tool that measures groundwater injection pressure as it is advanced into the subsurface, providing a continuous log of relative hydraulic conductivity versus depth. HPT data is combined with MIP contaminant screening to identify permeable zones where contaminants are concentrated — critical for optimizing injection well screen placement and reagent delivery.; See also:Geoprobe Services
Hydrogen Peroxide (H₂O₂): A strong chemical oxidant used in ISCO, typically at concentrations of 1–10%. When catalyzed by iron (Fenton's reaction), hydrogen peroxide generates hydroxyl radicals that rapidly destroy petroleum hydrocarbons, BTEX, and some chlorinated compounds. H₂O₂ is fast-acting but short-lived in the subsurface due to rapid decomposition, making it best suited for source zone treatment.; See also:ISCO Services

I

In Situ: Latin for "in place." In environmental remediation, in situ refers to treatment methods that destroy or immobilize contaminants underground without excavating or extracting soil and groundwater. In situ approaches avoid hazardous waste disposal costs, minimize site disruption, and can treat deep contamination inaccessible by excavation. All primary IET technologies are in situ.; See also:Remediation Overview
In Situ Chemical Oxidation (ISCO): An in situ remediation technology in which chemical oxidants are injected into contaminated soil and groundwater to chemically destroy organic contaminants in place. Common ISCO oxidants include persulfate, permanganate, hydrogen peroxide, and ozone. IET holds patented ferric iron-activated persulfate technology (U.S. Patent No. 9,126,245) that prevents contaminant rebound through sustained secondary bioremediation.; See also:ISCO Services
In Situ Chemical Reduction (ISCR): An in situ remediation technology using reducing agents — primarily zero-valent iron (ZVI), activated carbon, or chelating amendments — injected into contaminated groundwater to reduce and stabilize metal contaminants (e.g., Cr(VI) → Cr(III)) or reductively dechlorinate chlorinated solvents. ISCR provides long-term reducing conditions lasting 5–10+ years.; See also:ISCR Services
In Situ Geochemical Stabilization (ISGS): IET's proprietary, exclusively licensed technology using modified sodium permanganate (NaMnO₄) solutions for the in situ treatment of non-aqueous phase liquids (NAPL). ISGS reacts with NAPL contaminants to form stable mineral precipitates (birnessite: MnO₂) that physically encapsulate NAPL surfaces, reducing contaminant flux and stabilizing source zones. IET holds the exclusive North American license from Evonik Corporation for ISGS. Depending on site conditions, ISGS reagent is delivered by direct-push injection, injection wells, or soil mixing.; See also:ISGS Technology NAPL Treatment
Iron: Occurs naturally as a mineral in sediment and rocks, and enters water from mining, industrial waste, and corroding metal. Iron is not a health concern at typical concentrations, but it imparts a bitter, astringent taste to water and a brownish color to laundered clothing and plumbing fixtures. Elemental iron (zero-valent iron) is also the reagent of choice in in situ chemical reduction, where it drives reductive dechlorination and metal stabilization. Where dissolved iron is itself the nuisance, it is removed by oxidation and filtration in water treatment.; See also:ISCR Services
ISCO: See In Situ Chemical Oxidation (ISCO).; See also:ISCO Services
ISCR: In Situ Chemical Reduction — an in situ remediation technology that injects reducing agents (zero-valent iron, dithionite, or ferrous sulfate) into contaminated groundwater to chemically reduce and immobilize contaminants in place. ISCR is the primary treatment for hexavalent chromium (Cr(VI) → Cr(III)), uranium, and other redox-sensitive metals, and also promotes abiotic reductive dechlorination of chlorinated solvents. IET combines ISCR with bioremediation for synergistic treatment of mixed chlorinated solvent and metals sites.; See also:ISCR Services Heavy Metals Treatment

L

LNAPL: Light Non-Aqueous Phase Liquid — a contaminant that is less dense than water and floats on the water table. Common LNAPLs include gasoline, diesel, heating oil, and other petroleum products. LNAPL creates a floating lens of product that continually dissolves into groundwater. IET treats LNAPL-contaminated sites using ISCO, enhanced bioremediation, and combined approaches.; See also:NAPL Treatment
Lead: Enters the environment from industry, mining, plumbing, gasoline, coal, and, historically, as a water additive. Lead affects red blood cell chemistry and delays normal physical and mental development in babies and young children, causes slight deficits in attention span, hearing, and learning in children, and can cause a slight increase in blood pressure in some adults. It is a probable carcinogen, and is managed in groundwater through in situ stabilization under ISCR programs, where zero-valent iron and phosphate amendments form sparingly soluble lead phases that remain in the aquifer.; See also:ISCR Services Heavy Metals Treatment

M

Manganese: Occurs naturally as a mineral in sediment and rocks, and enters water from mining and industrial waste. Manganese is relatively non-toxic to animals but causes aesthetic and economic damage, imparting an unpleasant taste to water and dark brown or black stains to laundry and plumbing fixtures. It is toxic to plants at high levels. Dissolved manganese is removed by oxidation, using permanganate, ozone, or aeration, followed by filtration, and it is immobilized in situ under oxidizing conditions.
Mercury: Occurs as an inorganic salt and as organic mercury compounds, and enters the environment from industrial waste, mining, pesticides, coal, electrical equipment such as batteries, lamps, and switches, smelting, and fossil-fuel combustion. Mercury causes acute and chronic toxicity, targets the kidneys, and can cause nervous system disorders. Mercury is immobilized in situ using ISCR, where zero-valent iron reduces and stabilizes it onto iron surfaces, and treatment programs also track the anaerobic conditions that convert mercury to the more mobile methylmercury form.; See also:ISCR Services Heavy Metals Treatment
MCL (Maximum Contaminant Level): The legally enforceable maximum concentration of a contaminant in public drinking water, as established by the U.S. EPA under the Safe Drinking Water Act. MCLs are used as cleanup standards for many groundwater remediation sites. Common MCLs include TCE at 5 µg/L, PCE at 5 µg/L, and benzene at 5 µg/L.
Membrane Interface Probe (MIP): A direct push downhole tool that continuously screens soil for volatile organic compounds (VOCs) as it is advanced. The MIP heats soil and transfers volatile contaminants across a semipermeable membrane into a carrier gas stream, which is analyzed at the surface by a PID or FID detector. MIP profiling provides continuous depth-specific contaminant distribution data critical for ISCO and bioremediation injection design.; See also:Geoprobe Services
MGP (Manufactured Gas Plant): A facility that historically produced gas from coal for municipal use (1800s–1950s). MGP sites are characterized by complex NAPL contamination including coal tar, creosote, benzene, and PAHs. Hundreds of former MGP sites remain contaminated across the US. IET specializes in MGP site remediation using ISGS for NAPL stabilization and ISCO for dissolved-phase treatment.; See also:NAPL Treatment ISGS
Monitoring Well: A groundwater well installed for the purpose of sampling groundwater to track contaminant concentrations, water table elevations, and remediation performance over time. Monitoring wells are typically 1", 2", or 4" diameter PVC or stainless steel screens installed at specific depths. IET installs monitoring wells as part of site characterization and remediation performance monitoring programs.; See also:Monitor Well Installation
MTBE: Methyl tert-butyl ether — a fuel oxygenate added to gasoline to reduce air emissions. MTBE is highly water soluble and mobile in groundwater, forming large dissolved plumes from small releases. It is resistant to biodegradation under anaerobic conditions. IET treats MTBE-contaminated sites using ISCO (activated persulfate or Fenton's) and enhanced aerobic bioremediation.; See also:Petroleum Treatment

N

NAPL: Non-Aqueous Phase Liquid — a contaminant that does not dissolve in water and forms a separate liquid phase in the subsurface. NAPLs are classified as LNAPL (lighter than water — floats) or DNAPL (denser than water — sinks). NAPLs are persistent groundwater sources that continually dissolve, sustaining plumes for decades. Treating NAPL source zones is essential for achieving site closure.; See also:NAPL Treatment
Natural Attenuation: The reduction of contaminant concentrations in soil and groundwater through natural physical, chemical, and biological processes including dilution, dispersion, sorption, volatilization, and biodegradation. Monitored Natural Attenuation (MNA) uses performance monitoring to demonstrate that natural processes are reducing contamination at acceptable rates. MNA may be used alone or combined with active remediation.
Nickel: Occurs naturally in soils, groundwater, and surface water, and is widely used in electroplating, stainless steel and alloy products, mining, and refining. Lifetime exposure to large amounts damages the heart and liver of laboratory animals. Nickel is immobilized under ISCR, where zero-valent iron reduces it to less soluble forms and iron corrosion products sorb it from groundwater.; See also:ISCR Services Heavy Metals Treatment
Nitrate (as Nitrogen): The more stable form of combined nitrogen in oxygenated water, occurring naturally in mineral deposits, soils, seawater, freshwater systems, the atmosphere, and living organisms, and found at its highest levels in groundwater beneath extensively developed areas. Fertilizer, feedlots, and sewage are the primary sources. Toxicity results from the conversion of nitrate to nitrite in the body, causing methemoglobinemia, or "blue baby disease", which threatens the oxygen-carrying capacity of the blood. Nitrate is treated by enhanced anaerobic bioremediation, injecting electron donors such as emulsified vegetable oil to drive denitrification to nitrogen gas, and by ISCR with zero-valent iron, which reduces nitrate to nitrogen gas or ammonium.; See also:Bioremediation ISCR Services
Nitrite (Combined Nitrate/Nitrite): Enters the environment from fertilizer, sewage, and human or farm-animal waste. As with nitrate, toxicity results from the conversion of nitrate to nitrite in the body, causing methemoglobinemia, or "blue baby disease", which threatens the oxygen-carrying capacity of the blood. Nitrite is readily oxidized to nitrate in aerobic groundwater and is destroyed along with nitrate by biological denitrification under anaerobic conditions.; See also:Bioremediation

O

ORP (Oxidation-Reduction Potential): A measurement (in millivolts) of the tendency of a solution to accept or donate electrons, indicating the prevailing redox conditions. Positive ORP values indicate oxidizing conditions; negative values indicate reducing conditions. ORP is a critical indicator in bioremediation — anaerobic dechlorination of chlorinated solvents requires strongly reducing conditions (ORP < -100 mV). Geochemists monitor ORP to track bioremediation progress.

P

PAH (Polycyclic Aromatic Hydrocarbon): A class of organic compounds consisting of multiple fused aromatic rings, formed by incomplete combustion of organic matter. PAHs are found at creosote sites, MGP sites, gas stations, and areas affected by wildfire or industrial burning. Many PAHs are carcinogenic. IET treats PAH contamination using ISGS, ISCO (activated persulfate or permanganate), and enhanced bioremediation.; See also:NAPL Treatment
PCE (Perchloroethylene / Tetrachloroethene): A widely used dry cleaning solvent and industrial degreaser (also called PERC or tetrachloroethene, chemical formula C₂Cl₄). PCE is the most common chlorinated solvent at dry cleaner sites and a frequent groundwater contaminant. MCL is 5 µg/L. PCE degrades sequentially under anaerobic conditions: PCE → TCE → DCE → vinyl chloride → ethene. IET treats PCE using ISCO (persulfate/permanganate), ERD bioremediation, and EZVI for DNAPL zones.; See also:Chlorinated Solvents Bioremediation
Permanganate: A common ISCO oxidant (potassium permanganate, KMnO₄, or sodium permanganate, NaMnO₄) effective for oxidizing chlorinated ethenes (TCE, PCE, DCE) and some other organic contaminants. Permanganate is stable and persistent in groundwater, providing extended treatment. It produces manganese dioxide (MnO₂) as a reaction byproduct, which can reduce aquifer permeability if over-applied. IET uses permanganate in both ISCO and ISGS applications.; See also:ISCO Services ISGS
Permeable Reactive Barrier (PRB): A passive in situ treatment technology in which a reactive material (typically zero-valent iron) is placed in a subsurface trench perpendicular to groundwater flow. As contaminated groundwater passes through the barrier, contaminants are treated by reduction/degradation. PRBs require no energy input and provide long-term passive treatment, making them cost-effective for plume management.; See also:ISCR Services
Phase II ESA: A Phase II Environmental Site Assessment — a subsurface investigation conducted to characterize soil and groundwater contamination at a property. Phase II ESAs include soil borings, groundwater sampling, and laboratory analysis to identify, delineate, and quantify contamination. IET provides drilling and sampling services to support Phase II ESAs conducted by environmental consulting firms.; See also:Environmental Drilling
Piezometer: A small-diameter groundwater monitoring point used to measure hydraulic head (water level) at a specific depth. Unlike monitoring wells, piezometers are typically used for water level measurement rather than groundwater sampling. IET installs piezometers as part of hydrogeologic site characterization programs.; See also:Piezometer Installation
Plume: A zone of dissolved contamination that migrates from a contaminant source through groundwater, typically in the direction of groundwater flow. Plume delineation — defining the lateral and vertical extent of dissolved contamination — is a critical site characterization step that guides remediation design. IET uses direct push tools (MIP, HPT) and monitoring wells to characterize contaminant plumes.
Potassium Persulfate: A crystalline persulfate salt (K₂S₂O₈) used as an ISCO oxidant where a solid, easy-to-handle reagent is preferred. Its solubility is much lower than sodium persulfate — roughly 50 g/L in water at 20 °C, against more than 500 g/L for the sodium salt — so the oxidant strength achievable in a single injection solution is limited and the solid dissolves gradually once placed, giving a slower, more extended release into groundwater. IET applies potassium persulfate in shallow soil mixing and small-volume direct push programs where that longer release profile suits the treatment interval, and activates it — typically with ferric iron — to generate sulfate radicals (SO₄•⁻ at 2.60V) that destroy chlorinated solvents, petroleum hydrocarbons, and other organics.; See also:ISCO Services Persulfate Injection IET Patents
Sodium Persulfate: A highly water-soluble persulfate salt (Na₂S₂O₈, more than 500 g/L in water at 20 °C) and the standard persulfate oxidant for in situ chemical oxidation. High solubility allows concentrated reagent solutions and greater oxidant mass to be delivered per injection point, which reduces the number of injection points and the volume of water that must be handled to treat a DNAPL or petroleum source zone. Sodium persulfate is the reagent in IET's patented ferric iron-activated persulfate technology (U.S. Patent No. 9,126,245), which generates sulfate radicals (SO₄•⁻ at 2.60V) alongside ferrate (Fe⁶⁺ at 2.20V) and sustains secondary bioremediation for 2+ years after injection; the sulfate produced as the reaction proceeds also supports sulfate-reducing bacteria in that secondary phase. IET selects sodium persulfate for source zone and high-mass-loading ISCO programs.; See also:ISCO Services Persulfate Injection IET Patents
Pesticides: Herbicides, insecticides, fungicides, rodenticides, and algicides that enter groundwater from agricultural application, runoff, and improper disposal. Pesticides cause poisoning, headaches, dizziness, gastrointestinal disturbance, numbness, and weakness, and can damage the nervous system, thyroid, reproductive system, liver, and kidneys; many are associated with cancer. Many pesticides are destroyed in situ by ISCO using activated persulfate, and some are biodegradable under engineered aerobic or anaerobic conditions, though highly chlorinated compounds degrade far more slowly.; See also:ISCO Services Bioremediation
Plasticizers, Chlorinated Solvents, Benzo[a]pyrene & Dioxin: A group of industrial compounds used as sealants, linings, solvents, pesticides, plasticizers, components of gasoline, disinfectants, and wood preservatives. They enter the environment from improper waste disposal, leaching runoff, leaking storage tanks, and industrial runoff, and can cause cancer and damage to the nervous and reproductive systems, kidneys, stomach, and liver. Chlorinated solvents such as PCE and TCE are treated by ISCO, ERD, and EZVI, and PAHs such as benzo[a]pyrene by ISCO and bioremediation.; See also:Chlorinated Solvents Treatment NAPL Treatment

R

Reductive Dechlorination: The sequential removal of chlorine atoms from chlorinated solvents by anaerobic bacteria that use the compounds as electron acceptors. The dechlorination sequence for PCE is: PCE → TCE → cis-DCE → vinyl chloride → ethene (non-toxic). Complete dechlorination requires Dehalococcoides bacteria, adequate hydrogen as an electron donor, and strongly reducing geochemical conditions.; See also:Bioremediation
Remediation: The process of treating contaminated soil, groundwater, or sediment to reduce contaminant concentrations to acceptable levels that protect human health and the environment. Remediation technologies include in situ chemical oxidation (ISCO), enhanced bioremediation, in situ chemical reduction (ISCR), NAPL treatment, and ex situ approaches such as pump-and-treat.; See also:Remediation Services

S

Soil Vapor Extraction (SVE): An ex situ remediation technology that removes volatile organic compounds (VOCs) from the unsaturated (vadose) zone by applying vacuum to extraction wells. SVE is effective for relatively permeable soils contaminated with high-volatility compounds such as chlorinated solvents and gasoline. IET installs soil vapor points and SVE extraction wells as part of site investigation and remediation programs.; See also:Environmental Drilling
Source Zone: The area of highest contamination where residual or free-phase NAPL is present. Source zones continuously dissolve into groundwater, sustaining dissolved-phase plumes downgradient. Treating source zones — using ISCO, ISGS, EZVI, or excavation — is essential for achieving plume containment and site closure. IET specializes in aggressive source zone treatment using multiple technologies.
SPT (Standard Penetration Test): A geotechnical field test used to evaluate subsurface soil resistance by driving a split-spoon sampler into the ground with a standardized weight dropped a set distance. SPT "N values" are used for geotechnical design of foundations, retaining walls, and slopes. IET performs SPT testing for geotechnical investigations.; See also:Geotechnical Drilling
Sulfate-Reducing Bacteria (SRB): Anaerobic microorganisms that use sulfate (SO₄²⁻) as a terminal electron acceptor, reducing it to sulfide (H₂S). SRBs play an important role in natural attenuation and can contribute to reductive dechlorination at some sites. IET's ferric iron-activated persulfate technology generates sulfate that supports SRB activity for sustained long-term bioremediation after ISCO treatment.
Selenium: Enters the environment from naturally occurring geologic sources, sulfur, and coal. Selenium is a nutritionally essential element at low doses but toxic at high doses, causing acute and chronic toxic effects in animals including "blind staggers" in cattle. Selenium is immobilized in situ under ISCR, where reducing conditions convert soluble selenate and selenite to insoluble elemental selenium that remains in the aquifer.; See also:ISCR Services Heavy Metals Treatment
Silver: Enters the environment from ore mining and processing, product fabrication, and disposal, and is often used in photography, electric and electronic equipment, sterling and electroplating, alloys, and solder. Chronic exposure can cause argyria, a blue-gray coloration of the skin, mucous membranes, eyes, and organs in humans and animals. Because of the great economic value of silver, recovery practices are typically used to minimize loss. Silver is immobilized by precipitation as sparingly soluble sulfide or chloride phases and by sorption onto zero-valent iron under ISCR.; See also:ISCR Services Heavy Metals Treatment
Sodium: Derived geologically from the leaching of surface and underground deposits of salt and the decomposition of various minerals, with human contributions from de-icing and washing products. Sodium can be a health risk factor for individuals on a low-sodium diet, and is typically managed alongside chloride at salt-affected sites. Sodium is not destroyed or removed by in situ treatment; it is managed by source control and removed from extracted water by reverse osmosis or ion exchange.
Sulfate: Elevated concentrations may result from saltwater intrusion, mineral dissolution, and domestic or industrial waste. Sulfate forms hard scales on boilers and heat exchangers, can change the taste of water, and has a laxative effect in high doses. Sulfate is not destroyed in situ, and at high concentrations it competes with chlorinated solvents for electron donors in enhanced reductive dechlorination programs, so ERD designs must account for it and for the sulfide that sulfate-reducing bacteria generate.; See also:Bioremediation

T

TCE (Trichloroethylene / Trichloroethene): A common chlorinated solvent (CHCl=CCl₂) widely used as a metal degreaser and in dry cleaning. TCE is one of the most prevalent groundwater contaminants in the United States, listed as a probable human carcinogen. The MCL is 5 µg/L. IET remediates TCE-contaminated sites using ISCO (ferric iron-activated persulfate, permanganate), ERD bioremediation, ISCR (ZVI), and EZVI for DNAPL zones.; See also:Chlorinated Solvents ISCO Services
Terminal Electron Acceptor (TEA): In microbial metabolism, the compound that accepts electrons at the end of the electron transport chain, enabling energy generation. In aerobic environments, oxygen is the TEA. Under anaerobic conditions, microorganisms use nitrate, iron, sulfate, and carbon dioxide as TEAs in sequence. In enhanced bioremediation, understanding TEA availability is critical for predicting degradation rates and selecting electron donor amendments.
Total Petroleum Hydrocarbons (TPH): A broad measure of the concentration of a range of petroleum-derived hydrocarbon compounds in soil or groundwater, expressed as a sum. TPH encompasses hundreds of individual compounds including BTEX, alkanes, cycloalkanes, and PAHs. TPH measurements are used to characterize petroleum release sites and track remediation performance.; See also:Petroleum Treatment
Thallium: Enters the environment from soils, and is used in electronics, pharmaceutical manufacturing, glass, and alloys. High doses over a lifetime damage the kidneys, liver, brain, and intestines in laboratory animals. Thallium is immobilized in situ under ISCR, where iron corrosion products and sulfide phases adsorb and precipitate it into sparingly soluble forms.; See also:ISCR Services Heavy Metals Treatment

V

Vadose Zone: The unsaturated zone of soil above the water table, where pore spaces contain both air and water. Contaminants released at the surface migrate through the vadose zone before reaching groundwater. NAPL in the vadose zone can serve as a continuing source of groundwater contamination. Soil vapor extraction (SVE) and bioventing are common vadose zone treatment technologies.
Vapor Intrusion: The migration of volatile organic compounds (VOCs) from contaminated soil or groundwater through the vadose zone and building foundation into indoor air. Vapor intrusion can create health risks for building occupants at concentrations far below those that would affect groundwater users. IET investigates vapor intrusion pathways using soil vapor probes and direct push sampling.; See also:Geoprobe Services
Vinyl Chloride (VC): A chlorinated solvent (CH₂=CHCl) and known human carcinogen that is an intermediate daughter product of PCE/TCE reductive dechlorination. Vinyl chloride is more toxic than its parent compounds and has an MCL of 2 µg/L. VC accumulation ("VC stall") at a site indicates incomplete dechlorination. IET addresses VC stall through bioaugmentation with Dehalococcoides cultures or ISCO for direct destruction.; See also:Bioremediation
Volatile Organic Compounds (VOCs): A broad class of carbon-based chemicals that evaporate readily at room temperature. They are used to make plastics, dyes, rubbers, polishes, solvents, crude oil products, insecticides, inks, varnishes, paints, disinfectants, gasoline products, pharmaceuticals, preservatives, spot removers, paint removers, and degreasers, and enter groundwater from spills, leaking tanks, and improper disposal. VOCs can cause cancer and liver damage, anemia, gastrointestinal disorder, skin irritation, blurred vision, exhaustion, weight loss, and damage to the nervous system and respiratory tract. IET treats VOC contamination with ISCO, enhanced bioremediation, and soil vapor extraction.; See also:ISCO Services Bioremediation

Z

Zero-Valent Iron (ZVI): Elemental iron (Fe⁰) used in both ISCR and EZVI remediation technologies. ZVI reacts with chlorinated solvents through reductive dechlorination: Fe⁰ + RCl + H⁺ → Fe²⁺ + RH + Cl⁻. ZVI also generates hydrogen gas that supports anaerobic dechlorinating bacteria. IET uses ZVI in ISCR injection programs, permeable reactive barriers, and as the active ingredient in EZVI emulsions for DNAPL treatment.; See also:ISCR Services EZVI Technology
Zinc: Found naturally in water, most frequently in areas where it is mined, and entering the environment from industrial waste, metal plating, plumbing, and sludge. Zinc aids in the healing of wounds and causes no ill health effects except at very high doses, but it imparts an undesirable taste to water and is toxic to plants at high levels. Zinc is immobilized under ISCR, where zero-valent iron and its corrosion products sorb and precipitate it as sparingly soluble phases.; See also:ISCR Services Heavy Metals Treatment

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