In the United States, the most comprehensive set of Preliminary Remediation Goals (PRGs) is from the Environmental Protection Agency (EPA) Region 9. A set of standards used in Europe exists and is often called the Dutch standards. The European Union (EU) is rapidly moving towards Europe-wide standards, although most of the industrialised nations in Europe have their own standards at present. In Canada, most standards for remediation are set by the provinces individually, but the Canadian Council of Ministers of the Environment provides guidance at a federal level in the form of the Canadian Environmental Quality Guidelines and the Canada-Wide Standards|Canada-Wide Standard for Petroleum Hydrocarbons in Soil.
The rezoning is often resisted by local communities and local government because of the adverse effects on the local amenity of the remediation and the new development. The main impacts during remediation are noise, dust, odour and incremental health risk. Then there is the noise, dust and traffic of developments. Then there is the impact on local traffic, schools, playing fields, and other public facilities of the often vastly increased local population.
Also known as solubilization and recovery, the surfactant enhanced aquifer remediation process involves the injection of hydrocarbon mitigation agents or specialty surfactants into the subsurface to enhance desorption and recovery of bound up otherwise recalcitrant non aqueous phase liquid (NAPL).
A Brownfield as defined by the EPA is “a real property, the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant.” Brownfield remediation is being considered more and more often as a viable way to revitalize and spur economic development in communities. It is often dismissed by developers as being too expensive, but a number of studies actually show that remediation has a great number of public benefits as well as economic and environmental gains.
Excavation processes can be as simple as hauling the contaminated soil to a regulated landfill, but can also involve aerating the excavated material in the case of volatile organic compounds (VOCs). Recent advancements in bioaugmentation and biostimulation of the excavated material have also proven to be able to remediate semi-volatile organic compounds (SVOCs) onsite. If the contamination affects a river or bay bottom, then dredging of bay mud or other silty clays containing contaminants (including sewage sludge with harmful microorganisms) may be conducted. Recently, ExSitu Chemical oxidation has also been utilized in the remediation of contaminated soil. This process involves the excavation of the contaminated area into large bermed areas where they are treated using chemical oxidation methods.
One of the advantages of electrokinetics is that the remediation can be conducted in situ (within the remediation site) to treat contaminants in low permeability zones to overcome accessibility of contaminants or delivery of treatment. Remediation can also occur ex situ (removed from the natural site) to have contaminants tested and treated within a laboratory. This versatility of treatment location can be very cost effective. Electrokinetics has the advantage of use in saturated or unsaturated soils because of the insertion of pore fluid. Remediation can also occur despite soil stratifications or homogeneity. For soils that are low in permeability like kaolite and clayey sands it is possible to remove up to 90% of heavy metal contaminants. In many cases pretreatment of soil should be made to determine appropriate working conditions of the soil.
Traditional remediation approaches consist of soil excavation and disposal to landfill and groundwater "pump and treat". In-situ technologies include but are not limited to: solidification and stabilization, soil vapor extraction, permeable reactive barriers, monitored natural attenuation, bioremediation-phytoremediation, chemical oxidation, steam-enhanced extraction and in situ thermal desorption and have been used extensively in the USA.
Bioventing is an in situ remediation technology that uses microorganisms to biodegrade organic constituents in the groundwater system. Bioventing enhances the activity of indigenous bacteria and archaea and stimulates the natural in situ biodegradation of hydrocarbons by inducing air or oxygen flow into the unsaturated zone and, if necessary, by adding nutrients. During bioventing, oxygen may be supplied through direct air injection into residual contamination in soil. Bioventing primarily assists in the degradation of adsorbed fuel residuals, but also assists in the degradation of volatile organic compounds (VOCs) as vapors move slowly through biologically active soil.
The most common activated carbon used for remediation is derived from bituminous coal. Activated carbon absorbs volatile organic compounds from ground water by chemically binding them to the carbon atoms.
Remediation technologies are many and varied but can generally be categorized into ex-situ and in-situ methods. Ex-situ methods involve excavation of affected soils and subsequent treatment at the surface as well as extraction of contaminated groundwater and treatment at the surface. In-situ methods seek to treat the contamination without removing the soils or groundwater. Various technologies have been developed for remediation of oil-contaminated soil/sediments.
The process of identifying Sustainable Remediation is defined by The UK Sustainable remediation Forum (SuRF-UK) as “''the practice of demonstrating, in terms of environmental, economic and social indicators, that the benefit of undertaking remediation is greater than its impact, and that the optimum remediation solution is selected through the use of a balanced decision-making process''.”
Another major limitation of the electrokinetics process is the decrease the electric potential of the system. Different polarization effects can decrease how the system runs. For instance: Activation polarization can occur during the electrokinetic remediation process removing gas bubbles that form on the surface of the electrodes during conductivity. Resistance polarization can occur after the electrokinetic remediation process has started a white layer can be observed. Just like in hard water stains this layer may be the insoluble salt and other impurities that inhibit conductivity. Concentration polarization happens when hydrogen ions generated at the anode are attracted to the cathode and the hydroxide ions generated at the cathode are attracted to the anode. If neutralization occurs the potential between the system drops. Local flattening of the electrical potential profile can also cause the difference in migration.
New in situ oxidation technologies have become popular for remediation of a wide range of soil and groundwater contaminants. Remediation by chemical oxidation involves the injection of strong oxidants such as hydrogen peroxide, ozone gas, potassium permanganate or persulfates.
Sustainable Remediation is a term adopted internationally and encompasses sustainable approaches, as described by the Brundtland Report, to the investigation, assessment and management (including institutional controls) of potentially contaminated land and groundwater.
Ion exchange for ground water remediation is virtually always carried out by passing the water downward under pressure through a fixed bed of granular medium (either cation exchange media and anion exchange media) or spherical beads. Cations are displaced by certain cations from the solutions and ions are displaced by certain anions from the solution. Ion exchange media most often used for remediation are zeolites (both natural and synthetic) and synthetic resins.
A basic electrokinetics remediation site contains an external direct current source, a positively charged electrode (or anode) and a negatively charged electrode (or a cathode) placed into the ground. Placement of electrodes are based on size and shape of known contaminant plumes. The removal of contaminants and prevention of plume migration are big influences in determining the arrangement of electrodes. Each electrode is encased in a reservoir well in which an electrolytic solution can be injected. The electrolytic solutions serve both as a conducting media (or pore fluid) and as a means to extract contaminants and introduce chemicals or biological entities. Another use of the electrolytic solution is for control and/or depolarization of electrode reactions. Immersed in a solution the electrodes can result in oxidation at the anode site and the reduction at the cathodic site. The oxidation and formation of an acidic front are by products of the process and cause varying degree of influence to the system. By pumping, processing and testing the electrolytic solution at each electrode site you can extend the life and efficiency of the system.
One thing to note is that the potential profile in soils can be determined by the ionic distribution of pore fluid. Because ion distribution effects the efficiency of the electrokinetics system, engineers like John Dzenitis have done comprehensive study to find key reactions around the electrodes that can be used to create models for ionic flowrate prediction. These models can then be interpreted to determine if electrokinetics remediation is the best choice for a given site.
Environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water. Remedial action is generally subject to an array of regulatory requirements, and may also be based on assessments of human health and ecological risks where no legislative standards exist, or where standards are advisory.
Depending on geology and soil type, pump and treat may be a good method to quickly reduce high concentrations of pollutants. It is more difficult to reach sufficiently low concentrations to satisfy remediation standards, due to the equilibrium of absorption/desorption processes in the soil. However, pump and treat is typically not the best form of remediation. It is expensive to treat the groundwater, and typically is a very slow process to clean up a release with pump and treat. It is best suited to control the hydraulic gradient and keep a release from spreading further. Better options of in-situ treatment often include air sparge/soil vapor extraction (AS/SVE) or dual phase extraction/multiphase extraction(DPE/MPE). Other methods include trying to increase the dissolved oxygen content of the groundwater to support microbial degradation of the compound (especially petroleum) by direct injection of oxygen into the subsurface, or the direct injection of a slurry that slowly releases oxygen over time (typically magnesium peroxide or calcium oxy-hydroxide).
Current practices can still impact groundwater, such as the over application of fertilizer or pesticides, spills from industrial operations, infiltration from urban runoff, and leaking from landfills. Using contaminated groundwater causes hazards to public health through poisoning or the spread of disease, and the practice of groundwater remediation has been developed to address these issues. Contaminants found in groundwater cover a broad range of physical, inorganic chemical, organic chemical, bacteriological, and radioactive parameters. Pollutants and contaminants can be removed from groundwater by applying various techniques, thereby bringing the water to a standard that is commensurate with various intended uses.