Overview of Environmental Remediation and Containment Options
The strategies available for containing and remediating released chemicals are highly chemical- and situation-dependent. Effective methods differ with substance, and different approaches are needed depending on the substance’s physical and chemical properties, the release medium (air, soil, sediment, groundwater, or surface water), and release site-specific factors. Major approaches to chemical substance containment and environmental remediation include:
Destruction or Alteration of Contaminants
Thermal, biological, physical, and chemical treatment methods/destruction technologies can be applied to contaminated media at the release site (in situ) or following removal from the site (ex situ). Treatments may destroy or alter the substance; alterations include reduction of the substance’s mobility or mass and “phytotechnology” strategies that use plants to degrade contaminants in soil and water. Note that when treatment and/or disposal procedures cannot be performed on-site, substance identification and characterization are key to determining how to safely and efficiently package and transport contaminated materials for removal from the site.
Extraction or Separation of Contaminants from Environmental Media
Treatment technologies (including phytoremediation) are commonly used to extract and separate contaminants from soil and groundwater. The removal of chemicals in air is possible although applications are limited.
Immobilization of Contaminants
Immobilization technologies include stabilization/solidification and containment technologies. Stabilization and solidification processes immobilize substances, reducing their ability to move through soil, groundwater, or surface water. Containment (via booms, neutralizers, sorbents, etc. as described in KPF 4, Control the Spread of Contamination) is often chosen to prevent the migration of contaminants through environmental media when treatment is impractical.
Each approach carries risks and benefits in terms of cost and time needed for treatment. For example, in situ soil or sediment treatments do not require media excavation or transportation, thus affording potentially significant cost savings over ex situ treatments. However, longer treatment periods are generally required for in situ treatments, and the uniform progression of treatments can be difficult to verify. In contrast, ex situ soil/sediment treatments require excavation, leading to increased costs and requirements for engineering, equipment, permitting, and material handling/worker exposure considerations, but also generally require shorter treatment durations, and better uniformity in progression, promoted by the ability to homogenize, screen, and continuously mix the soil. For in situ groundwater and leachate treatments, cost savings come when the water can be treated without bringing it to the surface. However, as with in situ soil/sediment treatments, in situ groundwater treatments generally require longer time periods, and treatment progress can be difficult to verify. Pumping of water is required for ex situ water treatments; therefore, these treatments are more costly.
Specific thermal, biological, physical, and chemical treatment methods that can be applied to contaminated media at the release site (in situ) or following removal from the site (ex situ) for contaminant destruction/alteration, extraction/separation, or immobilization are briefly described in the table below.
Table 21: Environmental Containment and Remediation Options
| Treatment Type | Description | In Situ | Ex Situ |
|---|---|---|---|
| Biological treatments (soil and water) | Biological treatments destroy organic compounds by stimulating microorganisms to grow and use the contaminants as a food source. A key benefit of bioremediation is its low cost, with little to no residual treatment needed. However, processes are generally slow, may be sensitive to environmental conditions, and may leave behind less degradable or more toxic substances.
Remediation success has been achieved when treating petroleum hydrocarbons, solvents, pesticides, and wood preservatives. Biological treatments are not applicable to inorganic contaminants. | Soil, sediment: Bioventing Enhanced bioremediation Phytoremediation Water: Bioreactor Enhanced bioremediation Monitored natural attenuation Phytoremediation Biowall Enhanced in situ reductive chlorination | Soil, sediment: Biopiles Composting Landfarming |
| Physical/ chemical treatments39 (soil and water) | Physical and chemical treatments use the properties of the contaminants or the contaminated medium to destroy (i.e., chemically convert) or separate out the contamination. Key benefits include cost effectiveness and short cleanup times which are dependent on surrounding environmental factors (i.e., soil/sediment composition). However, the processes may increase the ability of remaining contaminants to spread, and treatment residuals may require after action treatment or disposal. | Soil, sediment: Neutralization/pH control In situ chemical oxidation/reduction Electrokinetic remediation Fracturing Soil flushing - Soil vapor extraction (SVE) Water: Neutralization/ pH control Neutralization via flocculants, gelling agents, activated carbon, complexing agents In situ chemical oxidation/reduction Air sparging Bioslurping Directional wells Multiphase extraction In-well air stripping In situ activated carbon Permeable reactive barriers - Dispersants | Soil, sediment: Soil washing Water: Air stripping |
| Thermal treatments (soil, water) | Thermal processes use heat to increase the volatility of (separate); burn, decompose, or detonate (destroy); or melt (immobilize) contaminants. Separation technologies such as thermal desorption and will have an off-gas stream that requires treatment. Destruction technologies such as incineration will typically have a solid (ash) and possibly a liquid residue that will require treatment or disposal. Ash may be suitable for use as clean fill on-site; if treatment occurs off-site, the ash may need to be pretreated before disposal in a landfill. Although a key benefit is short cleanup times, thermal treatments are often costly, particularly when used ex situ, due to energy and equipment needs. For these techniques, the residuals that require treatment or disposal are usually a much smaller volume than the original. | Soil, sediment: Electrical resistance heating Thermal conduction heating Steam enhanced extraction Thermally-enhanced SVE In situ combustion Water: Electrical resistance heating Thermal conduction heating Steam enhanced extraction In situ combustion (surface water) | Soil, sediment: Incineration Desorption |
| Air emissions/ Vapor phase treatments (air) | Air emission treatments include a host of technologies that remove industrial air emission contaminants prior to atmospheric release (e.g., air pollution control technologies like “scrubbers”). Many technologies focus on the removal of volatile organic compounds (VOCs). Air emissions treatments are likely effective only for indoor releases and, in some cases, off-gassing from volatile chemicals released into other media. A number of in situ remediation technologies including SVE, thermal treatment, in situ combustion, bioventing, and multiphase extraction as well as ex situ technologies such as air stripping, thermal desorption, incineration, biopiles, and composting generate a vapor stream that may require treatment. Enhanced in situ reductive dechlorination and in situ chemical oxidation also have the potential to generate gases that may need to be recovered and treated. A variety of treatment options based on physical (adsorption and condensation), chemical (oxidation), and biological (biodegradation) processes are available to treat the vapors generated by these remediation technologies. | Adsorption, physical or chemical (e.g., granular activated carbon, GAC) Biodegradation, using biofilters (natural materials such as peat, wood chips, compost, sludge, sand, and soil, or engineered materials such as vermiculite, GAC, and diatomaceous earth pellets) Condensation Oxidation (thermal, catalytic, photocatalytic) Scrubbing (physical or chemical absorption) | |
| Containment40 41(soil and water) | Containment measures prevent or reduce the movement of contaminants that cannot otherwise be inactivated or removed because of potential hazards, undetermined or inaccessible sources, unrealistic costs, or lack of adequate treatment technologies. They can also be used as a “stop-gap” solution until long-term remedial actions can be implemented. For solid media, key benefits include low to moderate costs and quick deployment times; for liquid media, containment measures can be costly as they often require heavy construction. Containment measures do not lessen the toxicity, mobility, or volume of the contained substance and should be viewed as temporary; they require periodic inspections for settlement, leaks, erosion, corrosion, and invasion by deep-rooted vegetation. Solidification and stabilization (S/S) technologies use both physical and chemical means to immobilize a contaminant. In S/S, various types of binders, additives, and chemicals are added to contaminated media to physically entrap the contaminant (e.g., encapsulation) or make it insoluble, thus reducing its ability to move through the environment. S/S treatment reagents are often used together, may be combined with other treatment methods, and may be used as interim or final remedial measures. S/S is best suited for metals and inorganic contaminants. A key benefit to S/S technologies is their ability to treat complex mixtures of wastes; they are also relatively quick to implement and low in cost (with the exception of vitrification). S/S measures usually do not lessen the toxicity of the treated substance and may increase the volume requiring management. S/S technologies use: Inorganic binders (cement, kiln dust, lime/fly ash, silicates) Organic binders (polymers, asphalt, clays, bitumen materials) Stabilization agents (phosphate, organoclays, activated charcoal) | Soil, sediment: Landfill cap, soil cap (single- and multi-layer) Sediment cap (single- and multi-layer, may include amendments) Dredging (may be treated/disposed ex situ) Excavation (may be treated/disposed ex situ) Diversion, diking, ditching, booming, fencing, damming, berming Sorbents (synthetic, organic, and inorganic Water: Booming, beach berming, diking, damming - Sorbents Pozzolan/ portland cement stabilization Soluble phosphate stabilization Vitrification | Bituminization Emulsified asphalt Modified sulfur cement Polyethylene extrusion Pozzolan/ portland cement stabilization Sludge stabilization Soluble phosphate stabilization Vitrification |
Selection of Treatment Approach
Certain containment and remediation methods have properties that make them poorly suited for use on certain types of materials or in certain types of ecosystems. The knowledge gained during event recognition and characterization activities (discussed in KPF 2, Recognize and Characterize the Incident) and throughout early response activities (discussed in KPF 4, Control the Spread of Contamination) will inform remediation course of action choices. Further, remediation strategies must be re-evaluated as conditions – and with them, method efficiencies – change throughout response and recovery. Often, multiple technologies are needed to fully remediate an entire site; several treatment technologies may be combined to form a “treatment train” at a site. In fulfilling the Emergency Planning and Community Right-to-Know Act (EPCRA), Clean Water Act, and Clean Air Act requirements, Responsible Parties (RPs)/facilities will provide much of the information needed to support containment and remediation/decontamination approach selection, such as the name and quantity of the chemical released, the media into which the chemical was released, and any actions taken to respond to and contain the release.
Rather than implementing a rigid regulatory framework for corrective action following a chemical release, the US Environmental Protection Agency (EPA) or US Coast Guard (USCG) assists the RP and responders with choosing remediation strategies, providing access to resources detailing remediation/decontamination and containment techniques, procedures and equipment, including the availability of greener, more sustainable treatment options. Further, the EPA has developed guidance and policy documents to assist facilities conducting cleanups. In some cases, the EPA/USCG will dictate response tactics and direct on-scene resources even when the RP itself supplies the needed resources. When remediation needs go beyond the capabilities of the RP, the EPA (for inland releases) or US Coast Guard (for coastal releases) will assist as described in the Federal Preparedness, Response and Recovery section of this document.
Table 22: Remediation and Containment Option Resources
| Asset | Description | Agency/Owner |
|---|---|---|
| Citizen’s Guide Series to Cleanup Technologies | Set of 22 fact sheets that summarize cleanup methods used at Superfund and other sites. | EPA |
| Ecosystem Services at Contaminated Site Cleanups | Provides ecosystem services information for cleanup site teams. Valuable for discussing future land use options or design of a cleanup that is consistent with anticipated ecological reuse, depending on the regulatory authority of the cleanup program. | EPA |
| Groundwater Remediation at NPL Sites | Documents technologies used to restore groundwater. Includes select National Priorities List (NPL) sites where the remedial action objective (RAO) was to restore groundwater for use as a source of drinking water. | EPA |
| Hazardous Waste Clean-Up Information (CLU-IN) | Provides information about waste remediation treatment and site characterization technologies. | EPA |
| In Situ Treatment Performance Monitoring: Issues and Best Practices | Discusses eight potential sampling/analytical issues associated with groundwater monitoring at sites where in situ treatment technologies are applied. Provides best practices to identify and mitigate issues that may affect sampling or analysis. Issues are grouped under three topic areas: issues related to monitoring wells; representativeness of monitoring wells; and post-sampling artifacts. | EPA |
| Interstate Technology and Regulatory Council (ITRC) Documents | A collection of documents ranging from technical overviews and case studies of innovative remediation technologies to technical and regulatory guidance documents for applying cleanup technologies. | ITRC |
| National Contingency Plan Product Schedule Toxicity and Effectiveness Summaries | The definitive, approved list of chemical countermeasures that may be allowed during a CWA/OPA response, pending approval by FOSC and RRT (and potentially other jurisdictions in non-NCP incidents). Lists effectiveness of spill response products on different oils as well as lethal toxicity levels in marine life after exposure to particular products/mixtures of products. | EPA |
| Remediation Technologies for Cleaning Up Contaminated Sites | Collected information about remediation technologies used to clean up contaminated sites, including decision-making tools, documents, and websites maintained by state and federal agencies. These address contamination of soil, sediment, groundwater, and surface water, and include information about costs and cleanup time, green remediation techniques, and issues that may affect sampling and analysis. | EPA |
| Superfund Remedy Report (SRR) | Provides information and analyses on remedies EPA selected to address contamination at Superfund National Priorities List and Superfund Alternative Approach sites. | EPA |
| Federal Remediation Technologies Roundtable (FRTR) Technology Screening Matrix and Reference Guide | Allows users to screen 49 in situ and ex situ technologies for either soil or groundwater remediation. Variables used in screening include contaminants, development status, overall cost, and cleanup time. In-depth information on each technology is also available, including links to over 200 cost and performance reports. | Federal Remediation Technologies Roundtable |
Footnotes
38. See the Federal Remediation Technologies Roundtable (FRTR) Technology Screening Matrix and Reference Guide, and the EPA’s Contaminated Site Clean-Up Information for more information on discussed topics.
39. Federal Remediation Technologies Roundtable (FRTR) Technology Screening Matrix and Reference Guide, EPA’s Contaminated Site Clean-Up Information
40. ExxonMobil. 2014. Oil Spill Response Field Manual. ExxonMobil Research and Engineering Company; ITOPF 2012. Response to Marine Chemical Incidents. Technical Information Paper 17. ITOPF Ltd., London, UK. ITOPF 2009. Are HNS Spills More Dangerous than Oil Spills? Interspill Conference & the 4th IMO R&D Forum, Marseille, France, May 2009. ITOPF Ltd., London, UK.; SONS 2017. Spill of National Significance: Public Affairs Reference. SONS Communications Coordination Workgroup.