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Remediation

Soil and Groundwater Remediation

The principal objective of soil and groundwater remediation at any site is to remove the waste material/free product and/or reduce the concentration of contaminants in the soil and/or groundwater to specific land use acceptable levels.

EMC prepares Remediation Plans or Corrective Action Plans (CAP) for sites with many different types of chemicals of concern.   In the preparation of the CAP, EMC will gather site specific data to aid in the remedial design, such as the following: groundwater and soil contaminant mass, groundwater velocity properties, soil properties, exposure pathways, and groundwater quality parameters.  EMC will also conduct the appropriate pilot tests to determine effective remedial strategies.  Some pilot tests that may be conducted on a site include, but are not limited to the following: slug tests, pump tests, soil vapor extraction tests, air sparge tests, and vacuum extraction tests.

In evaluating the various remedial alternatives for each site, the following items are considered: extent of remediation effort, technical feasibility to address the physical and chemical characteristics of the media, projected contaminant removal and treatment rates, protectiveness of human health, clean-up criteria, ability of each alternative to achieve clean-up criteria, community acceptance, anticipated volume of contaminated materials to be treated, ease of technology application or implementation, dimensions of major technologies and space limitations, process parameters, clean-up time frames, transportation distances, operation and maintenance costs and any other special considerations. Each viable remedial technology is compared using some or all of the criteria described above in determining the most cost-efficient and effective remedial technology for each site. If applicable, EMC will combine one or more remedial technologies to achieve the best remedial strategy.

EMC has experience in design, installation and operation of several remediation systems and treatment plans. These plans have been approved for projects in several states. We have obtained sixteen (16) No Further Action Letter closures of contaminated properties during the past three (3) years.  Additionally, eight (8) sites have been closed that were either non-regulated or have not yet enrolled in a state clean-up program.  Fourteen (14) sites are currently being evaluated for closure or have an on-going remediation system in operation and nineteen (19) sites have been closed via investigation utilizing Indiana Risk Integrated System of Closure (RISC) guidelines. 

Remedial designs can include the following technologies:

Speak to one of our project managers today by phone or e-mail for a confidential, no cost evaluation of your site.

The excavation remedial technology involves the removal and transport of impacted soil to either a permitted off-site location for disposal and/or treatment or to an on-site land treatment cell. Soil excavation is an accepted method for soil remediation and has the advantage of rapid removal of residual contaminants that act as sources of groundwater contamination. Excavation has been shown to be the most reliable, quickest and cost-effective method currently available for treatment of contaminated soils with very low hydraulic conductivities.

When contaminated soil is present, excavation is typically conducted in conjunction with underground storage tank (UST) removal activities. In cases of high volumes of contaminated soil, excavation can be utilized to remove a smaller volume of soil with the highest concentrations at the center of the plume.

The potential risks involved in excavation are predominately related to the equipment utilized in soil removal, the potential caving hazards around the open excavation(s) and the possible presence of subsurface utilities. For large volumes of contaminated soil, excavation can be a costly remedial alternative and highly disruptive to site operations.

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Soil vapor extraction (SVE) can be a cost-effective method to remediate volatile organic compounds when the contamination occurs in unsaturated soils with sufficiently high permeability. This remedial method is used to treat large volumes of contaminated soil effectively with minimal disruption to business operations. It can also remove contamination from near or under fixed structures.

Soil vapor extraction operates on the principle of initiating and maintaining air flow in the subsurface by applying a pressure gradient through vertical wells from air withdrawal. The soil vapor extraction air flow increases the rates of contaminant mass transfer to air in the unsaturated zone by evaporation of liquid phase hydrocarbons, by desorption of contaminants from soil particle surfaces, and by volatilization of contaminants present in soil pore space. The air flow through the contaminated soil also increases biological activity through enhanced oxygenation, thus promoting biodegradation by existing microorganisms. The soil vapor is extracted to the surface where it is treated, if necessary, and then discharged. This remedial method can be used in conjunction with air sparging, groundwater pumping or biodegradation systems.

Disadvantages of using SVE include the following: the effectiveness is limited in soils with high clay content and the airflow may not contact all parts of the soil. Additionally, if a high water table is present, soil vapor extraction may not be a feasible remedial alternative.

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Multi-phase extraction (MPE) involves removing contaminated soil vapors, free product and groundwater with one (1) remediation system and from common extraction wells under high vacuum conditions. MPE increases the vapor extraction zone of influence by lowering the water table and therefore increasing the air-phase permeabilities in the vadose zone which also allows for the smear zone and saturated soil zone to be addressed. The amount of groundwater treatment ex-situ is also reduced due to the in-well and in-line stripping of the contaminants as the groundwater is extracted. Introduction of oxygen into the subsurface during the vapor extraction process stimulates aerobic biodegradation and can promote in-situ remediation of soil contaminants that would not typically be volatilized and removed by the extraction system.

MPE is most effective when used in aquifers with medium to low permeability (silts and clays). The groundwater recovery rates are enhanced by the additive effects of hydraulic and pneumatic gradients generated by concurrent extraction of groundwater and soil vapors. This remedial method offers pumping rates that are three (3) to ten (10) times greater than conventional pump and treat rates. The increased pumping rates result in decreased remediation time. Both soil and groundwater are treated with this remedial method. MPE cannot be utilized at sites with extremely deep water tables due to the inability to draw the water from depth into the system with the vacuum.

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Pump and treat refers to physically removing the groundwater from the aquifer and then treating the groundwater at the surface. After the groundwater is brought to the surface, conventional treatment technologies, such as carbon absorption and air stripping, are typically utilized for contaminant removal. The main advantage to this remedial method is that it controls contaminant plume migration and reduces plume concentration.

Groundwater pump and treat is not very effective in aquifers with low permeability. The time frame to achieve clean-up concentrations is typically lengthy when utilizing groundwater pump and treat. The equipment and maintenance costs are usually high, and high iron content (or hardness) can require frequent cleaning of remediation equipment. Seasonal fluctuations of the water table can smear contamination and complicate clean-ups that utilize this remedial method.

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Biodegradation requires all of the following to be present in sufficient quantities: microorganisms, nutrients, electron acceptor, electron donor and a media. The electron donor is the compound that loses electrons during biodegradation and is usually a food source like organic matter. Preferred electron donors are small, simple molecules like sugars, organic acids, alcohols, alkanes, aromatics, man-made organics compounds and natural organic carbon. The electron acceptor is a compound that gains electrons during biodegradation. Preferred electron acceptors are the following: oxygen, nitrate, nitrite, manganese (VI), iron (III), sulfate, carbon dioxide and chlorinated solvents. Common nutrient additions are nitrogen, phosphate and trace metals. Usually only a starter addition of nutrients is necessary. Minerals and water are usually present in sufficient quantities.

Enhanced bioremediation involves providing one or more of these items which may occur in limited quantities at the particular site to stimulate biodegradation. Once sufficient quantities of the limiting factor is supplied, biodegradation can occur. Enhanced biodegradation is dependent upon transporting oxygen and other nutrients through the soils via groundwater movement and is most effective in permeable aquifers. A disadvantage to enhanced biodegradation is that the contaminants continue to move. Enhanced Biodegradation is not feasible in soil with conductivity less than 1.0 X 10-6 feet/second which typically has poor oxygen and nutrients exchange rates due to the predominance of clay-sized particles that lower the effective permeability.

Types of in-situ biological treatment include the following: aerobic biodegradation, anaerobic degradation and microbe addition. In aerobic degradation, oxygen is the electron acceptor and the limiting factor. Generally, aerobic degradation occurs ten (10) to one hundred (100) times faster than anaerobic degradation. In anaerobic degradation, the following may be used as the electron acceptor: nitrate, ferric iron, sulfate or carbon dioxide.

Bacterial addition is usually not necessary to promote microbial degradation. Microbe addition may be useful for the following reasons: to increase the speed of remediation, immediate expansion of degrader populations, recalcitrant compounds of concern and recovery from toxic shocks (sterile soil). One can either increase the biomass or increase the metabolism of existing microbes to accelerate biodegradation.

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In-situ chemical oxidation is increasing in popularity as a feasible remedial option at many sites. Chemical oxidation is a technically sound and potentially cost effective approach for affecting in-situ contaminant mass reduction in both the soil and groundwater in a relatively short period of time. A chemical oxidation reaction involves the breaking of chemical bonds and the removal of electrons. The electrons are then transferred from the contaminant to the oxidant. Chemical oxidation is a sequential process taking the parent target contaminant through a series of partially oxidized intermediate daughter products on the path to complete mineralization.

There are many compounds that can be used for chemical oxidation, such as the following: hydrogen peroxide, permanganate, persulfate, percarbonate, ozone and RegenOx™. Hydrogen peroxide has been shown to be effective on petroleum based constituents of concern (COCs), and permanganate has been used for chlorinated solvents. RegenOx™ is a proprietary in-situ chemical oxidation process using a solid oxidant complex (sodium percarbonate/catalytic formulation) and an activator complex (a composition of ferrous salt embedded in a micro-scale catalyst gel). RegenOx™ has very high activity, capable of treating a very broad range of soil and groundwater contaminants including petroleum hydrocarbons. Additionally, it has a significant longevity in the subsurface allowing for both the initial contaminant degradation and the continued treatment of contaminants desorbing from the matrix. Most importantly, RegenOx™, when handled appropriately, is safe and easy to apply to the subsurface without the health and safety concerns and lingering environmental issues that have become associated with other chemical oxidation technologies.

In order to reach low contaminant concentrations with chemical oxidation, there is a requirement for multiple injections. Typically, the dissolved concentrations will increase after a single injection as the sorbed contaminant mass decreases. Chemical oxidation is best coupled with accelerated bioremediation for more successful site management. This is usually achieved by utilizing chemical oxidation technology to reduce the contaminant mass in high concentration areas and follow up with a slow release bioremediation substrate to treat the remaining contaminant concentrations over time.

Disadvantages of chemical oxidation are typically associated with a specific chemical oxidant and can include the following: the environment is not favorable to bioremediation after the chemical oxidant is spent, significant heat is produced from the chemical reactions, energy is wasted on non-productive chemical reactions, acidic conditions are necessary (pH dependent), fast reactions, short transport distance, metals mobility, difficulty in achieving favorable conditions for contaminant oxidation, difficult in tight soils, success depends on the distribution and contact with the chemical oxidant, and the use of dangerous chemicals (safety handling issues).

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Soil that has been excavated may be treated in a land treatment cell. A land treatment cell typically consists of a cell that is lined with a minimum equivalent of one (1) layer of twelve (12) mil thick, chemically impervious, laminated plastic. The sides are bermed on all sides and also covered with a minimum equivalent of one (1) layer of twelve (12) mil thick, chemically impervious, laminated plastic. The height of the berm is determined from the volume of soil with volume allowed for freeboard. The depth of the soil in a land treatment cell is typically no greater than eighteen (18) inches. The soil in the land treatment cell is then treated by various remedial methods on a frequent basis. Land treatment cells are typically utilized for biodegradable or volatile contaminants of which nutrients and tilling are the typical means of remediation.

This remedial technology has the advantage of lower costs than disposal at a landfill facility and lower operational costs than other remedial methods. Depending on the volume of soil to be treated, available land on a property may exclude this as being a remedial technology for certain sites.

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Air sparge technology is utilized at sites with high hydraulic conductivity and permeable soil types such as sand and silt. The air sparging remedial technique involves injecting air into the saturated zone. The air forms bubbles that rise into the unsaturated zone, carrying trapped and dissolved volatile contaminants. Soil vapor extraction wells in the unsaturated zone then capture the air. Air sparge technology rapidly reduces volatile organic compounds contained below the water table. Air sparging can enhance and accelerate effectiveness of soil vapor extraction technology.

Air sparge technology is less expensive and has lower maintenance costs than remediation through groundwater pump and treat. Introduction of oxygen into the subsurface stimulates naturally occurring microorganisms which increases biodegradation of the contaminants.

Air sparging removes primarily volatile constituents. The effectiveness of air sparging is limited in low permeability or heterogeneous media. Air sparge technology does not provide hydraulic control of a groundwater plume which is necessary at most sites where groundwater is contaminated, and it is difficult to control air distribution in groundwater. Air sparging can promote vapor and plume migration if not utilized properly.

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The main remedial objective for any site that has free product is to remove the free product to the extent possible. Free product at a site prevents biodegradation from occurring, and it provides a constant source for the soil and groundwater. There are many ways in which free product can be removed, such as the following: socks or booms, bailing, pump with product skimmer, or vacuum truck.

The advantages to free product recovery are the following: recycling product, removing the source of soil and groundwater contamination and allowing natural biodegradation to occur. The disadvantages of free product recovery is the product disposal.

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Groundwater containment or barrier systems as forms is a remedial technology that can be used to prevent off-site migration of contaminants and/or for in-situ remediation of the contaminants. A reactive zone is an aquifer or vadose zone segment that is managed to chemically or biologically destroy contaminants as the groundwater flows through the reactive zone or treatment wall. The reactive zones may be sustained for a long time span to act as a migration barrier, or the reactive zones may be a short-term treatment strategy for elimination of a contaminant source zone.

Reactive zones or (groundwater containment barrier systems) are usually constructed through the injection of reagents within the treatment zone. There are numerous biological and chemical reagents that can be used in reactive zone treatment technologies that either oxidize or reduce the contaminants. The following describes some of the reagents or processes that may be involved in a reactive treatment zone system: aerobic biostimulation, co-metabolic aerobic biostimulation, enhanced reductive dechlorination, abiotic reduction, phytoremediation (root exude stimulation and rhizospheric reductive dechlorination), dithionite, zero-valent iron, and chemical oxidation (Fenton’s reagent, hydrogen peroxide, permanganate, persulfate, percarbonate, ozone and RegenOx™). Due to the depth of dense nonaqueous phase liquid contaminant plumes, the treatment of the groundwater can be very expensive. More and more of sites with those types of contaminants are utilizing groundwater containment and barrier systems as the preferred remediation technology, instead of the traditional pump and treat technologies.

A cap utilized as a remedial technology can prevent exposure of the contaminants to people, animals and the environment. Caps are traditionally utilized at landfills.

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A Vapor Intrusion Assessment (VIA) consists of working through four tiers as follows;

Tier 1 – Initial (non-invasive) Screening
Tier 2 – Semi-Site Specific Numerical Screening
Tier 3 – VIC Assessment
Tier 4 - Mitigation

The VIA process is tiered so that properties with a low risk of vapor intrusion would be screened out quickly and inexpensively as the data justified. The first two tiers of the process are used to determine whether a potential for VIC exists and if so, the third tier is designed to provide confirmation that a VIC exists or to reduce the level of uncertainty. The fourth tier provides general mitigation alternatives.

Mitigation of identified VIC can be performed in several ways dependent on the type or stage of building construction.

EMC has experience in conducting all phases of VIA and we have completed projects using each of the above types of remediation methods.

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The Environmental Protection Agency defines innovative technologies as "'alternatives to land disposal' for wastes and contained materials that are inhibited by lack of performance data and cost." The field of remedial technologies is ever changing as new technologies are discovered and old technologies are refined or utilized on new contaminants. EMC strives to stay current on the available remedial technologies for various contaminants.

PHYTOREMEDIATION
Phytoremediation is a set of technologies that use various plants to degrade, extract, contain or immobilize contaminants from soil and groundwater. The idea of using plants to change the environment has been around for awhile from when plants were used to drain swamps and to treat wastewater.

Plants are living organisms that require water, nutrients and oxygen. The pH, soil texture, pollutant concentration, salinity and the presence of other toxins must be within the limits of the plants’ tolerance for phytoremediation to be a viable remedial technology at the site. The soil, however, can be amended to add nutrients if necessary. The contaminants must be in the rhizosphere of the plants for uptake or treatment. Deep groundwater contaminants or leachate pond effluents can be treated if the water is pumped and then drip irrigated onto the plants. Trees are also being utilized to remediate deeper groundwater plumes.

Phytoremediation can be utilized at sites with large contaminated areas with huge remediation cost savings. Phytoremediation provides a ground cover that decreases the human exposure risk. Other advantages to this remedial technology are that there is a complete breakdown or immobilization of the pollutant, that the technology is aesthetically pleasing and considered a passive technique and that the soil is reclaimed for future use. Phytoremediation is most useful at sites with shallow, low levels of contamination. Some of the disadvantages to using phytoremediation is that the time to achieve clean-up levels may be longer than more conventional remedial methods. Also, the site must stay a “green” area and not redeveloped during the remediation time period.

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