Many environmental projects sooner or later will arrive at the remediation or clean-up stage of the project. The previous stage, often referred to as the groundwater characterization or hydrogeological stage , should have provided most of the necessary information on the contaminants present to design and implement a remediation solution for the necessary clean-up.
Litigation can evolve out of disagreements between joint-venture partners on clean-up approaches and associated costs, and alleged damages resulting from industrial operations. When attempting to clean up such spills, timely and comprehensive source control and associated hydrogeological investigations are needed once a release is detected. This includes:. Any remedial action initiated before the source is controlled is ineffective and has the potential of expanding the scope of the remedial action as uncontrolled sources continue to migrate in the subsurface.
Physical action, like excavation, is the usual approach to source control of small releases. Contaminated soils removed by excavation can be treated by disposal asphalt batching, daily landfill cover , or physical thermal desorption, or biological biopiles treatment. For larger releases, however, alternatives include free-phase LNAPL recovery, barrier installation, and hydraulic control of the groundwater plume.
A variety of single and multi-phase extraction techniques moves both liquid and gas phases to the surface for treatment. At the surface, dewatering and subsequent recycling treats the higher concentrations of recovered material.
Direct on-site thermal catalytic processes destroy lower concentrations and absorbents like Granular Activated Charcoal GAC polish the air or water before discharge. Over the past 20 years, most remediation involved the pump-and-treat solution. Although this type of system is expensive to operate over the many years required to remove the appropriate number of pore volumes of contaminated fluids, there were no alternatives to the approach.
The pump-and-treat system has undergone criticism because of its inherent inefficiency, more because of its cost to maintain than because there were alternatives in existence to the problem. Apparently, state and federal regulators are listening to the industrial complaints because some projects have been halted or terminated as a result, leaving significant contamination in the ground.
In recent years, however, EPA has encouraged the development of new remediation technologies in order to reduce the cost and duration of clean-up projects. Many such technologies are showing promise. Field tests and scaled-up tests are under way and are gaining support from regulators. The National Contingency Plan NCP encourages the use of new technologies and any reasonable attempt to reduce high concentrations of contaminants present which serve as sources of continuing contributions to plumes of dissolved-phase constituents.
For dealing with the truly difficult contaminants like the DNAPL group, such modifications include: in-situ enhanced bioremediation, solvent flushing, steam flushing, or a combination of all three. The fact remains that the old, inefficient, and costly pump-and-treat system still serves remediation projects as the core technology. The other aspects of the newer technologies are important, but only enhancements to existing technology.
Measured against some unknown but anticipated standard, they are still inefficient and costly, and a long-term solution. Incremental improvements will be realized. For the light hydrocarbons the LNAPLs and light, dissolved hydrocarbons , natural attenuation has its merits in many cases. So, fluid removal pump-and-treat , combined with new enhancements, will also probably continue in many cases.
The design of such pump-and-treat systems, even with enhancements, still require a knowledge of subsurface conditions. Hydrogeologic assessments of subsurface conditions are tedious and costly to perform, but they form the foundation of all pump-and-treat, and other remediation systems. In the recent rush to by-pass appropriate characterization of contaminants present in the subsurface, such short cuts may have contributed to the blanket criticism of the pump-and-treat technology.
In reality, the approach is all we have to bring to bear on the problems at hand today. Expectations of new technologies will be realized in due course. In the meantime, incremental enhancements of the standard technology will have to suffice until the new technologies can be brought into play. Optimizing the data from contaminant characterization, combined with realistic approaches toward groundwater modeling and contaminant fate and transport modeling, form the basis of the operation and maintenance of such remediation systems.
Improvements in equipment designs and sizing, combined with improved materials lifetimes pumps, piping, valves, etc.
The advancement of knowledge in the design and operation of remediation systems depends to a large extent on how effectively the case histories of such systems that are presented in the professional literature are integrated into the engineering and design of the systems. Many case histories are overviews of projects, many others are detailed in some aspects but lacking in detail in other aspects. These features are usually intended to avoid criticism or to avoid implicating the budget numbers for fear of criticism from competitors or clients.
The value of the technical literature, however, cannot be understated. It is being ignored by many professionals in the remediation field today. Many professionals prefer to continue re-inventing the wheel, at the expense of industry. However, subsurface clean-up incorporating microbiological processes and wells as delivery and recovery systems have made substantial advances over the past few years. The bioremediation discipline is a multidisciplinary field led by microbiologists and supported by a range of other professionals. Working closely with remediation engineers, microbiologists have developed bioremediation to a point now demonstrated to be effective in environmental cleanups throughout the country and overseas.
Many such projects have claimed successes, including bioremediation projects, but many successes are a result of volatilization, not to bioremediation per se. The primary need in bioremediation projects is to address hydrogeology issues, which will characterize the subsurface for use in designing effective bioremediation programs. Laboratory chemical analyses are used to characterize subsurface hydrochemical conditions, and a familiarization with biological processes in hostile, subsurface environments is important to resolve the numerous, complex issues involved in bioremediation. Hydrocarbons naturally degrade in the subsurface due to microbial-mediated reactions.
However, the reaction rates are slow because electron acceptors, like oxygen, are quickly depleted in contaminated groundwater and are slowly recharged. Contaminated groundwater has significant hydrocarbon concentrations but depleted electron acceptors, whereas the overlying unsaturated zone contains oxygen but lower hydrocarbon concentrations. Early response and intervention is the key to minimizing extent and costs of remedial action for gasoline and its components and is essential to protecting public health and the environment.
These laboratory tests were conducted at a range of temperature and at various geochemical conditions. The dimensions of the pilot-scale barrier at the Orivesi field site were designed on the basis of these laboratory experiments to ensure the removal of chlorinated solvents and their degradation products. Based on preliminary hydrogeological studies, the Asemanseutu aquifer at Orivesi was chosen for testing a pilot-scale granular iron PRB for remediation of chlorinated solvents. The aquifer had been contaminated with trichloroethene TCE and tetrachloroethene PCE , released from a dry cleaner that operated from until Due to the presence of a range of contaminants, the groundwater in the area has not been used for drinking water purposes since and the aquifer has been withdrawn from the list of classified aquifers since The extent of the contamination in Asemanseutu aquifer was studied in — The PRB construct was placed across the path of groundwater flow based on site investigations and groundwater modeling.
The PRB is a funnel and gate configuration with an additional control well.
Physical and Chemical Groundwater Remediation Technologies
In addition to hydrogeological site information, results from material and column tests were also used in dimensioning the PRB. The permeable barrier and the funnels were installed in summer at the south-east part of a ballpark situated m south of the dry cleaner. The performance of the PRB application and the removal of the contaminants in the aquifer were observed by the monitoring of the groundwater quality. Groundwater samples were taken from several observation wells once a month.
Samples were also taken via the control well from the observation tubes placed in the iron fill. The fracture zones in bedrock were filled with injection material to eliminate the contaminated groundwater's bypass below the PRB. It is possible to make a PRB work both hydraulically and remedially in Finnish hydrogeological conditions found in aquifers that are important for municipal water supply.
Though tetrachloroethene and trichloroethene degrade completely already in the beginning of the residence time in the iron fill and no remarkable bypass of contaminated groundwater from any side of the PRB has occurred, the influence of the remediated water on the groundwater quality in the downstream observation wells have appeared slowly by summer In addition to the chemical remediation also microbial activity affects the quality of the groundwater flowing through the PRB.
The changes in water quality in the PRB show that at least nitrate and sulphate reducing bacteria and methanogens were active. The field investigations, material studies and installation work comprise the main expenses of a PRB. The extent of the hydrogeological studies needed depend on the complexity of the area and the coverage of earlier investigations.
In eskers and end moraine formations with thick soil layers like those at the Orivesi field site, installation of a PRB is demanding and expensive. However, use of conventional groundwater treatment methods is ineffective at sites contaminated with chloroethenes. Even if a PRB was be the most cost-efficient method to treat the contaminated groundwater, due to the high costs of earthworks, a continuous reactive barrier would probably not come into question at areas with soil layers thicker than 10—15 m.
Groundwater Remediation Treatment Methods | Adedge
The PRB method is well suited for groundwater remediation in smaller-scale formations where hydraulic conductivity is 10 -4 —10 -6 m s-1 in order of magnitude and where both total soil layer and saturated zone thicknesses are less than 10—15 m. Temperature is a factor to be taken into account upon testing the reactivity of Finnish materials. For dimensioning a PRB, groundwater from the actual field site should also be used in the material tests to gain realistic estimates of the need for residence time and to assess the potential material passivation or mineral precipitation that might affect the long-term performance of the barrier.
In the Orivesi project, traditional open pit and cleat-supported excavation techniques were practically the only available earthwork methods. Suitable modifications to grouting equipment are probably the easiest way to enable passive methods using reactive material to treat contaminated groundwater flowing deep in the ground. Moreover, applying grouting, deep stabilization or various pile driving methods would enable the installation of PRBs in areas with limited access due to housing etc.
The results of the project can be used by environmental authorities and consultants in planning remediation procedures at the contaminated aquifers. The results are also applicable in other countries with similar climatic and geological conditions. Start year End year Stage Completed. The specific objectives of the project were: to study the performance of permeable reactive barriers PRB for the remediation of contaminated groundwater in Finnish climatic and geological conditions by installing and monitoring a granular iron barrier; to test the reactivity of Finnish granular iron materials with chlorinated solvents at a range of temperatures and under various geochemical conditions and to create test methods for PRB materials; to develop criteria for potentially feasible applications of PRBs.