Ground-Water Remediation Design, Operation and Maintenance

Most 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 ground-water 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, alleged damages resulting from industrial operations, and even as a result of the consultant's handling of the clients environmental characterization and monitoring activities.

As indicated, any of the above activities can be involved in litigation. Inappropriate or misrepresented data or methods are, in many instances, the basis of litigation involving activities conducted within the discipline involved, practiced in some cases by unqualified individuals not having appropriate training and experience and the associated professional geological and hydrogeological certifications and/or state licenses.

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. These complaints have developed into a chorus of resistance to continuing the approach on the basis that it doesn't work and it is too costly.

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.

The "new" technologies in ground-water remediation more often consist of modifications to the pump-and-treat system than of new technologies. 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. But, there are no other solutions on the immediate horizon, with the exception of the final solution: "natural attenuation." This solution may be appropriate for some contaminants but not for recalcitrant contaminants.

For the light hydrocarbons (the LNAPLs and light, dissolved hydrocarbons), natural attenuation has its merits in many cases. Some of the BTEX family, and MTBE is a cousin of it, may not degrade as well as at first believed. 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 (John Cherry and others). 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 ground-water 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.), are also important features in project operation.

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, can not 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.

Substantial information is available from the numerous federal agencies involved in clean-up activities. State standards for ground-water clean-up are published yearly by the Journal of Soil Sediment & Ground Water; click (here) for a summary of their reports. Another source of technical information is the searchable database produced over the years since 1972 by the National Ground Water Association. For the cost of membership only, more than 70,000 papers, publications, and texts are searchable by key words.

Bioremediation

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 volatilation, 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.

Gasoline spills (including MTBE, TBA, etc.) are common and can cause water contamination issues as hydrocarbons dissolve in ground water and travel offsite in the aquifer. 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 ground water and are slowly recharged. Contaminated ground water 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.

Source Control
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:

· Immediate control and cessation of the release,
· Repair or removal of the release source (tank, pipe, flange, pump, etc.),
· Removal / recovery of free product in both the saturated / unsaturated zones, and
· Removal of residual free product from the subsurface soils.

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 ground-water 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.

From Technology to Techniques
Two major objectives of site remediation include destruction of residual or dissolved gasoline constituents or their removal from the impacted area. Destruction can range from total mineralization/oxidation or reduction to inorganic components or transformation to some unlisted form. Chemical reaction, biological means, or thermal processes accomplish destruction. This is a brief description of the myriad of innovative techniques developed to refine and enhance the implementation of four basic technologies that have evolved for the active remediation of gasoline released to the subsurface:

1. Subsurface ventilation
2. Pump-and-treat technology
3. In-situ chemical oxidation
4. In-situ bioremediation

Visit the Institute of Environmental Technology's Web Resource Portal for more resources concerning Remediation.