Selecting the Remedy

A formal three-phase procedure for identification and evaluation of remedies is presented in "Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA" issued by the USEPA in October 1988. This procedure can be overly prescriptive and rigid if misinterpreted; however, it does facilitate the development of appropriate remedial alternatives for a given site. Unfortunately, in the absence of the proper context, criteria, and objectives, it is easy to follow this procedure through the development and selection of extremely expensive and unnecessarily complex and burdensome remedies.

The first step in the remedy selection process is a basic understanding of the problem—the nature and extent of contamination. It is not necessary to have completed the problem definition phase, known as the Remedial Investigation (RI), to begin to develop and evaluate solutions, that is, remedies. In fact, it is beneficial to begin to focus on the remedy as soon as there is a basic understanding of the site contamination and remedial objectives. This "early focus on the remedy" allows the problem to be defined in the context of the possible/probable solutions. This serves to streamline the RI and ensure that those conducting it obtain the site and contaminant information necessary to properly assess and select an appropriate remedy.

The initial information should define the media affected by contamination—groundwater, soil, sludges; the basic geology and hydrogeology of the site, and the type of contaminants— volatiles, semivolatiles, pesticides/PCBs, and inorganics. A preliminary assessment of whether or not there are active source areas of ongoing contaminant migration is very important at this early stage, as it will be one of the main factors to consider in the remedy evaluation process. In addition, one will need a preliminary assessment of the real risk imposed by the site contaminants. This will form the beginning steps of what is known as a "baseline" risk assessment, which will prove essential in proper and informed remedy selection.

Evaluating Remedial Technologies

Once you know these factors, you can begin to target the types of remedial technologies that will abate specific unacceptable conditions and satisfy remedial objectives. Each type of problem can be addressed by a technology or linked technologies. It is vitally important to build an array of remedial technologies beginning with one that ensures satisfaction of the protective-ness criterion for the targeted problem. This is often the least controversial criterion, as all parties in a remediation project are interested in ensuring protection of human health and the environment. Assumptions made in calculating risk to assess protectiveness are sometimes the subject of disagreement between the agencies and the owner, but the concept of protectiveness is rarely in dispute. Many of the other evaluation criteria are the subject of greater disagreement. Therefore, it is a good practice to identify a limited set of technologies that arguably achieve the protectiveness goal.

The potential remedies may fall into one or more of the following categories of remedial technologies presented in Section IV: no action, institutional actions, containment, removal, treatment, and disposal. Initially, one or more of the remedial technologies from these categories should be considered. At the early stages of the remedial investigation, one can afford to be somewhat broadbased in assessing which remedies show real promise in achieving the remedial objectives, including cost. However, it is a good idea to streamline the target remedies as soon as possible. Concurrent progress on the RI effort will help in the streamlining process.

Once a focused set of technologies and remedies have been tentatively identified that satisfy the protectiveness criterion, they must be compared to the additional criteria to see if the remedies are still in compliance. If the remedies do not comply with successive criteria, they must be modified or additional remedies developed as necessary to ensure satisfaction of the criteria.

After a targeted subset of remediation categories are identified, the next step is to define the basic method, or subcategory, within that category. That is to say, if treatment is one of the targeted categories, one must then identify whether that is best achieved through physical/ chemical, chemical, biological, or thermal treatment technologies.

The next step is to define the particular technology or process within the subcategory just defined. For example, within the physical/chemical subcategory for treating groundwater, there are several choices: air stripping, steam stripping, vacuum-enhanced stripping, carbon adsorption, resin adsorption, or other. For soil remediation within the physical containment subcategory, choices include clay cap, RCRA (layered) cap, soil cover with synthetic membrane, simple soil cover, and others.

Some practitioners will take the position that refinement of the remedy to the level displayed above should be deferred until the remedial design (RD) stage. However, the RD stage comes after the remedy is selected. At that point the flexibility to refine or modify the remedy is minimal and is burdened by regulatory procedural limitations. Therefore, it is advantageous to evaluate remedies down to the specific technology stage prior to remedy selection. This will sometimes require that treatability studies be conducted. This effort should also precede remedy selection.

It is more difficult and requires more skill and knowledge to evaluate specific technologies in the feasibility study (FS) stage and still maintain a focused and limited set of alternative technologies; however, that is the best way to lead to the selection of the optimal remedy; one that meets the remedial objectives including cost-effectiveness. It is often true that a wide array of technologies can be "made to work" at many sites. This reflects the concept of possible versus necessary. The goal of the technology evaluation and selection process is not just to identify any workable technology but to define the most balanced remedy.

Evaluating Remedial Alternatives

A remedial alternative is the combination of remedial technologies that have been targeted to address the sum of the individual problems at a site. Many times, it is appropriate to modify one or more component remedial technologies or partial remedies because of beneficial or negative "side effects" resulting from the combination of component remedies. For example, suppose there are two types of sludges on a site and the optimal technology for each is different when viewed separately. However, the volume of sludge A is five times that of sludge B. If sludge B is amenable to treatment via the targeted technology for sludge A, it may be more cost-effective overall to combine sludges A and B and treat them by the sludge A method, even though there is a more efficient technology available for sludge B. Overall, the elimination of the sludge B technology is likely to more than pay for the increased volume to be handled by the sludge A technology.

To put remedy selection in a logical context, it is useful to array the remedial alternatives as a function of residual site risk versus total cost. This is shown graphically in Figure 1. This "cost-risk" curve, when calibrated to an actual site, is a powerful tool that clearly shows the choices available and their implications. If implementation of alternative A yields an acceptable residual site risk, then it should be chosen unless there are compelling and rational reasons to implement one of the other alternatives. The graph clearly demonstrates that the residual risk curve approaches an asymptote at some point while total cost continues to increase dramatically with respect to risk. This is the point of diminishing returns concept previously mentioned.

After protectiveness is ensured, there are two of the remaining eight criteria that tend to move the "acceptable" remedy from left to right on Figure 1: compliance with ARARs and long-term effectiveness and permanence.

An often-quoted rule of thumb is that if it costs X dollars to achieve protectiveness, it will cost 3 X 5X dollars to achieve compliance with ARARs and 10-15X dollars to achieve "permanence" (when is viewed as "destruction" of contaminants). This is why it is essential to begin by developing remedies that achieve the initial threshold criterion, protectiveness. Then expand or modify the remedy, only as necessary, to progressively comply with the additional criteria. This "bottom-up" approach is the best way to ensure compliance in the most cost-effective manner achievable. Unfortunately, many remedies are selected on the basis of a "top-down" approach, which tends to result in unnecessarily expensive remedies. If you define a 15-20X remedy first, nearly all other remedies could be viewed as relatively cost-effective.

One of the fundamental areas of controversy in remediation projects between owners or PRPs and regulatory agencies is this cost escalation after protectiveness has been ensured. The disagreements essentially center around the argument that what is protective today may not be so in the future, especially if proper controls are not maintained.

Estimated Remediation Costs, Millions of Dollars Figure 1 Representative cost-residual risk relationship.
0 0

Post a comment