Remediation Strategies

Another attractive feature of CD molecules is the availability of numerous hydroxyl groups for chemical modification. The total number of OH groups on each CD molecule is considerable and varies with the size of the specific CD ( -CD = 18, j3-CD = 21, y-CD = 24) thus, the number of possible derivatives is nearly limitless (Szejtli, 1998). Examples of conversion of the OH group to the following functional groups have been reported iodide, azide, thioacetate, hydroxylamine. 

The electrochemical reduction and oxidation of CDs has not yet been fully investigated. A preliminary study by Kessler et al (2004) has shown the potential for various types of CD molecules to degrade in the presence of an electric field. 

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These explanations do not exhaust the possibilities with regard to underlying causes, but they do illustrate an important point the analysis of human error purely in terms of its external form is not sufficient. If the underlying causes of errors are to be addressed and suitable remedial strategies developed, then a much more comprehensive approach is required. This is also necessary from the predictive perspective. It is only by classifying errors on the basis of underlying causes that specific types of error can be predicted as a function of the specific conditions under review. 

The last category of techniques are various forms of checklists of factors that can influence human reliability. These are used mainly in a proactive auditing mode. They have the advantage that they are quick and easy to apply. However, considerable training may be necessary to interpret the results and to generate appropriate remedial strategies in the event that problems are identified. 

Checklists are quick and easy to apply. The answers to the questions in the checklist provide insights into remedial strategies. 

The overall conclusion that can be drawn from a survey of CPI data collection systems is that the better systems do attempt to address the causes of human error. However, because of the lack of knowledge about the factors which influence errors, the causal information that is collected may not be very useful in developing remedial strategies. General information in areas such as severity, work control aspects and the technical details of the incident will be required in all data collection systems. However, in almost all cases a structured process for causal analysis is lacking. Some of the requirements for causal analysis are set out in the following sections. 

The overall process of data interpretation and the development of suitable remedial strategies once a set of causes has been identified, is set out in Figure 6.4. The two-stage process of confirming the initial causal hypothesis is recommended to overcome the tendency to jump to a premature conclusion and to interpret all subsequent information on the basis of this conclusion. 

FIGURE 6.4. Data Interpretation, Remedial Strategy Generation, and Implementation. 

This stage is used to develop remedial strategies, based on the findings of... 

Evaluate Effectiveness on the Basis of Outputs and Acceptance Once the system has been implemented on its chosen site, its effectiveness needs to be evaluated at frequent intervals so that corrective action can be taken in the event of problems. The first criterion for success is that the system must generate unique insights into the causes of errors and accidents, which would not otherwise have been apparent. Second, the system must demonstrate a capability to specify remedial strategies that, in the long term, lead to enhanced safety, environmental impact and plant losses. Finally, the system must be owned by the workforce to the extent that its value is accepted and it demonstrates its capability to be self-sustaining. 

Three major themes have been emphasized in this chapter. The first is that an effective data collection system is one of the most powerful tools available to minimize human error. Second, data collection systems must adequately address underlying causes. Merely tabulating accidents in terms of their surface similarities, or using inadequate causal descriptions such as "process worker failed to follow procedures" is not sufficient to develop effective remedial strategies. Finally, a successful data collection and incident investigation system requires an enlightened, systems oriented view of human error to be held by management, and participation and commitment from the workforce. 

Where a specific incident leading to safety, quality or production problems has occurred, the plant management may wish to perform a very focused intervention. This will be directed at identifying the direct and underlying causes of the problem, and developing an appropriate remedial strategy. The process for performing an analysis of this type is described in the incident analysis section of Chapter 6. 

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

The remedial strategies of concern focus on how to select a remedial method and how to complete the remediation at the most effective cost. 

Hauser, V.L., Gimon, D.M., Hadden, D.E., and Weand, B.L., Survey of Air Force Landfills, Their Characteristics, and Remediation Strategies, Air Force Center for Environmental Excellence (AFCEE), Brooks AFB, TX, 1999. 

A more in-depth discussion of the subsurface hydrogeologic setting, areal extent of LNAPL and dissolved hydrocarbons in groundwater, remedial strategy, and current status is presented in Chapter 12 (LNAPL Recovery Case Histories). 

Testa, S. M., 1990, Light Non-Aqueous Phase Liquid Hydrocarbon Occurrence and Remediation Strategy, Los Angeles Coastal Plain, California In Proceedings of the International Association of Hydrogeologists, Canadian National Chapter, on Subsurface Contamination by Immiscible Fluids, April, in press. 

Residual hydrocarbons will continue to serve as a source of groundwater contamination thus, remediation strategies for DNAPLs should emphasize long-term control and management (i.e., source containment, pool control, and recovery) vs. short-term fixes. Regardless of an increased level of effort (i.e., additional wells, increased pumping rates, etc.), the overall time for remediation is not expected to shorten by more than a factor of five. 

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