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Conceptual Site Model Development

The conceptual site model synthesizes and crystallizes what is already known about a site that is pertinent to decision-making requirements.

The second step in the systematic planning process is the development of a conceptual site model (CSM). Using all available information and with the assistance of appropriate disciplinary expertise, the project team develops a CSM that distills what is already known about the site. The CSM, in turn, can then be used to identify what more must be learned in order to achieve project goals. There are several characteristics of CSM development and application that are important from a Triad perspective.

• A project's CSM may take any (or several) of a number of formats (or combinations of formats) that can effectively portray site concerns significant to the decisions that must be made. Formats are typically decision-need specific. For example, early in the site assessment process, a CSM may simply be a schematic of a site that indicates primary areas of concern along with accompanying text that describes for each area the basis for concern, sometimes accompanied by supporting information (e.g., photographs, interview information, site observations, process/infrastructure descriptions tied to the possibility of contamination being present, potentially pertinent regulations or regulatory guidelines, etc.). As a site moves to the equivalent of a remedial investigation and on to remediation, the CSM could possibly include a fate and transport model (numerical or analytical), a pathways analysis to support risk evaluation, if required, along with a supporting risk or dose model, a spatially correct electronic map of the site that incorporates pertinent contextual features such as roads, fence lines, building footprints, aerial photos, existing analytical data, pertinent infrastructure, topographical information, etc., a subsurface stratigraphic model, and possibly a depiction of where contamination is believed to exist at levels of concern, based on past sampling results.



• A project's CSM will evolve and mature as project work progresses. At any given point in time, the maturity of the CSM reflects both the level of site understanding and the amount of information and complexity of analysis required to support the decisions that need to be made. For sites with a long-term life-cycle (i.e., the characterization, remediation, and closure process will be measured in years), continuity in maintaining the CSM and carrying it forward as it evolves and matures becomes a critical management issue. The problem is two-fold. First, supporting technical contractors often have preferred software systems for developing and maintaining CSMs. These systems may include proprietary components. It is extremely important that project managers identify CSM specifications and deliverables that will facilitate the maintenance of the CSM even if contractors change. This can include identifying early on the spatial coordinate system that will be used for all data sets produced and delivered (e.g., State Plane feet NAD83), the base mapping system to be used (e.g., AutoCad, ArcView, MapInfo, etc.), electronic data deliverable (EDD) formats for all analytical data, etc. The second issue is staff related. A CSM is an electronic/hard copy snapshot of site conditions that really is a reflection of the understanding of core team members at a particular point in time. Loss or replacement of core team members over the life of a project, while at times unavoidable, can have significant impacts on CSM maintenance. This is especially problematic when the lost core team member is the project manager.



• A sufficient CSM not only captures what is known about the site, but also supports the evaluation of the uncertainty associated with decision-making based on what is currently known. Managing decision uncertainty will be discussed later in this section. Uncertainty may be addressed in a qualitative fashion, using a weight of evidence approach, or it may be more quantitative in nature, using statistical techniques and statistical concepts. The evaluation of uncertainty is an extremely important point of concurrence for the Triad project team. The result of an uncertainty evaluation may be that a decision can be made based on existing information as embodied in the CSM. Alternatively, the result may identify data gaps that, if addressed by additional data collection, would allow decision-making to go forward.



• For those decisions that would be made with an unacceptable level of uncertainty if only existing data were used, the CSM should provide the foundation for developing information-gathering programs to reduce decision-making uncertainty to acceptable levels. The CSM should lead to hypotheses or statements that are "testable" or verifiable via data collection (e.g., contamination levels within a particular decision unit do not satisfy cleanup requirements). From a Triad perspective, the CSM should do this in a manner that supports a dynamic work strategy for resolving those uncertainties. This assumes that the CSM can and will be updated and refined as activities that are part of the dynamic work strategy produce new information. The design of dynamic work strategies and their linkages with underlying CSMs are discussed in greater detail in the section entitled Dynamic Work Strategies.

The CSM can also serve several supporting roles in the implementation of a Triad approach. These include educating stakeholders, identifying required technical expertise, screening applicable analytical or characterization technologies, refining project strategies, identifying potential regulatory drivers, selecting points of compliance, estimating dose or risk and deriving risk or dose-based cleanup criteria, supporting cost estimation needs, evaluating and implementing remedial alternatives, guiding sampling efforts, visualizing contamination distributions, and supporting site closeout.

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