There are two types of decision scale, block scale and site scale. These parameters only apply to remedial design and to cost benefit analysis.
· Block Scale
With block scale, each block within the contour map will be remediated if it fails to pass the "criteria". For inverse distance, nearest neighbor, and natural neighbor interpolants, this "criteria" is simply the concentration or analysis-based decision basis. For ordinary kriging and indicator Kriging interpolants, the decision "criteria" is the decision basis value plus the level of confidence the user set for remedial design.
Confidence
Under ordinary kriging or indicator kriging with a block scale decision framework, enter the level of confidence to successfully remediate the site to meet the remedial goal (risk or concentration). For example, .90 means that all blocks with greater than 10% chance of exceeding the goal are included in the area of concern. A value of .50 corresponds to an area of concern based solely on the estimated values as seen in the estimation maps. At this point, there is no available method for determining the confidence one may have about the average of a group of correlated blocks exceeding the criteria with site scale.
· Site Scale
With this choice, the decision basis is applied to the entire site. If polygons are present, then the "criteria" applies to the interior of the polygon. Under site scale, the blocks are remediated by replacing the contoured value with the post remediation concentration. This process is implemented from most contaminated blocks to least contaminated blocks until the site average falls below the decision criteria. For certain choices of clean-up goal and post remediation values, a remedial design may not be possible. It is not necessary, however, that the post remedial concentration be less than the decision goal. For pooled data, the individual post remediation concentrations for each contaminant are used, and a resulting risk value from these pooled post remedial values is generated.
Post Concentration
This value is always used when site scale is chosen. Site scale calculates the average remaining concentrations over the site. Under this circumstance, one must consider the amount of contamination left in each block or artificially placed there by a back fill process. Given certain values for the decision goal, certain choices for post remedial concentration may lead to impossible remedial designs (e.g., a site decision goal of 1 and a post remedial concentration of 10,000). It is not necessary, however, that the post remedial value be less than the site decision goal. For example, one may begin with a site average of 5 and a maximum block value of 10. Depending on how the rest of the block values are distributed, a post remediation value of 6 may successfully bring the site average down to 5. Clearly though, the post remediation value must be less than the maximum block value.
This parameter is not used in the block scale method since the goal is to remediate each block below the decision criteria. Clearly, if the post remediation value is greater than the goal, then the block goal will never be achieved. On the other hand, if the post remedial value is less than the decision goal, then the remedial design can succeed. There are no other options.
Cost per Block
This box defines the cost to remediate one block as defined by the step Set cost information.