In its coarser form, cost accounting utilizes more aggregated estimates that are for groups of pay items rather than for individual pay items. Average cost values may be used, but a more reliable method would be to develop cost models as a function of facility attributes subsurface conditions, and geographical region. There may be other variables, depending on whether the costs being estimated are initial construction costs or whether they are costs incurred over the remaining life of the facility. The time-related variables (such as accumulated environmental and traffic effects) have little or on influence on initial construction cost but significantly affect subsequent costs/
At another level of disaggregation, average cost values and cost models can be developed for each treatment (a specific agency activity) that is comprised of multiple pay items or for each pay item.