12.6. Cost Estimation Methods in Drinking Water Technologies (WBS Approach)

Different models are used for estimating drinking water treatment system costs. Most of them has been developed for the evaluating cost and performance of the best available technologies for drinking water. To estimate treatment costs, EPA (United States Environmental Protection Agency) developed new cost modeling approach to developing unit costs for drinking water technologies The technique uses a work breakdown structure (WBS) methodology, which involves dividing technology into discrete components for the purpose of estimating unit costs. The models provide unit cost and total cost information by component. The models also contain estimates of:

• Add-on costs (such aspermits, pilot studies and land acquisition)
• Indirect capital costs (such assite work and contingencies)
• Annual operation and maintenance costs (EPA 2014) As with any technology treatment plant cost and operation scheme shown as follows Figure 12.4 under the model of the Work Breakdown Structure (WBS).

Figure 12.4 The structural features used to generate treatment costs in the WBS models (EPA, 2014)

Framework for Developing the WBS-Based Models Step 1: Identify the treatment requirements based on the contaminant requiring removal, the flow for which treatment is required, the influent water quality and treated water quality

[1] A work breakdown structure (WBS), in project management and systems engineering, is a deliverable-oriented decomposition of a project into smaller components. A work breakdown structure is a key project deliverable that organizes the team's work into manageable sections. The Project Management Body of Knowledge (PMBOK) defines the work breakdown structure as a "deliverable oriented hierarchical decomposition of the work to be executed by the project team." https://en.wikipedia.org/wiki/Work_breakdown_structure

requirement, and then select a treatment technology or combination of technologies capable of meeting the requirements.

Step 2: Develop the general design assumptions that apply to all the technologies (e.g., chemical storage capacity).

Step 3: Develop site- and technology-specific design assumptions that might affect treatment performance and, thereby, design requirements (e.g., assumptions related to influent water constituents such as alkalinity or water quality parameters such as pH).

Step 4: Construct a typical process flow diagram or P&ID showing the main unit processes for the technology and identify equipment requirements.

Step 5: Calculate the equipment requirements, including dimensions and quantities, for the core elements of each unit process. At each component (or group) level, identify choices of material (e.g., stainless steel or PVC pipe material).

Step 6: Link the treatment equipment requirements to a database that contains unit costs by equipment type, size and material. Multiplying the unit costs by the dimension and quantity requirements developed in Step 5 provides the component-level design costs.

Step 7: Tally the costs of the selected components to determine direct capital cost.

Step 8: Develop and add indirect and add-on costs to determine total system capital cost.

Step 9: Develop operation and maintenance cost estimates.