INTRODUCTION

It has been said that construction cost estimating is more an art than a science. This is true only to the extent that application of science also requires the use of sound judgment and experience. While a thorough understanding of the process mechanical elements of a water treatment plant would appear to be the most important aspect in estimating its cost, it is only one discipline of a multidisciplined project.

All cost estimates will contain a certain amount of experienced judgment or educated guesswork concerning the various cost elements, which comprise the estimate. An order-of-magnitude or preliminary cost estimate may be based on all judgment, while a definitive level estimate may only require judgment for those cost elements with historical cost fluctuations.

As an example, an order-of-magnitude estimate may require sound judgment in the identification of a previous project with similar scope of work characteristics that will be factored to estimate the cost of the project in question. A definitive level estimate may only require judgment concerning specialized concrete forming labor with historically wide labor cost fluctuations, with all other elements being based on verified vendor quotes or historical cost data with minimal deviations.

The various types of cost estimates used are based on the level of project design, which defines the known scope of work. The scope of work can range from only a daily treatment flow rate and major process facilities, to a complete set of plans and specifications for construction.