Page 39 - Water and Wastewater Engineering Design Principles and Practice

1-10 WATER AND WASTEWATER ENGINEERING

consent as they deem fit. This is not to say that the client must consent to the selection of every

nut and bolt in the project, but rather that critical decision points must be identified for the client.
At these decision points the client must be provided enough information to allow rational deci-
sions. This information should include the alternatives, the consequences of choosing one alter-
native over another, and the data and/or logic the engineer used to arrive at the consequences.

1-5 OVERALL DESIGN PROCESS
Project Design and Construction Delivery Processes
The design process is not like a computer program that is executed exactly the same way for
every project. The process described here is an overview of the classical engineering approach
to design- and construction-related activities. In this approach, vendor-furnished equipment is
procured according to performance or prescriptive specifications through contractors who are
bidding from drawings and specifications prepared by a consulting engineer. All funding and
ownership of the facilities rest with the owner in the classical approach. In actual practice some
of the steps described below will be bypassed and others, not described, will be inserted based on
the experience of the designer and the complexity of the design.
Other approaches to the design and construction process include (1) design-build, (2) con-
struction management-agent, (3) construction management-at risk, (4) design engineer/
construction manager. These alternative approaches are discussed at the website http://www.
mhprofessional.com/wwe .
The classic design procedure includes the following steps:

• Study and conceptual design
• Preliminary design
• Final design

These steps will be examined in more detail in the following paragraphs. Each of these steps
forms a major decision point for the owner. He or she must be provided enough information to
allow a rational decision among the alternatives, including the alternative to not proceed.
The design process is iterative. Each step requires reevaluation of the design assumptions
made in previous steps, the ability of the design to meet the design criteria, the compatibility of
processes, and integration of the processes. At key decision points, the economic viability of the
project must be reassessed.

Study and Conceptual Design
In this phase of the design, alternatives are examined and appropriate design criteria are estab-
lished. It is in this stage of the project that alternatives to facility construction are examined. For
water supply, the alternatives to facility construction might include purchasing water from a
nearby community, instituting water conservation, or having individual users supply their own
water by private wells. For wastewater treatment, the alternatives to facility construction might
include connection to a nearby community’s system or controlling infiltration and inflow into
the sewer system. In addition, the null alternative, that is the cost of doing nothing must also be
considered.