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DESIGN AND CONSTRUCTION 3.5

Regular meetings should be held with the owner during preliminary design to discuss
design issues and update the client on the process of design. Design disciplines pertain-
ing to design issues being discussed should be involved in client meetings whenever pos-
sible. Involving the regulatory agencies that will need to approve the project may also be
beneficial to the design effort. Quality control reviews should be conducted of the pre-
liminary design by a team of design professionals independent from the design team.
Value engineering is often conducted before the beginning of the final design to eval-
uate the cost-effectiveness and constrnctability of the preliminary design. At this stage of
design, value engineering focuses primarily on major design elements, such as number
and size of treatment units, plant layout, design parameters, and support facilities. The
value engineering comments should be reviewed with the owner and design team to de-
termine which ideas will be incorporated into the design.
During preliminary design, a preliminary cost estimate for the water treatment plant
project should be prepared to ensure that project cost is within the owner's budget estab-
lished during earlier feasibility studies. Cost estimates are important for (1) making deci-
sions between viable plant alternatives, (2) finalizing the treatment process train, and (3)
planning the project's budgeting and financing. The cost estimate should provide a break-
down of costs for each major component of the project. A construction contingency of
15% to 25% is usually included in the cost estimate at this stage of design to provide for
unforeseen costs not identified in a preliminary estimate.

FINAL DESIGN

The final design phase is initiated after completion of preliminary engineering and docu-
mentation of design decisions, obtaining approval of review agencies, and securing proj-
ect financing. The design criteria and schematics developed in preliminary design will be
used to guide the development of detailed drawings and specifications, modifying the pre-
liminary design only as needed to accommodate the other design disciplines.

Production of Design Documents
Final design involves preparing detailed drawings and specifications within the project
framework established during preliminary design. Contract documents must also be pre-
pared that establish the bidding and contractual requirements for the construction of the
plant facilities.
Drawings and Specifications. The final design drawings and specifications preparation
must take into consideration a number of constraints and requirements not identified in
the preliminary engineering phase. Treatment process design should be completed in
greater detail before the support disciplines undertake final design. Critical design ele-
ments that should be completed early in final design include

• Selecting process equipment to be installed, including equipment sizes, weights, utili-
ties required to support the equipment, equipment control requirements, access re-
quirements for maintenance, and provisions for variations in the requirements of equip-
ment from different manufacturers
• Delineation of ancillary facilities required, including piping, valves, chemical systems,
controls, pumps, and other equipment