Developing a Project Technical Criteria Document - Design-Build for Water and Wastewater Projects - page 166

is responsible for each anticipated permit. This allows the DB proposers to incorporate
the necessary time and staff into the project schedule and scope, respectively.
Design Criteria
Information that is typically included in the design criteria section is discussed herein.
Definition of flows and loads. The primary purpose of defining flows and loads is
to clearly establish plant capacity and influent composition. The owner should outline the
required plant capacity and any considerations for future expansion or operability. For
example, if the facilities need to operate at half capacity during the winter, the number
of treatment trains in the facility and the allowable flow through the process basins or
equipment need to match the desired flow rate.
The owner should also clearly define a raw water quality envelope. This includes all
pertinent water quality characteristics (e.g., pH, alkalinity, temperature, etc.) that could
affect the design or the design-builder's ability to meet any performance guarantees. If his-
torical data available for the water or wastewater, the owner should have a statistical analy-
sis of the data, with averages, median, and 90th percentile values so that the facilities can
be designed to meet the water quality. Owners should offer as much data to the bidders as
are available, because more data provide more confidence that the design will accomplish
the treated water goals. This includes any analyses that were nondetected by analytical
techniques. This knowledge helps focus the design on the contaminants of concern.
If no data are available, the owner should begin a rigorous sampling program of the
source water so that the range of concentrations of pertinent water quality characteristics
is known. Owners can also contact other utilities with similar sources or estimate a range
for the design. This is important because any ambiguity in the raw water composition will
be viewed as a risk to the design-builder. They may choose to not propose on the project,
add cost to cover the risk, or over-design the facility—all of which are not beneficial to
the owner.
Design criteria and requirements for the main facilities. The primary system
design criteria are for the main treatment processes at the facility. The owner should
outline the requirements and options for these processes with either performance-based
or prescriptive criteria. For example, a conventional sedimentation basin design criteria
could be as follows:
1. Prescriptive: The dimensions of the basin should be 80 ft (24.4 m) by 100 ft
(30.5 m) by 22 ft (6.7 m) deep, with a maximum surface loading rate of 1 gpm/
ft 2 (2.4 m/h), or
2. Performance-based: The sedimentation process can be conventional or other
state-approved clarification should achieve less than 2 ntu in the clarified water
95 percent of the time.
These criteria are also impacted by secondary systems, such as chemical feed and any
recycle streams.
This section of the technical criteria document should also identify the minimum
requirements for future capacity and system redundancy. For example, some main unit
processes can have “stealth” capacity, meaning they could treat more flow if it was needed