MIL-HDBK-1005/7A
6.12.2.5 Chemical Feeder Capacity and Standby Requirements.
Base feeder capacity on maximum expected instantaneous flow and
dosage. Essential (noninterruptible) chemical feeders such as
disinfection units must have a standby unit having capacity
equal to the largest unit. The need for standby units or other
treatment processes depends on raw water quality. Where two
chemical feed systems could use the same spare chemical feeder,
one standby unit to serve both is adequate. Refer to
EPA-430-99-74-001, Design Criteria for Mechanical, Electrical
and Fluid System and Component Reliability .
6.12.3
Sampling. Except where raw water quality is highly
variable during short time periods, composite sampling is
usually not necessary for raw water. Composite sampling or
continuous monitoring may be desirable for certain parameters in
treated water, such as turbidity. Turbidity, chlorine residual,
suspended solids, alkalinity, hardness, fluoride, and pH are the
normal process control variables in potable water treatment.
These are measured at least once per operating day. Other
parameters that are measured quarterly, or annually are total
trihalomethanes (TTHM), heavy metals, specific herbicides,
pesticides and synthetic organics, and total organic carbon
(TOC). Frequency of sampling these parameters depends on local
conditions and regulatory requirements. Sample for Total
Coliform as per U.S. EPA requirements as stated in 40 CFR Part
141.
6.12.4
Analytical Methods. Refer to APHA Standard Methods
for the Examination of Water and Wastewater and AWWA Manual M12,
Simplified Procedures for Water Examination, for laboratory
procedures. In addition to standard laboratory methods,
continuous monitoring is often required or desirable for certain
water quality parameters.
6.13
Metering, Instrumentation, and Control. Refer to
Water Treatment Plant Design, Chapter 20, "Process
Instrumentation and Controls," AWWA, third edition; AWWA Manual
M2, Automation and Instrumentation; and AWWA Standard Series
C700, Meters .
6.13.1
Guidance. Devices and systems should be as simple as
possible. In any installation or facility, equipment
procurement should be limited to the smallest practicable number
of manufacturers.
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