MIL-HDBK-1005/16
filters or stabilization ponds. Also, some treatment facilities
have multiple treatment units, bypass and recycle streams, and
other features that need to be considered when designing a
sampling system.
11.4.1
Selecting Sample Locations. Consider the following
five points when selecting locations for sample collection:
homogeneity, wastewater characteristics, water quality
degradation, flow measurement, and convenience. Each factor is
discussed below.
11.4.1.1 Homogeneity. Take samples from waters that are well
mixed. Areas of high turbulence and hydraulic jumps are usually
good sample sites. Take samples in the center of channels, where
velocity is highest and the possibility for solids settling out
is lowest. Avoid locations immediately upstream of weirs, where
solids tend to settle. Also avoid locations of different
densities and locations where oils and floatable matter tend to
collect.
Sample taps on pipes should be placed on the side of
the pipe in a horizontal run following a 90-degree bend, tee, or
valve that will produce turbulence and mixing. Avoid placing
sample taps on the bottom of any pipe or at the top of large-
diameter pipes that may not always be full. For large-diameter
pipes (greater than 18 inches [450 mm]) and all tanks, the sample
tap should extend toward the center of the pipe or tank, where
the samples tend to be more representative.
11.4.1.2 General Characteristics of the Wastewater. Collect
samples at representative sites in the individual wastestream.
For example, plant influent samples should be taken upstream of
the confluence with recycle flows. Effluent sampling locations
will be specified in the permit.
11.4.1.3 Water Quality Degradation. Consider the need for
sample preservation. For example, refrigerated composite
samplers must have a reliable power source. Power failure should
trigger an alarm to alert operators.
11.4.1.4 Flow Measurement. Most sample sites, including all
influent and effluent locations, should be located where flows
are known or can be easily determined.
11.4.1.5 Convenience. Accessibility and practicability are
important but secondary to the preceding considerations.
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