Water Chemistry Field Sampling
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location and sample collection logistics. Use of a Van Dorn sampler requires
low-to-moderate stream velocity and a stable position from which to collect
the sample, such as a bridge, raft, or float tube.
The water sample should be collected from a point where flow velocity is
high relative to other points along the cross section at the sampling location
and water depth is sufficient to submerse a collection device without disturbing bottom sediments. Side pools with low velocity or eddies should not be
used for sampling. Disposable, powderless latex, polyethylene, or nitrile gloves
should be worn while handling sampling equipment and collecting the sample
to reduce the chance of contamination. Care must be taken to avoid touching potential contaminating surfaces while wearing the gloves. Field personnel
should be alert to the possibility that some individuals are allergic to contact
with these glove materials.
A stream water sample can be collected from a deep stream at a specific
point along the channel cross section by (1) lowering a weighted collection
bottle with a handline, (2) collection with a discrete-volume water sampler, or
(3) drawing the water sample with a suction pump through a tube that is lowered into the water. The sample bottle should be rinsed with stream water three
times by partially filling the bottle, capping, shaking, and dumping. If wading
is required, and if it is both practical and safe at that location, the sampler must
stand downstream of the point of collection and avoid collecting particulates
resuspended by wading or bumping the streambed with the collector. Sample
collection with a tube and peristaltic suction pump can be useful when large
sample volumes are needed.
2.3.2.1.5 Autosampling
If high-flow events need to be sampled in a nonwilderness setting, in most
cases autosamplers should be used. Installation of autosampling equipment
is generally not allowed in a designated wilderness. If autosampling is done
during the winter at a location that experiences below-freezing temperatures,
the autosampler should be kept in a heated shelter to prevent collected samples
from freezing. In addition, the sampling tube should be buried between the
autosampler house and the stream to prevent formation of ice plugs in the tube.
Autosampling can be done with one of several types of commercially available autosamplers. All operate similarly and consist of a controller, a peristaltic pump, sample tubing that extends into the stream, and space-efficient,
custom-shaped sample bottles. The water sample is drawn through a weighted
suction head that is attached to the end of the tubing. The autosampler can be
set to collect at selected time intervals. This can reduce the frequency of site
visits. However, to collect samples timed to the hydrograph (plot of changes
in stream stage over time), the autosampler must be controlled by a programmable data logger that monitors water-level changes. Water level is most often
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location and sample collection logistics. Use of a Van Dorn sampler requires
low-to-moderate stream velocity and a stable position from which to collect
the sample, such as a bridge, raft, or float tube.
The water sample should be collected from a point where flow velocity is
high relative to other points along the cross section at the sampling location
and water depth is sufficient to submerse a collection device without disturbing bottom sediments. Side pools with low velocity or eddies should not be
used for sampling. Disposable, powderless latex, polyethylene, or nitrile gloves
should be worn while handling sampling equipment and collecting the sample
to reduce the chance of contamination. Care must be taken to avoid touching potential contaminating surfaces while wearing the gloves. Field personnel
should be alert to the possibility that some individuals are allergic to contact
with these glove materials.
A stream water sample can be collected from a deep stream at a specific
point along the channel cross section by (1) lowering a weighted collection
bottle with a handline, (2) collection with a discrete-volume water sampler, or
(3) drawing the water sample with a suction pump through a tube that is lowered into the water. The sample bottle should be rinsed with stream water three
times by partially filling the bottle, capping, shaking, and dumping. If wading
is required, and if it is both practical and safe at that location, the sampler must
stand downstream of the point of collection and avoid collecting particulates
resuspended by wading or bumping the streambed with the collector. Sample
collection with a tube and peristaltic suction pump can be useful when large
sample volumes are needed.
2.3.2.1.5 Autosampling
If high-flow events need to be sampled in a nonwilderness setting, in most
cases autosamplers should be used. Installation of autosampling equipment
is generally not allowed in a designated wilderness. If autosampling is done
during the winter at a location that experiences below-freezing temperatures,
the autosampler should be kept in a heated shelter to prevent collected samples
from freezing. In addition, the sampling tube should be buried between the
autosampler house and the stream to prevent formation of ice plugs in the tube.
Autosampling can be done with one of several types of commercially available autosamplers. All operate similarly and consist of a controller, a peristaltic pump, sample tubing that extends into the stream, and space-efficient,
custom-shaped sample bottles. The water sample is drawn through a weighted
suction head that is attached to the end of the tubing. The autosampler can be
set to collect at selected time intervals. This can reduce the frequency of site
visits. However, to collect samples timed to the hydrograph (plot of changes
in stream stage over time), the autosampler must be controlled by a programmable data logger that monitors water-level changes. Water level is most often