2.3 Field Methods
61
much below the surface. Very shallow streams and seeps may require creative
approaches to collecting samples without disturbing sediment. It may be necessary to create a small dam that allows water to drop into the bottle. The bottle
cap, pipettes, syringes, or even plastic basters used for cooking can be cleaned
and used to transfer samples from the stream to the bottle in extreme cases.
One option, using a syringe (use a new syringe at each site), is as follows:
1. Rinse the syringe three times with stream water, downstream of sample site as usual.
2. Use the syringe to put stream water in the sample bottle and rinse the
sample bottle three times.
3. Finally, use the syringe to fill the bottle to the brim with stream water
at the sample site. Cap the bottle and proceed as usual.
2.3.2.1.3 Pole Samples
An alternative to collecting grab samples by hand is the use of a bottle attached
to a pole made of noncontaminating material such as smooth fiberglass or
painted aluminum. This approach is safer than leaning over the water surface
or wading and often allows the sample to be collected farther from shore and
at greater depth than can be done by hand. This approach is not suitable for
streams with significant velocity because of excessive drag from the assembly.
The collection bottle can be larger than the sample bottle and can therefore
contain sufficient water to rinse and fill it. Alternatively, the sample bottle itself
can be directly attached to the pole. Because of buoyancy and leverage, it may
be impractical to use a bottle larger than about 500-ml capacity and a pole
longer than about 3 to 4 m. The bottle can be attached to the bottom of the pole
with stainless steel hose clamps or laboratory three-finger-style bottle clamps.
To minimize the possibility of contamination with surface debris or floating
slush, and to allow collection at a specific depth, the bottle can be plugged with
a noncontaminating silicone stopper attached to a line that the sampler pulls
when the bottle is at the proper depth. The depth can be estimated or can be
measured with a simple float and line attached to the pole near the bottle. Care
must be taken to avoid introducing into the sample any soil or other debris that
may have accumulated on the pole; it should be rinsed in an area away from the
sampling site prior to use.
2.3.2.1.4 Deep Samples
If the stream is deeper than about 2 m, it is recommended to sample at about
0.5 m below the surface if logistics allow or to select a shallower sampling
site a short distance further up- or downstream. Sample collection at a depth
of 0.5 m can sometimes be achieved using a pole sampler (described in the
preceding section) or a Van Dorn sampler. The choice will depend on site
61
much below the surface. Very shallow streams and seeps may require creative
approaches to collecting samples without disturbing sediment. It may be necessary to create a small dam that allows water to drop into the bottle. The bottle
cap, pipettes, syringes, or even plastic basters used for cooking can be cleaned
and used to transfer samples from the stream to the bottle in extreme cases.
One option, using a syringe (use a new syringe at each site), is as follows:
1. Rinse the syringe three times with stream water, downstream of sample site as usual.
2. Use the syringe to put stream water in the sample bottle and rinse the
sample bottle three times.
3. Finally, use the syringe to fill the bottle to the brim with stream water
at the sample site. Cap the bottle and proceed as usual.
2.3.2.1.3 Pole Samples
An alternative to collecting grab samples by hand is the use of a bottle attached
to a pole made of noncontaminating material such as smooth fiberglass or
painted aluminum. This approach is safer than leaning over the water surface
or wading and often allows the sample to be collected farther from shore and
at greater depth than can be done by hand. This approach is not suitable for
streams with significant velocity because of excessive drag from the assembly.
The collection bottle can be larger than the sample bottle and can therefore
contain sufficient water to rinse and fill it. Alternatively, the sample bottle itself
can be directly attached to the pole. Because of buoyancy and leverage, it may
be impractical to use a bottle larger than about 500-ml capacity and a pole
longer than about 3 to 4 m. The bottle can be attached to the bottom of the pole
with stainless steel hose clamps or laboratory three-finger-style bottle clamps.
To minimize the possibility of contamination with surface debris or floating
slush, and to allow collection at a specific depth, the bottle can be plugged with
a noncontaminating silicone stopper attached to a line that the sampler pulls
when the bottle is at the proper depth. The depth can be estimated or can be
measured with a simple float and line attached to the pole near the bottle. Care
must be taken to avoid introducing into the sample any soil or other debris that
may have accumulated on the pole; it should be rinsed in an area away from the
sampling site prior to use.
2.3.2.1.4 Deep Samples
If the stream is deeper than about 2 m, it is recommended to sample at about
0.5 m below the surface if logistics allow or to select a shallower sampling
site a short distance further up- or downstream. Sample collection at a depth
of 0.5 m can sometimes be achieved using a pole sampler (described in the
preceding section) or a Van Dorn sampler. The choice will depend on site