Environmental Engineering Reference
In-Depth Information
4.3.3 Sediment Sampling
Sediment sampling is conducted with several types of specialized equipment. One instru-
ment commonly used is called a Ponar Dredge. A Ponar dredge is equipped with a set
of jaws and is deployed in the open position while being lowered through the water col-
umn until it becomes embedded into the bottom sediment. Once the instrument is pulled
upward with minimal force to avoid pulling it off the bottom, the jaws are engaged and
come together as the instrument is raised. This sequence of events traps sediment in the
instrument bucket. These types of samplers allow the collection of small or large samples
depending on the size of the bucket (USEPA 2007).
Another popular sediment sampler is called a tube or grab sampler; it consists of a hol-
low tube typically constructed of stainless steel, PVC, or Teflon (Capri et al. 2005). These
types of samplers are intended for collecting shallow sediment samples within water col-
umns of less than 1.5-3 m (5-10 ft). Proper function of these devices depends upon the
presence of a strong water current or other associated factors that may cause the sampler
to drift and not collect an appropriate sample size, or sample the wrong location.
4.3.4 Surface Water Sampling
Sampling surface water uses many of the same procedures as groundwater sampling. The
first step in sampling surface water is evaluating the morphology and hydrology of the
surface water body so appropriate sampling location(s) can be identified. Collecting an
appropriate and representative sample of surface water also depends upon the type of
surface water body; e.g., a lagoon, stream, lake, river, or spring.
Factors affecting sampling location include
• Chemical compounds of concern
• Depth of water body
• Flow rate
• Size
• Whether there is a specific location of concern
• Topography and composition of the bottom of the water body
Each surface water sample location should be marked and surveyed in case a future sam-
pling event is required. Placements of stakes, flags, or buoys are common ways to mark
surface water sampling locations. The elevation of a surface water body is also measured
during every sampling event to assess the current hydrologic conditions; e.g., drought or
flood. Placing a benchmark on a stationary object, such as the bottom or side of a bridge, at
the edge of a paved roadway, or building corner usually works.
In complex surface water settings, when measuring water quality data such as tempera-
ture, pH, and dissolved oxygen it helps to know if any stratification exists either horizon-
tally or vertically within the water column. Monitoring these factors improves the chances
you will select appropriate sampling locations and an effective number of samples.
Surface water samples can be collected using a glass tube, pumps, or bailers, or
obtained directly using a sample container as depicted in Figure 4.28. Specialized
surface water instruments include the Kemmerer Bottle, Bacon Bomb Sampler, or Dip
Sampler. These types of instruments are used from a boat or a bridge and are lowered
into the water column and can collect a water sample from any depth. The exception
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