NSWC/WOL/TR 75-35 



sampling in reality is much more complicated than water sampling 

 because of the following reasons: 



(1) Sediment sampling is performed at or near the bottom of 

 the sampling site, which may be deep and inaccessible. Sampling 

 requires elaborate and heavy equipment. 



(2) Sediment is composed of various types of material with a 

 large size distribution range. Representative samples are difficult 

 to obtain. 



(3) Sediment sampling requires tedious steps in sample 

 processing and handling, such as extracting residual moisture from 

 core samples, transferring samples from samplers to storage con- 

 tainers, and preserving samples at freezing temperature. 

 Contamination and loss of samples may occur if they are not handled 

 properly. 



3.2.2 Sampling Techniques 



There are three types of sediment sampling, each one serving a 

 particular purpose: 



(1) Suspended-sediment sampling - The purpose of the suspended- 

 sediment sampling is to obtain a sampling that is representative of 

 the water-sediment mixture moving in the vicinity of the bottom. 



The sample can be collected with a Van Dorn water sampler (Section 

 3.1.3). The sediment is separated from the water by centrifugation, 

 and the sample is transferred into a glass container for storage 

 before analysis. 



(2) Grab sediment sampling - Grab sampling of the sediment is 

 performed by grab samplers which usually have the distinctive feature 

 of the shapes of an orange-peel or a clamshell. During sampling, 



the sampler is lowered to the bottom with its grab opened. The grab 

 is closed after being triggered by electrical or hydraulic means, 

 after closure the sampler is lifted to the surface. The sediment 

 sample is a composite sample of a several inch layer of sediment. 



(3) Core sampling - Cylindrical and box corers are used to 

 remove a vertical tube of sediment at a particular location in as 

 undisturbed a state as possible. The purpose may be to examine the 

 historical formation, the interrelationship of the biological 

 components and their environment, or the accumulation of polluted 

 materials from a particular source. These extractive devices can 

 be subdivided by the means utilized in forcing the penetration of 



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