Methods for Bulk Sediment Sampling This section presents guidelines for collecting

representative sediment samples, and targets the selection of appropriate equipment based upon a range of site conditions such as depth of water, depth of sediment to be sampled, and flow re-gimes.

Desirable attributes for sediment sampling gear include the following:

 Creates a minimal pressure wave when des-cending through the water

 Forms a nearly leak-proof seal when the sedi-ment sample is taken

 Prevents winnowing and excessive sample disturbance when ascending

 Allows easy access to the sample surface so that undisturbed subsamples may be taken

 Allows vertical sectioning of undisturbed samples for profile examination

 Penetration well below the desired sampling depth is preferred to prevent sample distur-bance as the device closes. A means of weight adjustment to assure penetration depths may be valuable.

5.5.1. Sediment Grab Sampling Methods Grab samplers are excellent for providing quantita-tive data at a relaquantita-tively low cost. Considerations for selection of core versus grab samplers are described below in Table 5-2.

Limitations of grab samplers include:

 Variability among penetration depth for sam-ples depending on sediment properties

 Oblique angles of penetration which result in varying penetration depths within a sample

 Folding or disturbing the sample, resulting in the loss of information concerning the vertical struc-ture of benthic communities in the sediments.

Some additional things to consider when choosing a sampler include:

 Water depth

- In less than 4 m of water, with low current conditions and smooth water, the Birge-Ekman, petite Ponar, Ponar, Van Veen, and Peterson mini-Shipek grabs are recommended

- For deeper waters or greater current, the Po-nar or Van Veen are recommended.

 Sub-sampling from sampler directly

- If sub-sampling from the sampler is desired, the Birge-Ekman, mini-Ponar, Ponar, Van Veen, or Shipek are recommended

- If not, a Peterson, Smith-MacIntyre, or mini-Shipek are recommended.

 Target sample depths

- Up to about 10 cm sample depth, a Birge-Ekman, Ponar, or Shipek or miniature ver-sions of any of these are suitable

- Up to about 30 cm, a Smith MacIntyre, Van Veen, or Petersen grabs are suitable.

 Target sample volumes to meet analytical requirements

- Up to about 3 L, the mini Birge-Ekman, pe-tite Ponar, or mini-Shipek samplers are suit-able

- 3 – 10 L samples may be collected with the Birge-Ekman, Ponar, or Petersen grabs - Above 10 L, Smith-MacIntyre or Van Veen

grabs are suitable.

The most common surface area sampled is about 0.1 m² in the Van Veen and Smith-MacIntyre grabs. Van Veen and box corers are also capable of sampling 0.06 m², compared to hand-held corers, which sample about 0.001 m².

Table 5-2. Selection Criteria for Core Sampler or Grab Sampler

Sampling devices such as a Ponar or VanVeen with removable or hinged bucket covers are preferred to allow access to the surface of the sediment sample without loss of water or fine-grained sediments. Key sample collection issues for grab samplers include:

 For Sediment Grab Samples to be Subsam-pled in the Laboratory. The sample should be transferred carefully and directly into a la-beled container that is made of a chemically inert material, tightly sealed, and air excluded.

 For Sediment Grab Samples to be Subsam-pled in the Field. Typically, the sediment is decanted into a cleaned bowl or bag for homo-genization and sub-sampling. To minimize se-diment handling and artifacts of sampling for volatiles, samples may be taken directly from the grab.

5.5.2. Sediment Core Sampling Methods Core samplers (corers) are used to characterize contamination over a depth interval that includes sub-surface sediments. They also are used to obtain sediment samples for geological characte-rizations and dating, investigate the historical input of contaminants to aquatic systems, and to characterize the depth of contamination at a site.

Corers are an essential tool for developing three-dimensional maps of sediment contamination.

Collection of subsurface layers in addition to the

surface layer of sediment permits evaluation of historical or long-term impact on site conditions, and development of site-specific sediment trans-port mechanisms to refine the CSM.

Selection of the most appropriate core sampler for a sampling event is determined based on water depth, particle size of the sediment, sediment sample depth, volume of sediment sample re-quired for analysis, and available lifting capacity of the sampling platform/boat and winch equip-ment. Core samplers seldom are suitable for sampling benthic macro invertebrate samples due to the small area sampled. See Figure 5-1 for factors to consider when selecting a core sampler.

Because of the potential for a “bow wave” of sediment at the leading end of the core, resulting in compaction and inefficient flow of the sedi-ment into the core sampler, percent recovery should be evaluated. Percent recovery is deter-mined by dividing the internal recovery by the penetration depth. Internal recovery is the depth inside of the core tube from the top of the tube to the surface of the sediment. Core penetration is measured from the outside of the core. In recent projects in the Pacific Northwest (e.g., WindWard 2006) 75 percent core recovery has been regarded as an appropriate control limit on core recovery;

however, it is recommended that project specific goals be determined.

Use a Core Sampler if: Use a Grab Sampler if:

 Characterization of contamination in deeper sedi-ments is important

 Comparison of recent surficial vs. historical deeper sediments is needed

 Reduced sediment disturbance needed

 Reduced oxygen exposure needed

 Sediments are soft and fine-grained.

 Large sediment volumes are needed

 Larger grain-size or hard sediments would hamper use of a core

 Larger surface area of surficial sediment needed (typical for benthic invertebrate sampling).

For more information on methods for bulk sedi-ment sampling, consult the following references:

 Standard Guide for Storage, Characterization, and Manipulation of Sediments for Toxico-logical Testing (Ref. 13)

 Guide for General Planning of Waste Sam-pling (Ref. 14)

 Guide for Core-sampling Submerged, Uncon-solidated Sediments (Ref. 15)

 Standard Guide for Selecting Grab Sampling Devices for Collecting Benthic Macroinverte-brates (Ref. 16)

 Handbook of Techniques for Aquatic Sedi-ments Sampling (Ref. 17)

 Manual of Aquatic Sediment Sampling (Ref.

18)

 Methods for Collection, Storage and Manipu-lation of Sediments for Chemical and Toxico-logical Analyses: Technical Manual (Ref. 1)

 Sampling for Contaminants In Sediments and Sediment Porewater (Ref. 6)

 A Compendium of Chemical, Physical and Biological Methods for Assessing and Moni-toring the Remediation of Contaminated Se-diment Sites (Ref. 7)

 Ocean Testing Manual Evaluation of Dredged Material Proposed for Ocean Disposal (Ref.

8)

 Inland Testing Manual: Evaluation of

Dredged Material Proposed for Discharge in Waters of the U.S. (Ref. 9).

5.6. Bulk Sediment Handling and Analysis