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Guidance Note 2

Guidance Note 2: Sediment sampling requirements

Legislative Context
Sediment Sample Requirements
Appendix A
 

Legislative Context


In the UK the introduction of pollutants (such as certain metals and organics) into the marine environment is managed in several ways. This is mainly through the Water Framework Directive and Marine and Coastal Access Act (2009). 

The Water Framework Directive is a key piece of European legislation which relates to the protection of water quality and the ecological status of freshwaters and coastal waters. The WFD is implemented in the UK under the Water Environment (WFD) (England and Wales) Regulation 2003. The Water Environment Regulations incorporate a number of existing regulations including the Freshwater Fish Directive, Shellfish Waters Directive and Dangerous Substances Directive. The Water Environment Regulations enforces a set of criteria (Environmental Quality Standards, EQSs) for both individual discharges and the receiving waters. In this way, water quality is managed with a view to achieving acceptable standards.

The Marine and Coastal Access Act (2009) superseded two Acts (among others) which were previously important for the previous marine licensing system ie the Food and Environment Protection 1985 (FEPA) and the Coast Protection Act 1949.  FEPA licences mainly permitted construction within the marine environment, or the deposition of materials of sea following environmental assessment. FEPA licences were replaced by marine licences under the Marine Act, however sampling and environmental assessment remain important considerations for activities.

The assessment of the effects of sea disposal is undertaken by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), based on OSPAR’s Dredged Material Assessment Framework. OSPAR guidance includes guidance on the number of sediment samples required for analysis. Sediment quality guidelines exist in the form of CEFAS Action Levels.

Dredging operations themselves do not fall under either piece of legislation, being neither a discharge nor a disposal operation. However, dredging does involve release of sediment into the water column (and therefore any sediment-bound contaminants) and may also redistribute contaminants from the sediment into the water column. The quantity and rate of sediment release varies according to the dredging methodology. A trailer suction hopper dredger (TSHD) releases sediment via the overflow of low density water, whereas a water injection dredger causes all the dredged material to be mobilised into the lower water column, the release from a backhoe is limited mainly to sediment falling from its bucket.

The type of sediment also affects the release rate of contaminants since fine sediment will be lost and dispersed to a greater extent than coarser sands. Sediment sampling helps to inform licencing procedures and to ensure that the dredging activity will not have a detrimental impact on the environment. Using the latest hydrographic survey, and information about the dredge (such as historic information, volumes, method and location) the PLA will work with berth operators and the MMO to come up with a sediment sample plan to ensure that the risks dredging poses to the environment of the Thames are mitigated against.

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Sediment Sample Requirements

Sample Numbers

Within the limits of the Port of London, dredging is regulated by both the PLA and the MMO. The PLA considers that an assessment of the effects of dredging on water quality at the dredge site and the sediment quality of the receiving environment is an integral part of the licensing process. Therefore, the provision of sediment samples is a requirement of all new dredging applications and samples must be provided once every two years for ongoing maintenance dredging operations or on renewal of the licence. The number of samples required is dependent upon the quantity of sediment to be dredged and guideline numbers are set out in Table 1 below, although the actual number required will be site specific.

 

Quantity of sediment to be
dredged (m3)

New dredge site
or site not dredged in last 10 years
(No. of sites)

Maintenance I:
dredged in last
3 years
(No. of sites)

Maintenance II:
dredged 4-10
years ago
(No. of sites)

<3,000

3 (surface only)

1

2

3-10,000

5 (surface and dredge depth)

2

3

10-50,000

6 (surface, dredge depth and mid-way)

3

4

50-100,000

8 (surface, dredge depth and mid-way)

4

5

100-200,000

10 (surface, dredge depth and mid-way)

5

6

>200,000

Determined on an individual basis


Table 1

Berth operators should contact the PLA Environment Team in advance for advice on the number and location of samples required. Samples should be taken in accordance with standard marine sediment sampling procedures.

The PLAs environment team will review applications, and will consider the dredge volume, dredge area, dredge method and latest hydrographic survey to determine the sediment sample locations.

Samples sites will be representative of the area to be dredged, for example, in a rectangular berth box, four samples could be taken from evenly distributed locations across the area. If an area is known or thought to be contaminated, sampling should include a site in the contaminated area, for example, adjacent to a slipway.

 

Figure 1 - Examples of possible sample locations

Provision of Sampling Equipment & Sample Storage

Samples should be taken by a competent, professional contractor from the locations and depths shown in plans provided by the PLAs environment team (and where appropriate other regulators) using appropriate techniques.  The containers provided by the laboratory should be used to store the samples. These samples should be filled, stored and transported in accordance with the laboratories instructions.

Sample Analysis

Samples should be analysed by a competent laboratory with the appropriate accreditation for the chemistry and material to be analysed.  As a minimum, the laboratory shall be UKAS accredited. It should be noted that the Marine Management Organisation will only accept sample analysis results from certain laboratories. To ensure sample results are can be used for both regulatory processes, it would be in the interest of the applicant that MMO accredited laboratories are used to carry out the analysis.

PLA requirements for chemical analysis where material is to be retained in the water column or disposed of to a licensed marine disposal site (for marine disposal, samples may also be required by CEFAS) stated within Appendix A. .

These appendix’s are the minimum requirements that the PLA will accept. It is essential that samples from different locations or depths are not mixed (or bulked) prior to sample analysis. This means samples should be analysed discretely, independent of each other in relation to both position and depth. 

Results from the analysis should be submitted to the PLA as a PDF report and also in excel format. The location of the samples in Ordnance Survey National Grid coordinates should be referred to for each separate sample, as should the depth of samples which have been taken in relation to the surface level.

Interpretation of Sediment Quality Data

In the absence of published sediment quality guidelines specifically relating to the effects of dredging on the water column and biological communities, the PLA has adopted the following approach:

1. Comparison of data with Canadian Interim Sediment Quality Guideline (ISQG) values;
2. Comparison of data against Kelly/ICRCL/CLEA land contamination guidelines;
3. Comparison against background sediment quality data for the Thames Estuary (this takes account of geological and anthropogenic effects); and
4. Comparison against CEFAS guideline Action Levels.

Should the data fall within or near the ISQG, Action Level 1 (converted to approximate dry weight) and be comparable with present-day background levels, the PLA will consider the dredging of the material to have an acceptable level of impact on both the water column and inter/subtidal habitats.

In the event that the sediment quality data falls above this acceptable level then further assessment will be undertaken. Depending on the level of contamination, this assessment would involve one or both of the following:

1. Further sampling to confirm contamination levels and delineate contaminated areas; and/or
2. Calculation of the likely input of contaminants to the water column (using the partition co-efficient) for comparison with the relevant EQS levels.

The results of the further assessment will inform any restrictions on the dredging operation (e.g. no overflow for TSHD, or use of a sealed bucket) and disposal location (e.g. special waste landfill site).

The results of the sediment quality assessment are factored into the wider environmental assessment and decision-making process.