Arbejdsrapport fra Miljøstyrelsen, 35/2005 – Havnesedimenter - Prøvetagning og analyser

Havnesedimenter - Prøvetagning og analyser

Summary and Conclusions

Denmark has ratified a number of international conventions, which are juridical binding. The convention puts demands on sampling and analysis of the harbour sediment before dumping at sea. The first convention of the sea, which limited dumping of substances and material at sea, including harbour sediments, was the London convention in 1972 (LC72). In the end of the 80ies the Oslo-Paris convention (OSPAR) adopted guidelines for the handling of sea bottom materials in the North Sea Area, and in 1992 the Helsinki commission adopted a set of guidelines for the Baltic Sea, which was based on OSPARs guidelines. Since then, the OSPAR guidelines have been updated in 1998 and LCs in 2001.

The guidelines in the conventions prescribes, that the dredging material is characterised with regard to physical, chemical and biological parameters, which can be used for evaluation of whether the dredging material will give rise to problems in the dredging area. The current Danish dredging legislation from 1986 is an implementation of the international guidelines in action at that time.

The international guidelines prescribes, that at least 3 samples are taken, unless it can be shown, that the material is free from contamination, either undisturbed sea bottom material, material of sand, gravel and/or stones, or free from sources of contamination or historical sources. For harbours the ships are considered a sources of contamination, and hence the only exception is material of sand, gravel and/or stones.

Usually harbours are designed so that water inside the harbour area are stagnant, so in stormy weather, the sea bottom material in the water face will tend to sink (sedimentation) in the harbour, which over time makes the water shallower, and harbour dredging is demanded to keep the depth. Removal and eventual dredging of the material is contained in the guidelines, and must therefore be examined for the possible contamination and a dredging permit must be in place. As harbours often are in the vicinity of larger cities, water treatment plants or stream mouth, there is a line of potential contamination sources that can contribute to the contamination of the harbour sediment When freshwater meets saline water, as in a stream mouth or waste water treatment outlet, many organic substances and metals will precipitate due to sedimentation of particles with high affinity for these substances.

Before planning the sampling, it is necessary to know sources of contamination of the harbour. This is checked by investigate which industries that have been in the area, in case of a new dredging operation, probably only since the last dredging took place, and control of historical accidents and industries, that could have had outlets into the harbour or streams and waste water treatment plants with outlets in or close to the harbour. Sources could be hospitals, plastic industry and many others, which is outside the harbour, or from the consolidated areas (parking lot and mooring space), and from the fuel depot with possible spills of oil and gasoline from tanking of engines. In the larger harbours some industries get raw material and transport its goods through shipping, both of which can be a local source of contamination during loading and unloading of cargo.

When the sources and their placement have been determined, the harbour can be split op into smaller areas, typically the different parts of the harbour, and for every part, it is estimated which sources can be expected to contribute. If there is a direct outlet, one can take samples at different distances from the mouth, which can be used to examine for exactly those substances, that is expected from this pollution source. For the more diffuse/general substances as most be investigated fore, due to their inherent presence in harbour sediment, it is usually a good idea to take 2-3 samples from each part of the harbour. From these samples, a pooled sample can be analysed for the substances expected to be found (typically copper, tributyletin (TBT) and PAH'es sometimes oil residues). The individual samples can be analysed for dry matter and loss on ignition (LOI) to get an idea on the homogeneity of the harbour sediment, but as a minimum, the pooled sample should be analysed for this. If the harbour is receiving water from a treatment plant of city waste, PCB's, mercury and cadmium can be added to the list of substances to analyse for, and if the historical and current sources indicate so, lead, nickel, zinc and chromium for metals and DEHP and nonylphenol as “model substances” of organic groups such as softeners and detergents.

During sampling, it is important to keep the equipment clean, to ensure that any contaminants can be attributed to the sediment and not the pollution of the sample from the survey vessel. Samples can be extracted in many different ways, by divers and kajaktubes, with a HAPS or profiling sampling tools. In any case, it is important that the equipment and sample containers are cleaned and kept tightly closed, so that the sample is not polluted after collection.

After analysis the results are evaluated by the authority, which shall give the dredging permit. As a support for this evaluation, it is important to have dry matter content, LOI and a sample description (how did the sediment look, how fine-grained was it?). These data ca be supplemented by

Total organic carbon content (TOC) for normalisation of organic contaminants when comparing to eco-toxicological assessment criteria's, and
Clay-silt fraction (<63 µm) or Lithium for normalisation of metals to the clay-fraction of the sediment

The procedure for planning of sampling can be summed op as:

Investigate historical sources in connection with the harbour and surroundings
Draw a map of the harbour
Add to the map the areas to be deepened and where most sedimentation occurs
Put in the known sources, e.g. outlet from drains, streams and wastewater treatment plants
Split up the harbour in different areas of equal contamination from water flow and contamination sources
Place sampling stations and suggest parameters for analysis based on the above considerations
Extract sediment samples from the sampling stations under as clean circumstances as possible, and leave it to the laboratory to perform pooling of sampling after reception of samples.

Samples should always be analysed for Copper, TBT, PAH and at the fuel-quay also for total hydrocarbons (THC), unless LOI can be shown to be very low, e.g. less than 2%, or if the sediment contains mainly pure sand or gravel. In these cases, it is possible to limit analysis to copper and TBT