2.1.1 The D-1 standard requires the vessel to exchange its ballast water
200 NM from the coastline in waters 200 m deep, or if this cannot be achieved for safety
reasons, 50 NM from the coastline in waters of the same depth. Therefore, the water in
exchanged ballast water should have a similar salinity to that of mid-ocean water.
2.1.2 Indicative analysis for the D-1 standard of the BWM
Convention could rely on the chemical parameters (e.g. salinity) of the water
in the ballast water discharge, or on an estimate of species present. However, the
latter might need trained personnel. If the ballast water discharge being tested has a
salinity significantly less than that of 30 PSU, then it is likely that the ballast
water has not been exchanged en route under the conditions required in the D-1 standard,
or that the exchange has not been completed successfully.
2.1.3 Two exceptions to this are:
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.1 when ballast water is taken up in port areas that are located in
high-salinity environments, above 30 PSU. In such a case ballast water with a PSU
of 30 may not originate from mid-ocean waters and therefore the ship may not be
compliant with the D-1 standard; or
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.2 when ballast water has been exchanged in designated ballast water
exchange areas within 50 NM from the coastline in waters that may be of less
salinity than the mid-ocean water. In this case the ballast water exchange would
be compliant.
Therefore, the origin of the last ballast water exchange should be known
before interpreting the results of salinity analysis.
2.1.4 Checking salinity could be backed up by further analysis of the
organisms in the ballast water discharge to determine the origin of the ballast water;
however, this would take time and need experienced staff. This can be done in line with
the visual analysis methodologies outlined in paragraph 2.4.3 below. However, it should
be noted that there are many external factors that could affect the salinity and the
organisms in the ballast water, such as wet sediments in the ballast tanks, the state of
the tide in the port concerned during its uptake and the fact that exchange may not
remove all coastal organisms.
2.1.5 There are many ways to quickly and easily monitor the salinity of
water on the market, and generic salinity measures should be used for indicative
analysis.