Rural Planning and Improvement Strategy - Minor Projects Environmental Guidance Note

Annex 4
Works Branch Technical Circular No. 22/92 - Marine Disposal of Dredged Mud

Appendix I - Guidelines for Sampling and Testing of Mud to be Dredged

When ontofying DEP and FMC of an intention to dredge and dispose of mud, the project department, consultant or developer mush provide a detailed programme for sampling and testing the mud. This programme, which is to determine whether the mud is contaminated, will include:

(a) A plan showing the area to be dredged, the locations to be sampled and their Hong Kong metric grid coordinates
  In areas unlikely to be contaminated, surface samples on a 200 x 200m grid will be adequate. In areas expected to be contaminated, a vertical profile of samples should be taken on a 100 x 100m grid. In areas near outfalls or nullahs, which are expected to be highly contaminated, the vertical profile of samples should be on a 50 x 50m grid. PEPO/SWC in EPD can advise in cases where there is doubt as to the apropriate sampling grid.
(b) A schedule of types of sample to be taken (eg grab samples, gravity coring, piston samples, vibrocores, etc) with their locations and depths
    where vertical profiles of samples are to be taken, samples should be continuous, and 100mm long sub-samples should be taken for testing. The top level of the sub-samples should be the seabed, 0.9m down, 1.9m down, 2.9m down, and then every 3m until the dredge depth is reached. Each sample should be sealed in a polythene bag and labelled with the date, station number, sample length, diameter and depth, together with a full description of the samle using the methods described in Geoguide 3 - "Guide to Rock and Soil Descriptions" (Geotechnical Control Office, 1988). Samples should be stored in chilled conditions. When, for logistical reasons, analysis cannot be initiated immediately, the sample must either be frozen or pretreated in a manner apropriate for the analytical parameter in question in order to prevent degradation of the sample.
(c) A schedule of tests to be carried out on the samples
    The concentration in mg/kg (dry weight) of cadmium, chromium, copper, mercury, nickel, lead and szine shall be determinded. Analysis for organic micropollutants, such as polychlorinated biphenyls (PCB;s), tributyl tin (TBT) and polyaromatic hydrocarbons (PAH's), may also be required in areas where contamination by such compounds is suspected. The analytical methods used for detecting trace metals in sediments should be in accordance with the methodology described in Table A1. The procedures, which should incorporate proper quality control methods including use of replicates, standards in, calibrating instruments etc. should be similar to those for the analysis of trace metals in sludge as outlined in "Standard Method for the Examination of Water and Wastewater" 17th Edition, published by the American Public Health kassociation.
Table A1 - Analytical Methodology
PARAMETER METHODOLOGY
Total Copper Direct acid digestion followed by Atomic Absorption Analysis
Total Chromium As above
Total Cadmium As above
Total Lead As above
total Nickel As above
Total Zine As above
Total Mercury Cold Vapour Generation
Dry Weight Constant Weight at 103-105C
(d) Timetable for sampling, testing and reporting
    The anticipated timetable for taking the samples, carrying out the tests and producting the Sediment Quality Report shall be provided.

 

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