This is a dredging works where the dredged material will be stockpiled. We are going to conduct 12 items of testing (base on Dutch Standard) for any contamination/heavy metal existance in the stockpile. THe stockpile height is 5m and one big area may cover up to 100,000 m3. Is there any standard for the amount for each test, let say one chemical test can cover 10,000 m3 of area.
Sorry, I have no knowledge of Dutch requirements. Here in US, sampling frequency is driven by either the disposal site, or the lead regulatory agency, if the material is to be reused. A typical number of samples for disposal purposes would be one 4-point composite per 2,000 cy (1530 m3 if I converted correctly).
In the Northwest (US; Washington, Oregon, and Idaho), testing of dredge material is regulated by the Dredged Material Management Office (DMMO) in the Seattle District of the USACE. They have testing manuals for the different project locations on their web site.