 Sediment from a site exposed to the same water mass as the corresponding bivalve site and no more than 2 km away is collected concurrently with the bivalves.Sediment criteria measured includes total organic and carbonate carbon, moisture content, particle size, concentration of "Clostridium perfringens", and concentration of Coprostanol (this was no longer measured after 1989).Different methods of bivalve collection are used depending on the site characteristics.