Guidelines for the Assessment of Dredge Material for Disposal in Irish Waters

Abstract

Prior to the present guidelines the assessment, by the Marine Institute on behalf of the Department of Communication, Marine and Natural Resources, of the suitability of dredged materials for disposal at sea had employed provisional action levels as an aid to evaluation. These provisional action levels were based entirely on sediment chemistry. The responsible agencies have decided that these levels now need to be updated and formalised. The approach proposed in this document aims to provide an improved, and more integrated, assessment of the ecological risks associated with individual sediment dredging and disposal activities. It offers flexibility to deal with issues on a case-by-case basis and improves transparency of the decision-making process. The list of parameters to be assessed has been revised and methods for setting numerical guidance values in other countries have been reviewed. Ideally, guidance levels should comprise chemical and ecotoxicological data specifically relating to Irish sediments. In the absence of a comprehensive dataset for Irish sediments, proposed threshold guidance levels have been based on ecotoxicological data from other sources. Wherever possible, lower threshold guidance values have been based on existing Irish background levels of contaminants. Where background data do not exist for a particular parameter, ecotoxicologically-derived values, corresponding to expected no-effect levels, have been taken from reputable sources. Similarly, upper threshold guidance levels (i.e. levels at which effects may be expected) have been based on ecotoxicological data from reputable sources. The assessment strategy has been designed so that decisions concerning the acceptability of sediments for sea disposal will take into account a range of intrinsic and environmental factors i.e. the strategy adopts a Weight of Evidence approach. The guidance will be reviewed and revised as necessary, as more information becomes available. Sampling and storage methodology is presented as well as quality assurance and reporting requirements. Guidance on analytical procedures and approval of analytical laboratories is included.