Management of dredge material in the Republic of Ireland - A review

Defining potential valuables through the characterisation of lake sediments: case study in Arkelstorp bay, Sweden

This study aims to characterise and discuss the potential use of sediment from the Arkelstorp bay located in the south of Sweden. Sediments from the Arkelstorp bay is collected and analysed on nutrient content, age, and potential contaminants. No organic environmental pollutants are found and the metal content are not elevated but still problematically high. For example, the amount of cadmium per phosphorus is 480 mg Cd kg−1 P. However, as the carbon 14-datings showed, the sediment is preindustrial. Therefore, the amount of registered cadmium comes naturally from the surrounding environment. Arkelstorp sediments present the potential to become a source of nutrition in agriculture. The results show that the material is a good source of nutrients, with a nitrogen content of 18 g kg−1 dry matter (DM), phosphorus 0.8 g kg−1 DM and potassium 2.4 g kg−1 DM respectively. However, the metal content is problematic to use the material without any pre-treatment. On the other hand, bioenergy production is expected to increase in the future, where this resource could potentially be helpful for the cultivation of bioenergy crops.

A novel systematic, risk based approach to support the designation of aquatic disposal sites

Humans rely fundamentally on the marine environment, which is at the same time subject to an increasingly broad range of anthropogenic pressures, leading to growing concerns and the need for effective management for marine protection. One activity is the dredging of ports and harbours which is necessary to maintain safe channels for commercial and recreational navigation. Regulatory authorities in developing countries have few resources to conduct full EIAs for determining dredged material disposal sites but are required to do so under international obligations. The Tool in this paper provides an effective, pragmatic, transparent, consistent, and robust approach to protect the environment whilst using limited technical and scientific resources through a risk based approach to defining need, characterising and designating disposal sites at sea for dredged material. Whilst this approach for dredged material disposal sites was developed for use in UK, this process is equally applicable to other waste types, worldwide.

Assessment of the use of dredged marine materials in sanitary landfills: A case study from the Marmara sea

Worldwide production of large volumes of dredged materials (DMs) has become a pressing environmental problem. In Turkey, the government has yet to develop management strategies that successfully prevent or minimize dumping into the Marmara Sea. One potential solution is the utilization of the DMs as a source of material for earthworks, particularly in sanitary landfills in Istanbul and Kocaeli. The most economically developed cities in Turkey, they were evaluated in terms of potential environmental impacts and regulatory compliance. Five ports/harbors representing specific portions of the study area and different industrial activities were selected as pilot regions. Physical, chemical, mineralogical, toxicological, and leaching potential measurements of DMs dredged from the seabed revealed they qualify as non-hazardous waste. Index and engineering tests performed on raw and processed DMs were assessed to determine the geotechnical requirements for soil-based materials (SBM) used in sanitary landfills. The results showed that non-hazardous DMs could be utilized as a cover, base/cap liner, and/or fill material at various sections within the landfills. This method provides environmental advantages not seen with other management strategies for DMs such as dumping at sea or upland disposal.

An Integrated GIS Methodology to Assess the Impact of Engineering Maintenance Activities: A Case Study of Dredging Projects

Engineering infrastructures require regular maintenance and/or repair activities that have important social, environmental, and economic impacts. Despite their growing importance, few studies have focused on fully integrated analyses. This work presents a general methodological approach to design databases of engineering maintenance activities for their assessment. This methodology was applied to the case of dredging projects in the ports managed by the Andalusian Regional Government (Spain). The resulting database contains 87 fields of information obtained from the analysis of 70 activities performed between 1993 and 2015. This database is free, public, and available to the scientific community, and it was implemented in PostgreSQL using the PostGIS extension for spatial data; therefore, it can be integrated in a GIS. The assessment of deviations from the initial projects and the comparison between locations enhanced our methodology, which represents a valuable tool not only for scientists and managers to improve the decision-making process when planning future strategies, but also to evaluate the environmental impacts.

Geotechnical and mineralogical characterisations of marine-dredged sediments before and after stabilisation to optimise their use as a road material

Dredging activities to extend, deepen and maintain access to harbours generate significant volumes of waste dredged material. Some ways are investigated to add value to these sediments. One solution described here is their use in road construction following treatment with hydraulic binders. This paper presents the characterisation of four sediments, in their raw state and after 90 days of curing following stabilisation treatment with lime and cement, using a combination of novel and established analytical techniques to investigate subsequent changes in mineralogy. These sediments are classified as fine, moderately to highly organic and highly plastic and their behaviour is linked to the presence of smectite clays. The main minerals found in the sediments using X-ray diffraction (XRD) and automated mineralogy are quartz, calcite, feldspars, aluminium silicates, pyrite and halite. Stabilisation was found to improve the mechanical performances of all the sediments. The formation of cementitious hydrates was not specifically detected using automated mineralogy or XRD. However, a decrease in the percentage volume of aluminium silicates and aluminium-iron silicates and an increase of the percentage volume of feldspars and carbonates was observed.

Screening-level risk assessment applied to dredging of polluted sediments from Guanabara Bay, Rio de Janeiro, Brazil

Guanabara Bay is characterized by predominant eutrophication and anoxic sediments with a mixture of pollutants. The risk prognosis associated with the dumping of its dredged sediments into the open ocean was addressed by our algorithm. Our algorithm could prioritize areas, characterize major processes related to dredging, measure the potential risk of sediments, and predict the effects of sediment mixing. The estimated risk of dredged sediment was >10-fold than that of ocean sediments. Among metals, mercury represented 50-90% of the total risk. The transfer of dredged material into the ocean or internal dumping in the bay requires a 1:10 dilution to mitigate the risk and bring the risk levels close to that in the EPA criteria, below which there is less likelihood of adverse effects to the biota, and a 1:100 dilution to maintain the original characteristics of the ocean disposal control area. Our algorithm indicator can be used in the design of both aquatic and continental disposal of dredged materials and their management.

Beneficial Use of Dredge Materials for Soil Reconstruction and Development of Dredge Screening Protocols

Upland placement of dredge sediments has the potential to provide beneficial reuse of suitable sediments for agricultural uses or urban soil reconstruction. However, the use of many dredge materials is limited by contaminants, and most established screening protocols focus on limiting major contaminants such as heavy metals and polycyclic aromatic hydrocarbons and generally ignore fundamental agronomic parameters. Since 2001, we have placed over 450,000 m of Potomac River fresh water dredge materials and 250,000 m of saline materials from various locations into monitored confined upland facilities in Charles City, VA, and documented their conversion to agricultural uses. Groundwater and soil quality monitoring has indicated no adverse effects from material placement and outstanding agricultural productivity for the freshwater materials. Once placed, saline materials rapidly leach and ripen with quick declines in pH, electrical conductivity, and sodicity, but potentials for local groundwater impacts must be considered. Our experience to date indicates that the most important primary screening parameter is acid-base accounting (potential acidity or lime demand), which should become a mandatory analytical requirement. Our second level of acceptance screening is based on a combination of federal and state residual waste and soil screening standards and basic agronomic principles. High silt+clay and total organic C may also limit rapid use of many dredge materials due to extended dewatering times and physical limitations. This dredge material screening system separates potential upland placement candidates into three soil quality management categories (unsuitable, suitable, and clean fill) with differing monitoring requirements. Similar use of these sediments in urban soil reconstruction is also recommended.

Numerical assessment of the dispersion of overspilled sediment from a dredge barge and its sensitivity to various parameters

Marine dredging operations are not uncommon in coastal waters since they are necessary for several beneficial uses, such as harbour maintenance, beach nourishment or removal/capping of pollutants, amongst others. They also constitute a significant risk for the environment, changing its physical, chemical and biological characteristics, as evidenced by many authors. In this study, two numerical models are used to simulate the dispersion pattern of fine suspended sediment spilled from a dredge barge, considering different hydrodynamic scenarios, particle sizes and dredging tracks in a mesotidal environment. The results show that, in this particular case, the currents (largely induced by the tide) are the main responsible for the final disposition of the settled particles, being the other variables of secondary importance.

A screening procedure for selecting the most suitable dredged material placement site at the sea. The case of the South Euboean Gulf, Greece

The selection of the best site for the placement of dredged sedimentary material (∼7,000 m(3)) from the Aliveri coastal area in the adjacent South Euboean Gulf (Greece) was accomplished through a screening procedure. The initial stage comprised the determination of physical, chemical, and biological characteristics of the dredged sediment before the commencement of any dredging operation. Grain size measurements, geochemical analyses together with the use of pollution/toxicity indices and empirical sediment quality guidelines, and the conduct of an acute toxicity test showed that the dredged material consisted of "unpolluted to slightly polluted" silty sands and sandy silts. However, the local authorities planned to place this sediment in the neighboring open sea area, i.e., the South Euboean Gulf, due to the absence of any beneficial use or alternative dumping option (i.e., dumping on public lands). Therefore, the next stage of the screening procedure, based on criteria such as the national legislation, seabed and seawater column characteristics, influence of the water mass circulation pattern on the post-placement migration of dredged sediment, impact on living resources and human activities (i.e., aquaculture and fishing), effect on significant marine sites (i.e., sites of scientific, ecological, and historical importance, navigation routes, military zones), and seafloor engineering uses, led to the evaluation of the suitability of the South Euboean Gulf as a potential dumping area. Then, the identification of the appropriate dredged material placement sites in the South Euboean Gulf was based on a cluster analysis, which tested the physicochemical resemblance of the dredged material and the surface sediments of 19 potential placement locations in the gulf. After the statistical process, only four sites situated near the north shoreline of the South Euboean Gulf were qualified as the best dredged material placement locations.