Marine litter poses a complex challenge in Indonesia, necessitating a well-informed and coordinated strategy for effective mitigation. This study investigates the seasonality of plastic concentrations around Sulawesi Island in central Indonesia during monsoon-driven wet and dry seasons. By using open data and methodologies including the HYCOM and Parcels models, we simulated the dispersal of plastic waste over 3 months during both the southwest and northeast monsoons. Our research extended beyond data analysis, as we actively engaged with local communities, researchers and policymakers through a range of outreach initiatives, including the development of a web application to visualize model results. Our findings underscore the substantial influence of monsoon-driven currents on surface plastic concentrations, highlighting the seasonal variation in the risk to different regional seas. This study adds to the evidence provided by coarser resolution regional ocean modelling studies, emphasizing that seasonality is a key driver of plastic pollution within the Indonesian archipelago. Inclusive international collaboration and a community-oriented approach were integral to our project, and we recommend that future initiatives similarly engage researchers, local communities and decision-makers in marine litter modelling results. This study aims to support the application of model results in solutions to the marine litter problem.

In the United Kingdom, disposal of radioactive waste may involve packages of grouted waste being placed in a geological disposal facility (GDF) and surrounded by a cementitious backfill. This paper describes modelling that has been carried out to develop an understanding of the possible spatial and temporal evolution within the GDF.

A single waste package is assumed to be filled with an encapsulation grout, placed in an underground vault and surrounded by a cementitious backfill. Groundwater from the host rock flows into the vault and through the backfill. A simplified model system examines the interactions between groundwater, cementitious backfill and grout.

In most cases the model predicts a reduction in the backfill porosity due to precipitation and dissolution reactions, particularly at the upstream edge of the vault. The degree to which this occurs depends on the groundwater composition. The model also predicts precipitation and dissolution reactions would occur in the grouts close to their interface with the backfill, reducing the local porosity significantly which may isolate the grouts from the backfill, so that the pH within the grouts would be unchanged over an extended period.

The risk of five pesticides (atrazine, simazine, bentazone, mecoprop and MCPA) contaminating a Quaternary phreatic aquifer (the water supply area of Sint-Jansteen, the Netherlands) is assessed based on laboratory experiments and solute transport modelling (MODFLOW-MT3D). Batch experiments either show long half-lives (at least 1500 days) or no degradation at all for bentazone, atrazine and simazine while mecoprop and especially MCPA degrade much faster (half-lives down to 4.1 days). Column experiments show significant sorption to the aquifer sediment only for atrazine and simazine under certain circumstances. A series of experiments were conducted during which the type of the sediment, the grain size, the content of the organic matter and the acidity of the groundwater were varied. These experimental results were subsequently incorporated in a solute transport model for the aquifer resulting in the following ranking of the contamination risk for the selected pesticides (from low to high): MCPA, mecoprop, simazine, atrazine, bentazone. This ranking was confirmed by observed pesticide concentrations in samples taken from piezometers and extraction wells from the aquifer.