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7Open framework gravels (OFGs) are an inherent textural component of alluvial gravel outwash deposited 8 by braided river systems. Being exceptionally permeable, they play a significant role in facilitating 9 transmission of water and contaminants through alluvial gravel aquifers. Understanding how connected 10 OFG facies are is helpful for making informed predictions about groundwater flow and contaminant 11 transport through such aquifer systems. In this work, an examination was made of a section of the Rakaia 12 fan, Canterbury, New Zealand. A 3x3 grid of large diameter auger holes were drilled in close proximity to a 13 sea cliff, which provided very good 3D exposure of the fan architecture. A novel smoke tracing experiment 14 and water tracing field tests were conducted to measure the dynamic connectivity of OFG facies. Smoke 15 proved to be an effective tracer for measuring the inter-connectedness of OFG over set distances of 5 m. 16The water tracing tests confirmed OFG are connected across much longer distances -in excess of 18 m. 17Results from both tests revealed how rapid, and non-uniform, aqueous transport can be through alluvial 18 outwash materials. The connectivity information will be used to improve realisations of heterogeneity of 19 the Canterbury Plains aquifer and inform hydrogeological modelling in the future. 20 21

Knowledge of how effectively microbes are transported through porous media is useful for water resource/wastewater management. Despite much research having been done to characterize microbial contaminant transport through various sedimentary materials, very little study has been made on coral sand, such as constitutes the primary substrate of many Pacific atolls. We conducted a set of laboratory column experiments as a preliminary examination of how effective coral sand is at attenuating model pathogens J6-2 and MS2 bacteriophage (phage) under saturated flow conditions mildly representative of field conditions at the Bonriki freshwater lens, South Tarawa, Kiribati. The very poorly sorted gravelly sand coral substrate tested proved very effective at attenuating the bacterial tracer, and spatial removal rates of between 0.02 and 0.07 log cm were determined for J6-2. The ability to determine precise removal rates for MS2 phage was compromised by the use of a plastic apparatus, although the evidence weights toward coral sand being less effective at attenuating MS2 phage than it is . Further research is required to fully assess the ability of coral sand to remove pathogens and to explore how this medium could be engineered into cost-effective water/wastewater treatment solutions on Pacific atolls. The phage data from this work highlight the limitations of using plastic apparatus in experiments targeted at characterizing the fate and transport of viruses.

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The vast majority of microorganisms in aquifers live as biofilms on sediment surfaces, which presents significant challenges for sampling as only the suspended microbes will be sampled through normal pumping. The use of a down‐well low frequency sonicator has been suggested as a method of detaching microbes from the biofilm and allowing rapid sampling of this community. We developed a portable, easy to use, low‐frequency electric sonicator and evaluated its performance for a range of well depths (tested up to 42 m below ground level) and casing types. Three sonicators were characterized in laboratory experiments using a 1 m long tank filled with pea gravel. These included a commercially available pneumatic sonicator, a rotating flexible shaft sonicator, and the prototype electric sonicator. The electric sonicator detached between 56 and 74% of microbes grown on gravel‐containing biobags at distances ranging between 2 and 50 cm from the sonicator. The field testing comprises of a total of 55 sampling events from 48 wells located in 4 regions throughout New Zealand. Pre‐ and post‐sonication samples showed an average 33 times increase in bacterial counts. Microbial sequence data showed that the same classes are present in pre‐ and post‐sonicated samples and only slight differences were seen in the proportions present. The sampling process was rapid and the significant increases in bacterial counts mean that microbial samples can be quickly obtained from wells, which permits more detailed analysis than previously possible.