Past studies of entrapped air dissolution have focused on one-dimensional laboratory columns. Here the multidimensional nature of entrapped air dissolution was investigated using an indoor tank (180 × 240 × 600 cm(3) ) simulating an unconfined sand aquifer with horizontal flow. Time domain reflectometry (TDR) probes directly measured entrapped air contents, while dissolved gas conditions were monitored with total dissolved gas pressure (PTDG ) probes. Dissolution occurred as a diffuse wedge-shaped front from the inlet downgradient, with preferential dissolution at depth. This pattern was mainly attributed to increased gas solubility, as shown by PTDG measurements. However, compression of entrapped air at greater depths, captured by TDR and leading to lower quasi-saturated hydraulic conductivities and thus greater velocities, also played a small role. Linear propagation of the dissolution front downgradient was observed at each depth, with both TDR and PTDG , with increasing rates with depth (e.g, 4.1 to 5.7× slower at 15 cm vs. 165 cm depth). PTDG values revealed equilibrium with the entrapped gas initially, being higher at greater depth and fluctuating with the barometric pressure, before declining concurrently with entrapped air contents to the lower PTDG of the source water. The observed dissolution pattern has long-term implications for a wide variety of groundwater management issues, from recharge to contaminant transport and remediation strategies, due to the persistence of entrapped air near the water table (potential timescale of years). This study also demonstrated the utility of PTDG probes for simple in situ measurements to detect entrapped air and monitor its dissolution.

BackgroundThe impact of geriatric medicine educational programs on patient level outcomes, as opposed to educational measures, is not well studied. We aimed to determine whether completion of a mandatory geriatrics rotation changed the clinical behaviors of clerks caring for older patients admitted to a medical clinical teaching unit.MethodsWe reviewed the charts of 132 older (>70y) patients, admitted to one medical clinical teaching unit (CTU) during 2005, and cared for by a clinical clerk, for documented functional assessment, cognitive assessment, recognition of medications that cause confusion, and early removal of indwelling urinary catheters. Performance of these outcomes was compared between clerks who had completed a mandatory 2-week geriatrics rotation immediately before the medical CTU rotation (n = 62) and those who completed geriatrics immediately after (n = 74). Patient outcomes were also measured and compared between groups.ResultsCompared to clerks without prior geriatric exposure, clerks with geriatrics exposure were almost 3 times as likely to assess function of their older patients within two days of assuming care (27% vs. 12%, OR: 2.73, 95% CI: 1.12 to 6.66). There were no significant differences in the other clinical behaviors. Patients cared for by geriatrics-exposed clerks were less likely to die or be institutionalized (10% vs. 31%, OR: 0.24, 95% CI: 0.09 to 0.63), and they had shorter lengths of stay by an average of -7.14 days (95% CI: -12.2 to -2.07). Adjustment for baseline differences in age and cognitive impairment did not alter the results.ConclusionsClinical clerks who had completed a mandatory geriatrics rotation were more likely to document functional status upon assuming care of their older medical CTU patients, and there was also an association with better clinical outcomes. This highlights the value of including a geriatric medicine rotation as part of the core clerkship curriculum.

The total dissolved gas pressure (PTDG ) probe has been used in groundwater studies for over a decade, but rarely in assessing contaminant degradation, despite the many degradation reactions that produce or consume dissolved gases. Here we present three studies to demonstrate the application of PTDG measurements to groundwater experiencing contaminant degradation, with discussion of its benefits and limitations. The first study is a pilot‐scale laboratory experiment simulating dissolved ethanol contamination of an anaerobic sand aquifer. Continuous monitoring of PTDG showed the rapid onset of microbial hydrocarbon degradation via denitrification and fermentation. The subsequent formation of a gas phase was revealed when PTDG began mimicking the bubbling pressure (PG *; sum of hydrostatic and atmospheric pressure), fluctuating with atmospheric pressure. Some deviations of PTDG above PG * occurred also, which may hold promise for signalling substantial changes in the rate or type of degradation process (here, the onset of methanogenesis). In the second study, synoptic field measurements at a petroleum plume site demonstrated how elevated PTDG could identify wells with evidence of hydrocarbon degradation (denitrification and/or methanogenesis). And finally, combined field measurements of dissolved oxygen (DO) and PTDG in monitoring wells of a nitrate‐contaminated aquifer (Abbottsford‐Sumas) revealed areas where denitrification was likely occurring. Limitations to PTDG use identified in these studies included the masking of degradation processes by the presence of a gas phase, as when trapped following water table fluctuations or formed from rigorous degradation reactions, and confounded assessment of PTDG patterns from other natural or anthropogenic processes that can also influence groundwater PTDG .

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