Approximate evaluation of contaminant transport through vertical barriers

Containment of groundwater contamination using physical barriers can be an important element of a subsurface remediation program. This work presents simple analytical tools for predicting the performance of barriers in terms of the steady-state contaminant flux across the barrier, the duration of the transient period following barrier installation, and the time-dependent contaminant concentration distribution within the barrier. The analytical expressions are developed from approximate boundary layer (BL) solutions to the advective–dispersive equation subject to conservative fixed concentration boundary conditions. Critical ranges of important dimensionless quantities are identified for use in barrier performance assessment, for both steady-state and transient conditions. Comparative calculations made with the BL equations and more exact semi-analytical solutions are used to characterize the accuracy and applicability of the BL approach.     

Moderating effects of self-efficacy for the relationship between training method and anxiety and stress reactions of newcomers

The purpose of this study was to examine the moderating effect of self-efficacy for the relationship between training method and newcomers' anxiety and stress reactions. The two methods of training examined were formal orientation and training and tutorial training. A sample of 198 newly-hired entry-level accountants completed a questionnaire following their first few weeks of entry. The results indicated that self-efficacy was negatively related to anxiety but not stress. However, a positive relationship between anxiety and stress suggested that self-efficacy was indirectly related to stress through its relationship with anxiety. Further, self-efficacy was found to moderate the relationship between training method and anxiety. Formal orientation and training was related to lower anxiety for newcomers with low technical self-efficacy. The opposite result was found for tutorial training. Tutorial training was related to higher anxiety for newcomers with low academic self-efficacy. The relationship between training and anxiety did not vary by training method for newcomers with high self-efficacy. The research and practical implications of a self-efficacy theory framework are discussed for the training, socialization, and adjustment of newcomers.     

Thermal radiation from vented dust explosions

The fireball from a vented dust explosion presents a danger to personnel who may be within the vicinity of the event. The risk of serious injury to people caught within the fireball is great, and anyone just outside the fireball may be at risk from thermal radiation. This report describes a project in which the effects of thermal radiation from vented dust explosions was studied. The aim was to establish the areas around a fireball in which people would be at risk from thermal radiation. Six dusts were tested in a large vented vessel and external fireballs were generated under a range of conditions. The fireball geometry and the heat flux from the fireball were studied. A range of material samples were exposed to the fireball. The safe areas around the fireballs were established for each of the six dusts. Generally, the larger vent areas resulted in the larger fireballs and high heat pulse values. However, the fireball was usually too brief to ignite fabric samples unless they were very close to the fireball. The work has shown that in most cases the safe area was relatively close to the surface of the largest fireball.     

Constructed Wetland Treatment of Nitrates: Removal Effectiveness and Cost Efficiency

A constructed wetland (CW) was strategically placed to treat nitrates in groundwater as part of a watershed‐based farmer engagement process. Using stream water quality data collected before and after installation, this CW was found to reduce stream concentrations of nitrogen from nitrate (NO₃‐N) during the growing season by about 0.14 mg/l at mean streamflow, a 17% reduction. Based upon realistic ecological and economic assumptions, about 80 kg of NO₃‐N were removed annually by the CW at a cost of around US$30/kg. This per unit cost is at the low range of small wastewater treatment plant costs for nitrates, but higher than the costs of reduced fertilizer application.