Civil and Structural Engineering

In Nigeria, there was a steady growth in per capita real government educational expenditure from 1970 to 1976, after which a continual decline set in to date. The trend after 1976 is a cyclic decline showing growing underdevelopment or falling levels of educational standards in ...

This study presents a new method to visualise forced-gradient tracer tests in 2-D using a laboratory-scale aquifer physical model. Experiments were designed to investigate the volume of aquifer sampled in vertical dipole flow tracer tests (DFTT) and push–pull tests (PPT), using a miniature monitoring well and straddle packer arrangement equipped with solute injection and recovery chambers. These tests have previously been used to estimate bulk aquifer hydraulic and transport properties for the evaluation of natural attenuation and other remediation approaches. Experiments were performed in a silica glass bead-filled box, using a fluorescent tracer (fluorescein) to deduce conservative solute transport paths. Digital images of fluorescein transport were captured under ultraviolet light and processed to analyse tracer plume geometry and obtain point-concentration breakthrough histories. Inorganic anion mixtures were also used to obtain conventional tracer breakthrough histories. Concentration data from the conservative tracer breakthrough curves was compared with the digital images and a well characterised numerical model. The results show that the peak tracer breakthrough response in dipole flow tracer tests samples a zone of aquifer close to the well screen, while the sampling volume of push–pull tests is limited by the length of the straddle packers used. The effective sampling volume of these single well forced-gradient tests in isotropic conditions
can be estimated with simple equations. The experimental approach offers the opportunity to evaluate under controlled conditions the theoretical basis, design and performance of DFTTs and PPTs in porous media in relation to measured flow and transport properties.

Heterogeneity in aquifer permeability, which creates paths of varying mass flux and spatially complex contaminant plumes, can complicate the interpretation of contaminant fate and transport in groundwater. Identifying the location of high mass flux paths is critical for the reliable estimation of solute transport parameters and design of groundwater remediation schemes. Dipole flow tracer tests (DFTTs) and push-pull tests (PPTs) are single well forced-gradient tests which have been used at field-scale to estimate aquifer hydraulic and transport properties. In this study, the potential for PPTs and DFTTs to resolve the location of layered high- and low-permeability layers in granular porous media was investigated with a pseudo 2-D bench-scale aquifer model. Finite element fate and transport modelling was also undertaken to identify appropriate set-ups for in situ tests to determine the type, magnitude, location and extent of such layered permeability contrasts at the field-scale. The...

Single well forced gradient tracer tests are a potential cost-effective approach to estimate in situ aquifer contaminant fate and transport parameters for use in natural attenuation assessments and remediation schemes. To date dipole flow tracer tests have been used to measure the conservative and hydraulic parameters of an aquifer, while push-pull tests are well characterised for use with biodegrading tracers. The effect of typical aquifer physical heterogeneity on the ability of single well tests to successfully estimate parameters has not yet been characterised. Also, the ability of single well tests to accurately and quickly measure aquifer parameters using tracer mixtures should be analysed. To investigate the effect of physical heterogeneity on single well tests scaled down ultraviolet imaging experiments were performed in a low profile box. Potential tracers for use in mixtures were investigated through column and batch experiments: Inorganic anions and fluorescein, inorganic...

Single well forced gradient tracer tests can be used to assess aquifer properties for natural attenuation and remediation design. Measurements of aquifer properties monitored in the well are depth-averaged and therefore may misrepresent or fail to identify important flow and mass flux paths. Such spatial information is critical for remedial system design. UV imaging tests were undertaken in a pseudo 2-D tank filled with glass beads, with a centrally positioned slotted well screen. Fluorescent tracer migration during dipole flow tracer tests (DFTTs) and push―pull tests (PPTs) were examined under isotropic and simple layered conditions. Results show that small variations in hydraulic conductivity significantly affect tracer flow. For DFTTs these produce discernable differences in breakthrough curves, which can be used to help identify important hydrogeological features.

Comprehensive hydraulic analysis of sediment retention ponds is commonly achieved through interpretation of residence time distribution and derivation of indices associated with short-circuiting and mixing. However, the availability of various indices indicates the need for careful selection of the most appropriate indices. This study compares some of the commonly used hydraulic performance indices, together with a new short-circuiting index, τ5, for five different flow regimes in a model sediment retention pond. The results show that τ5 was the best measure for short-circuiting. Among the mixing indices, only the Morril index correctly represented the physical behaviour of the experiments. In addition, two hydraulic efficiency indices, λ and a moment index (MI) were assessed and showed a good correlation with the short-circuiting and mixing indices, but MI was more reproducible than λ. Based on these results, this study recommends using τ5, Morril index and MI for analysis of hydra...

Baffles have been utilised in the ponds and wetland to improve the rate of treatment for the polluted water. However, there is limited research in the optimum configuration and type of baffles for sediment retention ponds (SRP). In this study, the effect of porous and submerged solid baffles on the hydraulic performance of a model SRP is assessed. In order to optimise the type and configuration of baffles, several configurations were tested with four different metal meshes (with different aperture size and open area) as porous baffles, and acrylic sheets as solid baffles. The porous baffles were more effective in increasing the retention time and improving the overall hydraulic performance than the solid baffles. The finest mesh with 0.415 mm aperture size and 40% open area had the highest performance for most of the configurations with 3 or less baffles. However, for four and five baffles, the medium-fine mesh with 1 mm aperture size and 42% open area was the best. For three porous...

Effective treatment of the polluted stormwater runoff from earthworks sites is a major concern for water authorities. Sediment retention ponds provide a quiescent place for settling the suspended particles in runoff. However, improper design of ponds can lead to significantly low treatment efficiency. As a retrofit practice, baffles have been utilised to improve the rate of settling of the suspended particles. Yet there is limited information in the design guides about the optimum configuration and type of baffles. This study investigates the effect of porous and submerged solid baffles on the hydraulic performance and trap efficiency of a model sediment retention pond. Several configurations were tested using four different metal meshes (with different aperture size and open area) as porous baffles, and acrylic sheets as solid baffles. The porous baffles were more effective in improving the overall hydraulic performance than the solid baffles. For 4 and 5 baffles, the medium-fine m...

In situ denitrification is a good method for reducing nitrate contamination,but is restricted by the lack of carbon in the groundwater.A slow-release organic carbon source was developed to supply the carbon.Simulations demonstrated that the material improves the denitrification.In a ...

We developed a biocompatible and highly efficient approach for functionalization of bacterial cell wall with magnetic nanoparticles (MNPs). Three Acinetobacter baylyi ADP1 chromosomally based bioreporters, which were genetically engineered to express bioluminescence in response to salicylate, toluene/ xylene and alkanes, were functionalized with 18 3 nm iron oxide MNPs to acquire magnetic function. The efficiency of MNPs functionalization of Acinetobacter bioreporters was 99.96 0.01%. The MNPs-functionalized bioreporters (MFBs) can be remotely controlled and collected by an external magnetic field. The MFBs were all viable and functional as good as the native cells in terms of sensitivity, specificity and quantitative response. More importantly, we demonstrated that salicylate sensing MFBs can be applied to sediments and garden soils, and semiquantitatively detect salicylate in those samples by discriminably recovering MFBs with a permanent magnet. The magnetically functionalized cells are especially useful to complex environments in which the indigenous cells, particles and impurities may interfere with direct measurement of bioreporter cells and conventional filtration is not applicable to distinguish and harvest bioreporters. The approach described here provides a powerful tool to remotely control and selectively manipulate MNPs-unctionalized cells in water and soils. It would have a potential in the application of environmental microbiology, such as bioremediation enhancement and environment monitoring and assessment.