DETERMINATION OF HYDRAULIC C.ONDUCTWITY TENSOR USING A NONLINEAR LEAST SQUARES ESTIMATOR1

ABSTRACT: Reliable and consistent estimation of the components of the hydraulic conductivity tensor provides information needed to make proper decisions regarding clean up and restoration of contaminated aquifers. In this study, the nonlinear least-squares estimation technique was applied to drawdown versus time data from three or more observation wells to determine a theoretical ellipse of equal drawdown. The angle of rotation of this ellipse with respect to the working coordinate axes was determined by a procedure based on contouring the drawdowns at a given time. This ellipse, in turn, was used to estimate the directions and magnitudes of the horizontal components of the hydraulic conductivity tensor. The technique is applicable to confined, as well as leaky, aquifers. Sources of error in this technique include nonhomogeneity of the aquifer and partial penetration of the pumping and observation wells into the aquifer. The procedure presented may be used as an additional tool to verify computations of hydraulic conductivity anisotropy based on other techniques.     

Correlation between lead exposure and cognitive function in 12-year-old children: a systematic review and meta-analysis

Environmental Science and Pollution Research - Lead exposure as a toxic material especially in children can be recognized as a harmful factor for cognitive function system. This meta-analysis was...     

Optimization of Headspace Solid Phase Microextraction Procedure for Trace Analysis of Toluene

This study describes optimization of headspace solid phase microextraction followed by gas chromatography equipped with a flame ionization detector for toluene at trace level in spiked urine. The parameters affecting the extraction and gas chromatographic determination of analytes were studied: extraction time and temperature; desorption time and temperature; addition of NaCl; and pH, volume and agitation of the sample. Optimized headspace extraction was carried out at 30 °C for 6 min in the presence of 0.2 g-m^-1of NaCl in the sample solution. Also, sample volume and sample pH were optimized at 5 ml and 7 (neutral pH), respectively. Desorption of the analytes was carried out at 250 °C for 60 s. The optimized procedure was validated with 3 different pools of spiked urine; it showed good reproducibility over 6 consecutive days and 6 within-day experiments. The study also determined the accuracy, linearity and detection limits of this method.     

Youth and sustainable waste management: a SEM approach and extended theory of planned behavior

The present study aims to develop the Theory of Planned Behavior (TPB) to explain comprehensively the establishment of intention and behavior toward source separation of waste. The extended TPB involves the significant structures affecting the behavior along with the original variables of TPB model. Data were gathered from 420 students in Ferdowsi University, Iran, using questionnaires, and analyzed by cluster analysis, discriminant analysis and structural equation modelling techniques (SEM). The cluster analysis identified three distinct grouping according to TPB constructs, and it was validated by discriminant analysis. SEM results displays that motivation had the most important impact on intention, followed by moral obligation, perceived behavior control, subjective norm, situational factor and attitude. Fit statistic of the extended TPB model was good and had better explanatory power compared to the original TPB. It describes 81 and 57% of the variance for intention and behavior toward source separation waste, respectively.     

Porous materials for the recovery of rare earth elements,platinum group metals,and other valuable metals: a review

Environmental Chemistry Letters - The demand for valuable metals such as rare earth elements and platinum group metals is rising fast in the context of the depletion of natural resources...