Hydrogeochemical evolution of groundwater in a Quaternary sediment and Cretaceous sandstone unconfined aquifer in Northwestern China

A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for the protection of water resources. To assess groundwater chemistry, groundwater sampling was performed from different representative aquifers in 2012–2013. A Piper trilinear diagram showed that the groundwater types can be classified into Na–SO4 and Na–Cl types. Only one groundwater sample was Na–HCO3 type. The dominant cations for all samples were Na+. However, the dominant anions varied from HCO3− to SO42−, and as well Cl−. The mean total dissolved solid (TDS) content of groundwater in the region was 1889 mg/L. Thus, only 20% of groundwater samples meet Chinese drinking water standards (< 1000 mg/L). Principal component analysis (PCA) combined with hierarchical cluster analysis (HCA) and self-organizing maps (SOM) were applied for the classification of the groundwater geochemistry. The three first principal components explained 58, 20, and 16% of the variance, respectively. The first component reflects sulfate minerals (gypsum, anhydrite) and halite dissolution, and/or evaporation in the shallow aquifer. The second and third components are interpreted as carbonate rock dissolution. The reason for two factors is that the different aquifers give rise to different degree of hydrogeochemical evolution (different travel distances and travel times). Identified clusters for evolution characteristic and influencing factors were confirmed by the PCA–HCA methods. Using information from eight ion components and SOM, formation mechanisms and influencing factors for the present groundwater quality were determined

Comparison of methods for calculating geometrical characteristics of discontinuities in a cavern of the Rudbar Lorestan power plant

© 2017 Springer-Verlag GmbH Germany Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical characteristics of discontinuities related to the rock mass around the powerhouse cavern of Rudbar Lorestan Pumped Storage Power Plant which is located in a extensional zone of an anticline measured based on linear and areal sampling (circular and rectangular) methods. These methods are used to calculate the geometrical properties of discontinuities at the Rudbar Lorestan powerhouse cavern. Quite a large quantity of scanlines and the window samplings used in this research indicated that the areal sampling methods are more time consuming and more cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, their associated statistical distributions of function, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties are related to four sets of discontinuities that were computed. There is an acceptable difference between the mean trace length measured using two linear and areal methods for the two joint sets. Due to the fact that the region under study is highly tectonized, there is as well the surveying results of the discontinuities at different locations that have given rise to the performance having an equality of two for the multi means and variances test (ANOVA) for studying the homogeneity of the data. The dominant tectonic of the region as well as the genetic type of the discontinuities have caused their Fisher’s constant to be decreased, and the joint sets with uniform genetics have given rise to the same probability density function of the trace length and spacing. It is difficult to estimate the volumetric intensity of the study area. Review of the results depicts that the volumetric intensity of a joint set computed using different methods is different up to 38%. So, it is necessary to measure the geometrical characteristics of discontinuities by some methods, and taking into consideration correcting biases, do calculation of the areal and volumetric parameters of joint sets, studying the homogeneity and genetic type of discontinuities to generate the 3-D discrete fracture network