Groundwater

Artificial Neural Networks (ANNs) have been found to be a robust tool to model many non-linear hydrological processes. The present study aims at evaluating the performance of ANN in simulating and predicting ground water levels in the uplands of a tropical coastal riparian wetland. The study involves comparison of two network architectures, Feed Forward Neural Network (FFNN) and Recurrent Neural Network (RNN) trained under five algorithms namely Levenberg Marquardt algorithm, Resilient Back propagation algorithm, BFGS Quasi Newton algorithm, Scaled Conjugate Gradient algorithm, and Fletcher Reeves Conjugate Gradient algorithm by simulating the water levels in a well in the study area. The study is analyzed in two cases-one with four inputs to the networks and two with eight inputs to the networks. The two networks-five algorithms in both the cases are compared to determine the best performing combination that could simulate and predict the process satisfactorily. Ad Hoc (Trial and Error) method is followed in optimizing network structure in all cases. On the whole, it is noticed from the results that the Artificial Neural Networks have simulated and predicted the water levels in the well with fair accuracy. This is evident from low values of Normalized Root Mean Square Error and Relative Root Mean Square Error and high values of Nash-Sutcliffe Efficiency Index and Correlation Coefficient (which are taken as the performance measures to calibrate the networks) calculated after the analysis. On comparison of ground water levels predicted with those at the observation well, FFNN trained with Fletcher Reeves Conjugate Gradient algorithm taken four inputs has outperformed all other combinations.

Background and objective: Today, use of models to illustrate the facts and better understanding them, as well as make accurate decisions about phenomena is very common. One of these models is groundwater flow simulation model used by experts in many countries, also, the accuracy and validity of their results has been proved. The object of this study is to evaluate the effect of current management plans of aquifer and Jajrood River basin on changes of the water table of unconfined aquifer and piezometric level of confined aquifer by numerical simulation. Using numerical models, it can be predicted that with the governing process or different management scenarios, how the aquifer reacts to abstraction and recharge.

Materials and methods: In this study, hydraulic behavior of Varamin Plain aquifer was simulated using the Modflow code in GMS software in stable and unstable states. After calibrating the model, hydrodynamic coefficients were corrected, then using the resulted model, quantitative behavior of the aquifer was predicted for two management scenarios in the future years. The first scenario expresses the existing quantitative conditions of the Varamin Aquifer. That is, water do not flow to the plain from southeast wastewater treatment plant of Tehran, but water flows to the Varamin aquifer from Jajrood River. The second scenario indicates situation of the aquifer if the planning are carried out by the relevant organizations. Under this scenario, assigned values from discharging of the southeast wastewater treatment plant of Tehran enter the study area, though due to the implementation of Mamlou storage dam, a significant portion of the surface water resources of Jajrood River will not enter the plain.


Results: According to the maps resulted from the first scenario, decline in groundwater level continues as in previous years, but in the second scenario, considering the utilization of wastewater treatment plant discharge, despite the cutting off the water entering from the Jajrood River to the plain, the groundwater decline rate will decrease, although this decline continues. Comparison of the model implementation under first and second scenarios shows that with the implementation of planned projects, part of the aquifer’s quantitative problems, particularly in the northern areas of the plain, will be decreased, so that in some northern areas the expected decline in groundwater (results of the first scenario) has decreased about 30 to 40 meters by 2041. In the second scenario, a balance of the groundwater is still decreasing, so that storage reduction rate of the aquifer is about 100000000 m3 annually.

Conclusion: Results of the simulation show that under both scenarios (current trend and after implementation of ongoing plans), balance of the groundwater is decreased and decline in water table will be continued, however in comparison to the first scenario, decline rate of water table under the second scenario will be decreased. It can be stated that in order to stop the decline in water level in Varamin aquifer, in addition to water entering plan from Tehran wastewater treatment plant to Varamin plain, recharge of the aquifer from Jajrood River (as the main source of aquifer natural recharge) should be continued.

The groundwater quality of Wadi Al Arab aquifer, northwest Jordan, was assessed for its high molybdenum concentrations, which reach 1.62 mg/L. This value of Mo-concentration was far beyond the Jordan Institution for Standards and Metrology (JISM) and World Health Organization (WHO) guidelines. Hydro-geochemical studies were carried out in order to assess the chemistry of the groundwater quality focusing on identifying the hydrogeo-chemical processes and mechanisms that are involved in the high Mo concentration. The water quality data of Wadi Al Arab boreholes (1986-2018) was collected, and the dataset analyzed. Interpretation of hydrochemical data showed that the anions are dominated by 3 HCO − with abundance order of 3 HCO − > 2 4 SO − > Cl − > 3 NO − , while the main cation is Ca 2+ , with abundance order of Ca 2+ > Mg 2+ > Na + > K + ; water type is 3 Ca-HCO −. The reason is the passage of groundwater through carbonate rocks. The distribution of the sampling points in the Gibbs diagram showed that the majority of samples are plotted within the field of rock weathering, which indicates that the main factor controlling dissolved hydrochemical components of the water samples is the dissolution of the rock-forming minerals. The scattered plot of the Mo with other critical heavy metals shows two different trend lines suggesting initiation of molybdenum to groundwater which is probably derived from oil shale and phosphate. The effects of pH and redox potential on Mo mobility in water are reviewed using the paurbaix diagram. The Mo species of the sampled wells are confined to the field of () 2 4 MoO − : anoxic/non-sulfidic condition (Fe reduction) which is located in the unconfined part of the aquifer, and () s 2 MoS which is sulfidic condition (low and high) in the confined aquifer. How to cite this paper: Hiasat, T.H., Ri-mawi, O.A. and Makhlouf, I.M. (2020) Hydrochemical Evaluation of Molybdenum

Intake of water with high concentration of nitrate is a major problem in many countries as it affects health of humans. The present study was carried out with the objective of determining the causes for higher nitrate concentration in groundwater in parts of Nalgonda district, Andhra Pradesh, India. The study area is located at a distance of about 135 km towards ESE direction from Hyderabad. Nitrate concentration in groundwater of this area was analysed by collecting groundwater samples from 46 representative wells. Samples were collected once in two months from March 2008 to January 2009. The nitrate concentration was analysed in the laboratory using Metrohm 861 advanced compact ion chromatograph using appropriate standards. The highest concentration recorded during the sampling period was 879.65 mg/L and the lowest concentration was below detection limit. Taking into consideration 45 mg/L of nitrate as the maximum permissible limit for drinking water set by BIS, it was found that ...