Study On Groundwater Vulnerability Based On Process Simulation

Groundwater vulnerability reflects the relative potential possibility of groundwater systems to be polluted. The groundwater environmental problems are more and more serious with the rapid development of economic and human activities. The groundwater vulnerability assessment can provide scientific basis on exploiting and protecting groundwater resources. They can also help the public to raise consciousness about protection of groundwater pollution risk and taking priority in groundwater protection.There are many methods for groundwater vulnerability assessment, including overlay and index method, the method based on process simulation model and statistical method, etc. The method based on process simulation model takes account of the whole processes of water and contamination transform in vadose zone and saturated zone, which is a kind of efficient method for assessment of groundwater vulnerability. In this paper, the method based on process simulation model is studied and applied for fresh groundwater vulnerability assessment in Tangshan plain. This method can overcome subjective impacts induced by other methods and improve the rationality and practicability of assessment results.According to the different targets of groundwater protection, groundwater level and pumping well are selected as the two protection targets of groundwater vulnerability assessment. Thus groundwater system is divided into two sub-systems: vadose zone and saturated zone. Assessment system of groundwater vulnerability based on the process simulation model is built up respectively.According to the first protection target, the vadose zone is selected as the assessment range. In the study of groundwater vulnerability assessment, Monte-carlo method and randomized parameters are coupled into the whole simulation process. Net recharge coefficient of groundwater, vulnerability index of groundwater quantity and leachning concentration of nitrate nitrogen are analyzed. Based on these parameters, complex index of groundwater vulnerability is used to assess vulnerability reflecting groundwater quality and quantity. The assessment results of groundwater area in Tangshan plain are fit well with actual measured data.According to the second protection target, saturated zone is selected as the assessment range. Aquifer thickness, net recharge and denitrification coefficient are used as the major factors for impacting groundwater vulnerability. Many scenarios are simulated by using MODFLOW model, which providing the ratio of concentration at groundwater level and in pumping well. The nitrate nitrogen concentrations in pumping wells are predicted by BP artificial neural network and groundwater vulnerability at saturated zone is assessed. The assessment results are tested by the measured data in field.Based on the assessment results of vadose zone and saturated zone, vulnerability of groundwater system is assessed by process simulation coupling with vadose zone and saturated zone. By compared with the overlay and index methods, the advantages of this method employing process-based on simulation models is to be anylized.