Research On Groundwater Safety Assessment

Groundwater is a precious natural resource, which was closely related with the human life and the physical infrastructure for human survival and development. With the population growth and economic development, the increase of groundwater withdrawal and the emissions of pollutants, causing serious groundwater safety problems, has caused wide public concern. This study relies on the program "111" of innovation and knowledge introduction plan as colleges and universities subject of ministry of education and state administration of foreign experts affairs—hydrological ecology and water security of innovation and knowledge introduction plan in arid and semi-arid areas, chooses the central region of Guanzhong plain for the typical region, carries out in-depth study on the groundwater safety problems.In this paper, we discuss several key issues as follows:①What are the groundwater safety problems, what are the main features of groundwater safety problems? what the types of groundwater safety problems should be classified into?②What is the difference between the Safety assessment of groundwater and the safety capacity assessment of groundwater, which should be selected for in-depth study?③According to the characteristics of groundwater safety problems, the safety assessment should be divided into the safety assessment of groundwater quality and quantity, what is the difference between the two assessment methods?④How to achieve safety assessment of groundwater in the practical application, how to test the reliability of the assessment results?The conclusions as follows:(1) Strictly speaking, any groundwater own safety problems and the external environment safety problems caused by the groundwater safety problems, can be classified as areas of groundwater safety. The groundwater safety problems can be classified into two categories:One called "groundwater own safety" that groundwater is affected by the external environment directly or indirectly and its safety status also changes; the other called "groundwater used safety" that the safety problems are caused by the external environment.(2) This paper focus on the "groundwater own safety". The difference between the safety assessment of groundwater and the safety capacity assessment of groundwater is that the former is a status assessment and the latter is a capacity assessment. In order to assess the capacity for groundwater which makes itself in a safety state, we try to determine two safety assessment methods for groundwater quality and quantity.(3) For the safety assessment of groundwater quality, this paper focuses on the groundwater vulnerability assessment. We improve the DRASTIC model which is used widely and point out that the model can only be applied to the unconfined aquifer. For the indexes selection, the unconfined aquifer vulnerability assessment determines the DRSTICH model which consists of depth of water-table, net recharge, soil media, topography, impact of the vadose zone, hydraulic conductivity of the aquifer, thickness of the aquifer. The confined aquifer vulnerability assessment determines the PDLCT model which consists of the results of the unconfined aquifer vulnerability assessment, depth of confined aquifer, category of aquiclude, continuity of aquiclude, and thickness of aquiclude. For the weight distribution, We determine the combined weight which consist of the subjective and objective weights. The subjective weight is achieved by the analytical hierarchy process (AHP) and the objective weight is achieved by the genetic projection pursuit method (GPPM).(4) For the safety assessment of groundwater quantity, we propose the concept of anti-consumption performance of groundwater to replace the concept of safety assessment of groundwater quantity. The anti-consumption performance of groundwater is the ability for the groundwater quantity to anti-consumption performance under the effect of the external environment. Based on the "pressure-state-response" conceptual framework, we build the assessment indexes system, which consist of the population density, GDP growth, water consumption for ten thousand Yuan GDP, water shortage rate, rainfall, drought index, the modulus of surface water resources, aquifer media type, the salinity of shallow groundwater, mining strength, the modulus of groundwater resources, sewage treatment rate, the rate for groundwater supply, the rate for groundwater supply to agricultural irrigation water, the groundwater consumption for ten thousand Yuan of agricultural output. We refer to previous studies to determine the grading standards. Weight distribution is still determined by the combined weight of the subjective and objective weights. (5) In this paper, we analysis the relationship between the safety of groundwater quality and quantity and point out that the groundwater requires both quality and quantity safety, if any has problems, the groundwater is not the really safe. Based on this idea, we establish the overall safety standards of groundwater, and propose the corresponding management strategies for groundwater.(6) The safety assessment method of the groundwater was used in the central region of Guanzhong Plain. Based on the GIS technology, we draw the zoning plan for the unconfined aquifer vulnerability assessment and the anti-consumption performance assessment of the groundwater below 300m. The sulfate concentration in 33 monitoring wells were used to test the vulnerability assessment results and the method of qualitative analysis was used to test the anti-consumption performance assessment results. The results show that the assessment results of both methods are reliable.