Evaluation Of Groundwater Vulnerability In Haiyan County, Zhejiang Province

Groundwater is an important resource of water supply and it is the basis for supporting the livelihoods of urban and rural residents, economic development and ecological and environmental protection. However, groundwater pollution has become an increasing concern with the rapid economy expansion in China. Groundwater vulnerability assessment is one of the prerequisites for protecting groundwater quality. Haiyan County in Zhejiang Province is located in the Hangzhou-Jiaxing-Huzhou plain where there are abundant surface water and groundwater resources, and is well known for its agricultural products such as silk, fishes, and rice. Nevertheless, fast increase in livestock and poultry industries and the consequent pollution from these facilities have greatly increased the potential to pollute groundwater.Since groundwater resources are facing increasingly severer pollution, this research targets at the groundwater nitrate leaching vulnerability assessment in Haiyan County. Using the local hydrological, geological and meteorological information, an improved overlay index system (DRST) and a process-based simulation model that combines HYDRUS-1D and Monte Carlo were used to assess the groundwater vulnerability in Haiyan County. The following are main findings from this research:(1) The groundwater vulnerability in Haiyan County is evaluated with an improved index system approach (DRST). Based on the vulnerability index values ranging from 88 to 114, the study area was categorized into four levels (low, medium, intermediate high, and high). The’high’vulnerability areas, where the groundwater is most sensitive to contamination were in the eastern coastal areas in Haiyan County and part of Wuyuan Town, and it accounted for 4.28% of the total study area.(2) A process-based simulation model that integrates Monte-Carlo process method with HYDRUS-1D was also used for groundwater vulnerability assessment. The simulation results indicated that the travel time of the contaminant (nitrate) was shorter and the groundwater vulnerability was greater when the vadose zone is coarser, the groundwater depth is shallower and the precipitation is greater. Through the combination of HYDRUS-1D and Monte-Carlo simulations, factor analysis was conducted on the groundwater depth and the precipitation, and the result. It indicated that the groundwater depth had the greatest influence on nitrate travel time. The process-based simulation also showed that the high vulnerability region, accounting for about 4.31% of the total study area, was mainly in the northeastern coastal area of Haiyan County and Wuyuan Town.We compared DRST with the process-based simulation model and found that the evaluation results of the two methods were very similar. The almost identical distribution of various (low, medium, intermediate high, and high) vulnerability areas by the two methods also validates the rationality and reliability of the results. The DRST and the process-based simulation results both indicated that the high vulnerability areas are located in the northeastern coastal areas of Haiyan County and part of Wuyuan Town, where groundwater protection is urgently required.