Groundwater Vulnerability Assessment In Tongliao Plain

As we know, water resource per capita in China is very poor, groundwater has made a large contribution in the total water resources volume. As an important part of water resource, the groundwater plays an important significance to water supply in North China. However, due to overdraft and poor awareness of protection, water table is deceasing and groundwater cones of depression are occurring. The groundwater has been polluted in different ways and contaminations are developing which caused a series of ecological environmental problems. Groundwater vulnerability reflects the capability of aquifer system to maintain its stability when faces with the adverse effect from the outside world. By distinguishing the degree of groundwater vulnerability in different regions, identifying the ranges in poor level, planning the groundwater functional areas, people are reminded to take reasonable exploitation and protection measures and the authorities are provided foundations to make a better management for groundwater utilization and protection.The groundwater resource comprises 95.46% of the total supply in Tongliao. Cones of depression in Kerqin has occurred and developed because of overdraft, the phreatic water in quaternary unconsolidated rock has been polluted in some extent. Therefore, making an assessment of groundwater vulnerability in Tongliao plain is necessary for protection and utilization.Based on the hydrogeological condition, available data,the realities of situation and the DRASTIC model, the two evaluation-index systems of groundwater pollution vulnerability and quantity vulnerability were established respectively. In this research, six indexes of depth of groundwater, modulus of net recharge, aquifer permeability coefficient, soil media type, aquifer thickness and land-use type were selected to represent groundwater pollution vulnerability and four indexes of coefficient of exploitation, difference of net discharge module and actual exploitable module, aquifer thickness and specific yield were selected for represent groundwater quantity vulnerability. With spatial analysis in Arc GIS and combined with SPSS software, the index weight was obtained through principal component and factor analysis, relative analysis and AHP. In the end, the score of groundwater pollution vulnerability and quantity vulnerability were estimated by raster calculator and then the two type of score were divided into five grades through natural classification. The result showed that the anti-pollution property is relatively well and the quantity vulnerability is in a high level. The sensitivity analysis indicated that the depth of groundwater is the most sensitive factor in the average effective weight of pollution vulnerability and the modulus of net recharge is in a high difference compared with its weight which reflected the unreasonable precision when we got the index. The result of sensitivity analysis for quantity vulnerability was in a good identity with the index weight, which showed that we have a good job in index choosing and weight allocation. Finally, the result was validated: water quality data of sampling points was chosen to validate the pollution vulnerability result which were in a good coherence and the average annul change in depth of groundwater was chosen to validate the result of quantity vulnerability which showed that the two were showed in same variation trend.Suggestions were made for the research of groundwater vulnerability evaluation and protection according to the shortcomings in this job and result.