Occurrence Pattern and Hydrochemistry Cause of The Shallow Groundwater Fluoride in the Dali County, Shaanxi Province

The Dali county lies in the eastnorth sagregion of Wei river down-faulted basin,There are many factors affecting the shallow groundwater fluorine occurrence,such as the hydrology,climate,terrain, geological backgro und,hydrogeologic conditions and hydrogeochemistry in this area.Based on the shallow groundwater survey data and USGS'PHREEQC soft ware,We studied the occurrence characteristics of fluoride in groundwater.The precipitation of the study areais low and the evaporation is strong.The type of high fluoride is evaporation and enrichment,or dissolution and enrichment.The main lithology is clay, sub-clay,fine sand、fine porosity,the mineral components of rich fluoride provides an abundance of matter resources.The level to groundwater depth is shallow,capillary height of the zone of aeration is high,the water conductivity is low,multilayer mutual aquifer construct provide advantaged store water space for fluoride enrichment.Integrating hydrogeo chemistry action,in order to reveal the regulation of fluoride flowing the groundwater path,studied the existence forms and percentum-densities of fluo ride and the main complicatedions,at the same time,researched dissolution-precipitation problems of their mineral sources.