Groundwater Hydro-Chemical Characteristics Studyin Hetao Plain

This paper firstly makes a global review over the researches, theories about distribution, accumulation of arsenic groundwater all over the world and in Hetao Plain, China. Secondly, based on geology, geological structure, hydro-geology, groundwater flow and recharges/ discharges conditions, this study analyses test data of over 800 samples from groundwater, surface water and sediment to depict the distribution characteristics, ove-standard ratio among the 14 measured indexes such as the p H, ORP, TDS, Cl-, SO42-, HCO3-, As, Fe, P and F-, thus to illustrate the hydro-chemical classifications for each subregions rpresenting various groundwater environment. Then this paper studies the correlation between components in groundwater of the typical high-arsenic region as wells as the whole Hetao Plain. Next, the distribution and formation mechanism of several over-standard components including As, Fe and F are discussed. Lastly, several tentative conclusions are made as following:1. Hydro-chemical characteristics, over-standard ratio and distribution of each groundwater components are studied all over Hetao plain(13000 km2) : 1) for locating in an arid to semi- arid area, alkalis metal-non-bicarbonate groundwater(49.29%) is the most dominant type comparing to the alkalis metal- bicarbonate(29.76%), alkalis metal-non-bicarbonate(16.06%) and alkaline-earth metal-non-bicarbonate(4.88%) types in the study area; 2) the primary over-standard components includes As、Fe、Cl-、F-、SO42-、NO3-、TDS, and the over-standard ratios of them are respectively 28.80%(As>0.05 mg/L)、61.56%、52.71%、20.74%、55.21%、2.50%; 3) high-As groundwater(As>0.05 mg/ L) in Hetao west has a banding distribution along the low-lying terrain of Langshan mountain front, and high-As groundwater distributes widely in Hetao middle-east. Arsenic density varies greatly between closely-proximate locations, which increases as the boreholes goes deeper within 80 m underground; High-iron groundwater distributes over the alluvial-lacustrine area in the middle Hetao plain, which presents larger density in low-lying or discharge zone; high-fluorine groundwater has a banding distribution on alluvial-proluvial fan nearby the mountain front.2. According to the results of multivariate statistical analysis, there exsits significant positive correlations between As and P, Fe, F, p H as well as F and p H for groundwater both in west area and the whole study area; for the whole study area, there exsits negtive correlation between As and ORP, SO42- oppositely.3. The genetic mechanism of high-As, high-Iron and high-fluoride for groundwater in Hetao Plain are concluded in this paer: 1) the high-arsenic for groundwater originates from Quaternaray sediments or deeper groundwater migrating along tectonic fracture; 2) iron in groundwater origins from abundant quaternary sediments carried by the Yellow river, which then dissolves out with the changing of Oxidizing reduction conditions; 3) the surrounding mountainous nearby the plain, and the geologic climate, structure, hydro-geology/chemical together contributes to the accumulation of fluoride in Hetao Plain.