Groundwater characteristics in the shallow aquifers of Huhhot region in Inner Mongolia, PR China : Implications on the mobilisation of arsenic

• Elevated arsenic (As) concentration ingroundwater is becoming a worldwide problem. In Huhhot Alluvial Basin (HAB) in  Inner Mongolia, People’s Republic ofChina, a population of over a million isexposed to severe health risk due to theconsumption of groundwater with high Asconcentration. In some arsenic seriouslyaffected areas, As concentration reach 1491µg L-1, 149 times over WHO’s drinkingwater guideline value for As and exceed theChinese drinking water standard by a factorof 30 times. Due to the acute shortage ofsafe water supply and inefficient watermanagement system, people are compelledto drink groundwater with high As concentration. Long period ingestion of water withhigh As concentration have lead to chronicarsenic poisoning among the residents ofthe region. This present work deals with thehydrogeochemical characterisation of thegroundwater of the shallow alluvial aquifers and their implications on the chemistryand its relation to the mechanism of Asmobilization in the HAB.Groundwater samples were collected during October 2003, from 29 sites in the village of Tie Men Jing, located about 100 kmfrom Inner Mongolia’s capital Huhhot. ThepH, redox potential (Eh), temperature andelectrical conductivity were measured atsites while major ions, trace elements including As total and As (III) were analyzedin laboratories at the Royal Institute ofTechnology and Stockholm University inSweden. Groundwater is generally neutralto alkaline and the pH varies from 6.67 to8.7. The redox potential (Eh) lies between74 and 669 mV. The electrical conductivity(EC) range varies from 581 to 5200 µS cm-1. Temperature ranges from 9.1 to 13.5 °C.Depths of wells are from 4 m to 75 m.Groundwater is mostly of Na-Mg-HCO3-Cl-type and dominated by HCO3-and Cl-asthe predominant anions. The concentrationsof SO42-range between 0.3 and 172.8 mg L-1and there is a trend of decreasing sulfateconcentrations with increase in well depth.The levels of NO3-were lower than theWHO´s guideline value of 50 mg L-1in 27wells. These high NO3-concentrations  could have been caused by anthropogeniccontamination due to the sanitation practices.The PO43-concentration ranges between 0.04to 2.6 mg L-1.Total As concentration ranged from belowdetect limit (5.2 µg L-1) to 141 µg L-1. In 28of the investigated wells, As levels exceededWHO’s guideline value 10 µg L-1and 17wells exceeded Chinese standard 50 µg L-1.Among the 42 groundwater samples of theshallow aquifers only three complied withthe WHO drinking water guideline value forAs. The dominant species in the groundwaterwas As (III). In the 29 wells of Tie MenJing, the concentration of Fe and Mn –exceeded the WHO’s guideline value by afactor of 10.The aquifers are composed of Quaternary(mainly Holocene) fluvial and lacustrinesediments. High As occurring in anaerobicgroundwater in low-lying areas is associatedwith high concenrations of dissolved Fe andMn. Improved water supply system, employment new water and energy resources,poverty fighting and expertise cooperationare recommended to solve Huhhot basinrural area’s drinking water problem.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Geoteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Geotechnical Engineering (hsv//eng)

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