Hydrogeochemical characteristics of karst groundwater in Tam Diep, Ninh Binh, Vietnam

Vu Thi Minh Nguyet, Vu Thi Minh Nguyet

DOI: http://dx.doi.org/10.3986/ac.v45i3.3588

Abstract

The Dong Giao karst aquifer is a major source of drinking water for domestic and agriculture use in Tam Diep city. Understanding of hydrogeochemical characteristics and water quality of the karst aquifer are useful information for sustainable use and protection of groundwater in the area. A total of 30 water samples from the main karst springs and domestic wells were collected to identify the physical property, chemical composition of karst water and water-rock interaction. Physico-chemical parameters (pH, water temperature, electrical conductivity and alkalinity) and major ions (Ca2+, Mg2+, Na+, K+, SO42−, NO3−, Cl−) were measured in situ and analyzed in the lab. Water samples from drinking water source Spring 18 and other important karst springs were taken to detect Escherichia coli (E.coli). A tracer test was also carried out for providing contamination information. Results show that the hydrochemical types of Tam Diep groundwater were of calcium magnesium bicarbonate (Ca-Mg-HCO3) and calcium bicarbonate (Ca-HCO3). The carbonate dissolution line and Ca/Mg ratios clearly indicated that the weathering of carbonate rocks (limestone and dolomite) is the dominant process controlling the chemistry of groundwater of the test site. Chemical quality of groundwater ranks from good to excellent for drinking and irrigation, and total hardness values are relatively high. In contrast, all microbial samples contain high number of E.coli and thus by microbial standards, spring water quality is unsafe for drinking. This bacterial contamination mainly results from untreated domestic wastewaters, city sewage, and human activities in the Tam Diep area.
Key words: karst hydrogeochemistry, karst water quality, drinking water protection, Tam Diep, Vietnam.

 

Hidrogeokemična karakterizacija in kakovost podzemne vode kraškega vodonosnika Dong Giao v Tam Diep, Ninh Binh, Vietnam
Kraški vodonosnik Dong Giao je poglavitni vir pitne vode za gospodinjstva in kmetijstvo v mestu Tam Diep. Razumevanje hidrokemičnih lastnosti in kakovosti vode kraškega vodonosnika so koristne informacije za trajnostno rabo in varovanje podzemne vode na tem območju. Skupno je bilo vzetih 30 vzorcev vode iz večjih kraških izvirov in vodnjakov za prepoznavanje fizičnih lastnosti in kemične sestave kraške vode ter interakcije vode in kamnine. Fizikalno-kemični parametri (pH, temperatura vode, električna prevodnost in alkalnost) in glavni ioni (Ca2+, Mg2+, Na+, K+, SO42−, NO3−, Cl−) so biliu merjeni in situ in analizirani v laboratoriju. Vzorci vode iz vira pitne vode Izvir 18 in drugih pomembnih kraških izvirov so bili preizkušeni na vsebnost Escherichia coli (E. coli). Izveden je bil tudi sledilni poskus, da bi pridobili informacije o onesnaženju. Rezultati kažejo, da spadajo podzemne vode vodonosnika Tam Diep v kalcijev-magnezijev-bikarbonatni (Ca-Mg-HCO3) hidrokemični tip in kalcijev-bikarbonatni (Ca-HCO3) hidrokemični tip. Meja raztapljanja karbonatov in razmerje Ca/Mg sta jasno pokazali, da je preperevanje karbonatnih kamnin (apnenca in dolomita) prevladujoči proces, ki pogojuje kemične lastnosti podzemne vode na testnem območju. Kemijska kakovost podzemne vode se uvršča med dobro in odlično za pitje in namakanje. Celokupna trdota vode je razmeroma visoka. Nasprotno, vsi mikrobiološki vzorci vsebujejo veliko število E. coli, torej z vidika mikrobioloških standardov kakovost izvirske vode ne ustreza vrednostim za pitno vodo. Ta bakterijska kontaminacija v glavnem izhaja iz neočiščenih gospodinjskih odpadnih voda, mestne kanalizacije in drugih človekovih dejavnosti v območju Tam Diep.
Ključne besede: kraška hidrogeokemija, kakovost kraške vode, varovanje pitne vode, Tam Diep, Vietnam.

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DOI: http://dx.doi.org/10.3986/ac.v45i3.3588

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