Hello Dear, these articles can help you:

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Thank you Seyed Mostafa Banihashem

Hello,

I think you will find the answer to this question in every better textbook of hydrochemistry. The balance between CO3-2, HCO3- and CO2 is determined primarily by the current value of the acid-base reaction and the buffering capacity of the system.

Thanks for your answer Dalibor Matýsek

Following on from Dalibor Matýsek above, atmospheric CO2(g) will contribute to the CO3-2, HCO3- and CO2 equilibrium system in rainfall which then recharges to groundwater. This is in addition to the dissolution of bi/carbonate containing minerals in the soils/rocks that groundwater comes into contact with.

Thank you for the valuable response Rebecca Fraser

It is due to the hydrogeology of the area.

You can use this paper

Article Hydrochemical evaluation of groundwater quality of the Tista...