Total Dissolved Solids and Alkalinity [closed]








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I need to calculate total dissolved solids (TDS) of various groundwater samples from chemical analyzes. I have concentrations of ions/molecules in mg/L. I’ve found various formulas to calculate TDS but the ions/molecules I have never match. I don’t have a lot knowledge in chemistry.


**Here are the three equations I have found. (As i said, I found many different equations and I don't know which one I should use):**


**Eq. 1** : TDS=Na(+) +K(+) +Ca(2+) +Mg(2+) + Fe^(2+) +HCO3(-) +Cl(-) +SO4(2-) +NO3(-)


**Eq.2** : TDS=0.6\*Alkalinity (as CaCO3) +Na(+) +K(+) +Ca(2+) +Mg(2+) +Fe(2+) +Cl(-) +SO4(2-) +NO3(-) **[1]**


**Eq.3** : TDS=cations +anions +SiO2


**Problems/questions I have:**


•I don’t have the concentration of HCO3(-).


•I have the concentration of CaCO3. In natural waters, alkalinity (mg/L CaCO3) is HCO3(-)+CO3(2-) +OH(-) +H(+). At pH under 8.3, could I simply convert the concentration of CaCO3 in HCO3(-)? If yes and if the pH is over 8.3, is there a way to calculate the concentration of both HCO3- and CO3(2-)?


•I don’t have the concentration for NO3-. I only have the concentration for NO3-+NO2. Is there a way to isolate the concentration of NO3(-)? 


•I don’t have the concentration for SiO2. I only have the concentration for Si. Could I simply use the concentration of SiO2?


•The pH of my water samples varies from 6 to 9.


•Also, I don't have the samples so I cannot titrate the water or measure electrical conductivity.


Thank you!


References:


**[1]** Federation, W. E., & American Public Health Association. (2005). Standard methods for the examination of water and wastewater. American Public Health Association (APHA): Washington, DC, USA.


