Dear Alaa,

the deuterium excess of your water sample is 43. It is very high, it means that your water plots far above the Global or Local Meteoric Water Line (GMWL or LMWL). There can be two explanations:

- your data are erroneous, something happaned during the measurement. E.g. your sample contains some dissolved organic material and it was measured using a cavity ring down laser analyzer. It is well known that certain kinds of dissolved organic compounds deteoriorate the d18O and dD data when the analysis is made by laser spectroscopy.

- your dara are real. In this case a kind of process modified the oxygen or hydrogen (or both) isotopic composition of the groundwater. E.g. if significant amount of CO2 flushes the aquifer it can shift the d18O value of water into negative direction. Zhonghe Pang mantioned the isotope exchange between the water and methane, which can incerase the dD value. Both processes would explain your case. Please, check the possibilities.

Hi, Alaa,

The initial isotopic composition of groundwater depands on its source of recharge. In case of atmospheric recharge (rainfall or snowfall), the initial values of delta O-18 and deuterium are lineally correlated. Your sample points fall on the global or local meteoric line. I guess this what you meant by "normal". The isotopic composition of groundwater is subsequently modified through interactions with the country rock and geofluids in place. E.g, exchange with methane may cause considerable enrichment of deuterium in groundwater. This is probably the one exception you observed.

Hope this helps. Good luck!

Hello, dear, Prof. Zhonghe Pang. Thank you for your answer. I appreciate your efforts. My problem with these values of staple isotopes are the relation between the deuterium and  d 18O. If the d 18O values are -6 per mil, the value of deuterium should be less than -40 compared to the normal data of all samples under study. in addition, this relation depending on the mass of  oxygen-18 and deuterium.

Thank you very much for your attention.

Hi, Alaa,

It would be easier to explain if you could attach the plot.

Dear Alaa,

the deuterium excess of your water sample is 43. It is very high, it means that your water plots far above the Global or Local Meteoric Water Line (GMWL or LMWL). There can be two explanations:

- your data are erroneous, something happaned during the measurement. E.g. your sample contains some dissolved organic material and it was measured using a cavity ring down laser analyzer. It is well known that certain kinds of dissolved organic compounds deteoriorate the d18O and dD data when the analysis is made by laser spectroscopy.

- your dara are real. In this case a kind of process modified the oxygen or hydrogen (or both) isotopic composition of the groundwater. E.g. if significant amount of CO2 flushes the aquifer it can shift the d18O value of water into negative direction. Zhonghe Pang mantioned the isotope exchange between the water and methane, which can incerase the dD value. Both processes would explain your case. Please, check the possibilities.

If you are a research scientist, presumably looking for phenomena not previously described, then you must accept your evidence (assuming you have been meticulous in sampling and analysis) unless you have good direct primary evidence (independent of the result) that the sample is anomalous. You should also remain skeptical. Holding these two in appropriate tension maximises the chances that you will be the author of new findings, rather than being regretful later. Can you obtain further samples from the same source, etc.? Otherwise, you probably have to wonder where the truth really lies, and resolve to be more diligent (e.g. resolve to collect multiple independent samples) in the future. Good luck!

 I agree with Chris. The best would be to repeat the sampling and analysis of the anomalous water to be sure that your data are real.

Kindly refer: 

US Geological Survey Water Supply Paper 2380. This paper is  on line avilable.