It appears that you performed a quick internet search for your information.
I said that as far as I knew manganese and iron are correlated. But I didn't remember where I got that info from and so did a quick internet search which confirmed my recall. I didn't know that the correlation was weaker with igneous rock though so I learned something![/QUOTE]
Unfortunately, iron and manganese are not always correlated and I wasn't going to assume so. Its odd that you would.
Well that's perhaps because I have been exposed more to correlation analysis than you have. I know what it means and I also know what it doesn't mean.
What it means is that there is an apparent relationship between random variables and suggests that it
may be a cause and effect relationship. What it does not mean is that you can say, for example, that as malt color and DI pH are demonstrably correlated DI pH is a*SRM where a is a constant determined by fitting a line to a scatter plot of SRM vs DI pH. Nor, in this context, does it say that [Mn] = b*[Fe] even though they are correlated. What is does imply, however, is that the probability distributions of, respectively, DI pH or [Mn] are going to be dense near a*SRM or b*[Fe] with the dispersions dependent on the correlation coefficient. Whether the distibutions are narrow enough that a*SRM or b*[Fe] are good enough predictions of DI pH or b*[Fe] depend on the application.
Statements like "iron and manganese are not always correlated" implies that you aren't quite up to speed on this concept. Correlation refers not to a single water sample but to a large (the larger the better) ensemble of water samples perhaps stratified in various ways. E.G. as I learned yesterday into samples from places where the underlying geology is sedimentary (high correlation) as opposed to igneous (lower correlation - but, note, still correlated). You can't say "Mn and Fe are not (or are) correlated in this sample". But you can say "Mn and Fe are more strongly correlated in some populations than others". You can also say "Low iron doesn't always mean low manganese in every sample". Again I emphasize that we are talking ensembles - not single samples.We are dealing with statistics here! You can say that if the sample is drawn from an area where the underlying geology is sedimentary that low iron
quite probably means low manganese. You can also say that if the sample is drawn from an area where the underlying geology is igneous that low iron may mean low manganese but one cannot be as confident in this case.
I guess I'll defer to your internet search in lieu of relying on my 35 years of professional experience dealing with groundwater and its quality. I appreciate your guidance that manganese is highly correlated to iron content and I'll only test for iron now. You're the best!
No problem but if your company has a statistician you might want to consult with him to help you understand concepts like correlation and how to use them in your work to best effect. Your general drift here would seem to say "Manganese and iron are uncorrelated. Iron concentration tells you nothing about manganese concentration so even if Fe is undetected you had better test for Mn!". That is, AFAIK, untrue but I don't have a lot of iron and manganese data to look at. Apparently you do. Why not make a scatter plot and have a look see for yourself? The statistician (or any one who knows a little about statistics) could help you with this. And, of course, we hope you would share that plot with us after it is made. Based on what you find you might be able to drop manganese testing on samples from some regions but retain it for others. Of course having the test data is always better than not having it if for nothing else than to bolster the size of the sample upon from which you calculate correlation.
If OP has read any of this and gotten this far: With the low iron you probably have low Mn but I can't say you definitely don't. Were I you I wouldn't worry about it. If you had any of the symptoms of Fe or Mn it would have to have been from Mn as you have no Fe but that doesn't matter as the treatment is the same.