Artesian Wells as a Source of Water Supply.
The second general principle regarding the waters from artesian wells can, I think, also be best understood by a special case, and for this purpose I will again take the Potsdam sandstone.
It seems safe to assume that we may regard about 28-30 grains of solids, calculated as in previous table, as the normal constitution of true Potsdam water. But other waters represented as coming from Potsdam sandstone give quite other results, of which I will cite a few typical cases from analyses collected from various miscellaneous sources, but not verified by the analyst or check analyses.
Many others might be given, some of them with even greater difference than these; but what 1 wish to call special attention to is this. That the Potadam water contains normally about 28-30 grains per gallon of water, of which only about one to two and one-half grains are the soluble salts of the alkalies, 1. e., the sulphates, chlorides and carbonates of potash and soda, leaving roughly about twenty-six grains of the other mineral matters, mostly the bicarbonates of lime and magnesia.
In these cases cited there is a marked increase in solids, but that increase is due to an increase of the soluble alkaline salts.
The carbonate of the lime and magnesia are usually somewhat diminished, being changed into the corresponding sulphate.
To explain and account for these deviations, we are therefore forced to one of two conclusions :
• Paper read by Prof. Krastus G. Smith of Beloit, Wit., at the Milwaukee convention of the American Water-works.
- Either the data furnished by some analyses are incorrect, or
- Waters from some points of the Potsdam sandstone are subject to local variations.
The first conclusion we will dismiss here, as many of the analyses are by men of acknowledged skill and reputation in the analyses of waters.
The second perplexing proposition finds its answer, it seems to me, from my study of these wells, that while the water from the sandstone is true Potsdam, it has been materially altered by infiltration from the superincumbent strata, which the drill has traversed and the infiltration from which have not been sufficiently cut off or plugged back.
I am not sure that this view will meet with the unqualified endorsement of all present, but it seems to me perfectly reasonable and to meet the case. In support of this view I would note that in drilling a well it is well known that many smaller water-bearing strata are traversed. None of them probably may come to the surface, but the waters would seep out and work out into the bore. When the head of the Potsdam strata was pierced and a flow established, we cannot expect that the waters rushing up the bore would, by its own momentum, plug back completely all superior infiltrations, but that rather they would be borne along with the waters. Admit this principle once and deviations in our Potsdam supply are explained.
When the essential features for a true artesian flowing well are recalled, conditions can be conceived where such superior infiltrations would be improbable, e. g., where in such superior strata their pressures and texture are such that the waters from the Potsdam under greater pressure find a partial escape along them. But in many true flowing wells it can be conceived how this infiltration would be perfectly true, and especially is it true for the great number of deep wells called artesian and used for a supply included also under this discussion, when waters do not rise fully to the surface, but are pumped.
It is further a matter of common experience to those studying the artesian supply that wells are thus frequently plugged either above or below a given stratum, thus cutting off undesirable waters and improving the quality. And finally we note that as we go further south and southwest on the Potsdam supply, the waters become more and more saline in character, or as we approach the coal districts, the alkalies and the sulphates become more permanent.
I have dwelt thus at length upon the Potsdam sandstone supply, because, in the first place, I was personally more familiar with it, and, secondly, because it has been so carefully studied that I deemed it the best method in which to clearly present to this body the principles underlying the study of wells and the laws of probabilities controlling them. We might repeat this study with good results in the great stratum known as the St. Peters sandstone, and would arrive at very similar conclusions.
Applying the study to general true artesian supply, and we will find the trouble and perplexity greatly diminished if we search diligently for the true strata water, apd distinguish carefully between it and the foreign infiltration.
A second source of perplexity in our study will be removed if we do not confound our true artesian service where waters flow or rise under head in the bore with simply bored wells, or worse than all, mere drift driven wells; in both latter cases we are dealing with quiescent waters, non-comparable with those from the deeper strata and under head; with these last two classes of waters this paper does not deal.
While it is true our sandstone furnish our best artesian supply, and their study essentially covers the study of the artesian service in the Mississippi basin, occasionally flowing wells are obtained from other strata, and even from the drift. The characters of the waters then partake of the character of the matrix. In the case of a limestone becoming more heavily charged with lime and magnesia, and in the case of drift becoming merely a modified surface water.
As compared with surface waters it will usually be found true that the deep artesian waters are more heavily loaded with saline matter. We do not expect to find an artesian water with much under thirty grains of solids per U. S. gallon (with lime and magnesia calculated as bicarbonates). About the same amount fairly represents our best surface waters. Rivers and streams contain less and the lakes least of all, Lake Superior heading the list with two to three grains of solids per gallon of water.
In artesian wells the dissolved solids rise rapidly to amounts giving the waters distinctly saline taste and forbidding their use for a general supply. For other sections of the country others must speak authoritatively. Some analyses made at the Beloit laboratory from artesian wells along the Gulf of Mexico would indicate that there the waters are feebly alkaline, and are superior to even our best artesian waters. Analyses from artesian wells at other points are too sporadic to justify us in drawing at present conclusions therefrom.
There is one other very important feature regarding the constitution of deep artesian waters to which I would call the attention of this convention, and this is, “ The significance of a sanitary analysis of water as applied to these deep artesian wells. There is no competent engineer or water-works manager but has an idea in a general way regarding the data furnished by a sanitary analysis of water. This aims to give such data as may lead to some accurate conclusions regarding the presence and amounts of organic matters in water and the consequent healthfulness or unhealthfulness of a supply. The data usually required are the volatile residue, fixed residue. total residue, hardness, chlorine, oxygen consumed after various intervals, and especially the condition of the nitrogen, as shown by the albuminoid ammonia, free ammonia, nitrous and nitric acids.
One unanswerable argument in favor of artesian wells hitherto advanced has been their positive freedom from organic and surface waters and sewage. The very conditions for an artesian well—deep strata, impervious superimposed strata seem to favor the idea. In the actual demonstrations to prove the presence or absence of organic matters, the methods of the sanitary analysis of surface waters have been quite widely applied. There may be no objection to this study of the waters, but I am sure that we will be led into serious error in formulating an opinion, unless extreme care is taken regarding the correct interpretations to be given to such analyses. I have made several such whole or partial sanitary analyses of artesian waters, and have collected some made by others from these wells. These almost without exception fall into one of two classes.
- Those where the data are reduced almost to zero in each determination, and therefore show the absence of organic matters.
- Those where the analyses show some astounding amounts in one determination, notably in the amount of free ammonia.
In the first class are found our free Potsdam sandstone waters, and probably our St. Peters sandstone waters, leaving little to be desired in the matter of purity, according to accepted standards, and with this word may therefore be dismissed.
It is the second class I wish to call special attention to at this time, as the results obtained are so abnormal, and reports based on these data have been made regarding such wells positively condemning them. So far as I know the literature of the analyses of water supplies is silent on these particular conditions, save an occasional fugitive allusion, merely citing the fact of the presence of a large amount of ammonia.
In a paper read before the American Association for the Advancement of Science at Madison, this summer, on “ The occurrence and distribution of nitrogen in deep artesian wells,” I called the attention to these peculiar conditions and phenomena, and will introduce one table used at that discussion. The analyst or hydraulic engineer who may have had much experience with these deep wells have noticed the extraordinary amounts of free ammonia some of them show; in fact, so much that our ordinary methods of estimating it is almost worthless. But as significant is the fact that while the free ammonia is so high, nitrogen in all other conditions, as albuminoid, ammonia, nitrous acid and nitric acid, are wanting. This is quite contrary to what we would expect or do find almost without exception in surface waters. To make more clear this peculiar condition of the nitrogen, I will give ten such analyses of waters from the artesian wells made at the Beloit laboratory, which are selected as well illustrating the phenomena.
The study of this table develops some noteworthy observations.
- The enormous amounts of free ammonia.
- The trace of albuminoid ammonia so lew as to suggest whether it really is not accidental or free ammonia, only expelled after the addition of the strong alkaline permanganate solution added to develop the albuminoid ammonia.
- The absence of nitrites.
- The absence of nitrates.
The presence of any such amount of free ammonia in any such surface water would be viewed with grave suspicion, if not positively condemned, and application of these same standards to the artesian wells might lead to condemnation.
It is to be specially noted, however, that we have the nitrogen all aggregated into the one form of ammonia, and not distributed through the four forms usually met with, and I think it becomes remarkable and atiracts attention, because thus aggregated into the single form and not distributed through the four forms. A simple calculation of the nitrogen changed into and distributed through these usual forms would show it to fall well within our accepted standards for maximum impurity of waters.
The fact of so much ammonia so often found in these deep waters, its significance and cause were to me for a long time a source of perplexity and anxiety on being required to pass a correct opinion on their sanitary nature. The samples had been very carefully collected in my own glass-stoppered bottles, thoroughly cleaned before leaving the laboratory and protected from intruding ammonia on return. Duplicate well checking analyses from different bottles proved that the amount of ammonia truly represented the ammonia normally present in the water.
A chance visit to one of the wells revealed the presence in traces of sulphurated hydrogen, and suggested a reasonable explanation of the difficulty. Personal inspection of seven of the wells in the table, expressly to determine this point, and correspondence regarding all others containing high ammonia coming under my observation, have shown the presence of this sulphurated hydrogen in the waters. So that the extraordinary ammonia can be explained on the basis that the sulphurated hydrogen has exerted its well known reducing action, either reducing the higher oxidized compounds of nitrogen back to ammonia, or preventing entirely their formation. This explanation seems to me perfectly satisfactory and reasonable and to meet the case. It may be that other agencies, as the iron oxide, dissolved in these waters also lend their assistance to the final result, but probably the sulphurated hydrogen is the principal one at work.
On this basis of explanation it is fair to question whether any amount of ammonia up to 1. + per million at least has any significance for these deep wells. This is the practical point I wished to develop to this body of practical men. You can see at once how our ordinary standards of maximum impurity (e. g., 0.08 free ammonia per million) utterly fail when applied to any such data as are cited above. The above explanation has satisfactorily met all cases coming thus farunder my observation, and it will be a matter of great interest to see whether it may coincide with the experience of others, and may sufficiently meet future inquiries and developments.
Regarding the gases present in these deep artesian wells, I would note the carbonic acid gas almost always present in the free state, and by virtue of which the carbonate of lime and magnesia are held in solution. Oxygen, according to the eminent analyst, Dr. Drown of Boston, is always absent in these deep wells.
Sulphurated hydrogen is very often present. It is, however, very elusive and disappears rapidly and wholly on relief of the waters from pressure and on aeration. In none of the analyses quoted above had I any suspicion of the presence of the gas when they reached the laboratory, and other analyses of artesian waters rarely make references to it.
In conclusion, then, to briefly sum up some observations on these artesian wells, I would note—
- The distinctively geological study and the distinctively chemical study, it is necessary to give the problem in arriving at intelligent conclusions before advising or attempting developing an artesian service for a public water supply.
- The confusion and perplexity which exist on collecting and comparing results of analyses of waters from other artesian wells, and attempts to intelligently and profitably use them.
- The fact that waters from a given stratum are presumably of a practically uniform character.
- That water from such strata are materially altered by infiltrations from superincumbent or inferior strata.
- In the application to the deep artesian wells of the method of sanitary analysis, as usually employed for classifying and properly valuing surface waters, care must be taken in the interpretation of results to arrive at correct views and knowledge regarding them.
These five points have been definitely in mind during the preparation of this paper, not that in any sense they exhaust the study of the water supply from our deep artesian wells, but with the hope they may form a distinct contribution to the resources of and may throw additional light upon one of the difficult problems of the engineer.
This paper is based upon my observation and analyses of these artesian supplies dotting our Mississippi basin, and have suggested some profitable lines for future inquiry. It is presented to this convention of engineers and managers of our great water-works system in the hope that from it may be gathered some hints to assist them in the great undertakings they may advise or control. If from it comes suggestions for practical use in determining a new supply or the better administration of the service or some stimulation to deeper purpose in this field for truly scientific inquiry and research, so that we may give added zest and vigor and intelligent study, and crown with success that greatest work of the engineer—the development and maintainance of a good, wholesome water supply, the purpose and presentation of this will have been fully accomplished.