Artesian Waters

ARTESIAN WATERS. Artesian waters, unlike groundwaters, are deep underground waters which, accumulating between two impermeable strata, are under the constant pressure of the entire mass of water filling the given water-bearing horizon. When the artesian horizon is opened by borehole pipes, the water under pressure rapidly rises through the well pipe to a certain height. Under certain geological conditions, artesian waters gush from the pipe like a fountain to a significant height. Artesian waters are far from encountered everywhere; they are formed only under specific geological conditions, namely: 1) when the water-bearing horizon (sands, fractured and porous limestones, sandstones), enclosed between two impermeable layers, such as clays, forms a gentle basin or syncline together with them, and 2) when the same system forms part of a syncline (unilateral dip). Under certain geological conditions, artesian waters are also found in massive rocks intersected by fissures. The movement of artesian waters in water-bearing rocks occurs according to the law of open communicating vessels, in which water always strives to occupy the same level. The height to which the level of artesian waters reaches in pipes is called the limiting height or the hydrostatic and piezometric level. If the water in the well rises above the ground level, the piezometric level is called positive, otherwise negative. Each artesian horizon has a recharge area and an accumulation or discharge area. The recharge area lies at the edges of the syncline, in places where the impermeable rocks containing the artesian horizons come to the surface. Due to groundwaters fed by atmospheric precipitation, the formation and constant replenishment of artesian water horizons occur in the recharge areas. The accumulation area is located in the bowels of the earth between the recharge areas. The schematic arrangement of artesian horizons with recharge and accumulation areas can be illustrated by the figure given on page 249. If the wellhead No. 3, as indicated in the figure, is located deeper than the pressure line CD, the water from the well will gush. In wells No. 1 and No. 2, whose wellheads are located above the pressure lines, the water will stand below the ground level. In the presence of several horizons, it is possible for water supply to stop at the horizon that provides water in sufficient quantity and of better quality. The movement, distribution, and acquisition of artesian waters by many geologists (S. N. Nikitin, I. V. Mushketov, V. G. Khimenkov, and others) is compared with the movement of water in water supply systems. Water supply pressure structures with a reserve water reservoir are compared with natural recharge areas where atmospheric waters feeding groundwater and artesian waters collect. The water supply network, always located below the recharge areas (reservoirs), is compared with the layers and veins of water-bearing rocks. Water supply fountains and taps correspond to artesian wells. The lower the discharge mouth (wells, taps, fountains) is located relative to the recharge area, the higher the water rises through the pipe. Practically, the height of water rise never exactly reaches the height of the surface of the water reservoir (recharge area).

E - well No. 1; F - well No. 2; H - well No. 3; A and B - artesian horizons; CD - pressure line for artesian horizon B; C₁D₁ - pressure line for horizon A; A₁ and B₁ - recharge areas; a, b, c - impermeable layers.

since mechanical obstacles in the form of friction, pinching of jets, and the like weaken the force of the head to a greater or lesser extent. The amount of water in a well of a given artesian horizon depends on the size of the recharge areas, the degree of porosity of the water-bearing layer, the amount of atmospheric precipitation falling and infiltrating in a given locality, the degree of drainage of the locality with respect to the given horizon, the number of wells exploiting the water-bearing horizon, the distance between artesian wells, and a number of other causes. The productivity of wells also depends on the size of their diameter, but the increase in discharge is disproportionate to the increase in diameter. The depth of occurrence of artesian waters also depends on geological conditions. The deepest well in the USSR is the Aibary well in the Crimea, which has not yet been brought to water and has a depth of 783 m; in Kharkov, artesian waters are obtained from a depth of 630 m; in Moscow, artesian horizons are located on average at depths of 70, 140, and 240 m. With intensive exploitation of artesian horizons, which does not correspond to their capacity, a sharp depletion of artesian horizons is observed with a corresponding drop in the water level. As an example, we can cite the Stavropol Governorate, where there are many self-flowing wells, the water of which is completely uselessly poured onto the surface of the earth in colossal amounts. This predatory attitude toward artesian waters is observed in other places as well. But even with more proper exploitation everywhere that water consumption exceeds natural replenishment, a greater or lesser depletion of artesian horizons is observed. Over a huge area of the European part of the USSR in many places there are favorable conditions for the formation of artesian waters, which are exploited by numerous artesian wells. Geologists S. N. Nikitin, A. A. Krasnopolsky, and others have collected the richest material on the characteristics of artesian wells. Based on the processed data, S. N. Nikitin came to the following conclusions: 1) There are no grounds to look for and obtain artesian water, not only self-flowing, but also possible for profitable exploitation by pumping at the main watersheds separating large river basins. 2) The most successful wells are confined to river valleys; on flat interfluve areas of the steppe, under favorable local conditions, one can have artesian water only that is not self-flowing. 3) Generally speaking, in the vast majority of localities we have no grounds to expect in central Russia to obtain self-flowing water on flat areas exceeding 149.3 m in absolute height. The significance of this conclusion stands out particularly vividly if we remember that the absolute height of most Central Russian areas (non-river valleys) fluctuates between 128 and 256 m. Only in a certain, very limited number of valleys (but not watershed areas) does the rise of artesian waters exceed the indicated limit. The water in the artesian wells of the deep valley of the Desna near the city of Bryansk reaches the greatest height (192 m) due to the exceptional proximity of watershed recharge areas reaching 256 m in height. Similarly, the artesian waters of some deep valleys of the Ulyanovsk Governorate, bordered by high hills of Tertiary water-absorbing sands, reach a height of 175 m (Guryevka). 4) The vast majority of wells, including all wells of central, southeastern, and southern Russia, raise water significantly below 21.3 m above the level of the main river of a given locality. Only the wells of Bryansk standing under exceptionally favorable conditions raise water to a height of 32 m above the river, and the boreholes of the Lake Ilmen basin up to 27.7 m. 5) The highest limit of the possibility of profitable use of artesian waters outside river valleys, subject to the use of suction steam and wind engines, almost nowhere exceeds the absolute height of 192 m; in many cases, this height is significantly lower." Extensive drilling material gave grounds for Russian geologists to distinguish on the territory of the European part of the USSR regions of actual and potential use of artesian waters. On the attached map, taken from the work "Artesian and Deep Groundwaters of the European part of the USSR" by A. M. Semikhatov, regions of artesian water use are distinguished. In total, 15 of the following large regions are distinguished on the map: 1) Cambrian-Silurian (Baltic), 2) Western Devonian (of the Main Devonian Field), 3) Central Russian Devonian, 4) Moscow Carboniferous, 5) Permian, 6) Tambov-Ulyanovsk-Saratov, 7) Volga-Kama region of post-Tertiary deposits, 8) Syrt clays, 9) General Syrt, 10) Caspian deposits, 11) Erga, 12) South Russian trough, 13) South Russian crystalline strip, 14) Black Sea, 15) Ciscaucasian. The chemical composition of artesian waters is very diverse, which depends mainly on the composition of the soil and subsoil through which atmospheric waters pass in the recharge areas of artesian horizons. Once in the soil, the water is enriched with carbon dioxide and the main components of the salt composition, which are products of biochemical processes taking place in the soil due to weathering, leaching, and the decay of organic substances accumulated by the soil. The intensity of biochemical processes and the composition of the soil determine in main features the salt composition of the water. Since the composition of the rocks through which the water flows has a relatively weak effect on the chemical composition of the water, further underground wandering of the water introduces only corrections depending on the composition and structure of the washed rocks. For this reason, the chemical composition of the water does not completely reflect the composition of the rocks from which artesian and groundwaters are directly obtained. Depending on its composition, water acquires to varying degrees the ability to dissolve mineral and organic substances encountered along the path of its movement in the soil and rocks. The chemical composition of the water, its saturation with carbon dioxide, temperature, the time during which it is in contact with the soil and rocks, their composition, structure, and solubility—all this, influencing the dissolving ability of the water, largely determines its mineral and organic composition. Penetrating into the ground, water quickly loses its supply of dissolved oxygen consumed in various biochemical reactions in the soil layers, so that underground waters, as a rule, do not contain free dissolved oxygen, instead of which the water receives free and bicarbonate carbon dioxide and salts of other oxygen acids (nitrates, sulfates, etc.) from the soil. With prolonged underground existence, water can gradually lose this bound oxygen of its salts as well, with nitrates being reduced first, being replaced by salt ammonia, as established for the Moscow artesian waters of Carboniferous limestones. Artesian waters with signs of sulfate reduction are frequently encountered, and the presence of hydrogen sulfide, in the absence of gypsum-bearing rocks, can be explained by the reduction of water sulfates. Water emerging from quartz rocks, granite, porphyry, basalt, gneiss, mica schist, as well as from shale, usually differs by an insignificant salt composition. Lime and dolomite, dissolving more easily, yield water richer in salt composition. "In general, acidic igneous rocks yield softer water than basic ones" (Semikhatov). The diversity of the chemical composition of artesian waters, depending on natural conditions that change even for the same horizon over relatively short distances, is characterized by protocols of chemical analyses of artesian waters obtained from various regions of the USSR (see table on pages 253–254). Proper sanitary evaluation of artesian waters requires a particularly thorough and comprehensive study of the regime of a given water horizon. Data of a hydrogeological, hydrological, general sanitary nature and the results of periodic chemical and bacteriological studies of water samples correctly obtained make it possible to produce an exhaustive hygienic evaluation of the water source. However, to this present time, not only among wide strata of the population, but also among water supply specialists (engineers, doctors), a false notion often reigns about artesian waters as being sufficiently protected from surface and groundwater pollution due to their depth. Meanwhile, a number of scientific observations have long shown that even deep artesian waters insufficiently protected by impermeable rocks can, depending on the geological structure and sanitary state of the locality, be more or less intensively polluted and be dangerous in an epidemiological respect. Pollution of artesian waters is possible with insufficient filtration through the overlying soil layer of surface polluted waters and sewage liquids or by the inflow of already polluted overlying groundwaters. Depending on the structure and thickness of those rocks through which the surface polluted liquid will penetrate, more or less obstacles are created for the introduction of pollutants into deep water-bearing layers. The thickness of the filtering layer in this case is of colossal importance, enhancing the effect of natural filtration. In addition to the thickness, structure, and arrangement of the rocks of a given locality, the distance of the wells from the recharge area of this water horizon is of very great importance in a sanitary respect. The closer the well is to the recharge area, the greater the conditions that create the possibility of pollution of the water horizon can be.

Contamination of the aquifer occurs most easily at sites of natural outcrops onto the surface or artificial exposure of water-bearing strata, especially fractured ones. Under such conditions, any contamination of the soil surface and especially the ground (cesspools, cemeteries, dumping sites, etc.) poses a major threat in terms of polluting the water horizon. In other cases, when the recharge area is located at a great distance from the wells and the underground movement of water takes a significant period of time (months, years), this factor alone may have a beneficial effect on the self-purification of the water. But even under such conditions, one cannot be limited to the results of single chemical and bacteriological studies alone; rather, it is necessary to prove the complete sanitary wholesomeness of the water through periodic (seasonal) studies. At the same time, the structure of the aquifer is of exceptional importance, enhancing or weakening the processes of self-purification. The aforementioned circumstances determine the significance of the sanitary state of the locality within the recharge area. Precise knowledge of the geological conditions and the boundaries of the recharge area, while facilitating the sanitary assessment of the water horizon, also provides the basis for establishing the boundaries of the sanitary protection zone of the source and other sanitary measures. A factor facilitating the assessment of artesian waters is their property of maintaining the constancy of their composition under normal conditions, regardless of atmospheric precipitation. The study of artesian wells in Moscow and other places has shown that a number of wells in the same horizon yield sharp changes in water composition. With the constancy of the composition of artesian water, any sharp change in the chemical composition of artesian water directly Chemical composition of artesian waters.* Date of sample analysis Dry residue at 110^° Hardness in German degrees Calcium oxide Magnesium oxide Iron Ammonia Nitric acid Nitrous acid Hydrochloric acid Sulfuric acid Oxidizability j Well location General Total Carbonate Permanent Saline Albuminoid 1 Horizons Moscow, "Utilizator" plant 6/II 1926 173.2 8.2 8.1 61.5 ! 14.5 ; 3.36 0.73 0.3 0.17 0.007 1.3 3.1 2.1 Nadgyur horizon j Moscow, "Sokolniki" sanatorium 14/IX 1925 166.7 8.4 8.2 49.1 25.1 0.57 0.58 ! 0.32 ! 0.05 | ! 0.001 1.7 I 6.6 1.6 i Upper Carboniferous (Gzhelian) horizon Moscow, Maryino baths 3/III 1926 304.4 14.4 12.9 55.2 63.6 56.6 0.12 0.46 0.08 i 0 0.005 4.0 28.9 1.0 Middle Carboniferous (Moscow) horizon Moscow, "Bogatyr" factory 3/II 1926 484.0 16.9 1 8.6 1 j 90.4 0.70 0.71 ! 1 ! i 0.23 ; 0 0 5.8 ; ' | | ; 156.7 0.9 Lower Carboniferous (Serpukhov) horizon Samara, wine warehouse 1903 612.5 23.8 11.5 169.3 49.7 - 0 0.4 0 | 71 126.0 0.4 Permian deposits Pskov 1900 396.8 16.3 - 6.9 116.0 34.0 0.1 - ] 20.0 | 30.16 5.4 Devonian from the lower sandstone strata Kharkov 516.4 17.58 - 3.6 - 26.9 94.1 2.1 Cenomanian horizon, Cretaceous deposits * The dash sign (-) indicates a lack of data. 25S indicates the inflow of some other waters. Depending on the origin and quality of the inflow, the question of the sanitary significance of the composition change is resolved. The wedging out of impermeable rocks overlying and protecting artesian waters from contamination is an extremely important factor of sanitary significance, facilitating the contamination of artesian waters. The places where impermeable layers wedge out in Moscow have been established through geological analysis of data from numerous drilling logs collected during the study of artesian waters in Moscow. This circumstance is also convincing evidence that a geological characterization made on the basis of isolated drilling logs is very often insufficient, since the protecting impermeable layers (even thick ones) can unexpectedly wedge out and sharply alter the natural conditions protecting water horizons from contamination. In addition to natural pathways for the penetration of contamination created by nature itself, improper construction of wells can very frequently create artificial pathways that allow upper groundwaters to penetrate deep artesian horizons either through seepage and the gradual expansion of channels along the outer wall of the well pipe, or through direct entry into the well cavity via damage (rusting) of the iron pipe walls and through gaps at the joints of the pipes. During the construction of artesian wells, special technical measures can to a large extent prevent the formation of such pathways for the inflow of overlying waters. In a number of cases, the direct inflow of contaminated groundwater into the well pipe was established through special inspection. In many places, it was noted that wells which yielded perfectly immaculate water in their first years, corresponding to the normal composition of a given horizon, later yielded water whose composition was sharply altered. It should be noted that normally this change occurred due to a sharp increase in solid residue, hardness, chlorine, oxidizability, and nitrogenous substances. This was far from always accompanied by bacteriological indicators of contamination. In other words, only chemical indicators of unquestionable contamination were present. But in a number of cases, the change occurs solely due to solid residue with a corresponding increase in carbonate hardness and chlorine in the absence of all other chemical and bacteriological indicators of contamination. This is apparently explained by the fact that in such cases, groundwaters that have already been purified to a significant degree by the soil enter the water horizon. To illustrate the sharp change over a 10-year period in the composition of an artesian well, one can cite the results of water research on a single well in 1915 by S. A. Ozerov at the Rublevo Laboratory and in 1926 at the Moscow Sanitary Institute. Research on the water of the artesian well of the Central Baths. S. Ozerov in 1915 466.0 18.0 6.6 130.6 0.002 0.102 Sanitary Institute in 1926 . . 1000.0 31.7 225.0 190.0 10.6 0.048 3.8 6.6 There are quite a few such wells with water failing to meet the normal composition of a given horizon in Moscow. Thus, a sharp change in the salt composition of artesian water is a very important factor for its evaluation. Every artesian well constructed in violation of sanitary and technical requirements, by creating favorable conditions for the inflow of waters from upper horizons (often contaminated), can turn into a good conduit for the contamination of artesian waters. Of particular sanitary danger are old and abandoned artesian wells with rusted pipes that absorb sewage; through defects in these pipes, upper waters enter the well and can contaminate artesian horizons. In Moscow and other places, there are quite a few artesian wells that, for the aforementioned reasons, have turned into conduits for the contamination of artesian horizons. The example of Moscow vividly illustrates how the failure to take timely measures to protect artesian waters deprives the population of valuable water supply sources and how necessary a careful attitude toward water reserves is in every locality. Proper protection of water reserves is possible under the condition of organized sanitary and technical supervision over both the artesian wells in use and the available artesian water reserves. The rules for the protection of artesian waters are set forth in a special order of the Supreme Council of National Economy of the USSR No. 687 of May 17, 1926, in addition to which rules taking into account local peculiarities may be issued.