How can calcium carbonate affect groundwater

These could be due to lack of communication of the aquifer with surface; otherwise the tritium activity would be higher. Sampling locations VA-4 and RTV situated near boundary between those two aquifers are exceptions with values of molar ratio between 1.

Groundwater of Ljubljansko Barje aquifer has a higher proportion of magnesium; therefore we can assume that groundwater from Ljubljansko Barje aquifer occurs at both sampling locations. This can be interpreted with the location of RTV in Ljubljansko polje aquifer, which lies further away from the border of the two aquifers where the influence on groundwater of Ljubljansko Barje is lower. The objective of the presented study was to obtain new data on mixing and dynamics of groundwater in Ljubljansko polje and Ljubljansko Barje aquifers based on hydrochemical and isotopical data of groundwater.

Obtained data were used to identify differences in recharging areas of those two aquifers. Groundwaters were separated into 4 groups. Groundwater of Ljubljansko polje aquifer with higher calcium content is recharged from infiltration of local precipitations and drainage of Sava River water having recharge area mainly in Julian Alps and Karavanke mountains where limestone rocks dominate.

Sava River water is depleted with due to its recharge area mainly from higher altitude areas. Pronounced depletion of was also detected at sampling locations in which the influence of recharged water from Sava River is important, while more positive values of were recorded at sampling locations where local infiltration of precipitation dominates, further away from the Sava River. The groundwater is more enriched in than in other part of the aquifer due to infiltration of local precipitations in lowland that have great influence on this open aquifer.

Groundwater of middle part of Ljubljansko Barje lies below surface cover of impermeable clay and has significantly lower mineralization due to less permeable low-carbonate Carboniferous and Permian rocks in their recharge area.

Also the depletion in in groundwater was indicated as a result of the isotope altitude effect. Additionally, also the groundwater age and residence time were estimated according to the tritium activity measured in precipitation and groundwater. Long-term tritium records showed that in the past mean annual tritium activity in precipitation decreased continuously after reaching a global atmospheric maximum in due to thermonuclear bomb-tests.

Tritium activity in precipitation at observation point at Geological Survey in Ljubljana is now around 6 tritium units TU. Decrease in tritium activity in those waters is a result of radioactive decay in a closed aquifer structure. Interaction of groundwater between Ljubljansko polje and Ljubljansko Barje aquifers was estimated also based on carbonate characteristics of groundwater. They lie near boundary of those two aquifers where influence of groundwater of Ljubljansko Barje is important since it drains in aquifer of Ljubljansko polje.

We estimated the extent of this influence on both sampling points. Quantitative results obtained represent the basis for improvement of hydrogeological conceptual models of both aquifers, which will enable more accurate simulation of the groundwater dynamics and transport of pollutants in the aquifer.

Obtained data will also provide the basis for further planning of exploitation of groundwater from both aquifers for drinking water supply and for planning measures for protection of water resources. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Academic Editor: H. Received 23 Sep Accepted 20 Oct Published 21 Dec Abstract Ljubljansko polje and Ljubljansko Barje aquifers are the main groundwater resources for the needs of Ljubljana, the capital of Slovenia.

Introduction The Ljubljansko polje and Ljubljansko Barje aquifers are the two most important groundwater sources for Ljubljana, the capital city of Slovenia, and its surrounding area. Characteristics of the Study Area The study area, situated in the central part of Slovenia, consists of two aquifers: Ljubljansko polje and Ljubljansko Barje.

Figure 1. Location map of study area and groundwater sampling points. Table 1. Descriptive statistics of relevant chemical and isotopic parameters in groundwater of Ljubljansko polje and Ljubljansko Barje aquifers. Figure 2. Figure 3. Figure 4. Figure 5. Isotopic composition of oxygen in groundwater of Ljubljansko polje aquifer. Figure 6. Relationship between and isotopic composition of oxygen in groundwater of Ljubljansko polje and line of mixing of groundwaters of different origin.

Figure 7. Isotopic composition of oxygen in groundwater and surface waters of Ljubljansko Barje aquifer. Figure 8. Relationship between and isotopic composition of oxygen in groundwater of Ljubljansko polje and Ljubljansko Barje aquifers. Arrow shows direction of increasing altitude of recharge area. Figure 9. Hard water forms scale in boilers, water heaters, and pipes. Hardness equivalent to the bicarbonate and carbonate is called carbonate or "temporary" hardness because it can be removed by boiling.

Any hardness in excess of this is called noncarbonate or "permanent" hardness. Noncarbonate hardness is caused by the combination of calcium and magnesium with sulfate, chloride, and nitrate.

Scale caused by carbonate hardness usually is porous and easily removed, but that caused by noncarbonate hardness is hard and difficult to remove. Hardness is usually recognized in water by the increased quantity of soap or detergent required to make a permanent lather.

As hardness increases, soap consumption rises sharply, and an objectionable curd is formed. In the development of a water supply, hardness is one of the most important factors to be considered. In general, water of hardness up to 60 ppm is considered soft; 61 to ppm moderately hard, to ppm hard, and more than ppm very hard.

Water turbidity is attributable to suspended matter such as clay, silt, fine fragments of organic matter, and similar material. It shows up as a cloudy effect in water and for this reason alone is objectionable in domestic and many industrial water supplies. Filtered water is free from noticeable turbidity. Unfiltered supplies, including those that contain enough iron for appreciable precipitation on exposure to air, may show turbidity. In surface water supplies, turbidity is usually a more variable quantity than dissolved solids.

Color refers to the appearance of water that is free of suspended matter. It results almost entirely from extraction of coloring matter and decaying organic materials such as roots and leaves in bodies of surface water or in the ground. Natural color of 10 units or less usually goes unnoticed and even in larger amounts is harmless in drinking water. Color is objectionable in the use of water for many industrial purposes, however.

It may be removed from water by coagulation, sedimentation, and activated carbon filtration. However, it may cause mottling of the teeth depending on the concentration of fluoride, the age of the child, the amount of drinking water consumed, and the susceptibility of the individual. A small number of minerals comprise nearly the entire mass of sandstone aquifers.

The average sandstone, as determined by F. Clarke , The data of geochemistry, fifth ed. Limestone and dolomite aquifers are primarily calcium carbonate and calcium magnesium carbonate, respectively, but impure ones may contain as much as 50 percent noncarbonate constituents such as silica and clay minerals.

Quartz, the main constituent of sandstones, is the least reactive of the common minerals and, for all practical purposes, can be considered nonreactive except in highly alkaline solutions Roedder, E. Clays have been demonstrated to react with highly basic or highly acidic solutions. Clay minerals are common constituents of sedimentary rocks. Roedder stated that sandstones containing less than 0. Clay minerals are known to reduce the permeability of sandstone to water as compared with its permeability to air Johnston, N.

Sweeney, , Effect of clays on the permeability of reservoir sands to various saline water, Bureau of Mines Report of Investigations ; Land, C. Baptist, , Effect of hydration of montmorillonite on the permeability of water-sensitive reservoir rocks, Journal of Petroleum Technology October. The degree of permeability reduction to water as compared with air is termed the water sensitivity of a sandstone by Baptist and Sweeney. The following characteristics of groundwater give it certain advantages over surface water.

Groundwater usually contains no suspended matter. The diffuser system has a better ability to saturate the water with oxygen, as well as to vent unwanted gasses compared to the previously used techniques. One of the main advantages of the diffusor system is that it can be modified to handle variations in the water flow and type of groundwater. An increase in the oxygen demand can be met by increasing the air flow; something, that cannot be done with the methods using the fall of the water for aeration.

These must be designed to meet the specific oxygen demand for each waterworks. The oxygen consuming species and their oxygen demand are shown in Table 4 along with the respective oxidation reactions:.

The relatively high oxygen demand of the methane and hydrogen sulfide oxidation reactions makes it important to vent these gases. Low oxygen concentration in the drinking water may result in anaerobic conditions in the piping system, leading to unwanted microbial growth. In case of microbial growth, nitrate may be reduced to nitrite, which may then increase to a level above the threshold limit. After aeration, the water may be lead to a reaction tank to allow for sufficient reaction time for the chemical oxidation reactions, but often the water is led straight to the sand filter s.

Sand filtration. In the sand filtration, solid precipitates are filtrated from the water, and it is here that the largest part of the oxidation reactions takes place. The ferrihydrite coats the sand grains, where it leads to autocatalysis of the oxidation reaction 7, 8.

The autocatalytic reaction makes the iron oxidation very efficient, and removes the need for a reaction tank before the sand filter 6. Because of the redox potential for the oxidation of ferrous to ferric iron, the use of oxygen as the oxidizing agent is sufficient, see Figure 3. An iron oxidizing bacteria often found in sand filters of Danish waterworks is Gallionella ferruginea that has been found to enhance the oxidation and precipitation velocity due to their production of exopolymers.

The exopolymers give a denser structure of the iron precipitate, and allows for more iron to be removed by the sand filter before a backwash of the sand filter for its cleaning is necessary 9. The redox potential for the oxidation of manganese II to manganese IV is higher compared to the iron II to iron III oxidation, see Figure 6 , and with oxygen as the oxidizing agent, the process is relatively slow. However, two processes in the sand filter aid the oxidation of manganese: Surface catalyzed oxidation and co-precipitation with ferrihydrate.

Both processes can be illustrated by the two step reaction scheme in Figure 4. Pourbaix diagram for iron, showing the most thermodynamical stable form as a function of pH and redox potential. Reaction scheme for the oxidation of manganese in sand filters, where Me symbolizes a transition metal ion. As with iron, the oxidation of manganese is catalyzed by metal oxide surfaces on the sand grains.

The hydroxyl groups on the metal oxide surface Me-OH attracts the Mn II ions and promote the oxidation, as illustrated in step two. If the metal surface is manganese oxides, the process is autocatalytic, but because of the ratio of iron and manganese in groundwater, the metal surface is most likely iron oxides in the first filtration step where manganese is then said to co-precipitate with iron 7.

In the second filtration step precoating of the sand grains with manganese oxide can help oxidizing the adsorbed Mn II ions, see step three.

The result is that it is not necessary to use stronger oxidizing agents than the oxygen found in atmospheric air to remove iron and manganese. Also present in the sand filter are nitrification bacteria.

These will oxidize ammonium first to nitrite and afterwards to nitrate 6. To ensure an efficient oxidation, a double filtration system is commonly employed.

The sand filters may be open or closed, with variations from waterworks to waterworks. The filters are back washed at regular time intervals, in a process where first air followed by water are sent backwards through the filter system.

The air will remove and lift the colloids adsorbed to the sand grains producing a floating sludge on top of the filter. Later it will be washed away by help of the back wash water. At some drinking water treatment plants, the backwash water is returned to the plant where it is treated with UV-light, filtrated, oxidized again, and brought to the drinking water container. When a sand filter is changed, some of the old sand is mixed with the new to preserve the microbiological environment and to increase the rate of re-population.

To demonstrate the effect of the processes included in a simple treatment at Danish waterworks, data has been collected at a specific waterworks at different points along the treatment process. Pourbaix diagram for manganese, showing the most thermodynamical stable form as a function of pH and redox potential. Simple drinking water treatment — Case Spangsbjerg waterworks, Esbjerg. Spangsbjerg waterworks is one of four waterworks in the city of Esbjerg.

The waterworks is equipped with a diffusor system for aeration and two open sand filters in series. After treatment the water is stored in a buried drinking water storage tank outside the waterworks. The results are plotted in Figure 6 with the x-axis representing the transport through the waterworks. Concentration levels of major constituents of groundwater through Spangsbjerg Waterworks simple drinking water treatment. As seen, iron and manganese are effectively removed by the sand filters.

Manganese are not affected significantly by the pure oxidation, but is almost completely removed already in the first filter.

Some iron is removed by the homogenous oxidation, and needs to go through both filters to be reduced to below the accepted threshold limit. Ammonium is not directly measured, but the graph shows that the ammonium in the water is effectively converted to nitrate in the first filtration step.

This is important since it shows that the conversion is complete in the first sand filter, meaning that no nitrite is left in the treated drinking water. The unchanged hardness is also to be expected since Spangsbjerg Waterworks only applies aeration and sand filtration, which do not affect the solubility of calcium and magnesium minerals significantly.

It requires a special permit if a Danish waterworks is to apply more advanced water treatment techniques than those already described in simple water treatment From here on techniques other than what constitutes the simple water treatment will be classified as extended water treatment techniques.

Before the municipality reform was enforced, a compilation of the applications for use of extended water treatment techniques was made, and it was found that the sources for need of further treatment of the water was distributed into four categories Treatment for:.

An overview of the application is given in Table 5. Overview of compounds causing need for extended water treatment in the Danish drinking water sector As a result of these applications, there were 29 plants operating with extended water treatment in The total amount of produced water from these plants was 2. The main problems may be divided into two groups: One correlated with the Danish geology, and a second with the anthropogenic activity.

Problems with calcium carbonate scaling and arsenic contamination belong to the first category, and are most prominent from Eastern Jutland and eastwards. This part of the country was covered by ice during the last ice age, while the western part of Jutland was left uncovered. As a result, carbon dioxide in the rain has dissolved much of the calcium carbonate in the underground in this part of the country.

The soil is also more sandy in the western part of Denmark, while the soil in East Denmark has a high content of clay; a fact which also influences the vulnerability of the groundwater aquifers 1, The second category, pollution caused by anthropogenic activity, is distributed over the entire country, although it is also influenced by the geology, mainly the type of soil.

The two main threats to groundwater quality are nitrate and pesticides. Chlorinated organic solvents are also a concern, but they are often found together with pesticide pollution 1. In Table 6 an overview of the techniques applied as extended treatment in the Danish drinking water sector is given. It is seen that for some of the problems only one type of technique has been investigated, as with the use of active carbon filtration for removal of pesticides, whereas for other problems, a wider range of techniques have been applied.

The use of different techniques is also correlated to the number of times the problem has been encountered. Overview of extended water treatment techniques applied for the different problems encountered in the Danish drinking water production To investigate the use of some of these techniques in greater detail from here on, a case study approach will be used.

As a result, many waterworks situated in places with marine clay sediments got issues with removal of arsenic In Figure 7 , it can be seen where in Denmark arsenic has been found in the drinking water, and it is clear that the clay rich eastern part of Denmark from east Jutland and eastward is the most affected. Arsenic is often bound to iron minerals and released when ferrihydrite Fe OH 3 is reduced or pyrit FeS is oxidized. However, it has been found that by applying reduced iron, arsenic can be made to co-precipitate The method has been found to be effective.

The permission was given, but only for a two year period based on the recommendation of the health inspector In Galten waterworks got permission to use FeCl 2 to remove arsenic Map of drinking water wells in which arsenic has been found in the period from to Areas with arsenic concentrations above the threshold limit in more than water wells are shown by red colour Frederiksberg waterworks — removal of chlorinated solvents.

In many places in Denmark, the groundwater is polluted with organic micropollutants such as chlorinated solvents. These originate from varying sources, including landfill leachate, colouring and varnish industry, pesticide production industry, gas stations and dry cleaning industry. Because the pollution is industrial related, it is often found close to population centers, where also many drinking water wells have been placed 1.

The remaining water is purchased by Copenhagen Energy. Water that is basic can form scale; acidic water can corrode. According to U. Environmental Protection Agency criteria, water for domestic use should have a pH between 5. In recent years, the growth of industry, technology, population, and water use has increased the stress upon both our land and water resources.

Locally, the quality of ground water has been degraded. Municipal and industrial wastes and chemical fertilizers, herbicides, and pesticides not properly contained have entered the soil, infiltrated some aquifers, and degraded the ground-water quality. Other pollution problems include sewer leakage, faulty septic-tank operation, and landfill leachates. In some coastal areas, intensive pumping of fresh ground water has caused salt water to intrude into fresh-water aquifers.

In recognition of the potential for pollution, biological and chemical analyses are made routinely on municipal and industrial water supplies. Federal, State, and local agencies are taking steps to increase water-quality monitoring.