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The Role of Geology in Influencing Water Chemistry Essay

The Role of Geology in Influencing Water Chemistry


       Water is and remains one of the important wants of the people, animals and the nature at large. Without water, they would be no life. Water is an unusual compound which has unique physical properties, and this makes it the compound of life, yet it’s the most abundant compound in the earth’s biosphere. The chemistry of water deals with the fundamental chemical property and information about water. Water chemistry can elaborate in terms of the following subtitles: composition of water, Structure, and bonding, Molecular Vibration, as well as geological composition and properties of water among many other aspects of water chemistry (Krauskopf and Bird, 1994). Geology is often responsible for how much water filters below the zone of saturation, making the water table easy to measure. Light, porous rocks can hold more water than heavy, dense rocks. An area underlain with pumice, a very light and porous rock, is more likely to hold a fuller aquifer and provide a clearer measurement for a water table. The water table of an area underlain with hard granite or marble may be much more difficult to assess (Krauskopf and Bird, 1994).

Hypothesis: surficial geology controls the chemistry of surface waters


       Water quality has become one of the essential aspects in life, and it’s defined in terms of the chemical, biological and physical composition of the geological factor. The water quality of rivers, lakes and many other water source changes from one geographical location to another. This is due to difference in the geological composition of the places, i.e., the rocks beneath the earths surface are different and in turn different quality in water quality. However, various factors influence water chemistry in the world (Drever, 1982). One of such vital elements is ‘geology’. This is the science deals with the dynamics and physical history of the earths’, the rock that makes the earth’s crust, and the physical, chemical, and biological changes that the earth undergoes or has undergone. In other words, geology is the science entails the study of rock-solid Earth, the rocks of which it is composed, and the processes by which they change. This branch of science is one of vital and major contributing factor in the water chemistry. In order to understand the impact of geology on the water chemistry, this paper will look into the ground water (Drever, 1982).

       Clear understanding of the nature of the bedrock layers of the region is essential as geology is in determining the quality and quantity of ground water that can be obtained from the underground at any given location. For example, in some parts of the earth, the bedrock consists of sedimentary layers of rocks that have profuse pore spaces between mineral grains. The rock layers can form creatively wide aquifers, or conduits for groundwater movement, that are of predictable depths, and from which apparently indefinite quantities of high-quality groundwater can be obtained. In such areas, groundwater is the clear way out for public water needs (Frape et al, 1984).

       Bedrock geology helps in determining the distribution and density of underground water-bearing fissures, as well as the nature of the soils that are obtained from the rock weathering. Different types of rocks contain more or less fractures that may or may not be interconnected with each other. The degree of interconnection among fractures, and their overall ability to move water, has a great deal to do with how productive a water well will be that intersects the fractures. Different rocks also make different soils when they weather, and the type of soil influences its ability to absorb rainwater that falls on the surface, and transmit the water to bedrock fractures beneath (Cooke et al, 2012).

       The composition of the underground water as well as the surface water is dependent on natural factors, (geological, topographical, meteorological, hydrological, and biological) in the drainage basin and varies with seasonal differences in runoff volumes, weather conditions, and water levels. The quality is, however, affected by both natural and human influences. The most vital or importance of the natural influences is geological, hydrological and climatic, since this affects both quality and quantity of the water available.

       Underground water is held in the pore space of sediments such as sands or gravels or in the fissures of fractured rock such as crystalline rock and limestone. The rocky body containing the water is termed an aquifer and the upper water level in the saturated body is termed the water table. Typically, groundwater’s have a steady flow pattern. Velocity is governed mainly by the porosity and permeability of the material through which the water flows, and is often up to several orders of magnitude less than that of surface water, as a result mixing is poor (Cooke et al, 2012).

       The rock or sediment in an aquifer is denoted by the permeability and porosity, whereby permeability is the measure of the ease with which fluids passes through the rocks. On the other hand, porosity is the ratio of pores and fissure volume to the total volume of the rock. The chemical composition of the rocks greatly influences the chemical composition of water. The different types of aquifers explain this difference in water chemistry all over the places (John, 1990).

       Underground formations are three types, hard crystalline rocks, and consolidated sedimentary and unconsolidated sediments. The example of hard crystalline rocks includes granites, gneisses, quartzite’s, schist’s, and a few rocks from volcanic rocks. These rocks have little or no porosity but it is further enhanced by weathering. For example, ground water in volcanic formations in regions of recent volcanic activity is mostly inhibited with fluoride, and boron elements, which makes it unsuitable uses. Chemical properties of the bedrock greatly influence the chemical properties and water chemistry. For example, water acidity is highly determined by the drift of the bedrock geology. The following example examines the influence of bedrock and soils on water acidity. When the bedrock constitutes of carbonates, the solution of the minerals assimilates H+ ions and hence acidifying water as water percolates through the rocks. CaCO3 + H+ = Ca2+ +HCO3 this results to acidified water (John, 1990).

Effect of Total Dissolved Solids in Groundwater

       A body of saturated rocks through where water can easily move is known as an aquifer. Aquifers contain rocks such as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel which are both permeable and porous. In addition, fractured volcanic rocks, i.e. columnar basalts also make good aquifers (John, 1990).

       Underground water tastes dissimilar from one place to the other or else at different times of the year for several reasons. In exploring those reasons, the paper looks first consider why water from one well might be different from another well, even one that is close by. What dictates groundwater taste is the quantity and type of dissolved minerals in it. In other words, this isn’t pure water as pure water has no dissolved minerals and hence does not occur naturally. The amount and type of minerals that are dissolved in water is what gives waters their initial taste. There are different factors that control the dissolved minerals in the ground water. (I) The type of minerals, making up the aquifer, (II) the chemical state of the ground water, (III), the duration or length of time which water makes contact with the minerals and the rocks (Frape et al, 1984).

       As the rain water passes through different types aquifers, it results in a different chemical composition of water. Almost all groundwater comes from precipitation that soaks into the soil and passes down to the aquifers. Within the aquifer, the groundwater moves not as an underground stream, but rather seeping between and around individual soil and rock particles. Rainwater has a slightly acidic pH; therefore it tends to dissolve solid minerals in the soil and in the aquifers. Sandstone, limestone and basalt all have different minerals. Therefore it is rational to expect groundwater in contact with these different geologic materials to have different chemical compositions {factor (1) above} and therefore different tastes. In addition, the length the groundwater is in contact with the minerals, the greater the extent of its reaction with those minerals and the higher will be the content of dissolved minerals (John, 1990).

       The table below can be used to illustrate the effect of mineral in water hence determining water chemistry. The table illustrates typical natural water compositions, from rainwater to seawater, groundwater in different aquifers, to groundwater that has been in contact with the aquifer for different periods of time.

Table 1.0


Ca 0.7 0.65 240 399 145 6.6 3.10 4530

Mg 1.1 0.14 7200 1340 54 1.1 0.7 162

Na 9.5 0.56 83500 10400 ~27 ~37 3.02 2730

K – 0.11 4060 370 ~2 ~3 1.08 32.0

Bicarbonate 4 – 250 27 620 75 20 56

Sulfate 7.5 2.2 16400 186 60 15 1.0 1.0

Chloride 17 0.57 140000 19020 52 17 0.5 12600

Silica 0.3 – 48 3 21 103 16.4 8.5

TDS 38 4.7 254000 35000 665 221 35 20330

PH 5.4 – 7.5 – – 6.6 6.2 6.5

Table 1; key

       Examples of the composition of natural water from a variety of locations and environments (all concentrations given in milligrams/liter). TDS = total dissolved solids. A dash (-) indicates that the component was not detected or the water was not analyzed for this constituent. A tilde (~) indicates that the analysis is approximate only (John, 1990).

       Key to the Analyses: (A) Rainwater from Menlo Park, California; (B) Average rainwater from sites in North Carolina and Virginia; (C) Great Salt Lake, Utah; (D) Average seawater; (E) Groundwater from limestone of the Supai Formation, Grand Canyon; (F) Groundwater from volcanic rocks, New Mexico; (G) Groundwater from a spring, Sierra Nevada Mountains: short residence time; (H) Groundwater from metamorphic rocks in Canada: long-residence time.

Chemical State of Ground Water

       A large amount of the seasonal and natural water quality disparities we observe are the result of small but considerable alterations in the chemical state of groundwater. The chemical state of groundwater is generally defined in terms of parameters such as, the temperature, oxidation-reduction potential, and PH. These three factors are greatly influenced by chemical reactions between the aquifer materials and the ground water, hence changing the water chemistry in the common water bodies such as lakes, rivers, oceans, etc. the chemical composition of the aquifer greatly controls the physical properties of water such as color, hardness, taste, odor and appearance (John, 1990).

Table 1.1 Water Characteristics and Its Causes (John, 1990)

Characteristics or Symptoms Cause(s)

Hardness: Low suds production with soap, mineral scale developed in water heater and plumbing High concentrations of calcium and magnesium

Color: Water has a color other than clear Red/Brown: iron

Black: manganese or organic matter

Yellow: dissolved organic matter such as tannins

Taste: Metallic or mineral taste Metallic: dissolved metals such as iron and manganese

Mineral taste: high concentration of common minerals such as sodium, Chloride, sulfate, calcium, etc.

Odor: Musty or rotten egg smell Musty: algae or bacterial growth pipes or well

Rotten egg: hydrogen sulfide

Appearance: cloudy with or without color Suspended mineral matter or microorganisms

       Control the chemical composition of groundwater. For example, the total dissolved solids

       (TDS) in groundwater, largely derived from aquifer minerals that dissolve in groundwater, will change significantly as a function of temperature and PH. Temperature. At any given temperature, there is a specific concentration of a dissolved mineral constituent in the groundwater that is in contact with that mineral. The actual concentration is temperature dependent, e.g., at higher temperatures, groundwater can dissolve more of the mineral. Even changes in groundwater temperature of only 5 to 10 C can cause detectable changes in TDS (John, 1990).

       The Natural pH of Groundwater, The pH is a determination of the acidity of groundwater: the lower the pH value, the more acidic the water is and vice versa (a measure of the hydrogen ion (H+) availability). At a pH of 7, water is said to be neutral. Natural rainwater is slightly acidic because it combines with carbon dioxide (CO2) in the atmosphere, forming carbonic acid (H2CO3) according to the reaction (1) H2O + CO2 = H2CO3. Some of the carbonic acid in the rainwater disassociates or breaks down according to the reaction (2), H2CO3 = HCO- + H+ producing bicarbonate (HCO-) and H+. This in turn reduces the PH of the rain water. In addition, the acidic water that is formed is able to dissolve more of the minerals in the aquifers hence greatly contributing to the change of water chemistry. The more amount of CO2 in the atmosphere the more acidic the water becomes (Verdonschot, 2013).

       Composition of the Earth’s Crust, The relative abundance of elements in the crustal material of the Earth has been a subject of much interest to chemists for many years. Although the subject of natural-water chemistry is only indirectly concerned with these averages, a knowledge of rock composition is essential to understanding the chemical composition of natural water, and it is therefore desirable to discuss the subject briefly. The Earth is generally considered to be made up of an iron-rich core surrounded by a thick mantle made up of magnesium- and iron-rich silicates and a thin outer crust made up of rather extensively reworked silicates and other minerals. Reversible and Irreversible Reactions in Water Chemistry, Many kinds of chemical reactions can be important in establishing and maintaining the composition of natural water. Concepts that are appropriate for evaluating these processes differ somewhat depending on the nature of the reactions involved. Therefore, some attention needs to be given to reaction types here, although this cannot be a rigorous classification scheme (Verdonschot, 2013).

Different types of rocks and the impact to the water chemistry

       There are three major types or classes of rocks, namely, sedimentary, igneous and metamorphic. The three are different from each other as they also have varying differences in terms of impact to the water chemistry. To start with, sedimentary rocks are rocks formed from particles of pebbles, shells, sand and other fragments. The different particles are brought together and hence called sediment, whereby they accumulate for a long time and in layers over a long time forming a rock (Verdonschot, 2013). Generally, sedimentary rocks are fairly soft and may in turn break or crumble easily. You can often see sand, pebbles, or stones in the rock and it are usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone among many other rocks. These rocks contain a lot of minerals much of which are soluble in water. As the rain water passes through the rocks, the minerals are absorbed and in turn contributing to the changing or different water chemistry from one region to the other. For example, carbonate-cemented sandstone that is composed largely of silica in the form of quartz might yield water containing mostly calcium and bicarbonate ions (Geology.com, 2014).

       One type of rocks under the class sedimentary is the chemical sedimentary rocks. This is formed when minerals dissolved in the water starts to precipitate forming a rock of minerals. However, not all minerals do precipitate and in turn become part of the water in the lakes and rivers. Many resistant sedimentary rocks are permeable and may, therefore, easily receive and transmit solutes acquired by water from some other type of rock. In the course of moving through the sedimentary formations, several kinds of alteration processes may occur that may influence the composition of the transmitted water (Verdonschot, 2013).

Fig 1.0 sedimentary rock image (Geology.com, 2014)

       The 2nd type of rocks is the Metamorphic, these are rocks formed under the surface of the earth from the changes which are caused by intense heat and pressure. Rocks formed through this process are mostly denoted by ribbon like layers and may also have shiny crystals that grow slowly over time. A good example of this rock type includes gneiss and marble.

Fig 1.1 an image of a metamorphic rock (Geology.com, 2014)

       Lastly, there is the ‘Igneous’. These are rocks formed when molten rock deep within the earth (magma) cools and hardens. This cooling and hardening may occur either inside the earth’s crust or else it blows up onto the earth’s surface from volcanoes (in this case, it is called lava). When the lava cools very quickly, there are no crystals form and the rock looks shiny and glasslike. Occasionally gas bubbles are ensnared in the rock all through the cooling process, leaving tiny holes and spaces in the rock (Buynevich, 2011). Examples of these rocks include basalt and obsidian. Igneous rocks consist predominantly of silicate minerals. As the solutions move through the soil and the underlying rock, the composition of the water should be expected to change. Rocks of igneous origin may be classified as extrusive or intrusive. Both the extrusive and intrusive rocks are further classified by geologists on the basis of chemical and mineral composition, texture, and other characteristics. Rocks of the same chemical and mineral composition have different names, but tend to yield similar weathering products to the water.

Fig 1.2 images of an igneous rock (granite) (Geology.com, 2014)

       Many of the rocks in the three classes contain numerous chemicals which contribute to the defining of water chemistry in one way or another. In ground water composition, seven solutes are the most commonly found salts in metals. These seven solutes make up nearly 95 percent of all water solutes (Buynevich, 2011). These salts include calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chloride (Cl), sulfate (SO4), and bicarbonate (HCO3). Sodium is derived from the dissolution of silicate minerals, such as plagioclase feldspars, which make up some of the sand and gravel that fill the water basin. Potassium is derived from the dissolution of some silicate minerals in granitic rocks and from reactions with some clay minerals. Few reactions remove these seven solutes from ground water. However, some minerals, such as calcite CaCO3, can precipitate from solution to form a solid phase (Buynevich, 2011).


       The interpretation of the water chemistry data has become vital and most reliably made within the conceptual framework on the ground water system that has been derived from several additional types of hydrologic and geologic data, such as water levels, that indicate general directions of ground-water flow. One of the major aspects of the geology of the human is the fact that it helps in maintaining the quality of water supplies. This helps understand the sources of water and in turn protect them from pollution. In addition, it helps in determining the suitability for various uses such as drinking, farming among many other uses (Dissanayake & Chandrajith, 2009).

       The chemistry of lakes, rivers, oceans, and stream water in many regions is strongly associated with the character and circulation of geologic materials in the watershed. For example, the dominance of glacial till and granitic gneiss rock in the North and East of Big Moose Lake region results in a geologically sensitive terrain distinguished by low alkalinity and chemical compositions of the surface water with only slightly modified from ambient precipitation. On the contrary, widespread deposits of substantial glacial till in the lower part of the system (e.g. Moss-Cascade Valley) allow for much infiltration of precipitation into the groundwater system where weathering reactions increase alkalinity and extensively alters water chemistry. In references to the hypothesis, ‘surficial geology controls the chemistry of surface waters’ holds true as seen in the water composition of different regions as the water chemistry and watershed being determined by the geological factors (Dissanayake & Chandrajith, 2009).


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