Definition
Groundwater is water found in layers of soil or rocks below the surface of the ground. Groundwater is a water resource whose existence is limited and its damage can have far-reaching impacts and recovery is difficult.
Apart from river/surface water and rainwater, groundwater also has a very important role, especially in maintaining the balance and availability of water raw materials for household (domestic) purposes as well as for industrial purposes and so on.
A resource that is used up but can be renewed or recycled is water. The earth’s water supply which can be renewed is regulated by the hydrological cycle (water cycle), which is a system of continuous circulation of water, starting from evaporation, continuing to the formation of clouds, down it becomes rain, is absorbed by plants, enters the soil, is filtered by the soil and some flows as streams outside and within the soil, finally arriving as water that flows into rivers and into the sea.
Water Characteristics
Water is found in three different forms on Earth, namely gas, solid, and liquid. The shape of water depends on temperature. Water on our planet flows as liquid in rivers, and the oceans are in solid form as ice at the North and South Poles and are gases (vapor) in the atmosphere. Water also resides underground and within plants and animals. All living things need water in some form to survive on Earth. People can live weeks without food, but can only live a few days without water. A water molecule consists of two hydrogen atoms, each connected by a single chemical bond to an oxygen atom. Most hydrogen atoms have nuclei consisting only of protons.
Two forms of the isotope, deuterium and tritium, whose atomic nuclei also contain one and two neutrons, are respectively found in small levels in water. Although its formula (H2O) seems simple, water exhibits very complex chemical and physical properties. For example, its melting point, 0 degrees C (32 degrees F), and boiling point, 100 degrees C (212 degrees F), are much higher than expected when compared to analogous compounds, such as hydrogen sulfide and ammonia.
The function of water is essential for all life, even though it seems that water is now available everywhere, clean water is the most important thing that all living things can access for their survival. The following functions of water include:
- Drink
- Water plants
- Washing and cleaning
- Cooking (don’t forget – water is needed by the plants and animals we eat to live and grow)
Many factories use large amounts of water to help make the goods we use every day). Water usually has other substances dissolved in it. Examples include the ocean, our blood and drinks as well as soft drinks. We can’t always see, or even taste, dissolved substances.
Our blood consists mostly of water. Many things dissolve in water in our blood. For example, waste is carried from throughout our body to our kidneys to be filtered. A can of soft drink shows how water can dissolve various substances such as sugar, colorings, flavorings, and dissolved gases, especially carbon dioxide, which makes fizzy drinks foamy. Water is all around us. It is in the air, in the soil and in every living thing.
Water is an important and inseparable part of the lives of all living creatures. The human body itself consists of 60-70% water. Therefore, it is important for us to have sufficient water intake every day to replace lost water. Water also provides a variety of other needs in daily life, for example for processing food, washing dishes and dirty clothes, and cleaning oneself. But what is water and what compounds make it up? Even though water seems clear and odorless, scientifically water is composed of several compounds.
Returning again to the definition of water, namely a substance composed of the chemical elements hydrogen and oxygen (H2O) and exists in gas, liquid and solid form. Water is one of the most abundant and important compounds. A tasteless and odorless liquid at room temperature, it has the important ability to dissolve many other substances. Life is believed to have originated from the aqueous solutions of the world’s oceans, and living organisms depend on aqueous solutions, such as blood and digestive fluids, for biological processes. Water also exists on other planets and moons both inside and outside the solar system. In small quantities water appears colorless, but water actually has an intrinsic blue color caused by slight absorption of light at red wavelengths.
Surface water
Surface water is water that flows on the surface of the earth, in general this surface water will be polluted during its flow, for example by mud, logs, leaves, industrial waste and others, or surface water is water that collects on the ground or in springs, rivers, lakes, wetlands, or the sea. Surface Water is found on the surface of the land spread unevenly such as rivers and lakes. Meanwhile, ground water is water that is absorbed in the underground rock layers known as the Aquifer (water strata in the ground). Groundwater is often pumped for domestic, industrial and agricultural purposes, while aquifers are water supplies that are free from evaporation. Water flow recharges groundwater during high flows, and conversely the aquifer will provide water during low flows in the dry season.
Surface water is related to underground water or atmospheric water. Surface water is naturally filled through precipitation and naturally reduced through evaporation and seepage below the surface to become underground water. Although there are other sources of underground water, namely trap water and magma water, precipitation is the main factor and underground water that comes from this process is called meteor water. Surface water can be divided into two types, namely Land Water. Land water is surface water that is above land, for example, such as swamps, lakes, rivers and so on, and Sea Water. Sea water is the surface that is in the vast ocean. For example, sea water in the sea.
A. Quality and Characteristics of Surface Water
Water quality is a variable that can influence the life of aquatic biota. These variables include: physical properties (color, turbidity, and temperature) and chemical properties (oxygen content, carbon dioxide, pH, ammonia, and alkalinity).
National surface water quality has been regulated in Government Regulation no. 82/2001 concerning Water Quality Management and Water Pollution Control. The quality of a water body depends on the characteristics and quantity of water that enters it. Therefore, liquid waste that enters waters also needs to be regulated in statutory regulations, so that it does not worsen the quality of surface water.
In general, surface water will become polluted during its flow, for example by mud, logs, leaves, city industrial waste, and so on. To understand the characteristics of surface raw water, this water is classified into 6, namely;
- Surface water with a high level of turbidity
- Surface water with low turbidity levels
- Surface water with a temporary level of turbidity
- Surface water with medium to high color content
- Surface water with high hardness.
- Surface water with very low turbidity levels
B. How to Calculate Surface Water Discharge
Discharge is the amount of water flow (volume) that flows through a cross-section in a certain time, generally expressed in volume/time units, namely (m³/second). Surface water discharge measurements can be done in 2 ways, namely direct and indirect.
- Direct Measurements: Direct measurements in the field include measuring the width, water height, drainage channel height, sloping side and diameter of each drainage channel.
- Indirect measurement of Velocity area methods. In principle, to determine the discharge of a stream, the flow velocity and wet cross-section of the river are measured. The flow velocity is assumed to be uniform at every point on the cross section whose magnitude is the same as the velocity.
C. Surface Water Treatment
In general, raw water sources from surface water must be considered in terms of turbidity and microbiology. Poor raw water conditions cause higher processing costs because more chemicals are needed or new processing units are even needed to maintain water quality in accordance with quality standards.
The aim of surface water processing is so that surface water can be used by the community as clean water and drinking water in accordance with the clean water and drinking water quality standards set by the government. Drinking water treatment can be done using 3 methods, namely:
1. Physics Processing
The principle of using a filtration process and gravity. The aim is to remove turbidity caused by dissolved particles in raw water.
- Sedimentation Sedimentation is a unit that functions to separate solids and liquids by using gravitational settling to separate suspended particles contained in the liquid (Reynols, 1982).
- Carbon Filter Activated carbon with granular media (Granular Activated Carbon) is a filtration process that functions to remove organic materials, disinfect, and eliminate odors and tastes caused by organic compounds. Principle: absorb pollutants using carbon media. The adsorption process that takes place in activated carbon depends on the surface area of the media used and is related to the total area of pores in the media.
- Membrane or Filtration This process is to filter water that has been coagulated and settled to produce good quality drinking water. Filtration can be carried out using several types of filters, including: slow sand filter, fast sand filter, or using membrane technology. The main advantage of membranes compared to slow sand filtration is that the processing unit required has a smaller size, larger processing capacity, and is able to produce drinkable water.
2. Chemical Processing
Chemical processing is carried out by adding certain chemicals which aim to remove organic and inorganic compounds in water. The addition of these chemicals is specific, depending on the type and concentration of pollutants in the raw water.
- Flocculation
Flocculation is the slow mixing stage that follows the fast mixing unit. This process aims to accelerate the rate of particle collision, thereby causing agglomeration of electrolytically destabilized colloidal particles to a precipitated and filtered size. Flocculation is achieved by applying appropriate stirring to enlarge the flocs resulting from coagulation. In general, the detention time in this tank is 20 – 40 minutes. This is done because floc that has reached a certain size cannot withstand the pulling force of the water flow and causes the floc to break again, therefore the mixing speed and detention time are limited.
- Disinfection
Disinfection is a process that aims to kill pathogenic microorganisms found in raw water entering drinking water treatment plants. This process does not apply to microorganisms that are in spore form. There are various methods for carrying out disinfection, including the use of oxidizing agents (ozone, halogen, halogen compounds), cations from heavy metals (silver, gold, mercury), organic compounds, gaseous compounds, and physical processing (heat, UV, pH ) (Chang, 1971 cited in Reynolds, 1982).
Source :
Book of Teknik Dan Pengelolaan Sumber Daya Air
Writer : Dra. Fauzia Mulyawati, ST, MT; Dr. Agung Wahyudi Biantoro, ST, MT.