FracFocus Discusses Groundwater & Aquifers

Nearly half of the U.S. population relies on groundwater as their primary source of drinking water. In rural areas, this figure approaches 95%. It is easy to see from these figures that groundwater is an importance source of water that should be protected. But what exactly is groundwater?

Groundwater is the water that is held within the interconnected openings of saturated rock beneath the land surface in much the same way as water would be held in a bowl full of marbles. Although the marbles would fill the bowl, there would be spaces between the marbles. These spaces can hold fluid. As shown in the diagram above, this is how water exists in the subsurface.

On the graphic below, the hydrologic cycle ‡ shows that when rain falls to the ground, some water flows along the land surface to streams or lakes (e) and (g), some water evaporates into the atmosphere, some is taken up by plants, and some seeps into the ground.

As water begins to seep into the ground, it enters a zone (a) that contains both water and air, referred to as the unsaturated zone or vadose zone ‡. The upper part of this zone, known as the root zone or soil zone, supports plant growth and is crisscrossed by living roots, holes left by decayed roots, and animal and worm burrows.

Below the root zone lies a capillary fringe ‡ which results from the attraction between water and rocks. As a result of this attraction, water clings as a film on the surface of rock particles.

Water moves through the unsaturated zone into the saturated zone ‡ (f), where all the interconnected openings between rock particles are filled with water. It is within this saturated zone that the term “groundwater” is correctly applied. Groundwater is held in aquifers which are discussed in the following sections.

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Groundwater myths:

• Groundwater moves rapidly.
• Groundwater migrates thousands of miles.
• There is no relationship between groundwater and surface water.
• Groundwater removed from the earth is never returned.
• Groundwater is mysterious and occult.
• Groundwater is not a significant source of water supply.

The diagram below shows how groundwater is held in the spaces between rock particles.

The Miriam Webster dictionary defines an aquifer as a “water-bearing stratum of permeable rock, sand, or gravel.” Aquifers may contain fresh, brackish or salty water in volumes ranging from minor to large enough to serve a public water system.

Aquifers that provide sustainable fresh groundwater to urban areas and for agriculture are usually located at depths of less than a few hundred feet below the ground surface.

Gravity is the dominant driving force in groundwater movement in aquifers that are not bounded above and below by impermeable rock. This is called an unconfined aquifer. Under natural conditions, groundwater moves “downhill” until it reaches the land surface at a spring such as the one shown below or through a seep in the side or bottom of a river bed, lake, wetland, or other surface water body.

Groundwater can also leave the aquifer via the pumping of a well. The process of groundwater outflowing into a surface water body or leaving the aquifer through pumping is called discharge.

Many rivers, lakes, and wetlands rely heavily on groundwater discharge as a source of water. During times of low precipitation, these bodies of water would not contain any water at all if it were not for groundwater discharge. It is important to note that because of discharge, contaminants in groundwater can flow into surface water bodies. This process can make the removal of contamination very complex.

Confined aquifers are bounded above and below by impermeable rock. The driving force of groundwater movement in confined aquifers is pressure, rather than gravity.

When the intersection between the aquifer and the land’s surface is natural, the pathway is called a spring. A typical spring is shown at left. If discharge occurs through a well, that well is a flowing or artesian well. To read more about the movement of groundwater go to the National Ground Water Association website. There you will find an excellent discussion about groundwater hydrology ‡.

You can also get more information about aquifers on the U.S. Geological Survey website. ‡

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The facts about bottled water.

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Many people in many developing countries seek out clean drinking water with much difficulty. But developed nations such as the US spend billions of dollars buying bottled water even though their respective countries provide clean drinking water from the tap. What is more is that the plastic bottles that this water comes in create billions of pounds of oil based trash destined to live out a thousand year lifespan in a trash dump.

Bottled water is in many ways an American obsession, with Americans drinking annually 8.6 billion gallons. Not only do they drink vast amounts but Americans are willing to pay 10,000 times the cost of tap water for the privilege of drinking an arguably inferior product. We get the 10,000 times number from the fact that on average bottled water cost $10 per gallon compared to tap water which costs $.0015 per gallon or about a tenth of a penny.

Globally some 53 billion gallons of bottled water are consumed creating a $63 billion dollar industry. One the most peculiar facts is that 40% of this bottled water is actually taken from municipal water sources also known as “tap water”. Another strange element of this puzzle is that far less testing is done on bottled water than on tap water. It turns out that unlike tap water, bottled water isn’t tested for e. coli. More still is the fact that it can be distributed even if it doesn’t meet the quality standards of tap water. Unlike tap water, bottled water isn’t required to produce quality reports or even provide it’s source.

Comically, the bottled water production process is fairly resource intensive. It actually takes 17 million barrels of oil to produce bottled water which is enough oil to fuel 1 million cars for a whole year. Oil isn’t the only necessary resource. Luckily tap water is very cheap because it takes about 3 times the amount of tap water to produce and fill 1 bottle of bottled water.

Sadly, it isn’t just expensive and potentially lower quality to drink bottled water but there is an environmental impact that should be considered. Even though most major cities in America have made recycling available, only 1 in 5 water bottles ever gets recycled. Instead, 4 go to the trash dump to create about 3 billion pounds of waste just from all of the discarded plastic.

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India water crisis: Overflowing sewage remains a perennial problem

Sewage health hazard: Overflowing of sewage in Srinivasa Second Street, West Mambalam. Photo: K. Kasturi: The Hindu: Chennai, T. S. Atul Swaminathan:June 17, 2012

“It is very common to see sewage stagnating on the road, which is because of poor construction of sewage chambers and frequent blockage in the pipeline.

“The stagnated sewage serves as a breeding ground for the mosquitoes. As mosquito menace has increased to alarming proportions, most of us keep our windows and doors closed,” say residents.

Residents of TNSCB flats are forced to endure stagnant pools while filling water from three ground-level Sintex water tanks. People residing opposite the flats complain about sewage mixing with drinking water stored in sumps.

“During Monsoon, sewage, mixed with rainwater, overflows from almost all the drainage channels and enters the sumps as the street is covered with layers of sandy subsoil,” residents point out.

They say that repeated complaints to Metrowater and Chennai Corporation to clear the overflowing sewage have fallen on deaf ears.

“We have made repeated representations asking the Chennai Corporation and Chennai Metropolitan Water Supply and Sewerage Board officials to re-construct the sewage network. No action has been taken till date,” the residents allege.

Demand

“The authorities concerned should re-construct the leaking manual chambers and construct the required sewage lines. A wall should be built between the TNSCB flats and houses to prevent sewage water from entering the houses on the streets,” the residents add.

Responding to the complaints, Councillor (Ward No. 140) N. Baskaran said that there are plans to improve the drainage system in the street and it would be implemented within a short time.

Interesting article:

Types of Bacteria Used in Wastewater Treatment

Bacteria are categorized by the way that they obtain oxygen. In wastewater treatment, there are three types of bacteria used to treat the waste that comes into the treatment plant: aerobic, anaerobic and facultative.

Aerobic bacteria are used in most new treatment plants in an aerated environment. This means that there is dissolved oxygen available for the respiration of the bacteria: read more>>

Information on sewage and sewage treatment

Origins of sewage

Sewage is generated by residential, institutional, and commercial and industrial establishments. It includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets.

Sewage may include stormwater runoff. Sewerage systems capable of handling stormwater are known as combined sewer systems. This design was common when urban sewerage systems were first developed, in the late 19th and early 20th centuries.^[3]:119 Combined sewers require much larger and more expensive treatment facilities than sanitary sewers. Heavy volumes of storm runoff may overwhelm the sewage treatment system, causing a spill or overflow. Sanitary sewers are typically much smaller than combined sewers, and they are not designed to transport stormwater. Backups of raw sewage can occur if excessive infiltration/inflow (dilution by stormwater and/or groundwater) is allowed into a sanitary sewer system. Communities that have urbanized in the mid-20th century or later generally have built separate systems for sewage (sanitary sewers) and stormwater, because precipitation causes widely varying flows, reducing sewage treatment plant efficiency.^[4]

As rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. (See urban runoff.)^[5] Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include retention basins, wetlands, buried vaults with various kinds of media filters, and vortex separators (to remove coarse solids).

Process overview

Sewage can be treated close to where it is created, a decentralised system (in septic tanks, biofilters or aerobic treatment systems), or be collected and transported via a network of pipes and pump stations to a municipal treatment plant, a centralised system (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of sewage often require specialized treatment processes (see Industrial wastewater treatment).

Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment.

• Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.
• Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.
• Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow rejection into a highly sensitive or fragile ecosystem (estuaries, low-flow rivers, coral reefs,…). Treated water is sometimes disinfected chemically or physically (for example, by lagoons and microfiltration) prior to discharge into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes.

Process Flow Diagram for a typical large-scale treatment plant

Process Flow Diagram for a typical treatment plant via Subsurface Flow Constructed Wetlands (SFCW)