A guest post by Hitesh Khant. Hitesh is an Earth Science student and a nature lover. His blog, Science Keeda, is about nature and natural processes.
Fill a glass of water for yourself.
Do you know where this water probably came from?
Years ago or maybe decades ago, rain clouds gathered over land that is now your city. It rained. Rainwater slowly percolated through the soil and stored itself in the ground. It remained there, before a borewell sucked it out and delivered it to you.
You are holding a part of history in your hands.
Imagine letting a part of history (that you might one day drink) mix with your bodily wastes.
Groundwater is an important source of water. We use it for irrigation, industries and homes.
But we can’t see groundwater; so, it is easy to forget that like any other source of water, it too can get contaminated. Groundwater contamination is a serious problem today.
What is groundwater contamination?
Groundwater contamination (or groundwater pollution) is artificially induced degradation of the natural quality of groundwater. Any change in the taste, smell, or composition of groundwater that can harm the living beings when consumed it qualifies as groundwater contamination.
Unfortunately, most contamination we see today happens because of human activities.
There are four main sources for groundwater contamination….
- Human waste
- Industrial sources
- Agricultural sources
- Miscellaneous sources
Today, we will look at the first source: our waste. We’ll also discuss what you can do as an individual to stop it from polluting our groundwater.
Flashback: London, 1854
In August and September 1854, Broad Street in London was one of the most dangerous places for you to live in. In two months, almost 600 people lost their lives. It was a cholera outbreak unlike any England had seen in the last 20 years. The outbreak is commonly referred as “Broad Street outbreak”.
Until then, the English believed that toxic air caused cholera. Neither the city authorities nor the local water utility wanted to believe John Snow, when he suggested that this disease was caused because of polluted water being supplied to citizens. Snow, a physician, had theorized that water was spreading cholera many years earlier. As he lived close to Broad Street, he got a chance to test his theory. He started visiting the area and talk to the local people.
He prepared a dot map where he marked all the groundwater sources. He analysed the patterns of groundwater consumption and found that the outbreak was concentrated around a well on Broad Street.
Some more investigation revealed that a few days before the outbreak, a mother had washed the nappies of her baby at that well. That baby had been suffering from cholera.
How does human waste elements get into the groundwater?
Open waste dumps and landfills are a common cause for groundwater contamination. In 1830s and 1840s London, human and animal waste was directly dumped into the Thames River or in open pits called cesspools. These cesspools would leak and happily contaminate the groundwater below.
Open waste dumps and landfills continue to be a threat to groundwater. Toxic elements from the waste dissolve in the rainwater, and enter aquifers as the rainwater percolates through the soil.
If the rainwater cannot directly infiltrate the soil—because the layer below the landfill/waste dump is impermeable—it can still contaminate groundwater through the bathtub effect.
This is how it works: Water starts to accumulate under the landfill above the impermeable layer, and after certain point, it spills out into the groundwater reservoir.
In modern cities, sewer and septic tank leakage is the most common cause for groundwater contamination. Sewers can leak because of poor workmanship, natural activities (like tremors), artificial vibration activity (like construction), broken sewer pipes (by tree roots, heavy loads) or cracked due to corrosion.
What’s the problem with groundwater contamination?
Highly toxic organic materials, inorganic materials, bacteria, viruses, heavy metals and nitrates leak into the groundwater from sewage. Our health faces the biggest danger from consuming such water.
Ask the thousands who died in mid-1800s England.
Or you can ask the many millions living along the Ganges. Cities and towns on the banks of the river release untreated sewage into the river—6 billion litres of sewage every day (Mallet, 2017). Pilgrims and locals use the river’s polluted surface water for drinking, washing and rituals. But a significant portion also percolates into the groundwater, contaminating the large system of interconnected aquifers underneath the alluvial soil.
Water-related ailments like amoebic dysentery, gastroenteritis, tape-worm infestations, typhoid, cholera, and viral hepatitis are common in the Gangetic plains.
Similar instances of pollution have been observed in Hyderabad, where septic tanks leaked and polluted the aquifer underneath.
Can we stop waste from contaminating our groundwater?
Yes. These problems can be avoided with resilient sewer structures, sewage treatment plants and better landfill design, which are in the hands of the city municipalities.
Resilient sewer structures
Sewers are usually the first point of contact between human waste water and the ground. As such, the sewer structures should be designed with the following in mind:
- Always use sturdy materials
- Piping systems must be deep enough to avoid contact with roots
- Always design pipes to carry greater volume of sewage than what is expected
- Ensure a strong foundation for the sewer system
Sewage treatment plants
Sewage treatment plants take the dirty untreated sewage and remove most of the pollutants in it, before discharging it into natural streams. It is a complex procedure lasting 48-72 hours going through 2-3 stages of treatment.
Design is not the biggest consideration here; it’s the capacity. The sewage treatment capacity of a city must match or exceed the quantity of sewage produced in the city. Unfortunately, few cities in India meet this criterion. Untreated sewage is often disposed into water bodies, which then seep into the groundwater.
Site selection is key. The landfill should be design by accounting for local geological conditions:
- The soil above and below the landfill should not be permeable, like sand. Highly permeable layers allow the contaminants from the landfill to leach into groundwater aquifers.
- If the soil is permeable, it must be covered with plastic liners, which are impermeable to water.
A landfill has multiple procedural options. Take “secure landfills”. The toxic waste and chemicals are sealed into drums and placed in the landfills. The bottom is further secured by plastic liners or impermeable materials.
Another option is the deep well disposal. Leachate from the landfill is pumped and disposed deep into the ground into rock layers that are isolated from groundwater aquifers.
When the sanitary landfill reaches its capacity, the land can be repurposed into gardens. By growing plants with phyto-remedial properties, they can remove lingering toxins from the soil (which otherwise could have leached with rainwater). The municipality can also earn revenue!
What if a leak occurs?
Despite our best efforts, leaks sometimes happen and are detected late. In such cases, it’s best to avoid using groundwater sources for a few days.
Meanwhile, municipal authorities fix the leak and use a variety of techniques to reduce the influence of leaked contaminants. For example, landfills often pump clean water into the aquifer to dilute the groundwater and reduce toxin concentrations.
How can you help as an individual?
Living in cities, we can always keep an eye on sewers. Here are some steps you can take, as an individual and a community, to prevent groundwater contamination from sewer leaks.
- Make sure that there are no leaks near your house. If there are, immediately call the MCD.
- Check your home’s plumbing regularly.
- Don’t throw medical waste wrappers or old liquid medicines into the sink/toilet. Dispose them properly.
Most importantly, request your local leaders to take action. You don’t have to go protest; if you know local citizen groups petitioning for sewage treatment plants to cater to your society/locality, just donate to them or sign their petitions! (If you are worried about the smell factor, latest technologies completely prevent it.)
It’s our waste, and our water. Let’s take responsibility!