Groundwater contamination belts

Topic: Water Resources of India: Availability, Use and Conservation · NCERT: Beyond NCERT

Meaning

Groundwater contamination belts are large regions of India where groundwater carries a harmful substance above the safe drinking-water limits set by the BIS (Bureau of Indian Standards). Each belt is linked to one main contaminant, and the rock or soil below decides which one: arsenic in the Ganga-Brahmaputra plains, fluoride in the dry hard-rock areas, uranium in Punjab's Malwa, salinity on some coasts, and nitrate almost everywhere.

They matter because millions of people drink untreated well water. Heavy pumping is making these belts worse, so falling groundwater is now a health crisis as well as a water crisis.

Explanation

Two kinds of source

• Geogenic (natural, coming from the rocks and sediments):
• Arsenic, fluoride and uranium.

• The rock below decides which one shows up. So each belt follows the geology of the area.

• Anthropogenic (coming from human activity):

• Nitrate from nitrogen fertiliser and from leaking sewage and septic tanks.
• Heavy metals from industry.

• These do not follow the rocks. They follow farms, towns and factories, so they are spread out, not packed into one belt.

• Seawater intrusion is a third case. Too much pumping near the coast pulls salt water into fresh aquifers (underground water-bearing layers).

How the main belts form (cause → process → result)

• Arsenic belt (young alluvium):
• Rivers lay down young Holocene alluvium (silt and sand dropped by rivers in roughly the last 10,000 years). This alluvium is rich in iron oxide, and arsenic sticks to its surface.
• Underground, the water has little oxygen. The iron oxide dissolves → arsenic is released into the water.

• Heavy pumping pulls this water quickly through the aquifer and makes things worse.

• Fluoride belt (old hard rock in dry areas):

• Water stays in contact with fluoride-bearing hard rocks such as granite and gneiss for a long time → fluoride dissolves into it.
• Low rainfall means little fresh water to dilute it → the fluoride level builds up.

• Over-withdrawal (pumping out too much) brings up older, deeper water that holds more fluoride.

• Salinity belt (coasts):

• Too much pumping near the sea → the pressure of the fresh groundwater falls.

• Seawater moves inland into the aquifer → wells turn salty and cannot be used for drinking or irrigation.

• Over-withdrawal makes both kinds worse. It has raised fluoride in Rajasthan and Maharashtra and arsenic in parts of West Bengal and Bihar.

Contaminants and their health effects

Contaminant	Source	Setting	Health effect
Arsenic	Geogenic	Young Holocene alluvium	Skin lesions (dark patches and hard spots on palms and soles), cancers of the skin and internal organs
Fluoride	Geogenic	Granite and gneiss in dry areas	Dental fluorosis (stained, mottled teeth); skeletal fluorosis (stiff, bent bones and painful joints)
Uranium	Geogenic, made worse by pumping	Alluvium of semi-arid south-west Punjab	Kidney damage
Nitrate	Anthropogenic	Farmland and settlements	Blue-baby syndrome in infants (the baby's blood cannot carry enough oxygen)
Salinity	Seawater intrusion	Coastal aquifers	Water unfit for drinking and irrigation

How widespread it is: CGWB report, 2024

• The Annual Ground Water Quality Report 2024 (CGWB, released December 2024) used samples from 15,259 monitoring locations [1].
• Nitrate was above the limit in 19.8% of samples, which makes it the most widespread problem [1].
• Fluoride was high in 9.04% of samples [1].
• Arsenic was high in 3.1% of samples [1].
• 100% of samples met BIS standards in Arunachal Pradesh, Mizoram, Meghalaya and Jammu and Kashmir [1].

Where it occurs

• Arsenic belt: the Ganga-Brahmaputra plains of West Bengal, Bihar, Uttar Pradesh and Assam. It continues across the border into Bangladesh. This is the world's worst-known arsenic belt.

• In Punjab, arsenic above the limit has been found in Mansa, Faridkot and Sangrur [2].

• Fluoride belt: Rajasthan, Maharashtra, Telangana (Nalgonda district), Andhra Pradesh, Gujarat and Karnataka. This is mostly the dry Peninsular hard-rock belt and the edge of the Thar.

• Uranium belt: Malwa, the part of Punjab south of the Sutlej. Uranium has been found in 9 districts: Bathinda, Moga, Faridkot, Fatehgarh Sahib, Ferozepur, Ludhiana, Muktsar, Patiala and Sangrur [2].

• In CGWB's 2024 data for Punjab, 32.6% of samples were above the uranium limit, 4.85% above the arsenic limit and 0.44% above the selenium limit. Trace elements were tested at 908 locations [3].

• Salinity intrusion: Saurashtra (Gujarat) and coastal Tamil Nadu.

• Nitrate: spread across farmland and towns all over India, not tied to one belt [1].
• Isolated pockets: contamination was found in isolated pockets of Rajasthan, Haryana and Andhra Pradesh [1].

Don't confuse with

• Groundwater depletion: this is about quantity. More water is pumped out than is recharged (refilled), so the water table falls. Contamination is about quality. The two are linked, because heavy pumping pulls up arsenic, fluoride and uranium.
• Soil salinity vs salinity intrusion: soil salinity is a salt crust on farm soil caused by too much irrigation and poor drainage in places like Punjab, Haryana and western UP. Salinity intrusion is seawater entering coastal aquifers, as in Saurashtra and coastal Tamil Nadu.
• Geogenic vs industrial arsenic: arsenic in the Ganga-Brahmaputra plains comes from natural Holocene alluvium, not mainly from factories. This is a common trap.
• Most widespread vs most famous: arsenic is the best-known contaminant, but nitrate is the most common (19.8% of samples), ahead of fluoride (9.04%) and arsenic (3.1%) [1].

Prelims Hooks

• Arsenic and young Holocene alluvium are a pair: the Ganga-Brahmaputra plains of West Bengal, Bihar, UP and Assam, running on into Bangladesh.
• Fluoride and Nalgonda (Telangana) are a classic pair. Fluoride comes from granite and gneiss in dry areas and causes dental and skeletal fluorosis.
• Order of how widespread they are (CGWB 2024): nitrate (19.8%) > fluoride (9.04%) > arsenic (3.1%) [1].
• Uranium in groundwater is linked to the Malwa belt of Punjab (Bathinda, Moga, Faridkot and others) [2].
• States where 100% of samples met BIS standards: Arunachal Pradesh, Mizoram, Meghalaya, Jammu and Kashmir [1].
• Nitrate causes blue-baby syndrome; uranium causes kidney damage. Watch for these two being swapped in options.

Mains Points

• Geology decides the contaminant (GS-I): young alluvium gives arsenic in the Ganga-Brahmaputra plains. Old hard rock in dry areas gives fluoride in the Peninsula and Rajasthan. Farms and towns give nitrate everywhere. Pumping on the coast draws seawater into Saurashtra and Tamil Nadu. Over-withdrawal makes every belt worse, so depletion and contamination have to be tackled together.
• Effects (GS-III):
• Health: skin lesions and cancer from arsenic, fluorosis from fluoride, kidney damage from uranium, blue-baby syndrome from nitrate.
• Livelihoods: salty coastal wells are lost for both drinking and farming.

• Punjab carries a double burden: heavy pumping and farm chemicals seeping into aquifers have brought depletion and contamination together, with uranium found in 32.6% of samples [3].

• Policy responses (GS-III):

• Monitoring: CGWB's Annual Ground Water Quality Report tracks the belts [1].
• Arsenic: arsenic-free wells under the Jal Kranti Abhiyan (2015).
• Fluoride: rainwater recharge (sending rainwater down into the aquifer) to dilute it.
• Safe supply: piped drinking water under the Jal Jeevan Mission (2019).
• Less pumping: crop diversification and power-subsidy reform to cut over-withdrawal.

Related concepts

• Groundwater depletion
• Punjab groundwater crisis
• Arsenic contamination
• Fluoride contamination

Read more

• Groundwater depletion and contamination