Hydrogeochemical impact of water infiltration on water quality of Bastacolla area of Jharia Coalfield, Jharkhand, India

Deep beneath the earth's surface, water acts as a silent traveler, moving through cracks and pores in rock and soil. In many parts of the world, this water is a vital resource, but in places where the ground has been torn open by mining, its journey can become dangerous. When rain falls or surface water seeps into abandoned or active mines, it encounters coal seams and the rocks that hold them. This contact triggers a chemical reaction, often loading the water with dissolved minerals and heavy metals. While this process is frequently associated with acid mine drainage, the water in this specific region is not uniformly acidic; instead, it often remains neutral to alkaline while still carrying significant chemical burdens. This contamination can transform a clear stream into a hazardous flow, threatening the health of communities and the stability of the local ecosystem. Understanding exactly how this happens, and measuring the extent of the damage, is essential for protecting the water that people rely on for drinking and daily life.

In the Bastacolla area of the Jharia Coalfield in eastern India, researchers set out to trace this invisible journey of contamination. This region is a hub of coal extraction, where the ground has been disturbed for over a century. The team, led by geologists from the Central University of Jharkhand, focused on how water infiltration—the seeping of surface water into the ground—alters the quality of the local water supply. They collected water from various sources, including open wells, boreholes, and pumps that draw water directly from the mines. By testing these samples in a laboratory, they aimed to map the chemical changes occurring as water moves through the fractured landscape of the coalfield. Their goal was not just to list pollutants, but to understand the specific processes that degrade the water and to determine if it remains safe for human use.

The analysis revealed a landscape where the water has been significantly altered by its contact with the earth beneath it. The researchers found that the water is rich in dissolved solids, with levels of total dissolved solids ranging from 544 to 969 milligrams per liter, and electrical conductivity values between 756 and 1493 microsiemens per centimeter. These high numbers indicate that the water is picking up a heavy load of minerals as it filters through the rock. The chemical makeup of the water is dominated by calcium, magnesium, chloride, and sulfate, a signature that suggests the water is actively dissolving carbonate rocks and reacting with sulfide minerals left behind by mining. This chemical fingerprint points to a complex mixing of water types, driven by the fractured geology of the area and the ongoing interaction between water and the disturbed earth.

The most concerning findings, however, relate to the presence of heavy metals and the overall safety of the water for drinking. The study measured several toxic elements, including iron, manganese, lead, cadmium, and zinc. The results showed that manganese levels were particularly high, ranging from 432 to 697 micrograms per liter, which is significantly above the acceptable limit set by Indian standards (300 µg/L). Lead and iron also exceeded safe thresholds in many samples. When the researchers combined all these factors into a single score to assess overall water quality, known as the Water Quality Index, the results were stark. None of the water sources tested were considered safe for drinking without extensive treatment. Half of the sampling locations were rated as having "poor" quality, while more than a third were classified as "very poor." One specific site, located near an ecological park, scored so high on the pollution scale that it was deemed completely unsuitable for drinking purposes.

To understand the severity of the metal contamination, the team calculated a Heavy Metal Pollution Index. The average score across all samples indicated a level of contamination that poses a serious risk. Two locations, in particular, showed extremely high scores, driven largely by elevated levels of lead and cadmium, both of which are highly toxic even in small amounts. The researchers also looked at how much each pollutant exceeded the natural or safe baseline. Manganese stood out as the most significant contaminant, showing a "considerable" level of pollution. While the overall pollution load, which averages the impact of all metals together, suggested a moderate level of cumulative pollution, the specific spike in manganese and the presence of other heavy metals create a localized but severe hazard.

The study concludes that the water in this area is not merely slightly dirty; it is chemically transformed by the mining landscape. The infiltration of surface water into the mine workings accelerates the release of minerals and mobilizes heavy metals from the surrounding rock. This process creates a cycle where water quality deteriorates as it moves through the ground, even if the pH remains largely neutral to alkaline. The researchers suggest that simply waiting for the water to clean itself is not an option. Instead, they recommend active intervention, such as constructing wetlands that can naturally filter out metals or using limestone drains to neutralize acidity. They also emphasize the need for continuous monitoring to track how the water quality changes over time. Without these measures, the water in the Bastacolla area will remain a threat to public health, particularly for children and the elderly who are most vulnerable to waterborne illnesses. The findings serve as a clear warning that in mining regions, the health of the water is inextricably linked to the management of the land above it.