1.TEMPs OF STAGNANT groundwater will be anything between 10 and 20 degress centigrade--that of geotherml water maybe anything between 30 to 300 degres centigrade 2. stagnant water has pH ranging between 6 and 8 whereas geotherml water is very acidic at ph

Arun Kumar Shrestha

To precisely differentiate stagnant groundwater from geothermal water, it is essential to analyze key physicochemical parameters that vary significantly depending on the source, origin, and the processes through which the water has passed. These parameters include temperature, mineralization, pH value, dissolved gas concentration, viscosity, specific gravity, and isotopic composition.

Temperature is one of the most reliable indicators, as stagnant groundwater typically has a temperature in equilibrium with the surrounding environment and does not exceed 15–20°C, while geothermal waters can have much higher temperatures, ranging from 30°C to over 100°C, due to internal geothermal processes. This temperature difference reflects the geological conditions in which the water is found and can serve as the first indicator of the water’s origin.

Mineralization and chemical composition are other crucial parameters. Stagnant groundwater typically has lower mineralization and contains fewer dissolved salts and minerals, as it has been confined to shallow depths, where its contact with mineral-rich layers is limited. In contrast, geothermal waters often have high concentrations of dissolved minerals such as silicon dioxide (SiO₂), sulfur (H₂S), boron, and other minerals formed through geothermal processes at deep Earth layers. High mineralization is characteristic of geothermal sources and may also include elevated concentrations of metals such as iron, copper, and magnesium.

pH value of the water can also be key in distinguishing these sources. Stagnant groundwater typically has a pH close to neutral (around 7), but it can vary depending on local conditions and organic matter content. Geothermal waters, on the other hand, often display an acidic pH, typically below 5, due to the presence of dissolved gases like carbon dioxide (CO₂) and sulfur dioxide (SO₂), which are produced in deep geothermal systems and contribute to their acidity.

Dissolved gas content is another parameter that can indicate the water's origin. Stagnant groundwater typically has very low concentrations of dissolved gases, while geothermal waters can contain high concentrations of gases such as carbon dioxide (CO₂), radon (Rn), sulfur gas (H₂S), and methane (CH₄), which result from the water's passage through hot geothermal layers. These gases can influence the color, odor, and pH of the water, making it more acidic and rich in dissolved gases.

Furthermore, viscosity and specific gravity of the water can be useful indicators. Stagnant groundwater typically has low viscosity and a standard specific gravity (around 1.0–1.1 g/cm³), while geothermal waters, due to their higher content of minerals and gases, may exhibit increased viscosity and specific gravity, making them denser than stagnant groundwater. These parameters are often analyzed in combination with other factors for precise differentiation between these types of water.

Finally, isotopic analysis can provide another significant insight. Geothermal waters often show a distinctive isotopic signature due to their prolonged contact with high temperatures and geothermal processes, which can lead to changes in isotopic ratios (such as hydrogen and carbon isotopes). In contrast, stagnant groundwater typically has a "younger" isotopic signature, similar to the composition of infiltrating rainwater.

By combining these parameters, such as temperature, pH, mineral and gas concentrations, viscosity, specific gravity, and isotopic composition, we can reliably distinguish stagnant groundwater from geothermal sources. Geothermal waters typically exhibit higher temperatures, greater mineral and gas content, acidity, and specific isotopic signatures, while stagnant groundwater tends to have a more stable chemical composition, lower temperatures, and lower mineralization.

To distinguish stagnant groundwater from geothermal water using physicochemical parameters, measure temperature profiles (geothermal waters are significantly warmer than local ambient groundwater), dissolved gases (elevated CO₂, H₂S, or CH₄ in geothermal fluids), major-ion chemistry and isotopes (geothermal signatures often show silica, sodium, chloride enrichment and isotopic shifts from deep sources), and tracer/age indicators; combine temperature with chemical and isotopic fingerprints for robust classification.