This paper deals with the detailed physicochemical characteristics of groundwater resources from different lithological units in the Siliguri subdivision of Darjeeling district which have been evaluated on 18 parameters. The study reveals that groundwater is hard and contains more iron percentage than the permissible limit. The concentrations of calcium, magnesium and fluoride ions are significantly lower than the safe limits prescribed for drinking purpose, causing health hazards, such as cardiovascular problems, gastrointestinal irritation, dental caries, respiratory disorders and spinal cord system diseases. The rapid soil erosion and the associated runoff were caused by geomorphological conditions, deforestation due to shifting cultivation, and climatic factors, which are probably responsible for the low concentration of groundwater.

Groundwater is the potential source of drinking water in the Siliguri subdivision of Darjeeling district. Its quality depends upon the geoenvironmental framework and plays a vital role in the health conditions of the population. However, it is never found in a pure state. The rainwater reacts with soil and earth's materials and attains certain characteristics before entering the ground. Hence, during percolation into the geological formations, its chemical properties may change from its place of entry to the point of exit. Keeping in view the large populations, the problem of scarcity of drinking water becomes even worse during the summer season, often leading to unhygienic conditions in and around the Siliguri subdivision. The present study was undertaken to ascertain the physicochemical characteristics of the groundwater resources for environmental control over these resources from Siwalik as well as alluvial deposits.

The study area comprised an area of about 832.11 sq km and located in between 26° 26' N to 26° 50' N and 88° 05' E to 88° 27' E (Figure 1). The climate of the study area is pronounced with continental characters, i.e., maximum temperature rises up to 39 °C and the minimum touches below 7 °C. The atmosphere is highly humid, with relative humidity ranging from 80% to 83% in rainy season, while it is less humid in winter season, raging from 68% to 70%. The average annual rainfall for the last 22 years was 3,698 mm with 133 rainy days. The stream order and drainage density values are extreme variables, i.e., from 1 to 4 km/km².

Except for the lesser Himalayan zone of Siwalik deposits of Tertiary Age in the northern part, the main geologic formation encountered in the area includes the sub-areal formations and alluvial deposit of recent age (Jana and Haque, 1999). Most of the formation materials have been deposited cyclothermically. The study area is a monoclinal structure, more or less parallel to the foothill of the lesser Himalaya in the north. The general slope of the area is North-East to South-West direction ranging from 0° 54' to 22° 58'.

Earth Sciences Journal, Groundwater Resources, Geological Formations, Geoenvironmental Framework, State Water Investigation Directory, Physicochemical Characteristics, Groundwater Contamination, Gastrointestinal Irritation, Soil Erosion, Environmental Degradation, Human Consumption, Gastrointestinal Disease.