|
Ground Water Quality Observations |
|
The groundwater quality is monitored by the Central Ground Water Board once a year (April/May) through a network of observation wells located all over the country. The hot spots for groundwater in districts coming under basin states are identified on the basis of six main parameters: salinity (EC>3000 micro simen/cm), chloride, fluoride (>1.5 mg/l), iron (>1.0 mg/l), arsenic (>0.05 mg/l) and nitrate (>45 mg/l). The states of Bihar, Uttar Pradesh and West Bengal is affected by arsenic (where the concentration is greater than the permissible limit of 0.05 mg/l as per IS: 10500), fluoride, iron & nitrate. More than permissible level of salinity and chloride has been identified in Haryana, Delhi, Himachal Pradesh, West Bengal, Uttar Pradesh, Rajasthan and Madhya Pradesh.
In the central alluvial trough, the groundwater has low mineral contents. The mineral content increases near the southern fringe of the alluvial formation, especially in certain parts of Agra, Aligarh, Mathura, Mainpuri and Ballia districts of Uttar Pradesh, near the delta area in West Bengal, the water in certain aquifers turns saline due to incursion of sea water. According to India-WRIS database there are 571 Ground Quality Observation sites in 124 districts of 10 states which fall in Ganga Basin. There are 181 sites of Rajasthan, 169 of Madhya Pradesh, 62 of Uttar Pradesh, 50 of West Bengal, 47 of Haryana, 27 sites in Bihar, 21 sites in Delhi, 10 in Jharkhand, 3 sites in Uttarakhand and 1 site in Chhattisgarh.
According to the CGWB, the Ganga basin is severely affected by arsenic, fluoride, nitrate, chloride and salinity. The problem of arsenic contamination in ground water from the vast tract of alluvial aquifers in West Bengal, Bihar and Uttar Pradesh has affected a large population in different districts of Ganga basin. A large population of West Bengal live in the arsenic belt and few places are also affected by fluoride. Arsenic in ground water have been reported in a range 0.05-3.2 mg/l in shallow aquifers in 8 districts of West Bengal namely Malda, Mushirbad, Nadia, North and South 24 Pargana, Bardhaman, Howrah, and Hugli. The incidence of arsenic problem is due to excessive use of groundwater irrigation. For e.g. up to 80 percent of the annual replenishable recharge in North 24 Parganas district of West Bengal for multiple cropping which causes dropping of water levels resulting exposure of the arsenic rich beds to air. In Ganga basin there are 152 arsenic affected ground water observation sites in 31 districts of 3 states that are contained in Ganga basin. There are 74 sites of West Bengal, 42 sites of Bihar and 36 sites of Uttar Pradesh.
Salinity/Electrical Conductance (EC) is the saltiness or dissolved salt contents of a water body and is an important factor in water use. Salinity always exists in ground water but in variable amounts. It is mostly influenced by aquifer material, solubility of minerals, duration of contact and factors such as the permeability of soil, drainage facilities, quantity of rainfall and above all, the climate of the area.
Chloride is present in all natural waters, mostly at low concentrations. It is highly soluble in water and moves freely with water through soil and rock. The recommended desirable limit of chloride concentration in drinking water ranges from 250 -1000 mg /l. However few districts in the basin are observed relatively high values of Chloride are Gurgaon, Jhajjar, Rohtak and Sonepat districts of Haryana, Bhind and Ujjain districts of Madhya Pradesh, Bundi, Chittaurgarh, Dausa, Jaipur, Karauli, Nagaur, Sawai Madhopur, Nagaur, Sikar, Tonk and Udaipur districts of Rajasthan, Aligarh, Agra and Mathura districts of Uttar Pradesh, North 24 Parganas, South 24 Parganas of West Bengal and all districts of Delhi.
Fluorine is the most electronegative and reactive of all elements that occur naturally within many type of rock. The desirable limit of fluoride concentration in drinking water ranges from 1.0 - 1.5 mg/l and more than 1.5 mg/l are not suitable for drinking purposes. Almost all parts of the basin are affected by fluoride and the severities are seen in the parts of Bihar, Chhattisgarh, Delhi, Haryana, Jharkhand Madhya Pradesh, Rajasthan, Uttar Pradesh and West Bengal. Nitrate is a naturally occurring compound that is formed in the soil when nitrogen and oxygen combine. The dissolved nitrogen in the form of Nitrate is the most common contaminant of ground water. The maximum desirable limit of Nitrate concentration in ground water is 45 mg/l with no relaxation. The parts of all 11 states that are falling in the basin, Bihar, Chhattisgarh, Delhi, Haryana, Himachal Pradesh, Jharkhand Madhya Pradesh, Rajasthan, Uttar Pradesh, Uttarakhand and West Bengal has observed nitrate greater than 45 mg/l. (Source: India-WRIS) |