Radon Concentration Measurement in Groundwater of Roorkee , Uttarakhand , India

Groundwater is the largest fresh water resource and radon is a radioactive naturally occurring noble gas that may be found anywhere in soil, air and water due to decay of uranium in rocks. It is important to investigate the radon in groundwater to safeguard against the health hazard caused due radon. The results presented here are from radon concentrations measured using RAD7 detector in 9 representative groundwater samples collected from hand pumps from southern parts of Roorkee in Haridwar district of Uttrakhand. Radon activity concentration was found in the range of 0.55+0.22 Bq L-1 to 3.39+0.28 Bq L-1 with an average value of 2.16+0.37 Bq L-1. Radon values were compared with United State Environmental Protection Agency value of 11 Bq L-1. The radon activity trend was found within the permissible limit. article history Received: 21 July 2017 Accepted:19 August 2017


Introduction
Human beings are vulnerable to more than half of the dose exposure from natural radiation sources 1,2 of the radon ( 222 Rn) and its progeny, produced during the radioactive decay chain of uranium ( 238 U) contributing approximately 55% of internal radiation exposure to human life 3 .Radon coming on to contact with the land surface get mixed with the groundwater depending on various factors and its level depends on the radium concentration.Groundwater can create a health risk while acting as a carrier of radon into domestic environment 4 and the levels of radon in indoor dwellings can be enhanced partially by radon derived from water supply 5,6 .The exposure to high concentrations of radon can lead cancers of lung 7 and stomach and gastrointestinal 8 .Many researchers have conducted research all over the world for monitoring radon concentrations in different environments and efforts are on to find out the methods to reduce its adverse effects on the human beings [9][10][11][12][13][14][15][16] and on the other side simultaneously finding its applications [17][18][19] .In Uttarakhand various studies had been carried out in river waters of Garhwal and Shiwalik Himalayas and groundwater of the Doon valley where high radon concentrations have been reported [20][21][22] .In Shivalik Himalyas of Himachal Pradesh20, the radon concentration varied from 1.0 ± 0.3 to 653.5 ± 8.0 Bq L-1 where as in Doon valley 21 , in tube wells and hand pumps radon concentration varied from 25.4 ± 1.8 to 92.5 ± 3.4 Bq L-1 with an average of 53.5 ± 2.6 Bq L-1.Keeping in view the above points, the present study is carried out in southern part of Roorkee area of Uttarakhand, India to investigate the radon levels in groundwater as it is widely used for drinking.

study area
Roorkee lies on the coordinates 29°52' N latitude, 77 °53' E longitude and altitude 268m.Normal rainfall is 1156.4mm and monthly average maximum temperature range observed between 20.4 -39.2 and minimum temperature range varied between 10.6 -27.223.Roorkee is a part of Gangetic alluvial plains and lithologically, the alluvium is formed of unconsolidated to semi-consolidated deposits of sand, silt, clay and kankar.The ground water conditions in alluvial parts are considerably influenced by the varying lithology of the subsurface formations which has been found in various studies of parts of Gangetic basin [24][25][26][27][28][29][30][31] .Methodology 9 representative groundwater samples from the hand pumps collected using standard methodology9 from the locations shown in table 1.The pH, EC and temperatures were recorded using hand held pH meter, EC meter and thermometer, respectively.Radon concentrations in these samples were measured with RAD7 (Fig. 1), an electronic radon detector connected to a RAD-H 2 O accessory (Durridge Co., USA), within 12 hours of sample collection [9][10] .

Results and Discussion
Table 2 reveals that the varied values, due to different geological conditions 4 , of 222 Rn ranged between 0.55 ± 0.22 and 3.39 ± 0.28 Bq L-1 with an average value of 2.16 ± 0.37 Bq L-1, well within the EPA's maximum contaminant level of 11.1 Bq L-1and these values were correlated with EC, pH and temperature.There was a weak positive correlation of radon with EC and a moderate negative correlation of radon was found with pH and temperature (Table 3) means that there is a tendency of high radon scores to go with low pH and temperature scores.In arid regions of Rajasthan where the temperature is high, Mittal et al., (2016) 33 reported radon concentration from 0.50 to 22 Bq L−1 with the mean value of 4.42 Bq L−1 in groundwater samples.However, EC values ranged between 240 -550 µS/cm with an average value of   2).Akawwi (2014) 34 suggested radon concentration increases with temperature and similar results were also found by Garg et al., 22 .Some researchers have reported poor correlation of radon concentration with pH and TDS 35 due to inert nature of radon.

Conclusion
The values of natural radioactivity measured in groundwater in southern part of Roorkee area of Uttarakhand, India covered in the present survey is within the permissible limits prescribed by USEPA (1991) 36 but a regular monitoring is required.No significant correlation of radon values were found with other parameters viz.EC, pH & temperature and it was found that pH & temperature are moderately negatively correlated and a weak positive correlation was found with EC.However, some of the factors, such as precipitation, geologic and hydrologic variables are important and must be investigated.

acknowledgments
Authors thank Director, National Institute of Hydrology, Roorkee for support and encouragement.