|Year : 2011 | Volume
| Issue : 1 | Page : 50-54
Measurements of radon concentrations in ground water samples of tectonically active areas of Himachal Pradesh, North West Himalayas, India
Vishal Arora, Bikramjit Singh Bajwa, Surinder Singh
Department of physics, Guru Nanak Dev University, Amritsar, India
|Date of Web Publication||17-Mar-2012|
Department of physics, Guru Nanak Dev University, Amritsar
Source of Support: None, Conflict of Interest: None
The paper discusses the result of systematic measurement of activity concentration of radon in ground water samples of seismically active areas of N-W Himalayas, Himachal Pradesh, India. Himalayan region is being subjected to intense neotectonic movements and seismic activities. For systematic study, the study area has been divided into three Zones on the basis of lithology and thrust systems of the area viz. Zone-I, Zone-II and Zone-III. Water radon concentrations were measured using RAD-7 equipped with an appropriate unit (Aqua kit) following a protocol proposed by the manufacturer. Water samples have been collected from the different sources and wide range of the villages from the Zone-I, II and III respectively. The radon concentration in water samples collected from Zone-I has been found to be varying from 8.4Bq/l to 314Bq/l with average value 61.2 Bq/l. The radon concentration in water samples collected from Zone-II has been found to be varying from 14.4Bq/l to 140Bq/l with average value 50.8 Bq/l. The radon concentration in water samples collected from Zone-III has been found to be varying from 9.3Bq/l to 77.8Bq/l with average value 23.2 Bq/l.
Keywords: Radon measurements, RAD-7, seismotectonic, North West Himalayas
|How to cite this article:|
Arora V, Bajwa BS, Singh S. Measurements of radon concentrations in ground water samples of tectonically active areas of Himachal Pradesh, North West Himalayas, India. Radiat Prot Environ 2011;34:50-4
|How to cite this URL:|
Arora V, Bajwa BS, Singh S. Measurements of radon concentrations in ground water samples of tectonically active areas of Himachal Pradesh, North West Himalayas, India. Radiat Prot Environ [serial online] 2011 [cited 2019 Dec 10];34:50-4. Available from: http://www.rpe.org.in/text.asp?2011/34/1/50/93955
| 1 Introduction|| |
Radon contents of groundwater sources have led to a great interest in hydro geological and geological engineering. In situ field measurements of radon in natural water/soil are useful in (a) field measurements of uranium deposits; (b) search for hidden faults/thrusts etc; (c) continuous monitoring of radioactivity of drinking, mining and thermal water for radiation protection purposes and (d) search for seismic related changes in radon content of water and soil.
Radon in subterranean water arises from the decay of radium present at low concentrations in water and through the diffusion of 222 Rn from rocks and other deposits. Radon in water can diffuse over large distances in water. A World wide survey of ground water indicated a 222 Rn mean concentration of about 183Bq.L -1 (NCRP, 1984).
Exposure to water borne 222 Rn may occur by ingestion (drinking water containing 222 Rn) and by inhalation (breathing 222 Rn gas which has been released from household water). Both mechanisms pose potential health hazards (Yu et al., 1994; Barnett et al., 1995; Tayyeb et al., 1998). The radon water solubility at 0°C is 510cm 3 /l decreasing at higher temperatures (UNESCAR, 1993). Thus the domestic use of showers and cooking, washing up, laundering etc. may lead to additional increases in indoor radon concentrations. The elevated levels of 222 Rn inside dwellings increase the radiological risk of developing lung or bronchial cancer (Lubin & Boice, 1989). The ingestion of radon in water can give rise to an additional exposure dose to the stomach and the whole body. However, this manner of exposure is much less important than radon inhalation (Crawford-Brown & Cothern, 1987; Gosink et al., 1990). The aim of the present work is to establish the 222 Rn concentrations in water samples collected from the selected seismotectonic regions, along with studying the relationship between the ground water radon concentration and geology/active tectonics of study regions.
| 2. Geology of Area|| |
Himalayan region is being subjected to intense neotectonic movements and seismic activities. For systematic study, the study area has been divided into three Zones on the basis of lithology and thrust systems of the area. Zone-I forms a part of the wide longitudinal valley that lies between the Zanskar and Dhauladhar ranges in the north and south, respectively. The valley trends NW-SE and is considered to be of tectonic origin (Gansser, 1964; Wadia, 1957) The southern part of the longitudinal valley is known as the Chamba valley and the northwestern part is known as Kashmir valley. The area is seismically active and lies in Zone IV of the Seismic Zoning Map of India (IS 1893: 2002). Among the major seismic events of the region are the Kangra earthquake of 1905 (M=8), Chamba earthquake of 1945 (M=6.5), Dharamshala earthquake of 1986 (M=5.5) and Himachal earthquake of 1968 (M=4.9). Zone-II of the N-W Himalayas lies on the southern slope of the Dhauladhar range. Diverse lithology within a short span of distance makes the study area tectonically significant and shows the features of ductile shear zone due to the presence of distinct thrust planes popularly known as MBT-2 (locally known as Drini Thrust), MBT and MCT (or Chail Thrust). In this region the individual formations and groups are separated from one another by longitudinal thrust systems (Mahajan and Virdi, 2000) and the area is cross-cut by transverse faults/lineaments trending northeast-southwest. Zone-III also comprises of various thrust planes and is also tectonically active.
| 3. Experimental Techniques|| |
RAD-7 procured from Durridge Company U.S.A has been used for monitoring radon concentration in water. The method employs a closed loop aeration scheme whereby the air volume and water volume are constant and independent of the flow rate. In the present study 250 mL vial has been used and the measurement is done using protocol provided by the manufacturer because this controls the pumping and counting cycle, and the calculation according to the size of sample vial. The details of measurement technique are given elsewhere (Badhan et al, 2010). Sampling stations were identified in selected locations for collecting potable water. The maps showing the sampling locations are shown in [Figure 1], [Figure 2] and [Figure 3]. Minimum detection limit of RAD-7 for radon in water is approximately 0.4 Bq/L. The samples were immediately analyzed at site after the collection without any delay therefore decay correction is neglected
|Figure 1: Geological map of Zone-I under study along with various sampling locations and tectonic features|
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|Figure 2: Geological map of Zone-II under study along with sampling locations and tectonic features like Main Boundary Thrust (MBT), Main Central Thrust (MCT) and drainage systems Sarah Khad (SK), Churan Khad (CK), Manjhi Khad (MJK), Manuni Khad (MK)|
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|Figure 3: Geological map of Zone-III under study along with sampling locations and tectonic features ((like Main Boundary Thrust (MBT), Panjal Thrust, Suloh thrust)|
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| 4. Results and Discussion|| |
The results of radon concentration measurements in ground water samples collected from the three prescribed Zones are represented in the form of histograms [Figure 4], [Figure 5] and [Figure 6]. Water samples have been collected from the different sources and wide range of the villages from the Zone-I, II and III respectively. The radon concentration in water samples collected from Zone-I has been found to be varying from 8.4Bq/l to 314Bq/l with average value 61.2 Bq/l. The radon concentration in water samples collected from Zone-II has been found to be varying from 14.4Bq/l to 140Bq/l with average value 50.8 Bq/l. The radon concentration in water samples collected from Zone-III has been found to be varying from 9.3Bq/l to 77.8Bq/ with average value 23.2 Bq/l l.
The various type of rock formations in Zone-I are Manjir formation, Pukhri formation, Chamba formation and Salooni formation. Salooni formation is overlain by Sahoo volcanics, while Manjir, Pukhri and Chamba formations mainly consists of slates. Comparatively higher Radon concentration values are obtained in samples collected from upper Salooni and Sahoo volcanics as compared to the other formations of this zone. Reason can be attributed to interaction of groundwater with the various rock types of this area. Sample no. 5, 6, 11 and 12 in the zone-1 are showing exceptionally higher concentration as compared to the other samples of this region, which may be again due to their existence in the salooni formation, being overlain by sahoo volcanics contributing to higher radon concentration or may be due to presence of granite rocks in the specific zone, as radon concentration can reach several of thousands Bq.L -1 in water from drilled wells in the region with granite rock formation (Salonen, 1994). The results obtained corroborates the earlier studies carried out in the quartzite and volcanic rocks of Rampur formation in Mandi-Manali area, Himachal Himalaya, India (Choubey et al., 2006)
In Zone II, Radon concentration has been found to vary from 14.4Bq/l to 140Bq/l, with highest observed concentration in water sample collected from one of the natural springs near village Dari, which is located near a well known local fault in this region. Natural water sources in the villages viz Ther and Khaniara (sample no. 1 and 2) located near the same fault, also have comparatively elevated level of ground water radon concentration of the order of 80 Bq/l. The comparatively higher ground water radon concentration in these villages indicates the influence of local fault systems of the region on the radon concentration in water, along with the other geological parameters. Most of the samples collected from natural springs are showing comparatively higher values, as compared to the samples collected from hand pumps. This might be due to the reason that natural water interacts with various types of rocks and dissolves various radioactive elements in it, during it's course of flow, resulting into comparatively higher emanation of radon.
In zone-III, with main tectonic features are Suloh thrust and Panjal thrust, radon concentration observed is comparatively less than other zones. The observed values are in close agreement with the values of radon concentration reported by Choubey et al in neotectonic Doon Valley, Outer Himalayas, India, (Choubey, et al, 2001) expect few natural spring samples showing exceptionally high values. The observed values in the study zone are much higher as compared to the values reported in groundwater samples of Punjab, Hamirpur and Mandi district of Himachal Pradesh, India (Singh et al, 2005).
Moreover, as has been observed, superficial and shallow fluvial and colluvial spring/hand pump are showing relatively low radon concentrations as spring systems are related to higher porosity and transitivity that neither allows accumulation or emanation of radon gas, thus corroborating the earlier studies carried out by Choubey et al., 2000. On the other hand higher radon concentration values are generally to be associated with springs that are controlled by faults/joints or thrust, lineaments even irrespective of the underlain rock type within same geological formation, as has been observed in most of the springs in the Zone-I, II and III. Therefore radon contents in the spring samples are found to be highly variable in accordance with it's genetic type and depth of groundwater circulation, whereas the hand pumps on the other hand being shallower generally show low radon concentration. However, few hand pumps which are right on or close the thrust (sample no-7, 9 and 10 in Zone-I; sample no-9, 10, 11 and 13 in Zone-II), shows comparatively higher radon concentration, suggesting that radon emission is influenced with the deep seated thrust structures. Even that is why, particularly the thermal springs being deep seated in origin and being related to thrust planes show exceptionally high radon concentration of the order of 600 Bql -1 compared to adjacent normal springs. (Walia et al, 2005).Therefore it can be concluded that radon content of springs /hand pumps can be a good indicator of the underlying geology/faults/thrust planes and the depth of the water circulation versus the shallow depth local springs.
As far as health hazard effects are concerned, although the radon concentration levels have been found to be higher in the ground water samples as compared to the other regions, but they are mostly within internationally recommended safe limits. The European Union issued a non-binding recommendation in 2001, setting 100 Bq.l -1 as a reference level; a concentration above this level warrants a remedial action. The EU recommendation also sets 1000 Bq.l -1 as the upper bound, above which a remedial action is definitely required (EU, 2001).Although, the recorded radon concentration in groundwater of selected seismotectonic active areas of Himachal Pradesh, N-W Himalayas were below the international recommendations, but the values obtained are comparatively higher than reported from some areas along the foot hills of N-W Himalayas in Punjab (Singh et al, 2009) and Upper Siwaliks, India (Singh et al, 2008). The observed values obtained are also much higher as compared to the values reported in ground water samples of Punjab, Hamirpur and Mandi district of Himachal Pradesh, India, but are lesser than the values reported in the thermal springs of Kullu district (Singh et al, 2005, Walia et al, 2005).Overall, the radon concentration in water samples of Seismically active areas of N-W Himalayas, India is comparatively higher, than the adjacent non active areas in Punjab, but overall the water samples are safe for drinking purposes.
| 5. Conclusions|| |
Average Radon concentration in the groundwater samples of seismotectonic zones of Himachal Pradesh, India is comparatively higher as compared to the non active areas in Punjab.
Ground water radon concentration appears to be affected by the local faults and thrust systems of area along with the other geological parameters.
Water samples collected from natural springs in this area have comparatively higher average concentration of radon as compared to the samples collected from hand pumps.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]