e-journal Earth Science India, Vol. 3 (I), January, 2010, pp.73-80 http://www.earthscienceindia.info/; ISSN: 0974 8350 Study on Bromide in Groundwater in Parts of Nalgonda District, Andhra Pradesh K. Brindha and L. Elango * Department of Geology Anna University, Chennai, Tamil Nadu, 600 025 *Email: elango34@hotmail.com; elango@annauniv.edu Abstract The quality of groundwater is under constant threat due to urbanization. The purpose of this study is to understand the seasonal and temporal variations with special reference to bromide in groundwater and to determine the reasons behind the presence of this ion in groundwater. This study area is located at a distance of about 135 km towards ESE direction from Hyderabad. The concentration of bromide in groundwater of the study area was analyzed by collecting the groundwater samples from forty six wells once every two months from March 2008 to January 2009. Groundwater level and ph were measured in the field. The concentration of the minor ion namely bromide was determined by analyzing the groundwater samples in the laboratory using ion chromatograph. The bromide concentration ranged from below detection limit to 5.5 mg/l. The permissible limit for bromide in drinking water according to Indian standards specification is not mentioned. However, literature based on toxicity data puts forth 1 mg/l as the maximum admissible level of bromide. In this study, only a few groundwater samples had concentration of bromide above this limit. It is evident from this study that the groundwater quality is good with respect to bromide in this region. By the proper use of fertilizers and pesticides for agriculture, the groundwater quality can further be maintained in its current form or can be improved. Key Words: bromide, groundwater, Hyderabad, pollution, drinking water Introduction Groundwater is widely distributed than surface water and is used for domestic, industrial and agricultural purposes throughout the world. More than 95% of rural population depends on groundwater for all needs. Because of the rapidly increasing population, several environmental problems are created which includes groundwater quality degradation. Any ion in groundwater present beyond the limit that cannot be admitted by the human body can be considered as pollution of the groundwater. Bromide is a minor constituent in natural waters and toxicity of bromide in human leads to vomiting, nausea, drowsiness, mental dullness and loss of motor coordination. In urban areas, due to treatment of water for drinking by disinfection processes, bromide gets converted into bromate which is a potential carcinogen. There is no standard permissible limit available for bromide in the Indian standards specified for drinking water (BIS, 1992). However, literature based on the toxicity data has set up a groundwater quality criterion of 1 mg/l (Flury and Papritz, 1993). Although there are several studies that have dealt with bromide and bromate concentration in tap water, bottled water and public drinking water supplies (Alessandro et al. 2008) and their health effects, there are no major studies worldwide with respect to bromide content in groundwater. In Nalgonda district, Andhra Pradesh, India, a major groundwater quality investigation is being carried out (Rajesh et al., 2009). The present study forms a part of this major study with the objective of understanding the 73
Study on Bromide in Groundwater: Brindha and Elango present status of groundwater quality with respect to bromide and its spatial and seasonal variation. Fig. 1: Location of the study area. Fig. 2: Drainage pattern of the study area.
e-journal Earth Science India, Vol. 3 (I), January, 2010, pp.73-80 http://www.earthscienceindia.info/; ISSN: 0974 8350 Study area The study area forming a part of Nalgonda district, Andhra Pradesh is located at a distance of 135 km ESE of Hyderabad (Fig. 1). The Nagarjuna Sagar reservoir is located in the southeastern side of this area and the southern side of the area is bounded by Pedda Vagu River. The northern boundary is partially along a water divide. The climate varies from arid to semi-arid. The temperature during the summer ranges from 30 o C to 46.5 o C and in winter it varies between 16 o C and 29 o C. The rainfall in this region is mostly due to southwest monsoon (June- September) and the average annual rainfall of this area is about 1000 mm. The surface runoff has resulted into the development of dentritic to subdentritic drainage pattern in this area (Fig. 2). The highest elevation in the study area is 348.1 m and the lowest elevation is 169.5 m. Geology Granite forms the basement which is traversed by numerous dolerite dykes and quartz veins (Figure 3). Granites are generally medium to coarse grained. Rocks such as pink and grey granites occur at most parts of the study area. Most part of the investigated area has exposures of granitic/ granite gneisses which belong to late Archaen. The Srisailam formation, the youngest member of the Cuddapah super group directly overlies the basement granite with a distinct unconformity. The Srisailam metamorphic formation is exposed in the southeastern part of the study area. The litho units of this formation are dipping at an angle ranging from 3º to 5º towards SE. The sediments of Srisailam formation are mainly arenaceous and include pebbly-gritty quartzite shale with dolomitic limestone, intercalated sequence of shale-quartzite and massive quartzite (Fig. 3). The generalized stratigraphic sequence of this area is given in Table-1 (after GSI 1995). Table-1: General stratigraphic sequence of the study area (after GSI, 1995) Cuddapah Supergroup Srisailam Formation Massive quartzite Upper shale Quartzite with shale intercalation Lower shale with limestone intercalation Pebbly and gritty quartzite/ arenite ----------------------------------------Eparchean Unconformity---------------------------- Late Archean/ Lower Proterozoic Granite/granitic gneiss intrusion of dolorite dykes and quartz veins Methodology An intensive field survey was carried out and nearly 240 wells were considered for sampling. The Electrical Conductivity (µs/cm) was measured in all the wells and a representative well in about every 15km 2 was chosen for the collection of groundwater samples. Based on this survey, a total of 46 wells were selected (Fig. 4) for sample collection from March 2008 to January 2009. Groundwater samples were collected once in two months from these 46 wells. The depth of the wells varied from 1.45 m to about 20 m 75
Study on Bromide in Groundwater: Brindha and Elango Fig. 3: Geology of the study area (after GSI 1995).
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