Physio-chemical and heavy metal assessment of groundwater near dumping sites in Srinagar District, Jammu & Kashmir, India

Water is one of the essential compounds for all forms of plant and animal life (Vanloon & Duffy 2005), thus, its pollution is generally considered to be more severe than that of soil and air. Due to its specific characteristics, this liquid bears unique properties. It is the most effective dissolving agent and adsorbs or suspends many different compounds. Besides rivers being the most important source of water supply, nearly 90% of the lithogenic and anthropogenic waste materials that are transported in both dissolved and particulate phases are delivered by rivers to the sea and oceans (Garrels et al. 1975). The major portion of water exists in liquid form and is found mostly in oceans which account for 96.5% of total water found in all the three spheres of the physical environment. Groundwater (1.69%), lakes (0.013%), marshes (0.0008%), rivers (0.0002%) and biological water (0.0001%) also contribute a good share of the liquid water.

Surface water (fresh water lakes, rivers, streams) and groundwater (borehole water and well water) are the principal natural water resources. Nearly three quarters of the world's annual rainfall comes down in areas inhabited by less than one third of the world's population while two thirds of the world's population live in areas receiving only a quarter of the world's annual rainfall (Prakash & Prakash 2001). Nowadays one of the most important environmental issues is water contamination.

Heavy metals are among the major pollutants of water sources (Marcovecchio et al. 2007) and are sensitive indicators for monitoring changes in the marine environment. Due to human industrial activities, the levels of heavy metals in the aquatic environment are seriously increasing and have created a major global concern (Ghasemi et al. 2011; Khodabakhshi et al. 2011). Some of these metals are essential for the growth, development and health of living organisms, whereas others are not as they are indestructible and most of them are categorized as toxic to organisms (Underwood 1956). Nonetheless the toxicity of metals depends on their concentration levels in the environment. With increasing concentrations in the environment and the decreasing capacity of soils to retain heavy metals, they leach into groundwater and soil solutions. Thus, these toxic metals can be accumulated in living tissues and concentrate through the foodchain.

Heavy metals are elements having atomic weights between 63.546 and 200.590 and a specific gravity greater than 4.0 i.e. at least 5 times that of water. Elevated levels of heavy metals lead to toxicity in living organisms (Murugavelh & Vinod 2010). With sufficient surface water infiltration, soil contaminants such as heavy metals can leach to underlying groundwater. For instance, leachates are formed by slow decomposition of municipal solid waste. These leachates may run off in the nearby natural water resources such as ponds, lakes and rivers and percolate to groundwater causing water pollution (Arneth et al. 1989). The leachates when mixed with a water body increase the concentration of heavy metals, nitrates, sulphates and other organic and inorganic substances. In India more than 60 million people suffer from flurosis by drinking fluoride contaminated water (Raju et al. 2009). Once the groundwater is contaminated it may remain in a hazardous state for decades or even centuries. Higher concentration of zinc can cause impairment of growth and reproduction (Nolan 2003). In view of ever increasing environmental concerns, in the near future, it will be difficult for people to meet the ever increasing demand for safe water and thus the exploration of nonconventional sources of water might be one of the priorities for the human race. Under such circumstances, groundwater sources such as shallow wells and boreholes might be exploited and utilized more extensively. The qualitative parameters of groundwater are generally associated with the local geology of the area. However, the quality of these groundwater sources are also affected by the characteristics of the media through which the water passes on its way to the groundwater zone of saturation (Adeyemi et al. 2007).Thus, the heavy metals discharged by industries, traffic, municipal wastes, hazardous waste sites as well as from fertilizers for agricultural purposes and accidental oil spillages from tankers can result in a steady rise in contamination of groundwater (Vodela et al. 1997; Igwilo et al. 2006).

The Kashmir valley is very famous for aquatic ecosystems ranging from springs, rivers, wetlands and lakes. However, due to ever-increasing surface pollution from unscientific disposal of municipal wastes, industrial effluent and biological wastes, the quality of surface water has deteriorated greatly and, thus, there is a great need to assess the quality of groundwater too. Groundwater in the Kashmir valley has received very little attention regarding estimation of quality, quantity, conservation and management. Thus the present study aims to illustrate the current status of heavy metal contamination in groundwater around dumping sites in Srinagar.

The Kashmir valley is nested in the north-western folds of the Himalaya, with geographical coordinates of 33°30′–34°30′ N latitude and 74°00′–75°30′ E longitude, covering an area of 15,120 km² at an average height of 1,800 meters above mean sea level and experiencing a continental climatic condition with marked seasonality resembling a sub-Mediterranean type. The present study was confined to Srinagar District of Kashmir valley only. The study area consisted of 6 different locations in Srinagar and thus is expected to give reliable inferences about the impact of waste dumping on the quality parameters of groundwater in Srinagar. The study area also included a particular site which is untouched by hazardous effluent dumping and thus facilitated a strong basis for application of statistical significance tests and to make more effective and valid inferences. In precise terms, the study area consisted of four biological/municipal waste dumping sites (GW2, GW3, GW4 and GW5) and two reference (control) sites: one highly hazardous dumping site (GW1) and another one having no dumping impact (GW6).

For collection of data for the present study, the samples were taken from dug wells from each site. The details of sampling locations are presented in Table 1.

Groundwater samples were collected from 6 distinct sites across central Kashmir (Srinagar) on the basis of simple random sampling during June-July 2020 in polyethylene (PET) bottles, which were previously carefully cleaned, rinsed three to four times with distilled water (APHA et al. 2005). Groundwater water samples were analyzed for their chemical constituents such as temperature, pH value, electrical conductivity, total dissolved solids, hardness, calcium concentration, alkalinity, magnesium concentration, sodium concentration, potassium concentration, chloride concentration, nitrate concentration and heavy metals in accordance to American Public Health Association ‘standard methods for the examination of water and waste water’ (APHA et al. 2005)’.

The groundwater increases its major ion concentrations during the after-melting season (June-July) as compared to the pre- melting season (Jan-Feb), which may be attributed to the evaporation, precipitation and environment weathering as shown in Table 2.

In the best round of statistical analysis the data collected from the sample sites during the study was compared with the data pertaining to heavy metal concentrations during 2012, available as a by-product of the regular monitoring mechanism of the Public Health & Engineering Department, Jammu & Kashmir.

The series are given in Table 3.

Graphical representation of the two data series of 2012 and 2020 is given in Figure 1.

Behavioral analysis reveals that there is an increase in the concentration levels of most of the heavy metals across all the sampled geographical contours of the study area. However, the increase is statistically significant only for site GW1. Though statistically the increase in concentration levels is significant only for one dumping site, GW1 (Achan), the values of the test statistics are close to ‘rejection criteria’ especially for GW2, GW3, GW4 and GW5 and thus the consistent increase in the concentration levels is a matter of concern requiring further investigation.

The groundwater quality of central Kashmir was analyzed in terms of concentrations levels of lead, cadmium, copper, arsenic and zinc. The samples were collected from 6 diversified locations across central Kashmir by way of systematic sampling. The observed data indicate varying degrees of concentration of trace metals in the groundwater sources of the study area. The bird's eye view of the observations is given in Table 4.

From Table 4 it emerges that a very strong positive correlation exists between copper and zinc concentration values having a correlation coefficient of 0.99. All other concentrations also exhibit almost similar kinds of positive correlations with correlation coefficients ranging from 0.80 to 0.97. The arsenic and lead pair exhibit relatively weaker correlation having a correlation coefficient of 0.65.

From this study's point of view, the inter-location correlation is more significant than factor correlation. Thus, an inter-location correlation table was generated (Table 5).

The correlation matrix (Table 5) displays an interesting depiction. The concentration levels exhibit strong positive correlation across all the sites except Reference Site I with correlation coefficients ranging from 0.94 to 0.99. Reference Site I exhibits very small correlation in terms of concentration levels of heavy metals which primarily suggest that the dumping of wastes at GW1 is extremely hazardous and following a perilous tendency in terms of heavy metal concentrations.

The strong correlation of other sites with Reference Site II (least effected by dumping) suggest that the dumping of biological/hospital wastes is within scientific norms and has least effect on quality parameters of groundwater in terms of heavy metal concentrations. However, the correlation coefficient is only a basic statistic and thus this conclusion is not decisive and final. So the data has been subjected to further rigorous analysis as discussed below. The p-values associated with Reference Sites I and II have been calculated to ascertain whether dumping of biological/hospital wastes is being carried out in a scientific way or not. The analytical results are presented in Table 6. A simplified representation is presented in Figure 2.

Based upon analysis it emerges that the heavy metal concentrations vary significantly, both in magnitude and tendency, when compared to Reference Site I (Figure 2). However, when the metal concentrations of test sites are compared with Reference Site II, it appears that GW2 and GW3 exhibit significant deviation from the general tendency followed by the heavy metal contaminations over the period from 2012 to 2019. These two sites follow a different tendency when compared to the non-dumping Reference Site II, suggesting that the disposal mechanism at these sites need further improvement to maintain the quality parameters of groundwater in the context of heavy metal concentrations.

The data obtained was subjected to rigorous statistical analysis so as to analyze multiple dimensions involved in the study. The statistical analysis of the data was carried out in a manner that reduced the overall complexity of the data and facilitated finding the localized causal processes responsible for heavy metal concentrations. Based upon an analysis of variance exhibited for the metal concentrations from one location to other, it is revealed that the biological/hospital waste dumping at different sites needs more stringent scientific control. Moreover, the tendency shown by GW2 and GW3 is altogether different as compared to the non-dumping Reference Site II (GW6). The data further suggests high contamination loading by anthropogenic factors.

This indicates that the contamination of groundwater is mainly due to anthropogenic activities rather than geological factors. Reference Site I (GW1), which is the largest dumping site for all kinds of wastes exhibits extremely hazardous contamination levels, as expected. Though the contamination levels are by and large within permissible limits, the tendency is not so encouraging. In other words, the statistical inference drawn from this parameter suggests that high concentration of heavy metals at any particular site is not due to geology but mainly due to some other factors which include, but are not limited to, the degree of municipal/ hospital waste segregation and mechanism of waste disposal. The presence of high concentration levels of heavy metals at GW1 suggests that contamination is through surface water–groundwater interaction rather than due to geological factors. Actually this area a receives a large quantity of untreated and unsegregated municipal wastes which act as a principal contributor towards the heavy metal contamination of groundwater. Likewise, the disposal/dumping of municipal and hospital wastes at GW2 and GW3 contribute towards the contamination of groundwater aquifers as evident from the results.

The study reveals that the dumping of municipal wastes cause a significant increase in the concentration of heavy metals in groundwater aquifers. On the basis of meticulous statistical analysis, it can be fairly interpreted that metal concentrations across the selected geographical contours exhibited a statistically significant rise over the period. Though a dip in the heavy metal concentration was observed at a couple of sites, the behavioral analysis indicates that there is an overall increasing tendency for heavy metal concentrations across all selected contours. In the case the aquifer at GW1, the levels of heavy metal concentration are dangerously higher and in fact the water is hazardous for human consumption. Likewise GW2 and GW3 possess heavy metal concentrations (copper and arsenic) with a tendency to cross over the thresholds prescribed by the Indian Standards Institution (ISI) regarding the safety parameters of groundwater. Though in other cases the levels are lower than ISI-specified maximum contaminant levels, the findings reveal that the factors responsible for increased concentrations of heavy metals are predominantly expanding. Under such a scenario, there are real worries regarding the deterioration of quality parameters of groundwater aquifers in the area under study. This study advocate further research to be conducted in the field to analyze and assess the exact impact of probable sources of these contaminants and also to explore a restorative strategy for conserving the quality parameters of groundwater aquifers in the region.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.