Evaluating the impact of Nalla Lai contamination on drinking quality of groundwater in Rawalpindi city, Pakistan

Groundwater is the drinking water source of one-third of the global population. It is a valuable freshwater resource used for household, farming, and industrial purposes (Li et al. 2013; International Association of Hydrogeologists 2020). The freshwater of Earth is about 2.5 and 30% of this resource exists in groundwater (USGS 2016). The world is facing a crisis of water quality due to the contamination of freshwater resources from rapid urbanization and industrialization (Poonia et al. 2021). Groundwater contamination is a very noteworthy environmental concern of the time (Momodu & Anyakora 2010). Regardless of its importance, water resource is not properly managed on earth (Fakayode 2005). As compared with other water resources, groundwater can be less polluting by open discarding of waste (Tariq et al. 2008). Various researches have been conducted to determine the fate of emerging organic pollutants in the subsurface through the downward movement of wastewater and industrial effluents (Lapworth et al. 2012). Groundwater contamination can be resulting from the leakage of sewage (Eiswirth & Hötzl 1997). The primary source of groundwater contamination in Lahore, Pakistan is leakage of sewer lines and landfill sites where percolation of leachate and sewage contaminates the groundwater quality (Akhtar et al. 2014). The main sources of groundwater pollution in Pakistan are the discharging of waste effluents into water bodies by many industrial units including textiles, fertilizers, pesticides, steel, dying chemicals, cement, leather, etc. (Tariq et al. 2006). The groundwater quality deterioration resulting from leachate percolation mainly occurs during monsoon season and escalates the diseases related to groundwater contamination. Groundwater contamination occurs mostly in the vicinity of landfill and municipal waste disposal sites and increases the chances of percolation in aquifers (Butt & Ghaffar 2012). The organic pollutants such as oil and pesticides in groundwater are present mostly due to anthropogenic activities whereas geological sources are the cause of inorganic pollutants in groundwater (Memon et al. 2011). In groundwater, heavy metals can be present from natural and anthropogenic sources (Singh & Kamal 2017; Reza & Singh 2019). Environmental contaminants including heavy metals, pesticides, trace organic contaminants, nanoparticles, hydrocarbons, and microplastic are a menace to both human health and ecological services, and also to sustainable social and economic development (Li & Wu 2019; Li 2020). Groundwater contamination is a well-known topic in research studies which is a huge challenge to human populations (Lin 2010). Groundwater remediation is challenging as well as costly because it is found in surface geological strata (Su et al. 2020; Wang et al. 2020). Due to the presence of groundwater in subsurface geological strata, its remediation is challenging as well as expensive. The sources of groundwater pollution in metropolitan areas include point sources, non-point sources, and linear sources (Choi et al. 2005). The natural remediation process of groundwater can take 10 years to hundreds of years, even if the contamination source is removed (Tatti et al. 2019). Heavy metals and metalloids are a danger to both human health and the natural environment. The metals present in groundwater include zinc, mercury, chromium, lead, cadmium, and metalloids such as arsenic and selenium. Although a small concentration of these elements is a necessary micronutrient, exposure to these chemical substances can cause severe poisoning (Hashim et al. 2011). Groundwater used for irrigation if contaminated with heavy metals can results in health risks due to the accumulation of toxic elements in vegetables and cereals (Jenifer & Jha 2018; Njuguna et al. 2019; Yuan et al. 2019). Groundwater contamination is an environmental as well as a social issue. Therefore, a mutual collaboration between the natural scientist and social scientist is mandatory (Ciner et al. 2021). The rapid economic development and population growth have built pressure on groundwater resources. There are 2.8 million wells only in China (Han 2003) and the heavy extractions of groundwater have dropped their level. Groundwater contamination is the most important concern because it is connected to the survival of humans. The identification, remediation, and assessment of groundwater contamination are the most significant topics these years (Domínguez-Mariani et al. 2004). Globally 3.4 million deaths occur due to waterborne diseases (Berman 2009). In developing countries, 2.2 million people lose their lives each year because of drinking contaminated water and inappropriate sanitation system (WHO & UNICEF 2000; UNESCO 2003). Water contamination is the paramount health and environmental issue in Pakistan. Waterborne disease such as hepatitis, diarrhea, typhoid, dysentery, and cholera occupies 20–40% of the beds in the hospital and become a cause of one-third of all mortalities in Pakistan (Farooq et al. 2008; Azizullah et al. 2011). Drinking water contaminated with heavy metals can affect vital human organs like the liver, kidney, and central nervous system (Khan et al. 2011). The surface and groundwater quality is polluted by microbial and a variety of toxic chemicals (Azizullah et al. 2011). The underground lithological environment is the principal influencing factor of contaminant migration to groundwater (Rahman 2008). The research study is conducted along the Nalla Lai which is a perennial wastewater stream containing both domestic and industrial effluents. It is an open sewer of twin cities (Rawalpindi and Islamabad). The study has been conducted by keeping the given prime objective to evaluate the impact of the Nalla wastewater stream on groundwater quality in its proximity.

Rawalpindi is a city in Punjab province and it is located near the capital city of Islamabad. The population of the city is 2.09 million with an area of 259 km² (Atta et al. 2020). The latitude of Rawalpindi city is 33.5984°N and the longitude of the city is 73.0441°E (Shahid et al. 2019). Due to rapid urbanization, the city is facing extreme environmental conditions (Mehmood et al. 2019). Five different seasons are experienced by Rawalpindi city such as winter, summer, spring, autumn, and monsoon. June is the hottest month and January is the coldest month in Rawalpindi city with the highest and lowest recorded temperatures of 48 and −3.9 °C (Asghar et al. 2012; Khan et al. 2019). Water pollution, inappropriate sanitation facilities, and solid waste dumping are the most significant environmental problems in the city (Nisar et al. 2008). Energy-efficient buildings, urbanization impact on groundwater, and seismic mapping are the relevant issues in the city (Maqsoom et al. 2021).

A previsit of the research area was carried out to delineate the sampling boundary of the research area and to select the sampling point's location by using the Global Positioning System (GPS) from IJP road to Soan River. A weekly sampling plan was prepared for the effective implementation of the sampling strategy. The sampling plan includes the preparation of a list of pre-selected sampling points location, requisition or hiring of transportation, selection of sampling day and time, cleaning of water sampling bottles, preparation of preservative, Icebox, personal protective equipment (PPE), first aid box, DO meter, pH meter, TDS meter, notebook, permanent marker, ballpoint pen, and checklist.

To characterize the wastewater and groundwater quality of the research area, the samples were collected by following the internationally recognized sampling procedure ‘Standard Methods for the Examination of Water and Wastewater’ (APHA 2012). Water sampling of the study area was divided into two types:

• I.

  Groundwater sampling

• II.

  Wastewater sampling

• I.

  Groundwater sampling

Groundwater samples were collected by using the grab sampling technique (Kamble 2015). Forty-nine groundwater samples were collected in pre-sterilized polypropylene bottles. Before sterilization, the bottles were properly washed with water (hot) and detergents followed by thrice rinsing with distilled water. The samples were collected from both source and consumer levels in September 2016 at least 1 week after rainfall. Thirty-six groundwater samples were collected from the proximity of Nalla Lai. Thirteen control samples were taken from at least a 1 km distance from both sites of Nalla Lai.

The water samples of (17) tube wells, (29) boreholes, (1) dug well, and (2) springs were collected from different inhabitant colonies of the study area. A 1,000 ml (1 L) sampling bottle was used to collect a water sample from each sampling point for the detection of non-metals. Similarly, a 500 ml sampling bottle was used to collect a water sample from the same point to analyze heavy metals and added preservatives of nitric acid (−HNO₃) to bring the water sample to pH <2. The sampling bottles were properly tagged or labeled with sampling type, sample number, date, time/hour, location, and source.

• II. Wastewater sampling

• I.

  In situ analysis

In situ water testing of parameters like pH (pH scale), temperature (°C), DO (mg L⁻¹), EC (μS/cm), and TDS (mg L⁻¹) were determined by pH meter, thermometer, DO meter, and TDS meter, respectively, and followed the ‘Standard Methods for the Examination of Water and Wastewater’ (APHA 2012).

• II. Detection of E. coli in groundwater

Microbial samples of groundwater were collected by using the grab sampling technique (Tahir et al. 2011). A total of 36 samples were collected in October 2016 from the study area for bacteriological tests. A 50 ml water sample in a sterile container was taken for the qualitative analysis of drinking water quality by using water check kits of ‘Merck company’. First, the blister pack was placed in a sterile container with care and shook well to dissolve the granules and not touch the inner part of the container. Enough air space was left in the sampling container and the cap firmly screwed on. The container was placed at room temperature for 48 h. The color changed to blue and green showing bacterial contamination and the samples having yellow, off-white, and brownish or no change in color represented that water was fit for drinking purposes.

• III. Physicochemical analysis

The analysis of physicochemical parameters was performed by shifting the water samples to CLEAN laboratory Pak-EPA and left in a refrigerator at 4 °C to preserve the integrity of the samples. The analysis of chemical parameters of both groundwater and wastewater samples was performed by using the instrument mentioned in Table 1.

• IV. Data analysis

The statistical analysis and interpolation maps of wastewater and groundwater high vulnerable localities were performed by using Microsoft Excel Environment, XLSTAT, and GIS tools.

The results of many analyzed samples of wastewater of Nalla Lai were beyond the standard value of NEQs, 1997. Iron was detected elevated from the recommended value in three wastewater samples, and cadmium value was higher in five wastewater samples. BOD (biological oxygen demand) results of all wastewater samples and COD (chemical oxygen demand) values of 13 samples were elevated from the standard values of NEQs, 1997. Maximum contamination was observed in the groundwater samples which were collected from the proximity of Nalla Lai. Out of the total of 49 groundwater samples, 36 groundwater samples were collected from the proximity of Nalla Lai. The analyzed results showed that iron concentration was elevated from the recommended limit value in 10 groundwater samples, cadmium was higher in five groundwater samples, manganese was detected in elevation concentration in four groundwater samples, zinc and TDS were beyond the standard limit in one groundwater sample, pH value was very low in three groundwater samples, the color value was high in one groundwater sample, hardness concentration was beyond the recommended value in 30 groundwater samples, and microbial contamination of fecal coliform was detected in 30 groundwater samples.

pH stands for potential hydrogen. It determines the concentration of hydrogen ions in a solution. pH specifies the acidity and basicity of water. pH values ranging from 7 to 14 are alkaline or basic. pH values from 0 to 6 are acidic whereas 7 pH is neutral (Dohare et al. 2014). As stated by Dohare et al. (2014), both acidity and basicity are specified by the pH values. The NSDWQ, 2010 (National Environmental Quality Standards, 2010) range value of pH in drinking water is 6.5–8.5 and NEQs, 1997 (National Environmental Quality Standards, 1997) range value for pH in wastewater is 6–10.

As reported by Ahmed et al. (2013), temperature plays a key role to detect microbial contamination and it has a significant role in the survival of aquatic life (Akbari et al. 2017). The NEQs, 1997 standard value of temperature in wastewater is 40 °C.

Turbidity in water is the cloudiness that happens due to pollutants such as silt, wood ash, coal, chemicals, colloidal dispersions, and microorganisms (Srivastava & Pandey 2012; Akhtar et al. 2014). According to WHO and NSDWQ, 2010, the standard value of turbidity in drinking water is <5 NTU.

Turbidity was detected at zero in all groundwater samples. In wastewater samples, the average turbidity value was 3,257.27 NTU. The turbidity values in wastewater samples of Nalla Lai were in the range of 1,940.24–4,610.20 NTU. The descriptive statistics of turbidity in wastewater and groundwater samples are shown in Tables 2 and 3. Turbidity values of all the groundwater and wastewater samples are mentioned in Tables 4 and 5. The analyzed wastewater samples of Nalla Lai showed that turbidity value was very high in sample number 1 which was collected from the wastewater stream carrying industrial wastewater of sector I-9, Islamabad and finally merged with the main wastewater stream of Nalla. The analyzed results resembled the work done by Tariq et al. (2006) on groundwater contamination due to the discharge of wastewater from the industrial locality in Hayatabad, Peshawar. Because of the high load of organic matter and various kinds of effluents, very high turbidity was observed in the wastewater of Nalla Lai. The elevated level of turbidity ultimately decreases the dissolved oxygen level in the water stream. Aquatic life cannot survive in such an environment.

According to Tiwari (2015), color of the water is very important for domestic and industrial uses and they generally prefer colorless water. The WHO standard value of color in drinking water is <15 TCU.

Dissolved oxygen is an important marker to judge the quality of water (Subramani et al. 2005). It represents the physical and biological processes occurring in the aquatic environment. DO concentration is the indicator of pollution level in the water. It is the dissolved concentration of gaseous oxygen in water (Prajapati & Dwivedi 2016).

Electric conductivity (EC) is the capability to pass an electric current. EC in water estimates the amount of TDS or ions (Pal et al. 2015).

TDS include minerals, salts, or metals dissolved in water (Sagar et al. 2015). The WHO standard value of TDS in drinking water is <1,000 mg L⁻¹. The concentration of TDS elevated from 1,000 mg L⁻¹ is not fit for drinking purposes (Akhtar et al. 2014). The TDS value indicates both salinity and quality of water and a high concentration of TDS alters the taste and hardness of water (Akhtar et al. 2014; Pande et al. 2015).

The mineral sulfur occurs in different valence states, i.e. S²⁻, S⁰, S⁴⁺, and S⁶⁺. Sulfate (S⁶⁺) has six electrons in its valence shell for chemical bonding and exists in tetrahedral coordination with oxygen (Hawthorne et al. 2000). The US EPS standard value of sulfate in drinking water is 250 mg L⁻¹ and the NEQs, 1997 wastewater standard of sulfate is 600 mg L⁻¹.

As reported by Rao (2011) and Ramya et al. (2015), water hardness primarily depends on the concentration of calcium and magnesium ions in water. The prime reason for the excess concentration of hardness in groundwater samples was the presence of high mineral contents, i.e. calcium and magnesium cations. The NSDWQ, 2010 standard value of hardness in drinking water is <500 mg L⁻¹.

The WHO standard value of copper in drinking water is 2 mg L⁻¹. The NEQs, 1997 standard value of copper in wastewater is 1 mg L⁻¹. The average copper value in groundwater and wastewater samples was 0.09 and 0.08 mg L⁻¹. The range value of copper in groundwater samples was 0.038–0.139 mg L⁻¹, whereas the copper value in wastewater samples was in the range of 0.012–0.204 mg L⁻¹, respectively. The descriptive statistics of copper in wastewater and groundwater samples are shown in Tables 2 and 3. Copper results in all the wastewater and groundwater samples are mentioned in Tables 4 and 5. Copper was detected in seven wastewater samples and three groundwater samples, it was observed above the BDL (below detection limit) value. Nasrullah et al. (2006) analyzed the concentration of copper higher than the permissible limit in groundwater near the industrial area of Swabi as well as in the wastewater sample collected from the main drain of the marble industry. Although several marble factories are located in the industrial area of Islamabad, it was detected in low concentration because the marble factory's waste and effluents are not discharging in the wastewater stream (Nalla Lai). Although copper is a necessary element present in enzymes, its minute concentration is critical for the synthesis of hemoglobin (Tiwari et al. 2013). However, copper excess concentration can cause neurological problems, hypertension, kidney, and liver failure (Krishna & Govil 2004). In infants, its intake can cause death, vomiting of short-lived, and diarrhea (Barzilay et al. 1999).

The WHO standard value of lead in drinking water is 0.01 mg L⁻¹ and the NEQs, 1997 standard value of lead in wastewater is 0.5 mg L⁻¹. The average lead value in groundwater and wastewater samples was 0.02 and 0.10 mg L⁻¹. The range value of lead in groundwater samples was 0.002–0.04 mg L⁻¹, whereas the lead value in wastewater samples was in the range of 0.008–0.268 mg L⁻¹, respectively. The descriptive statistics of lead in wastewater and groundwater samples are shown in Tables 2 and 3. Lead values in all the wastewater and groundwater samples are mentioned in Tables 4 and 5. A minute level of lead naturally exists in soil and water (Raviraja et al. 2008). As mentioned by Haq (2009), the concentration of lead detected in drinking water is due to industrial discharges, waste dumping, gaseous emissions from traffic sources, and domestic paints (Haq 2009). Its chronic exposure can damage human organs like the digestive and nervous system, cardiovascular system, reproductive system, hematopoietic system, skeleton, and kidney (Gidlow 2004; Venkatesh 2004).

The NEQs, 1997 standard value of BOD in wastewater is 80 mg L⁻¹. The average BOD value in wastewater samples of Nalla Lai was 120.21 mg L⁻¹. BOD values in wastewater samples were in the range of 87–194 mg L⁻¹. BOD values in all wastewater samples of Nalla Lai were elevated from the recommended value of NEQs, 1997. The descriptive statistics of BOD in wastewater samples are shown in Table 2. BOD results of all the wastewater samples are mentioned in Table 4. The elevated values of BOD in the analyzed samples revealed the presence of a high load of organic pollutants in the wastewater stream of Nalla Lai. The guideline range of BOD in domestic wastewater is 100–300 mg L⁻¹ (Abdalla & Hammam 2014). BOD measures the organic pollutants and level of gaseous oxygen in the water and BOD value reveals the microbial utilization of oxygen in the water to break down the organic substances (Bhatnagar 2015).

The NEQs, 1997 standard value of COD in wastewater is 150 mg L⁻¹. The average COD value in wastewater samples was 240.15 mg L⁻¹. The range value of COD in groundwater samples was 186–315 mg L⁻¹. COD results of all wastewater samples were elevated from the recommended value of NEQs 1997. The descriptive statistics of COD in wastewater samples are shown in Table 2. COD results of all the wastewater samples are mentioned in Table 4. The elevated COD values revealed the presence of a high concentration of both organic and inorganic pollutants in the wastewater stream of Nalla Lai. COD is the measure of the oxygen level required to decompose both organic and inorganic matter in water (Bhatnagar 2015). COD is the chemical breakdown of pollutants where oxygen is necessary to execute absolute oxidation to carbon dioxide and water (Dogar et al. 2013).

The reciprocal relationship between two variables is called correlation. The increase in one variable causes the increase in another variable and is called positive correlation, whereas the increase in one variable tends to decrease in another variable and is called negative correlation. The correlation coefficient is a value that ranges from +1 to −1. A value of 0 means there is no linear correlation between the two variables. The strong correlation between the two parameters ranges from ±0.8 to ±1.0, the moderate correlation ranges from ±0.5 to ±0.8, weak correlation ranges from 0.0 to ±0.5 (Shroff et al. 2015). The correlation coefficient (r) of groundwater quality parameters is calculated in Table 6 and the values are highlighted with blue, white, and red colors.

Table 6

Correlation matrix of physicochemical parameters of groundwater of the study area

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The values of the correlation coefficient ranging in blue colors represent strong, moderate, and weak positive correlation among water quality parameters and the values in white color shows no correlation, whereas the correlation coefficient values ranging in red colors represent negative correlation among water quality parameters.

The study revealed that groundwater reflects the wastewater stream of Nalla Lai in terms of heavy metals and microbial contamination. The heavy metals detected in high concentrations in the wastewater stream of Nalla Lai were also examined in an elevated concentration in the groundwater of the vicinity area, especially within a 100-m distance along both sites of Nalla Lai. Physicochemical and microbial contamination was detected in many groundwater samples collected from bore water, hand pumps, tube wells, and dug wells located in the proximity of Nalla Lai. Cadmium, iron, BOD, and COD levels were elevated from the recommended values in many wastewater samples. Nalla Lai is an open sewer and the potential anthropogenic source of groundwater contamination that also carries both domestic and commercial effluents of Rawalpindi as well as the industrial effluents of sectors I-9 and I-10, Islamabad. Iron, steel, and paints industries of Islamabad are discharging waste effluents directly into the wastewater stream of Nalla Lai without adequate treatment in wastewater treatment plants. Many drinking water quality parameters such as pH, color, hardness, TDS, manganese, and zinc were exceeding the national standards in one or more groundwater samples that were collected from the nearest distance of Nalla Lai. Microbiological contamination of fecal coliform was detected in 83% of the analyzed groundwater samples. A similar kind of study was conducted on the groundwater quality of Nalla Lai, Rawalpindi city, Pakistan. Water samples were collected from (220) tube wells from different locations in the year 2007. The analyzed results revealed that 50% of groundwater samples of tube wells showed bacterial contamination. The prime source of microbial contamination is the percolation of Lai Nalla wastewater. Nalla Lai acts as an open sewer that carries 65% sewage of the city (Islam-Ul-Haq & Ahmed 2007). Maximum contamination was observed in the 36 analyzed samples, collected from bore water and dug well located adjacent to the Nalla Lai wastewater stream and minimum contamination results were obtained from the 13 control samples that were taken from at least a 1 km distance along both sites of Nalla Lai. The study concluded that pollutants enter the wastewater stream from domestic, commercial, and industrial sources due to the unavailability of a proper wastewater treatment facility and percolate downward and finally contaminating the groundwater quality in the vicinity.

• Tube wells, boreholes, hand pumps, and dug wells should be installed at least 300–400 m away from Nalla Lai to prevent any type of percolation and leaching from the wastewater of Nalla Lai.

• There should be proper laboratory testing of physicochemical and microbiological parameters of newly installed tube well or bore water before water supply to the public.

• Periodic monitoring of all tube wells and bore water should be conducted to cope with wastewater percolation issues.

• Groundwater extraction should be promoted from the deeper aquifer and increase the depth of existing shallow water boreholes.

• Enforce effective and efficient management plan for domestic and commercial solid waste of Rawalpindi and industrial waste effluents of sectors I-9 and I-10, Islamabad.

• Solid waste should not be dumped on the banks of Nalla water which increases the chances of leachate formation and percolation of contaminants into groundwater.

• Groundwater percolation can be prevented through proper management of wastewater of Nalla Lai which includes the proper sanitation system of Rawalpindi city.

• Water filtration plants should be installed in each inhabitant colony to ensure public health.

• The percolation of wastewater from Nalla Lai can be fully prevented through proper cementation by using concrete in the base of Nalla Lai and by the construction of concrete walls on the banks of Nalla Lai.

All relevant data are available from an online repository or repositories: https://github.com/Shahid1378567ghj/science.git.

The authors declare there is no conflict.