Journal of Earth Science & Climatic Change
Open Access

WQI, HHRA; Seawater Mixing Index; Saltwater intrusion

Introduction

Water is one of the vital natural resources in our daily life. Water is used for various purposes like domestic, industrial and agriculture. Humans mainly depends on the groundwater to fulfill their basic needs [1]. Due to increase in population and industrialization the usage of groundwater is increasing day by day. The water bodies were under danger situation due to rapid increase in population and also urbanisation, this automatically leads to use of chemicals in irrigation in order to get more yield which eventually causes contamination of water by surface runoff. In coastal areas, the excess usage of groundwater leads to difference in sea level which results in intrusion of seawater on groundwater, so there is a risk of contamination of groundwater [2]. The migration of saltwater into freshwater aquifers as a result of human or natural activity is known as seawater intrusion. The seawater intrusion decreases the storage capacity of groundwater and also in some cases it leads to abandonment of wells. Areas which are adjacent to coastal waters are having more risk of seawater intrusion [3]. It is a serious issue that affects coastal aquifers globally. Reductions in groundwater levels or elevations in seawater levels can result in seawater intrusion. A cone of depression is created in the aquifer when freshwater is pumped out quickly, lowering its height. In a conical ascent, the sea level increases 40 feet for every foot of freshwater depression. Saltwater intrusion into freshwater bodies affects the soil condition, vegetation, and water quality it seems as a global problem. Higher concentration of chlorides in water is unfit for drinking and industrial activities, higher concentrations of sodium ions in water can lead to high blood pressure in humans [4]. To assess the groundwater quality various parameters were determined. The most effective way to evaluate the quality of ground water is WQI. We computed the Seawater Mixing Index (SMI) to figure out how ground water is affected by seawater intrusion. Due to consumption of this polluted groundwater and also through agricultural activities like usage of excessive fertilizers and unsanitary conditions human health is at risk. To examine the fluoride content in both adults and children Human Health Risk Assessment (HHRA) was calculated. Intruded groundwater can have a negative impact on irrigation indices. To know the effect on irrigation we had also calculated the Irrigation Indices(II) [5]. The present study was undertaken in Kanchipuram district(12.8185° N, 79.6947° E) located at northern east coast of Tamil Nadu. Kanchipuram district covers a total area of 1448 Sq.Kms, where 87.2km is the coastal length. It has a normal rainfall of 1200-1300mm. The river basins of the Palar, Araniyar & Kosasthalaiyar, and Thondiar, are utilized for irrigation and drinking purposes. This study’s primary goal is to determine the groundwater quality in different blocks of Kanchipuram district and also mapping the results using Q-GIS.

Materials and Methods

Study area : Figure 1 illustrates The Kancheepuram district's study area is near Chennai city and located on Tamil Nadu's northern east coast. The district has a total area of 1448 Sq.Kms. It lies between 11° 00' to 12° 00' latitudes and 77° 28' to 78° 50' longitudes. The maximum and minimum temperatures of Kanchipuram district are during summer 38.5°C (101.3°F) , 29.1°C (84.4°F) and during winter 27.7°C (81.9°F), 19.0°C (66.2°F). The maximum rainfall of 9.8 inches occurs in October and the least amount of rainfall occurs in February with average of 0.4 inches. The average humidity conditions range from 73 to 90%.The research was conducted using 60 groundwater samples that were collected all over the Kanchipuram district. The samples were tested by Central Groundwater Board of India (CGWB) (Table 1).

Figure 1: Location of sampling stations of Kanchipuram district, Tamil Nadu, India.

Table 1: Latitude and Longitude details of sampling locations.

Water Quality Index (WQI): WQI provides the overall quality of the water for any intended purpose by expressing the water’s quality as an index number. For calculation of WQI physicochemical parameters of water are taken into consideration [6,7]. Based on WQI the water quality is classified as Excellent (0-25) , Good (26-50) , Poor (51-75) , Very Poor (76-100) and Unfit (>100).

Where,

– is the quality rating of each water quality parameter;

– is the unit weight of each water quality parameter;

– is the actual concentration of each water quality parameter;

– is the constant value of each parameter (for pH it is 7 and for remaining all it is zero);

K – is the proportionality constant;

– is the standard permissible value of each water quality parameter.

Seawater Mixing Index (SMI): The SMI is proposed by Park and Aral and it is used to estimate the relative index of saltwater mixing with fresh water.

The concentration of Na+, Mg+, C, Sare used to calculate the sea water mixing index. It had been calculated using the following equation.

Where, Constants a, b, c and d denotes a relative proportion of Na+, Mg+, C, Srespectively, there values are (a = 0.31,b = 0.04, c = 0.57, d = 0.08), T is the regional threshold values and C is the calculated Concentration of groundwater samples. The threshold value is obtained by drawing the graph between the sampling stations vs cumulative probability.

Human Health Risk Assessment (HHRA): Nitrate and fluoride are the two most pervasive contaminants found in groundwater that can be harmful to human health (Table 2). Worldwide reports of nitrate contamination in shallow groundwater, particularly in agricultural areas, are on the rise [8-10].

Table 2: HHRA Standards for the calculation of HI of fluoride.

Where

– is the actual concentration of water quality parameter in the water (mg/L);

IR – is the ingestion rate (L/day);

EF – is the exposure frequency (day/year);

ED – is the exposure duration in years;

BW – is the average body weight (kg);

AT – is the average time (days);

ET – is the exposure time (h/day);

SA – is the average surface area of the skin exposed to water in ;

– is the coefficient of water for dermal activity ( 0.001 for ,,and ).

– is the average daily exposure dose through ingestion (ing);

– is the average daily exposure dose through dermal (der);

RfD – is the reference dose of water quality parameters in mg/kg/day (is 0.06 and is 1.6);

– is the Hazard Quotient of ingestion ;

– is the Hazard Quotient of dermal;

HI – is the Hazard Index.

Irrigation Indices (II): In order to know the irrigation indices the following were calculated Sodium Adsorption Ratio(SAR), percentage of Na, Magnesium Adsorption Ratio(MAR), Permeability Index(PI) and Kelly’s Ratio(KR) [11-14].

Results and Discussion

The presence of higher amounts of cations and anions results in seawater intrusion. As we can clearly observe that most of the sampling locations are having higher concentrations of anions and cations.

The above physico-chemical parameters shows that TDS values varies from 266 mg/L to 5213 mg/L. As per BIS standards 10 samples are less than 500 mg/L.

The pH values varies from 6.9 to 7.9. All the 60 samples are below the desired limit (pH:6.5-8.5).

Total hardness values varies from 70 mg/L to 2780 mg/L. The desired limit is 300mg/L. 16 samples are in desired limit as per standards (Table 3).

Table 3: Physical and chemical characteristics of water samples from the Kanchipuram district (pH is the only unit not in mg/L).

As per BIS standards the desired limit for fluoride is 1.5mg/L and nitrate is 45 mg/L. For fluoride sample 17 and 56 are not within the limits.

Water Quality Index (WQI): In general the water quality depends upon the values of iron, manganese and arsenic. Increase in these values indicates decrease in its quality. Water quality index values ranges from 21 to 233. Out of 60 samples, 13 samples have exceeded the desired limit of drinking water as per BSI standards (Figure 2).

Figure 2: Geographical distribution map of Water Quality Index (WQI) of Kanchipuram district.

For WQI if the value is greater than 100 it is unfit for consumption, out of 60 stations 13 stations recorded are unfit for consumption,12 stations are very poor and 17 stations are poor. we observed that manimangalam (station 28) has a highest value of 233 which is greater than 100, Uthikadu has 193, Shollinganallore has 157 and many more. These are unfit for drinking because that area covered by many dyeing factories. Whereas places like Chitlapakkam have WQI value of 21 comes under excellent category. This area has no risk of mixing water from sea. From Fig.2 it is clear that the Kanchipuram district, Tamil Nadu was moderately polluted (Figure 3).

Figure 3: WQI values of different sampling stations of Kanchipuram District.

Seawater Mixing Index (SMI): The threshold values obtained from the graph (Actual frequency vs Concentration) are Na =93mg/L , Mg=44mg/L ,Cl =440mg/L , SO₄ =50mg/L. From results obtained the SMI values varies from 0.18 to 4.92.

Generally, SMI value >1 signifies that the seawater is mixing with the groundwater. Out of total ,38% of the sampling stations namely Uthiramerur(4.92), Kancheepuram(3.21), Muthukadu(2.06) has SMI values above 1 are affected by seawater intrusion . Majorly seawater intrusion in that area causes due to climatic conditions, hydraulic gradient, rate of groundwater extraction and sea level rise. The people of Kanchipuram district uses more groundwater during summer this results in the decrease of groundwater table and due to this seawater intrusion takes place (Figure 4,5).

Figure 4: Geographical distribution map of Seawater Mixing (SMI) of Kanchipuram district.

Figure 5: SMI values of different sampling stations of Kanchipuram District.

Human Health Risk Assessment (HHRA) for fluoride: From above HHRA we conclude that fluoride content in children is greater than adults. For adults the HI concentrations is less than 1 in all sampling stations, as fluoride content is not having much impact on adults. For adults the HI concentrations of Fluoride varied from 0.06 to 0.81 has an Average=0.37 and Children varied from 0.104 to 1.538 has an Average=0.69. Kancheepuram (station 17) area has high fluoride content in children (1.54). The main reason behind this is by consumption of these groundwater fluoride content is having much impact on children than compared to adults. 8 stations having HI value greater than 1 in children (Figure 6-8). The samples analysed from the research area has high fluoride content in children ranging from 0.1 to 1.53. From results it shows that most of the samples having high fluoride content in children than the permissible limits. Due to the excessive fluoride content present in groundwater can cause dental problems, bone damage, joint-related problems, change of colour of teeth (Table 4).

Figure 6: Geographical distribution map of Human Health Risk Assessment (HHRA) for adults of Kanchipuram district.

Figure 7: Geographical distribution map of Human Health Risk Assessment (HHRA) for children of Kanchipuram district.

Figure 8: Human Health Risk Assessment (HHRA) of Kanchipuram district.

Table 4: Different parameters of HHRA for sampling stations.

Irrigation Indices (II)

Sodium Adsorption Ratio (SAR): SAR values of Kanchipuram district varies from 2.99 to 148.94. In general, the SAR value should be less than 10mEq/L. Out of 60 samples, only 20 samples are below the desired limit. These sampling stations has no effect on irrigation whereas remaining 40 stations are unfit for irrigation (Figure 9,10).

Figure 9: Geographical distribution map of Kanchipuram district for Irrigation Indices (II) based on sodium adsorption ratio (SAR).

Figure 10: Irrigation Indices (II) of Kanchipuram district based on sodium adsorption ratio (SAR).

Kelly’s Ratio (KR): Kelly’s ratio depends on sodium , magnesium and calcium concentrations. 24 stations are having value greater than 1 which indicates excessive sodium present in the water. So, these stations are unsuited for irrigation (Figure11,12).

Figure 11: Geographical distribution map of Kanchipuram district for Irrigation Indices (II) based on kelly’s ratio (KR).

Figure 12: Irrigation Indices(II) of Kanchipuram district based on Kelly’s ratio (KR).

Magnesium Adsorption Ratio (MAR): Higher concentration of magnesium present in the groundwater effects the quality of soil and lowers the crop yield. The desired value for MAR is less than 50 (Figure 13,14).

Figure 13: Geographical distribution map of Kanchipuram district for Irrigation Indices(II) based on magnesium adsorption ratio (MAR).

Figure 14: Irrigation Indices (II) of Kanchipuram district based on magnesium adsorption ratio (MAR).

Percentage of Na: Ground water is categorized according to its percentage of Na, which ranges from excellent (<20%) to good (20–40%), acceptable (40–60%), dubious (60–80%), and inappropriate (> 80%). (Khodapanah et al.2009) (Figure 15,16).

Figure 15: Geographical distribution map of Kanchipuram district for Irrigation Indices (II) based on percentage of Na.

Figure 16: Irrigation Indices (II) of Kanchipuram district based on percentage of Na.

Permeability Index (PI): From results PI values varies from 30.13 to 98.22. The average value of PI was reported as 54.91.As per desired limits PI value less than 25 unsuited for irrigation.

For the irrigation indices we conclude that out of 60 stations, SAR values of 21 stations is less than 10meq/L, so in those areas the water is fit for irrigation, the crops doesn’t give much yield. Due to the saltwater intrusion these ions will mix up with the ground water (Figure 17,18). This water will carry through the irrigation fields. The water with high SAR content is supply to soil for years, The calcium and magnesium ions in the soil may be replaced by the sodium in the water. The soil's fertility will decline as a result of this.. For the percentage of Na, 98% of stations is less than 80 percent, this water will impact on irrigation crops (Table 5).

Figure 17: Geographical distribution map of Kanchipuram district for Irrigation Indices (II) based on permeability index (PI).

Figure 18: Irrigation Indices (II) of Kanchipuram district based on PI.

Table 5: Different parameters for Irrigation Indices (II) for sampling stations.

Conclusion

From the investigation, the following results was concluded.

WQI values concluded, out of 60 stations it was observed that around 30% of groundwater is above good quality (WQI: 0-50), around 42% is very poor and unfit for drinking purpose (WQI: 76 - >100) and 28% of the sampling stations are poor (WQI: 51-75) respectively.

The SMI values concluded that, out of 60 stations it was observed that 23 stations which means 38% of the sampling stations are affected by seawater intrusion greater than 1.

There are 7 sampling stations which are affected by both WQI and SMI. Due to SMI these 7 areas will have impact on WQI.

HHRA study concludes for Children, 13% of the sampling station is having a health impact due to fluoride. The analysis shows that children’s average fluoride content is higher than adults.

Irrigation efficiency concludes that 65% of sampling stations, SAR values greater than 10 mEq/L and 2 stations having percentage of Na greater than 80% therefore the water is unfit for irrigation. Nearly 40% of sampling stations having KR value less than 1, which means those areas are suitable for irrigation purpose and Almost 12 sampling stations having PI value greater than 65% therefore water is suitable for irrigation purpose. 9 stations having MAR value greater than 50, so those stations are not recommended for irrigation purposes.

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