Evaluation of Groundwater Quality for Drinking and Irrigational Purposes in a Coastal Alluvial Aquifer using Multivariate Statistical Approach: A Case Study from West Godavari Delta, Andhra Pradesh, India


 The present study investigates the groundwater quality for drinking and irrigational purposes in a coastal aquifer of the West Godavari delta region based on geochemical evaluation and multivariate statistical analysis. The study area is underlain by the Quaternary sediments with unconsolidated and semi consolidated sand, silt and clay formation. The significant hydro chemical facies of groundwater observed throughout the study is Na-Mg-Cl-HCO3, Na-Cl- HCO3, and Mg- Na- Cl -HCO3 −. The results revealed that the area occupied high salinity ground waters controlling by evaporation and also rock weathering-solubilization to some extent. The abundance of chemical parameters are Na+ > K+ > Mg2+ > Ca2+ = Cl− > HCO− 3 > SO42− > NO32−. The analyzed water quality parameters were compared with the Bureau of Indian Standards for their suitability for domestic usage. The chemical constituents of samples TA (85%), TDS (100%), TH (83%), Mg2+ (91%), Cl− (81%), and SO42− (12%) exceeded the limits, hence, are unsuitable for drinking. The irrigation suitability parameters such as Na%, SAR, RSC, PI, CAI, KR, and CCR were calculated for assessing groundwater for agriculture purposes. Most of the samples show excess values, which revealed that the ground waters was not even suitable for irrigation because of providing low productivity. However, some samples ranging between the good and moderate categories can be used for irrigation with proper management. The multivariate statistical analysis was performed to understand the relationship of chemical constituents presents in groundwater. TDS is highly correlated with EC, TH, Ca2+, Mg2+, Na+, K+, HCO− 3, and Cl−. Principal component analysis (PCA) applied to the data sets showed that the first three PCs accounted for 65% of total variance cumulatively 94.5% for a total of seven PCs. It represents the quality of groundwater deviation is possibly attributed to various anthropogenic and geogenic factors, rock-water interactions and ion-exchange processes in groundwater. The uncontrolled drawl of sub-surface waters and aqua forming at an advanced rate when compare to recharge led to the coastal aquifers in critical stage, particularly in the study region Godavari delta of Andhra Pradesh state in southern India.


Introduction
Groundwater is a vital natural resource and has a signi cant role in the global economy. For irrigation purposes, groundwater is a reliable source of water and can be used in a exible manner (USGS, 2001). According to World Bank (2012), the largest consumer of groundwater in the world is India, with an estimated annual groundwater use of 230 km3. Due to the pressure created over hydrologic and hydrogeological systems about the impact of climate change the quality of groundwater will mainly degrade in coastal areas. Seawater intrusion and salinization of groundwater because of overexploitation of freshwater aquifers will establish a negative water balance in the coastal regions (Gleeson and Tom, 2012). Hydro chemical studies of groundwater have vigorously been conducted by several researchers globally to identify and interpret the human-induced impact on groundwater chemistry (Loh et 2020) conducted groundwater quality studies in the Anayari catchment area which is predominantly dependent on groundwater for agricultural purposes. They found that the water containing a low percentage of Na + with moderate salinization can be usually used for irrigation purposes without any prior treatment. In recent years, with an increasing number of chemical and physical variables of groundwater, a wide range of conventional tools and techniques of statistical methods applied for proper analysis and interpretation of data (Belkhiri et al. 2010; Machiwal and Jha, 2010). Multivariate statistical analysis was applied in hierarchal cluster analysis by some researchers, being a simple approach to distinguish the multivariate similarities in groundwater quality. Principal Component Analysis (PCA)/Factor Analysis (FA) and Cluster Analysis (CA) explains the data set matrixes for understanding environmental systems and quality of water in uenced either by natural or anthropogenic conditions (Lee et  quality problems in comparison with the other regions. Keeping this in view, the present study was carried out to evaluate the hydro chemical characteristics and groundwater quality and its suitability for domestic and irrigation purposes in an alluvial coastal aquifer using multivariate statistical techniques.

Study area
The study area is located within the West Godavari delta region of coastal Andhra Pradesh (AP) in Southern India. The district West Godavari of AP is bounded by the district`s East Godavari in the North and Krishna in the South, Telangana State in the West and Bay of Bengal in the East. The area is under research lying between 16º 19' N to 16º 40' N latitudes and 81º 19' E to 81º 43' E longitudes (Fig. 1). It has a 23 km coastline covered by natural vegetation, cashew, casuarina and coconut plantations on its sandy tracts. The study area receives rainfall, mostly from the south-west monsoon (June to September), and the average annual rainfall recorded is about 875 mm. The climate is maritime tropical humid noting with 20ºC in December and 38ºC in May. The River Godavari is a major river and its tributaries namely Tammileru, Yarrakalva and Ramileru are owing through the West Godavari district and providing abundant water supply for vast tracts of agriculture elds and aquaculture ponds. The river Godavari bifurcates into Gautami Godavari and Vasishta Godavari in the district region. The Gautami Godavari river marks as a district boundary on the right side and drains through the present study area ultimately debouches into the Bay of Bengal at Antarvedi. The delta area is aided by the large canal system and numerous other drains. The oceanic saline water from creeks is also extensively used for aqua farming near the coastal tracts. The largest shallow freshwater lake in Asia is Kolleru Lake in the southwestern part with in the study area and designated as a wetland of worldwide importance under the international Ramsar Convention. The study area accommodates nearly 0.5 million population spreading over one major town and 79 villages. Agriculture and aquaculture are the predominant activities found throughout the study area. The area is known for the large-scale production of paddy, sugarcane, pulses, oilseeds, coconuts, etc., and it is considered to be one of the largest aqua farming regions of the country. The study area is infested by a huge number of sh and prawn ponds during the last three decades resulting in the ecological and environmental imbalance (Swarna Latha, 2018).

General Geology and Geomorphology
Geologically, the study area is underlain by the Quaternary sediments with unconsolidated to semi consolidated sand, silt and clay formations. In general, the delta sediments consist of brown, grey, gravelly sands and silty clay. The thickness of the sediments gradually increasing towards the sea and is of the order of 400 m in the Godavari delta (Raju et al., 1994;Ramesh, 2008). The quaternary sediments comprised of thick layers of alluvium, gravel and colluvial deposits, beach sand, kankar and soils of various types. Different geomorphic features such as ood plain, alluvial plain, levees, paleochannels, beach ridges, active tidal ats, mud at, swamps, and backwater, etc. are observed. Flood plains are built up of alluvium carried by the river during oods and is deposited in the sluggish water. The at or nearly level sloping grounds of these ood plains are yielding high groundwater potential zones. Beach ridges are low dunes formed as continuous mounds of beach materials (sand, gravel, shingle, etc.) parallel to the shoreline. Another important feature is tidal ats, which are characteristically extensive, nearly horizontal, marshy or barren stretch of lands alternately covered and uncovered by the rise and fall of the tides. It consists of unconsolidated sediments, mostly of mud and sand. Soils predominantly are in deep black clay and sandy; and some extent gravelly dark brown and silty soils. Groundwater extraction structures in the study region are mainly open, bore or tube wells. The average depth of the dug well recorded is 7 meters below the ground level (m bgl). Bore well depth varies from 10 to 65m. The average uctuation of the water table is recorded at 0.91 m in the study area (CGWB, 2017).

Materials And Methods
A total of fty eight (58) groundwater samples were collected with proper care from the bore wells covering the entire study area during May 2017 (Fig. 1). The 1L polyethylene bottles were used for collecting groundwater and were properly rinsed with distilled water before carrying out the sampling. At the sampling location, the bottles were rinsed several times with the same bore well water to avoid any contamination before lling. These samples were cautiously sealed and labeled and taken to the laboratory for carrying out the analysis within a week. The samples were preserved by adding appropriate reagents in the laboratory by adopting standard protocols (APHA, 1998). pH, electrical conductivity (EC), total dissolved solids (TDS) were analyzed using multi parameter digital meter. Total alkalinity (TA), total hardness (TH), calcium (Ca 2+ ), bicarbonates (HCO 3 -) and chlorides (Cl -) were measured by titration method, sodium (Na + ) and potassium (K + ) by a ame photometer whereas sulphates (SO 4 2-) were analyzed by using spectrophotometry. Magnesium (Mg 2+ ) was estimated by the formulae [TH-  Table 1. Bureau of Indian Standards (BIS, 2012) were considered for comparing chemical constituents in groundwater for its utilization both domestic and agricultural purposes.
The following selected parameters were computed for assessing the groundwater suitability for irrigation purpose.
Where the concentration of ions used in the calculations is in meq/L except for KR and CR for which mg/L used. The results of all irrigation quality parameters are given in Table 2. Multivariate statistical analysis methods, including principal component analysis, factor analysis and correlation were used to analyze the groundwater chemistry characteristics. XLSTAT 2018 was utilized for preparing graphs and data table analysis. The Piper, USSL, Wilcox`s diagrams were generated using Aquachem 2014 software.

Results And Discussion
Box plot helps in summarizing the distribution of a data set by the median, the variation, the skewness, outliers and extreme values in a graphical form. From Fig. 2, it is noted that TA, EC, TDS, Mg 2+ , HCO -3 , SO 4 2are approaching normality. The data of the variables Ca 2+ , Na + , Cl -, and NO 3 2depart from a normal distribution only in the skewness. There are outliers for pH, TH and K + but data depart from a normal distribution only in the skewness. The unexpected outliers are may be due to the usage of fertilizers in agricultural and aqua pond regions.
The abundance of chemical parameters are as follows: HYDRO CHEMICAL PROCESSES Piper (1944) plot explains the evolutionary trends of water quality parameters in order to classify the similarities and differences in the chemical composition of waters into certain water types. The ground waters were categorized into different hydro chemical facies based on major cations Ca 2+ , Mg 2+ , Na + , K + , and major anions HCO 3 − , Cl − , SO 4 2− using Piper's trilinear diagram (Fig. 3). The prominent types shown are Na-Mg-Cl-HCO 3, Na-Cl-HCO 3 , and Mg-Na-Cl-HCO 3 -. It can be observed from the plot that the majority of groundwater samples fall in the eld of 4 suggesting that strong acids exceed weak acids. The exceeding primary salinity ( eld 7) and alkalies exceed alkaline earths ( eld 2) are also found ( Table 3). The samples in the Na-Mg-Cl facies indicate the leaching of primary/secondary salts and exchange of ions from the clay deposits. The mechanism controlling the geochemical process of groundwaters with respect to atmospheric precipitation, rock-water interaction and evaporation, has been presented by Gibb`s plot (1970) for the present study (Fig. 4). The ratios of dominant cations (Na + +K + )/(Na + +K + +Ca 2+ ) and anions (Cl -/(Cl -+HCO 3 -) were plotted against the value of TDS. It is found that the most of sampling points fall towards evaporation dominance indicating the groundwater with high salinity controlled by evaporation and also rock weatheringsolubilization. Cation exchange is the in uence factor controlling hydro chemical processes. The limited interaction of rock water generally includes the chemical weathering of the rocks, the precipitation dissolution of secondary carbonates and the exchange of ions between the water and the clay minerals.

IONIC GROUNDWATER USE FOR DRINKING
The chemical constituents present in the groundwater is showing a wide variation in different individual parameters ( Table 1). The pH of groundwater samples ranged from 7.2 to 8.7, with a mean of 7.8, indicating the slightly alkaline nature of groundwater in the study area. pH generally varies between 6.0 and 8.5 and low pH allows to dissolve more minerals (Weiner 2000). The concentrations of physico-chemical parameters in ground waters and their effect upon human health are presented in Table 4.
The minimum and maximum values of alkalinity ranged from 124 to 466 mg/L with a standard deviation of 81.8. Above 250 mg/L concentration of total alkalinity in the water gives an unpleasant taste (BIS 2012). Nearly 85% of the water samples in the study area contain alkalinity values higher than the desirable limits. The high alkalinity values for the study area are raised due to the action of carbonates on the basic materials on the soil which gives an unpleasant taste to water. EC uctuated from 1675 to 3881 µg/L µS/cm, with a mean of 2800 µg/L while TDS ranged between 985 and 2283 mg/L with a mean of 1647 mg/L. High EC explains that the more dissolved inorganic substances in the ionized form present on the water. EC of water is considered to be an indication of the total dissolved salt content (Hem, 1985). All the groundwater samples recorded above the desirable limits of TDS (more than 500 mg/L), and 84% of samples have TDS > 2000 mg/l hence these cannot be recommended for drinking (BIS, 2012). TH as CaCO 3 varied from 114 to 688 mg/L with a mean of 386.
There are ten samples that fall within the desirable limits and the remaining samples (83% of total samples > 300 mg/L) to very hard water category. The cations Ca 2+ , Mg 2+ , Na + , and K + ranged from 11-69 mg/L, 10 -139 mg/L, 98 -414 mg/L, 29 -143 mg/L, respectively. The anions HCO -3 , Cl -, SO 4 2-, and NO 3 2varied from 162 -610 mg/L, 156 -602 mg/L, 28 -227 mg/L, 2 -41 mg/L, respectively. Calcium bicarbonate is the prime cause of the hardness in water. Concentrations of Ca 2+ and Mg 2+ are well below the permissible limits. In sea waters, magnesium present in large quantities and high magnesium in the groundwater causes scaling in boilers, pipes and water heaters, and abdominal disorders, etc. and is not desirable for domestic use. Higher values of Na + (mean 250 mg/L) and K + (mean 95.2 mg/L) were found in the groundwater may be attributed to saline water intrusion, discharge of aquaculture wastewaters and domestic sewage. Normally, these ions become not toxic to humans. However, excess intake causes hypertension and vomiting, etc. Whereas K + is an essential element for plants and animals. Cldirectly relates to the mineral content of water and is mostly identi ed by salt taste in potable water. Only 19% of groundwater samples showed less than 250 mg/L, which is acceptable for drinking as per BIS. It explains that the probable cause for the abnormal concentration of chloride is the seawater intrusion and rocks in the study region. SO 4 2-concentrations in seven locations showed as slightly high above limits. All the samples of NO 3 2falls under permissible limits of BIS. Overall, the majority of water-quality parameters of the groundwater samples analyzed in the study area were recorded above desirable levels.

IONIC GROUNDWATER USE FOR IRRIGATION
In the study area, the groundwater samples were analyzed for monitoring the suitability of quality for irrigation purposes. It can be observed from Table 2, the groundwater recorded as high to very high salinity condition (Richards 1954). About 85% of total samples have recorded electrical conductivity very high (>2,250 μS/cm). High EC in the water proportionate to the salt content which explains that the groundwater can severely affect the plants and soils thus reducing productivity. Na% ranged between 41 and 87.9 meq/L with a mean of 63 meq/L. Nearly 69% of water samples were found with high percent sodium (> 60%) thereby unsuitable even for irrigation (Ramakrishna 1998 Table 5). The SAR values in the study area vary from 2.0 to 13.2 meq/L and nearly 45% of sample`s exhibit increase problems as SAR > 6 meq/l (Herman Bouwer 1978).
According to the U.S. Salinity Laboratory Diagram (USDA 1955), more than 80% of the water samples comes under the elds of C4S2, C4S1, C4S3, C3S2 indicating high-very high salinity and low-high alkali water ( Fig. 6 and Table 6). The groundwater is unsuitable for irrigation in the drainage restriction as it leads to low permeability and poor cultivable. RSC varied from -6.1 to 3.8 meq/L with a mean of -1.8 meq/L in the study area. More than 82% of samples shown negative values and are safe for irrigation purpose. The best irrigation practices must be adopted to use the marginal RSC water for irrigation. The high concentration of Na + , Ca 2+ , Mg 2+ and HCO -3 in irrigation water can affect the soil's permeability condition. More than 80% of the groundwater samples unsuitable for irrigation purposes. (Donen 1964). The range of KR values is 0.7 to 8.5 mg/L, and most of the groundwater samples (91%) recorded above 1, hence, the groundwater is t for irrigation (Kelley, 1951). The CR values (range 0.7-5.3 mg/L) recorded in the study area indicating the corrosive nature of water thus it cannot be transported through the metal pipes.

PRINCIPAL COMPONENT AND FACTOR ANALYSIS
The data set of analyzed parameters was veri ed for variable reduction by PCA and FA using Kaiser-Meyer-Olkin and Bartlett's sphericity tests. The results of the KMO and ρ were 0.58 and less than 0.001, respectively, hence the data set was used for analysis (Wang et al. 2017). The results of the principal factors, eigenvalue, explained variance and vari max-rotated loads are summarized in Table 7 . This could be due to the in uence of carbonate weathering as the main source of these minerals. Factor 2 contributed 20.3% of the total variance with high positive loadings on Na + and Clwhich probably due to seawater intrusion. Factor 3 accounts for 10.8% of the total variance. The closely related parameters were SO 4 2and K + ; this was probably due to the application of organic and inorganic fertilizers, manure and sewage. With the loading of Mg 2+ , factor 4 contributed 9.74% to the total variance; this indicates the impact of clay minerals and rock weathering. All the hydro chemical parameters applied by Pearson's correlation indicating that TDS was signi cantly correlated with EC, TH, Ca 2+ , Mg 2+ , Na + , K + , HCO -3 and Cl -( Table 8). The Na + and Cl -, TA and HCO -3 are correlated highly signi cant. It can be observed from the Table that these chemical components are the main source of TDS.

Conclusions
The evolution of groundwater chemistry was explained through geochemical plots, ionic ratios, bivariate scatter plots, principal component and factor analysis for the coastal aquifer of Southern India. The chemical constituents in the groundwater were determined for their suitability for drinking and irrigation purposes. The average ionic concentration found in the study area is Na + > K + > Mg 2+ > Ca 2+ = Cl − > HCO − 3 > SO 4 2− > NO 3 2− . The high concentrations of Na + , Cl − , and SO 4 2− found in the groundwater may be attributed to the dissolution of mineral phases in the aquifer systems. Bivariate scatter plots strongly supported the process of reverse ion exchange and seawater intrusion. PCA and FA explained that the factors responsible for the variation in the groundwater chemistry as weathering, leaching of secondary salts, reverse ion exchange, seawater intrusion, and agricultural return ow. All the groundwater samples were compared with BIS for potability indicating the groundwater in the study area is un t for drinking in most of the areas. The quality indices for irrigation revealed that the groundwater studied in the locations is ranging between the good and moderate category hence the water can be used for irrigational purposes with proper management. Various anthropogenic activities such as intense agricultural and aquaculture practices, aquaculture waste discharges without treatment, etc. are also the probable causes of deterioration of the quality of water. This research database provides baseline information that may be used for detecting signi cant trends more precisely with the help of modern tools like the Geographic Information System.

Declarations Con icts of interest
The author declares that there is no con ict of Interest

Data Availability Statement
All data generated or analysed during this study are included in this article.
. CGWB (2014) Central Ground Water Board Report on status of ground water quality in coastal aquifers of India.     Figure 1 Location map of the study area. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Classi cation of hydrochemical facies using the Piper plot.

Figure 5
Gibbs plot showing the geochemical process of groundwaters.

Figure 6
Wilcox diagram represents the presence of sodium content in the groundwaters Figure 7 The suitability of groundwater for irrigation exhibiting by USSL diagram Figure 8 Scree plot and dominance of ions in groundwaters