Groundwater Assessment Research Articles

Water quality assessment and reuse potential of groundwater combined saline solution for irrigation

Abstract This study aims to evaluate the water quality and reuse potential of groundwater combined with a saline solution for irrigation. The brine dilution process was done by adding groundwater by determining the total dissolved salts (TDS) value according to the irrigation criteria and then by calculating the amount of groundwater to be added using the law of concentrations to obtain the water mixture, as the TDS value decreased from 4922 and 3810 mg/l to 2587 and 2200 mg/l, respectively. The assessment aimed to determine the suitability of the water for irrigation, and the quality indices used were sodium adsorption ratio, magnesium hazard ratio percentage, sodium percentage, residual sodium carbonate, permeability index, Kelly index, and irrigation water quality index. The results indicated that the water after mixing is suitable for irrigation. The USSL diagram was used to evaluate the post-mixing water at two stations, Touggourt and El-Oued, and the results showed that the post-mixing water at Touggourt falls in the C4–S1 group (extremely high salinity with low sodium), and the post-mixing water at El-Oued falls in the C4–S2 group (very high salinity with medium sodium).

Response of microbial taxonomic and nitrogen functional attributes to elevated nitrate in suburban groundwater

Anthropogenic nitrogen (N) input has led to elevated levels of nitrate nitrogen (NO3−-N) in the groundwater. However, insights into the responses of the microbial community and its N metabolic functionality to elevated NO3−-N in suburban groundwater are still limited. Here, we explored the microbial taxonomy, N metabolic attributes, and their responses to NO3−-N pollution in groundwaters from Chaobai River catchment (CR) and Huai River catchment (HR) in Beijing, China. Results showed that average NO3−-N and NH4+-N concentrations in CR groundwater were 1.7 and 3.0 folds of those in HR. NO3−-N was the dominant nitrogen specie both in HR and CR groundwater (over 80 %). Significantly different structures and compositions of the microbial communities and N cycling gene profiles were found between CR groundwater and HR groundwater (p < 0.05), with CR groundwater harboring significantly lower microbial richness and abundance of N metabolic genes. However, denitrification was the dominant microbial N cycling process in both CR and HR groundwater. Strong associations among NO3−-N, NH4+-N, microbial taxonomic, and N functional attributes were found (p < 0.05), suggesting denitrifiers and Candidatus_Brocadia might serve as potential featured biomarkers for the elevated NO3−-N and NH4+-N concentration in groundwater. Path analysis further revealed the significant effect of NO3−-N on the overall microbial N functionality and microbial denitrification (p < 0.05). Collectively, our results provide field evidence that elevated levels of NO3−-N and NH4+-N under different hydrogeologic conditions had a significant effect on the microbial taxonomic and N functional attributes in groundwater, with potential implications for improving sustainable N management and risk assessment of groundwater.

Hydrochemical Characterization and Quality Assessment of Groundwater in Hatiya Island, Southeastern Coastal Region of Bangladesh

Groundwater is a vital source of fresh water for drinking and agricultural purposes in the region of Hatiya Island, Bangladesh, yet it is subject to contamination by natural and anthropogenic activities. Over time, the contamination has resulted in a variety of negative effects on human health. This research aims to examine groundwater hydrogeochemical characterization and suitability for irrigation and drinking purposes on different indices utilizing a combined geochemical method, multivariate statistical approaches, and geospatial analysis. Results of hydrogeochemical analyses of 15 groundwater samples from the intermediate aquifer (60–90 m depth) represent the order of cations, anions, and metal concentrations as Na+ &gt; Mg2+ &gt; Ca2+ &gt; K+, Cl− &gt; SO42− &gt; HCO3− &gt; NO3−, and Fe &gt; I &gt; Br &gt; Mn &gt; As, respectively. Saltwater intrusion has been determined to be the most important hydrogeochemical process influencing the chemistry of groundwater. Principal component analysis, Pearson’s correlation matrix, and hierarchical cluster analysis indicate that groundwater quality is highly governed by geogenic influences. This information has been evaluated using a drinking water quality index map, which found that six (40%) of the groundwater samples are suitable for human consumption, whereas the other nine (60%) are unfit for drinking. The analysis of irrigation quality parameters revealed that eight (54%) of the groundwater samples are in excellent or good condition for agricultural uses; however, the other seven (46%) samples are unsuitable.

Construction and Application of a Groundwater Overload Evaluation System Based on the PSR Model

Groundwater assessment has several technical deficiencies, especially because the decision-making platform for basic data collection, analysis, and evaluation has not been established. Based on the computer architecture theory and business processing logic, we designed a set of groundwater resource overload evaluation systems using the ArcGIS platform and Python language based on the comprehensive analysis of many research schemes. According to the pressure–state–response (PSR) theoretical programming model, the system pre-sets the evaluation index from three aspects: overexploitation, bearing capacity, and overload. The entropy weight method was used to determine the factor weight. The system was used to evaluate and analyze the groundwater overload in Xi’an, and the performance and accuracy of the system were also verified. The results showed that the serious overload area of groundwater in Xi’an was located in the alluvial fan area of Yanliang District, Gaoling District, and Huyi District, and the alluvial fan area of Lintong District, City Six Districts, and Zhouzhi County. The general overload area was located in the alluvial plain area of City Six Districts, Chang’an District, the flood plain and the first terrace of Huyi District, the loess tableland area of Zhouzhi County, and the alluvial fan area of Lantian County. The remaining areas were not overloaded. The evaluation results matched the study, which confirmed that the evaluation system was stable and that the results were reliable.

Quality and Health Risk Assessment of Groundwater for Drinking and Irrigation Purpose in Semi-Arid Region of India Using Entropy Water Quality and Statistical Techniques

The continuous intake of contaminated drinking water causes serious issues for human health. In order to estimate the suitability of groundwater for drinking and irrigation, and also conduct human risk assessments of various groups of people, a total of 43 sample locations in the semi-arid southern part of India were selected based on population density, and we collected and analyzed groundwater from the locations for major anions and cations. The present study’s novelty is integrating hydrochemical analysis with the entropy water quality index (EWQI), nitrate pollution index (NPI) and human health risk assessment. The results of the EWQI revealed that 44.19% of the sample locations need to be treated before consumption. About 37.20% of the study region has a high concentration of nitrate in the groundwater. NPI revealed that 41.86% of the samples had moderate or significant pollution levels. The non-carcinogenic risk evaluation showed that 6–12-year-old children are at a higher risk than teenagers, adults and elderly people in the study area. The natural sources of nitrate and other contamination of groundwater are rock–water interaction, weathering of rock, dissolution of carbonate minerals and evaporation processes, and the anthropogenic sources are the decomposition of organic substances in dumping yards, uncovered septic tanks and human and animal waste. The results suggest taking mitigation measures to reduce the contamination and improve the sustainable planning of groundwater management.

Hydrochemical characteristics and quality assessment of groundwater in Guangxi coastal areas, China

Groundwater is a main source of water supply in Guangxi Province, China. The urbanization expansion and ocean dynamic may change the groundwater quality, which is an important issue due to its effects on human health. In this paper, the influence of seawater intrusion and anthropogenic activity on the Guangxi coastal aquatic environment was assessed by geochemical and multivariate statistical methods. The result indicated that the chemical composition of groundwater in the study area is obviously associated with seawater and the main groundwater types were Ca·Na–Cl, Ca·Na–HCO3, and Ca–HCO3·Cl. The groundwater evolution path from land to sea in Guangxi is Ca–HCO3 → Na·Mg–Cl. The origin of salts in the study area is mainly controlled by mineral weathering, the hydrogen and oxygen isotopes contents point to the aqueous source of atmospheric precipitation. According to the results of PCA, seawater intrusion and pollution caused by human activities play an increasingly important role in the evolution of groundwater characteristics. Seawater intrusion is the main factor for the increase of groundwater salinity in Guangxi, while domestic sewage, industrial waste, fertilizers, and pesticides may contribute to the nitrate pollution of groundwater, especially in Beihai. The degree of groundwater nitrate pollution is as follows: Fangchenggang < Qinzhou < Beihai, which is associated with the degree of urbanization in the coastal area. Finally, the results of the water quality index (WQI) assessment show that 82.8 % of the samples were classified as excellent, while there is still a need to be vigilant about groundwater pollution caused by seawater intrusion and groundwater pollution. The results will be valuable for sustainable groundwater resource management in Guangxi coastal zone.

Application of Environmental Isotopes and Hydrochemistry to Identify the Groundwater Recharge in Wadi Qanunah Basin, Saudi Arabia

The current study focuses on the Wadi Qanunah basin, which is considered one of Makkah Al-Mukarramah’s most important watersheds. It is located in the southwestern part of the Al Qunfudhah governorate. The identification and characterization of the recharging sources for the quaternary aquifer is one of the most important goals of this study. In this context, different methods will be applied for the identification of the different factors impacting groundwater. Such methods will be based on the integration of geographic information system (GIS) and modern hydrochemical methods ranging from graphical plots, bivariate and multivariate analysis to geochemical modeling. The salinity of the groundwater studied varied from fresh to brackish, according to the seasonal influx of dilute runoff and the dissolution of the weathered rocks, as well as the cementing materials within the aquifers’ matrix. Ionic ratios indicated that ion exchange, silicate weathering and evaporation played a significant role in the enrichment of the groundwater with major constituents including calcium, sodium, magnesium, sulphate and chloride. Furthermore, four factors accounted for 73.92% of the total variance, calculated using SPSS’s statistical program. These factors accounted for leaching and dissolution, silicate and carbonate weathering, anthropogenic effects and evaporation. The δ18O vs. δD, TDS vs. δ18O and δ18O vs. d-excess relationships revealed that local rainfall is the main recharging source for groundwater; some samples were affected by evaporated rainfall, while others with lower salinity (&lt;1000 mg/L) were diluted through seepage from the underlying fractured basement aquifer. Netpath geochemical modeling was applied to calculate the amount of evaporation or dilution which had affected an initial body of water as it moves from the upstream to downstream. The output of this program is consistent with what has been proved by stable isotopes, where the groundwater extracted from the final water is a mixture of an enriched recent precipitation with depleted older water. This study is an attempt to shed light on the assessment of groundwater and the extent at which it is affected by various factors in order to benefit from it in a way that ensures its sustainability.

Suitability Assessment of Shallow Groundwater for Industrial Uses in Terms of Storability and Corrosivity

Maximum industry uses groundwater which is consumed for cooling, product treatment and cleaning, processing, boiler make-up, etc. To assess the industrial water quality, the groundwater samples were collected from pre-monsoon and post-monsoon periods and investigated some selected water parameters. The lower values of pH, Cl-, SO42-, CO32, and NO3-; and the higher levels of total dissolved solids, water hardness, total alkalinity, Ca2+, HCO3-, copper, and iron were the dominant chemical characteristics in the study area. This water chemistry proved that the circulated and feed cooling water have a less corrosive tendency, but it produced scale in equipment. Approximately 100% of the samples were less suitable for the wood, food, paper, and sugar industries, and about 85% of the samples were unsuitable for the canned fruit and polymer industries. The storability and corrosion potential of water were assessed using several indexes based on analyzed water parameters. The results revealed that the bicarbonate regulating index values of the samples indicated a moderate to strong corrosive nature, whereas there was a less scale-forming tendency for boiler use. The study observed the need to continually monitor the corrosion potentiality in industrial systems and conduct laboratory analysis to maintain water quality standards including pH, alkalinity, Ca2+, and HCO3- to control corrosion and scale generation.

Spatial variability of hydrochemistry and health risk assessment of groundwater of taluka Hala, district Matiari, Sindh, Pakistan

Spatial variability of hydrochemistry and health risk assessment of groundwater of taluka Hala, district Matiari, Sindh, Pakistan

Topical Collection: International Year of Groundwater—managing future societal and environmental challenges

Groundwater’s role in maintaining the well-being of the planet is increasingly acknowledged. Only recently has society recognised groundwater as a key component of the water cycle. To improve public understanding and the proper use of groundwater, the hydrogeological community must expand its efforts in groundwater assessment, management, and communication. The International Association of Hydrogeologists (IAH) intends to help achieve the United Nation’s water-related Sustainable Development Goals (SDGs) by the adoption of innovative hydrogeological strategies. This essay introduces a topical collection that encapsulates IAH’s 2022 ‘Year for Groundwater’.

Impact and Health Risk Assessment of Groundwater in the Vicinity of Dumpsites in Keffi Metropolis, Nigeria

Impact and Health Risk Assessment of Groundwater in the Vicinity of Dumpsites in Keffi Metropolis, Nigeria

Hydrochemical assessment of groundwater in the Kert aquifer using a GIS application: an overview of the control factors for fluoride, arsenic and silica enrichment

Our study was based on using a freshwater aquatic species to assess the short-and long-term toxicity of an organophosphate insecticide commonly adopted by the Moroccan agriculture sector. Recently, groundwater pollution has emerged as one of the most severe environmental challenges, with a particular emphasis on levels of heavy metal pollution. Conservation efforts and efficient management of groundwater resources are required to determine the full scope of this damage. The current research answers the physical-chemical evaluation of the middle Kert basin’s water quality (Mediterranean area, Driouch province, Eastern Morocco) by collecting 42 samples and measuring pH, TDS that vary between 451 and 5841 mg/l, and EC that range from 0.72 to 9.41mS/cm2 according to ISO 5665. The samples were analyzed by ICP-MS and flame atomic absorption spectrometry to detect fluoride and arsenic content. Whose fluoride in the survey area varied from 0.01 mg/l to 2.85 mg/l. The hydro-chemical classification resulting from the Geographic Information System (GIS) statistical data analysis was used to interpret the analytical data on the phenomena responsible for the mineralization. This quantity is considerably higher than the maximum allowable level of 1.5 mg/L, which is the regulation for drinking water in Morocco. It indicates that both natural and artificial factors have contributed to the effects. Most stations have a fluoride concentration in the water, which can be used to identify them. It is a significant amount less than the values that would be ideal; just four wells have concentrations higher than the values that are legally allowed to be. The fluoride levels in the region’s water sources directly result from the natural elements that make up this particular geographic location.The same happened for arsenic, which exceeded 0.1 mg/l in just two samples.

Quality assessment of groundwater sourced from nearby abandoned landfills from Industrial City in Nigeria: Water pollution indices approach

The study assessed the quality of groundwater sourced from nearby abandoned landfills in an industrial city in Nigeria. Nine (9) groundwater samples were collected from three (3) abandoned landfills in Port Harcourt city and analysed for physicochemical and heavy metal parameters. Water pollution indices such as water quality index (WQI), Pollution load index (PLI), heavy metal evaluation index (HEI), and heavy metal pollution index (HPI) were computed for groundwater quality analysis. The concentration of heavy metals analysed are within WHO limit except for Nickel (Ni-0.06 mg/l) across all locations. The WQI computation classified groundwater as “Excellent water (35.12)” to “Good water (60.97)”, PLI (0.142 to 0.17), and HEI (4.893 to 5.133) indicated no pollution, and low pollution level, respectively. The HPI of the groundwater was deemed “Suitable for Drinking (59.11) to “Unsuitable for Drinking” purposes; hence, need for treatment prior to use.

Hydrogeochemical Characterization and Quality Assessment of Groundwater Based on Water Quality Index in Imo state, South Eastern Nigeria

Water Quality Index (WQI), Principal Component Analysis (PCA), Correlation matrix, Metal Pollution Index (MPI), Contamination Factor (CF), Pollution Load Index (PLI), Geoaccumulation Index (Igeo), Health Risk Assessment, and Hydrogeochemical facies were used to analyze statistical indexes and hydrogeochemical facies in groundwater resources in Imo state, Nigeria. All across the study area, twenty (20) groundwater samples were collected in a systematic manner. The samples were examined in accordance with the American Public Health Association standard (APHA) method. Findings from the study revealed that WQI, is of poor quality and should only be used for irrigation. Weathering and redox reactions are important in groundwater geochemistry, according to PCA results. TDS and Cl, HCO3 and Zn, Cl; Mg and Ca, Ca and Na were all found to have a positive correlation in the correlation matrix while PH and K, HCO3 and Fe, Cl and SO4 are found to have a negative correlation in the correlation matrix. The findings show that the items have a weak correlation and that there is no relationship between the two variables. Further MPI, CF, and PLI findings revealed that groundwater is pure, the main source of pollution is geological and anthropogenic processes, and there is no pollution in sampled groundwater. Hydrogeochemical trend revealed that groundwater is Na++K+ &gt; HCO3¯+CO3&gt; Mg+ &gt; SO4&gt; Cl¯ &gt; Ca+. Based on the finding, pre-use treatment of water resources is strongly advised.

Characterization and assessment of groundwater from Obafemi Awolowo University campus, southwestern Nigeria

This study deduced groundwater contaminant sources and the processes controlling groundwater chemistry using Principal Component Analysis (PCA), rock source deduction and Water Quality Index (WQI), all with a view to characterize and assess the groundwater. Groundwater sampling was performed at Obafemi Awolowo University (OAU), Ile-Ife, Southwestern Nigeria. A total of 41 groundwater samples were collected in dry season (November) and subjected to physicochemical analyses. Twelve (12) parameters (pH, TDS, electrical conductivity, temperature, Calcium, Magnesium, Sodium and Potassium, Bicarbonate, Chloride, Sulphate and Nitrate) were analysed. PCA analysis highlighted five principle components (PC–I, PC-II, PC-III, PC-IV and PC-V), which explained 82% of the total variance in the hydrogeochemical data. PC-I to PC-V had loading for Ca2+ and SO42−; Na+ and K+; EC and TDS; Mg2+ and HCO3−; and pH and temperature, respectively. The PCA and source rock deductions revealed that the groundwater chemistry is influenced by geogenic effects of weathering and rock-water interaction, and non-geogenic effects of precipitation and organic processes. Based on the WQI assessment, the groundwater quality was adjudged good to excellent.

Hydrogeochemistry, solute source identification, and health risk assessment of groundwater of cancer-prone region in India

Abstract The Bathinda district of Punjab, India has been reported with the highest per capita number of cancer patients. Groundwater is the major source of drinking and irrigation in the district. The hydrogeochemical analysis indicated Na-HCO3 and Na-SO4/Cl type water in the district, and rock-water interaction and irrigation return flow influenced the major cations. Only 10% of samples were in the very poor category for drinking purposes, which increased to 95% in the post-monsoon period due to elevated U, As, Ni, F and NO3 concentrations. Further, the average cumulative risk posed by the contaminants in the drinking water was &amp;gt;1 for almost all the samples indicating a higher risk of non-cancerous health issues. The average carcinogenic risk to males, females, and children due to ingestion of groundwater laden with As, Ni, Cr, and Pb was 1643 × 10−6, 1415 × 10−6, and 3066 × 10−6 during pre-monsoon and 2091 × 10−6, 1802 × 10−6, and 3904 × 10−6 during post-monsoon period respectively. The principal component analysis (PCA) indicated NO3 of anthropogenic origin and other contaminants of geogenic origin, and nitrate further influences the mobilization of U. Removal of U, As, Ni, F, and NO3 from the groundwater samples will help in changing the status of 100% and 85% of groundwater samples to the low-risk category for pre-monsoon and post-monsoon periods respectively.

Identification and Assessment of Groundwater and Soil Contamination from an Informal Landfill Site

Landfills are a potential source of local environmental pollution of all kinds, and the gradual destruction of seepage-proof structures in informal landfills will lead to contamination of the surrounding soil and groundwater environment. In this study, an informal landfill site in eastern China is used as the research object. Using technologies such as unmanned vessels and monitoring well imaging to delineate the amount and distribution of polluting media, sampling of the surrounding soil, sediment, groundwater, and surface water for testing, analysis, and evaluation is carried out visually and finely for heavy metals, petroleum hydrocarbons, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and other indicators. The test results show that volatile phenols are the main contaminant species in the shallow groundwater, chlorinated hydrocarbons and benzene were prevalent in the deep groundwater, hexachlorobenzene and lead in the surface soil, and di(2-Ethylhexyl) phthalate in the deep soil (5.5 m), with a maximum exceedance of 1.24 times. Nearly 10 years have passed since the waste dumping incident at the landfill, but characteristic contaminants are still detected in the topsoil of the dumping area, which shows the long-term nature of the environmental impact of illegal dumping on the site. The study recommends that when developing a comprehensive remediation plan, the persistence of the environmental impact of the waste should be considered and appropriate remediation measures should be screened.

Hydro-chemical characterisation and quality assessment of shallow groundwater in parts of the Kathmandu Valley, Nepal

Groundwater is the main source of water for drinking and irrigation in the Kathmandu Valley of Nepal. Although quality of groundwater is crucial for public health, there is little information available. Considering this, groundwater samples were collected during the post-monsoon and winter from 35 dug wells of Lalitpur Metropolitan City located in the Kathmandu Valley. Chemical analysis of these samples has revealed alkaline nature of groundwater. Factor analysis (FA) and correlation analysis (CoA) have identified lithology, geogenic, and anthropogenic activities as the main factors governing groundwater chemistry. Cluster Analysis (CA) segregated samples into five clusters indicating difference in their hydrochemistry. The Weightage Arithmetic Water Quality Index (WAWQI) has revealed unsuitability of groundwater for drinking. Among the chemical constituents, Fe, Ca2+, Mg2+ and PO43− are found most influential. Concentration of iron, and calcium were much higher than the recommended limit for drinking water. High total coliform (TC) content in particular makes groundwater of the valley totally unsafe for drinking. While percentage of sodium (Na%), sodium adsorption ration (SAR), and salinity hazard values of the samples are found suitable, on the basis of the Permeability Index (PI), several winter and post-monsoon samples were unsuitable for irrigation. This study strongly recommends for treatment and purification of groundwater before supply and use for drinking and irrigation purposes to minimise health-risk.

Geomatics-Based Modeling and Hydrochemical Analysis for Groundwater Quality Mapping in the Egyptian Western Desert: A Case Study of El-Dakhla Oasis

Groundwater is the single source of water in El-Dakhla Oasis, western desert, Egypt. The main objective of this study is an assessment of groundwater in the area for agriculture and drinking compared to Egyptian and World Health Organization criteria. Most the contamination of water in the study area comes from human and agricultural activities. Thirty soil profiles were studied in the area and we assessed soil quality. Seventy-four samples were taken from the area’s groundwater wells to assess the chemical characteristics of the groundwater. Moreover, the contamination of groundwater by farming and anthropogenic activities was assessed using a land use/land cover (LULC) map. Nine standard water criteria were determined to assess groundwater quality for agriculture. Furthermore, the resulting risk to human health and agricultural crops has been addressed. Therefore, the drinking quality of groundwater samples is graded as low as the hydrochemical study showed high TH, EC, TDS, Ca2+, Mg2+, Mn2+, and Fe2+ contents of 40.5%, 2.7%, 1.4%, 3.8%, 1.6%, 86.5%, and 100%, respectively. Human health is risked by drinking this water, which negatively affects hair, skin, and eyes, with greatest exposure to enteric pathogens. Using these criteria, the majority of groundwater samples cause harmful effects on soil types and are toxic to sensitive crops (vegetable crops). In conclusion, the output of this research is a map showing groundwater suitable for consumption and agriculture in El-Dakhla Oasis based on all indices using the Geographic Information Systems (GIS) model. Additionally, there was evidence of a linear relationship between soil quality and irrigation water quality (R2 = 0.90). This emphasis on tracking changes in soil/water quality was brought on by agricultural practices and environmental variables.

Modeling of groundwater potential in Kericho County, Kenya, using GMS_MODFLOW

Groundwater is a major source of water supply in Kericho County, Kenya. However, this water source is threatened by the rise in the human population and climate change. Under these conditions, it is crucial to assess the sustainability of the groundwater resource in Kericho County. Thus, this study aimed to investigate the potential of groundwater in Kericho County, Kenya. Groundwater Modelling System (GMS) software was used to develop a conceptual model to aid in the assessment of groundwater. Results from calibration showed hydraulic conductivity values varying from 0.279 to 1.12 m/d, while the recharge rates ranged from 0.5 to 0.00022 m/d. Also, a predictive run was conducted in the calibrated model to examine the aquifer's response to abstractions under three different scenarios. Scenario 1 assessed the impacts of population growth on groundwater resources; scenario 2 evaluated the effects of climate change on groundwater; scenario 3 assessed the effect of population growth and climate change on groundwater in the study area. The results showed that excessive pumping rates interfere with the surface water and groundwater interactions. There was slight decline in constant head for location near the river. However, the recharge rate was higher than the abstraction, indicating that groundwater will remain sustainable as the primary source of water supply for the residents. In conclusion, the volumetric budget for the three scenarios shows that the aquifer has sufficient water supply to be used by the population despite the effects of climate change and population growth. Despite the availability of adequate water supply from the aquifer, there is a need for an effective and sustainable use of water from the aquifer, especially in the face of climate change and population increase.