Evaluation of groundwater quality and assessment of scaling potential and corrosiveness of water supply networks, Iran

Sustainable development of social and economic conditions throughout the world depends on the availability of water resources. Water with appropriate quality and quantity is required for the development of industrial, agricultural, and household activities (Aslam et al. 2016; Mirzabeygi et al. 2016; Swan et al. 2016). As a major result of population growth, water demand for domestic as well as agricultural and industrial consumption is dramatically increasing. This has caused excessive use of groundwater resources as the main water supply (Nouri et al. 2006; 2008; Gharibi et al. 2012; Shirmardi et al. 2012). Since there is a possibility of heavy metal and organic pollution in groundwater, proper methods should be applied for removal of pollutants (Mahvi et al. 2008; Maleki et al. 2011; Bazrafshan et al. 2012). Chemical quality of groundwater depends on many factors, such as the composition of precipitation, the geological structure, the mineralogy of the watersheds and the aquifers. From hygienic and economic points of view, these factors play an important role in corrosion and scaling in water supply utilities (Smith et al. 1999; Hayes et al. 2016). Corrosion is a physicochemical process which occurs between a substance and its surroundings and results in changing the properties of materials (Long 1994). Pitting in pipes, reducing the lifetime of facilities, and loss of water are consequences of the corrosion characteristics of water (Wang et al. 2015). According to some studies, damage related to the corrosion process in countries such as Japan, America, Great Britain, Australia, and several other countries was several times higher than their gross domestic product. In addition, the most important health problems related to corrosion are the presence of heavy metals like lead, copper, zinc, and arsenic in drinking water (Edmunds et al. 2015). The most important factors which can effect the corrosion rate include pH, temperature, hardness, alkalinity, residual chlorine, total dissolved solids (TDS), gases, dissolved salts, and microorganisms in water. Scaling is a process in which divalent cations such as calcium and magnesium react with other water-soluble substances and form a thin layer in the inner walls of water pipe lines (Mirzabeygi et al. 2016; Sorlini et al. 2016). The most common scaling layers are made of calcium carbonate. The scaling process can cause problems such as blocked tubes, reduction of the water discharge and the water pressure in the distribution network as well as increasing the operation and maintenance costs (Sun et al. 2014).

Various indices have been used for determining calcium carbonate saturation. Langelier index, Ryznar, Aggressiveness, Puckorius, Larson–Skold, driving force, excess moment and the saturation level of index are the most common indicators used to determine the scaling or corrosiveness of water (Swan et al. 2016). Mathematical formulae for determining the potential sustainability of water have been developed. The first method for predicting the corrosion or deposition of water was conducted by Langelier (1936). The Ryznar index determines the severity of corrosion in water pipelines. According to the Ryznar index, when the value of the index is less than 7, calcium carbonate is deposited on the pipe wall and when the value of the index is higher than 7, there is no deposition on the wall (Ryznar 1944). The buffer capacity of water and the maximum amount of natural deposited water are generally ignored for calculation of the depositing and corrosiveness of water. The Puckorius index presents the relationship between the state of saturated water and scaling. The Larson–Skold index assesses the corrosiveness of water in the presence of steel pipes with low-carbon steel and cast-iron pipes (Larson & Skold 1958). The Invasion scale index is concerned with the water tendency to damage pipes. It was developed according to a request of American consulting engineers to choose a type of asbestos-cement pipe and ensuring the durable structural of pipes at temperatures between 4 and 27 °C (American Water Works Association 1995).

Khorasan-e-Razavi province with an area of 118,854 square kilometers, is located in the northeastern part of Iran. Khorasan-e-Razavi has a population of over 5,994,402 inhabitants and consists of 28 cities, 46 districts, and 156 villages. This province is located between longitude of 33° 52′ to 37° 42′ N and latitude 56° 16′ to 61° 16′ E. The province is characterized by a semi-arid climate, average rainfall of 210 mm, and an annual average temperature of 15.6 °C. Regarding the geographical, geological situation and low rainfall in the region, the main source of water in this area is underground water and the major part of the water is provided through deep and semi-deep wells. The aim of this study is to investigate the physical and chemical characteristics of the water and examine the corrosiveness or scaling tendency of water in rural areas of Khorasan-e- Razavi province, according to Langelier, Ryznar, Puckorius, Larson–Skold, and Aggressiveness indices.

The results of physicochemical parameters of water are presented in Tables 2 and 3. The average concentrations of calcium, magnesium, and fluoride are 53 (±22.7), 22.7 (±13.6), and 0.57 (±0.23) mg/L, respectively, which are in the range of acceptable levels. According to these values, Langelier, Ryznar, Aggressive, Larson–Skold, and Puckorius indices for the water resources situation in the villages of Khorasan-e-Razavi province were determined. Table 4 illustrates the calculations related to these indices. According to the results obtained, most of the water resources were corrosive and the values of LSI, RSI, PSI, Larson ratio, and AI were 0.33 (±0.17), 7.36 (±0.37), 7.4 (±0.6), 2.1 (±1.4), and 12.03 (±0.18), respectively.

Due to the health effects of corrosiveness and the high population in this area (537,920 inhabitants), ground water monitoring in this area is crucial. According to Table 3, the average pH in the studied water wells was 8.03; in comparison with the internal standard, the average of pH was within the standard limit. In addition, TDS, apart from in the central city of Gonabad, the Sangan, Zozen plain of Khaf, and forestry sector of the Roshtkhar, where they are higher than the standard limit, were at a desirable level. High levels of TDS can lead to such problems as scaling in pipes and changing the taste of water. Opacity was within the allowable range except in the central part of the Mahvelat and in Khaf of Gonabad city. The color in all areas was in the standard range. The average hardness of the water sources in many parts of Khorasan-e-Razavi province was more than the desirable range, but in the central city of Gonabad it exceeded the permitted limit. High amounts of hardness (carbonate and bicarbonate hardness) may cause clogging in pipes as well as disruption in some household appliances like water heaters. Also, comparing the hardness of water in the villages of Khorasan-e-Razavi province with internal and external standards, it was found that the water sources are in the range of hard water class (WHO 2004). According to Table 2, the average concentration of calcium, magnesium, and fluoride were in the acceptable range, but the concentration of sodium in many parts was higher than the standard. In most parts of the studied area, the amounts of chloride and sulfate exceeded permitted limits. High levels of chloride and sulfate in water can accelerate corrosiveness in the distribution networks. In addition, the presence of high sulfate can create an undesirable flavor, as well as reducing the quality of water. Nitrate concentration in all areas was less than the allowed maximum and the color and carbonate were zero. According to Table 4, the Langelier index illustrates that water has a scaling grade. Also, according to the RSI, the water resources of Torbat city had a stabilization grade and the index for this region was 6.99. RSI for the central part of Gonabad was 6.4 (consolidation grade). However, RSI for other parts of the study area was in the range of corrosive. According to the Aggressive index, many parts of the studied regions are in the range of scaling and some parts of the studied area are in the range of corrosive. Based on the LSI, water in the central part of Bardeskan city and Baieg of Torbat city has been precipitated without the interference of chloride and sulfate ions; however, in other parts of the area, a protective film interference with chloride ions and sulfate was formed. Based on the PSI, all areas have a corrosive grade. It is essential to note that PSI for areas with pH less than 8 is not a good indicator for scaling and corrosion (Colin 2008). It was found that the Langelier, Ryznar, Aggressive, and Puckorius indices in the Tabriz water distribution network (northwest Iran) were −0.79, 8.16, 8, and 11.16, respectively, and show the corrosive condition of Tabriz water (Taghipour et al. 2012). Also, a study of the rural water distribution network of Urmia city (northwest Iran), that used the Langelier, Ryznar, and Puckorius indices, indicated corrosive water in some of the investigated regions (Khorsandi et al. 2016). In a study done for monitoring scaling and corrosion of the water in Ilam using the Langelier, Ryznar, Larson–Skold, Puckorius, and Aggressive indices found that water in Ilam city (west Iran) tended to be corrosive (Davil et al. 2009). According to the Langelier index, Ryznar index, and calcium carbonate precipitation potential, assessment of tap water sources in Tafila province showed the corrosion and scale formation (Al-Rawajfeh & Al-Shamaileh 2007).

In this study, it was found that the physical and chemical parameters, cations and anions of water in most villages located in Khorasan-e-Razavi were desirable, only the parameters of hardness, alkalinity, sulfate, chloride, sodium, and TDS exceeded the standard level in sectors such as central villages of Gonabad city, central villages of Bajestan city, central villages of Sangan and Zozen plain of Khaf city. The main reason for this could be the existence of minerals and ions in these areas. Based on these results, the following conclusions can be drawn:

• According to the Langelier index, water in all regions has a tendency to sedimentation.

• Based on the Ryznar index, in all regions, there is a poor tendency towards corrosion.

• The Puckorius index showed that water resources in all parts of study tended to be corrosive.

• Based on the Larson–Skold index, water resources in Kashmar and Zaveh cities tended to be deposition and in other studied cities in the range of corrosive.

• The water resources in Roshtkhar city tended to be corrosive and in other regions was in the range of corrosive (based on water invasion).

• Some factors, such as high levels of chloride, total dissolved solids, and sulfate result in aggravating the corrosion process in some areas. Therefore, it is necessary to control the corrosion process. In order to control this difficult and expensive process, some methods, such as painting the pipes, using polyethylene pipes instead of metal pipes and asbestos-cement materials, covering plumbing, maintenance, implementation of cathodic protection for metal pipes, pH adjustment and inject inhibitors have been used in the distribution system. Selecting the best method to prevent the corrosion process depends on chemical properties of water. Using lime as a pH adjustment is the most common method for control of the corrosion process.

The author would like to acknowledge the financial grant supported on this research as NIMAD grant with official code number 943616 supported by the Ministry of Health, Iran. In addition, we would like to thank the Water and Wastewater Company of Khorasan-e-Razavi province for providing information on the drinking water quality in rural areas.