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Water quality is fundamental for river health and sustains ecological processes that support native populations of fish, vegetation, wetlands, and bird lives. Improved water sources are essential for environmental protection and development of economic, political, social and cultural in a country (1). River pollution is one of the most important problems of today's world, especially in developing countries that also Iran faces this problem with its four thousand years old civilization (2). Despite water shortages, misuse of water is widespread. Small communities and large cities, farmers and industries, developing countries and industrialized economies are all mismanaging of water resources. In recent decades, increasing population, industrialization and production of a variety of pollutants in urban areas, industrial and agricultural have increased the pollution of rivers. Monitoring and management of rivers water quality is important, because they are more directly exposed to contaminants (3). In addition, since the rivers directly effect on public health (in drinking water) and aquatic life (through the raw water), the assessment of river water quality is very important (4). Surface water is exposed to pollution more than other water. Looking for rain, especially heavy rain, particles of plant, animal, even industrial and toxic transport with water and contaminate the waters (5). High concentrations of natural organic matter may cause the production of harmful compounds in water and human compounds are considered as the biggest portion of natural organic matter (6). Human compounds are considered the most portion of natural organic matter (NOM) found in many surface water sources. High concentrations of NOM may cause harmful compounds in treated drinking water (7). Also, the leachate from a landfill contains a large variety of different substances, both inorganic and organic matter. Therefore, the site of landfill is as an important factor that effect on the water quality (8).
Water quality is the main factor inhibitor of health in human and animals (9,10). Water pollution also plays a big role in the survival of animals, plant, and human. Recognition and assessment of water resource quality is very important in management and optimal use of it (11). Because water supplies are ultimate recipients of contamination derived from various human activities. Most of human activities such as agriculture, food production, industry, nutrition, and housekeeping are dependent on sufficient and proper quality of water (12). Assessment of water quality characteristics is necessary in the planning related to water resources management as well as basin health assessment and management of its changing (13). Protection of water quality is considered as one of the pillars of planning in integrated management of water, particularly in arid and semi-arid area (14). Sometimes the term of 'risk' is used to express vulnerability. If the vulnerability is only express the inherent characteristics of natural environment in order to determine the probability affected by the adverse effects of pollution on the environment. Risk is generally defined by two characteristics: 1. the vulnerability of physical environment and pollutions 2. The threat comes as a result of human activities. These two factors interact with each other.
Water is a source that is faced with different changes over the time and space; also, it is exposed to many hazards such as pollution. In the nineteenth century, human factors were the most important source of water pollution that created several risks in the field of water quality and public health (15). Risk assessment is a logical method to determine the quantitative and qualitative risks and potential consequences of accidents on people, materials, equipment, and environment. Today, the use of risk assessment methods in different industries is growing; so that there are more than 70 different types of quality and quantity risk assessment methods in the world now. These methods are commonly used to identify, control, and mitigate the consequences of risks (16). Given the importance of this issue, yet several studies in order to assess the quality of water resources and water quality parameters and risk assessment of river pollution carried out that mention some of them.
Khara et al (17) examined the quality of Ashmak river water in Gilan province, Iran. The results of this study showed that the pollution level in the Ashmak river is moderate to high. Parastar et al (18) were evaluated the water quality index of Hiroochaei river in the area of Khalkhal in Iran in 2013 that was based on NSFWQI and WILCOX indices. According to the results of that, the water quality of this river has been reported in a moderate-good range. Dehghanzedeh et al (19) examined the quality of Mehran river in Tabriz, using NSFWQI index and concluded that the water quality was in a bad range. Shokuhi et al (20) evaluated the water quality in Idghamoosh dam with NSFWQI index. The results showed that the water quality is good for different uses. Mirmoshtaghi in 2011 (21) studied the water quality of Sefidrood river by investigation of 20 samples at 5 sampling stations according to NSFWQI index. The re¬sults showed very bad water quality of Sefidrood river during the study.
Also, Liu and colleagues (22) were examined the indicator of pollution in Liu and Xiang rivers that generally the amount of river water pollution in Xiang river was more than Liu river and its quality was lower. Mirmoshtaghi et al (23) examined the quality of Sefidrud river water and concluded that this river is faced with an agricultural and municipal wastewater and industrial effluent that entered to river. So that the contamination of coliform has increased from upstream to downstream stations and use of this water for drinking, agricultural and other expenditure is perilous. Bayati and colleagues (24) examined water quality changes trend in Ahar river and it's possible effect on human health and concluded that three indicators sodium, sulfate and total dissolved solids during the study of 40 years, increasing trend has been observed and total dissolved solids indicator is located in a bad range for human consumption based on standard thresholds. Meftah (25) classified Atrak river based on water quality. Classification of water quality of this river has studied by NSFWQI, BCWQI index and simple management methods. The results showed that all stations have bad conditions except one of them. Hosseiniyan and colleagues (26), Saadati and colleagues (27), Jamshidiyan and Alavimoghadam (28), Basir and Nabavi (29) and Mirzaei et al (30) used NSFWQI index to classify different rivers water quality and by measuring the required parameters, the quality of the rivers were classified based on annual quality index. Their results showed the effectiveness of this method. Samantray and colleagues (31) examined the quality of Mahanadia and Athavabanki rivers in India, using NSFWQI index. The results showed that the water quality based on the indicators has declined due to human activities and industries.
Karoon water quality among 2001-2006 based on WQI index indicated that Karoon river water quality in Ahvaz is in the range of medium and threatened (32,33). Madadinia and colleagues assessed the water quality of Karun river in Ahvaz range, using NSF's quality index in 2014 and concluded that Karoon water is not suitable for irrigation and drinking, but it is better to preserve an aquatic life (34). Bateni and Soffianian (35) evaluated Zayandehrud river water quality, using WQI index that the results indicated that this river has no appropriate conditions in terms of water quality status. However, Choom bridge, Ziyar bridge, Ajiye bridge and Varzaneh stations always set bad and very bad qualitative classification.
Ranjbar Jafarabadi and colleagues (36) examined the causes of river pollution in Zayandehrud river and it's quality, using their NSFWQI and based on this index, the river was in the middle class. Niknia (37) evaluated the pollution risk assessment in Chaharbagh basin by WRASTIC (Wastewater-Recreational-Agricultural-Size-Transportations avenues- Industrial -cover of vegetation) index. Results of index showed that the risk of pollution is 50 in this basin and this value of risk represents middle pollution risk due to human activities for this hydrological environment.
Rahimi and colleagues (38) evaluated the quality of water entering into the wetland, using risk assessment index and vulnerability of water resource pollution by WRASTIC index. Consequently, the index reflects the large impact of basin components in wetland pollution.
Ghorbani and Azimi (39) evaluated the pollution risk assessment in Golestan basin of Khorasan province, using WRASTIC model that the risk derived from the calculation of this index indicate a high risk caused by human activities for this hydrological environment.
Water quality in each area reflects the effect of different factors such as geology, climate and human pollution sources and monitoring the quality of water resources often produce complex data which are contain rich information about the behavior of water resources and they need to appropriate methods for analysis and interpretation. Indexes are appropriate and simple tools to determine the status and water quality conditions which incorporate data from multiple water quality parameters into a mathematical equation that rates the health of a water system with number. This number classified as a relative scale from poor to excellent that represent water quality.
 Aims of the study:
The aim of this study is evaluation of surface water quality, using NSFWQI index and pollution risk assessment by WRASTIC index in 2015.
 

Materials & Methods

Study area
This study has been carried out in the Zayandehrud basin which is located in west-central Iran with semi-arid region (latitude 31°12’N, longitude 50°02’E). Zayandehrud is one of the most important rivers of the central plateau of Iran. Zayandehrud watershed extends over a total area of 41500 km2. Zayandehrud River flows in this watershed with a length of about 350 km from west to east. This river is originated from the Zagros mountains in the west of Isfahan province and ends in Gavkhuni wetland. Life of Isfahan area is dependent to Zayandehrud river and thus maintain the quality of drinking water, agriculture, industry and preserve the aquatic environment are very important. In Figure 1, Zayandehrud basin with the main and tributary rivers and studied hydrometric stations are shown.
Method of study
Water quality indices are one of the simplest methods to determine water quality conditions that are helpful for the selection of an appropriate treatment technique to meet the concerned issues (40).
Among these indices, national sanitation foundation water quality index (NSFWQI) has been implemented in many locations of the world which its calculation, different  physical, chemical and biological parameters are measured including dissolved oxygen, PH, all of the  solids, the required biochemical oxygen, turbidity, temperature, phosphate, nitrate and excremental  coliform. This index is easy to calculate and has been a popular index (41). This research is an experimental study. In this study, NSFWQI index is used for monitoring and assessing water quality of Zayandehrud river.
Data Collection
Water quality data collected from 7 sampling sites during 4 seasons from March to February 2015. Since river water was not open and cannot be sampled monthly, sampling was carried out quarterly. In each station, water quality parameters including dissolved oxygen, pH, total dissolved solids, biochemical oxygen demand, turbidity, temperature, phosphate, nitrate and fecal coliform was measured.
Data analysis
National Sanitation Foundation Water Quality Index (NSFWQI) calculation
The parameters of temperature, soluble oxygen, and in-site PH are measured. The level of soluble oxygen is calculated with the DO-meter device- Winlab model. PH and temperature are also calculated, using the PH-meter- Multi 340 i model which are all portable. The turbidity of the samples is also read in laboratory, using the turbidity-meter device- Hach model 2100N made in U.S.A, and the parameters of TS, phosphate, Nitrate, BOD and fecal coliform are also measured based on the methods available in the standard book of method.
In calculating the index of NSFWQI, according to the Eq. (1), two factors of the weight and quality of parameters are involved, and in this study, the value of index is obtained for each stationary, using the online software of NSFWQI calculator (Figure 2). In this way, by placing the value of each parameter in the mentioned software, the value of index is calculated for each parameter and finally, the index is determined for each considered stationary or month through obtaining the average of the values. This index has a value between 0 and 100 which rates the water quality to excellent (90-100), good (70-90), moderate (50-70), bad (25-50) and very bad (0-25) situations based on Table 1 (42). This index is a decreasing index (i.e. the index decreases with increasing pollution).
NSFWQI=ΣW_i Q_i                    (Eq. 1)
 
 

Figure 1) Zayandehrud basin and studied hydrometric stations
 
Table 1) The guide of the water quality index

The index limit	Water quality	Classification of the type of water resource usage
90-100	Excellent	Having natural state, it has no need to be treated if it is used to provide the drinking water, it is appropriate for training the fishery and water-resistant species.
70-90	Good	If it is used to provide the required drinking water, it requires conventional treatment. Appropriate for fish farming and water sensitive kinds, appropriate for recreative purposes like swimming
50-70	Moderate	If it is used to provide the drinking water, it requires the advanced treatment, appropriate for fishery and water-resistant types, appropriate for the domestic animals as the drinking water
25-50	Bad	Appropriate for irrigating the agricultural lands
0-25	Very bad	It is not appropriate for any of the mentioned usages, and it has only the ability of supporting a limited number of the aquatic animals

To obtain quality parameter (Q), index curves are used that these curves for the various parameters are shown in Figure 3. It should be noted that if the number of fecal coliform colonies is greater than 100,000, the quality index equals 2, if total solids is greater than 500 ppm, the quality index equals 20, if dissolved oxygen is greater than 140 percent, the quality index equals 50, if pH is greater than 12 or less than 2, the quality index equals 0, if turbidity is greater than 100 NTU, the quality index equals 5, if biochemical oxygen demand is greater than 30 ppm, the quality index equals 2, if nitrate is greater than 100 ppm, the quality index equals 1, and if phosphate is greater than 10 ppm, the quality index equals 2.
 Required factors and selected weight in NSFWQI index is given in table 2.
 

Table 2) factors and their weight in NSFWQI index

parameter	unit	weight
Dissolved oxygen	%	0.17
BOD	Mg/lit	0.11
phosphate	Mg/lit	0.10
nitrate	Mg/lit	0.10
temperature	°c	0.10
Total solids	Mg/lit	0.07
Fecal coliform	Most probable number (MPN)	0.16
turbidity	NTU	0.08
pH	-	0.11

 
 
 
 
 
 
 
 
 
 
 
 

Pollution risk assessment of water resources systems, using WRASTIC index
 
WRASTIC is a method developed to evaluate watershed susceptibility to surface water contamination in any hydrogeological setting based on major watershed characteristics and land uses. It was developed for US-EPA, in 1991, by the American Water Works Association and afterward adapted by NMED/DWB (New Mexico Environment Department Drinking Water Bureau).
 

 
WRASTIC is an acronym for the following parameters: Wastewater discharges (W); Recreational land use impacts (R); Agricultural land use impacts (A); Size of watershed (S); Transportations avenues (T); Industrial land use impacts (I); and the amount of vegetative ground Cover (C).
The equation for determining the WRASTIC Index for any watershed is:
       (Eq.2)
Where: R = Rating factor and W = Weight factor.
The higher WRASTIC Index, the higher the surface water pollution potential. Professional judgments are commonly applied to refine the WRASTIC Index. WRASTIC index uses very simple features that are weighted considering their influence in surface water pollution. The sensitivity rank to pollution considers four categories, i.e., very high, high, moderate and low sensitivity of the water supply.

Figure 2) online software of NSFWQI calculator
 

a- curves for fecal	b- curves for total solids	c- curves for DO
d- curves for pH	e- curves for turbidity	f- curves for BOD
g- curves for NO3	h- curves for PO4

Figure 3) Index curves to determine the quality parameter (Q) in the NSFWQI model

 

Table 3 shows the parameters of this indicator and its rating and Table 4 shows the amount of index for each risk class.

Table 3) parameters of WRASTIC Index and its rating

parameter	range	rating	weights
Wastewater discharge (W)	Public WWTP effluent introduced into watershed area and private septic systems present	5	3
	Public WWTP effluent introduced into watershed area	4
	> 50 Private Septic systems present	3
	< 50 Private Septic systems present	2
	No Wastewater discharges present	1
Recreational impact (R)	Motorized activity allowed on water	5	2
	Non-motorized activity allowed on water	4
	Vehicle Access	3
	No Vehicle Access	2
	No Recreational Access	1
Agricultural impact (A)	5 or more activities present	5	2
	4 activities present	4
	3 activities present	3
	2 activities present	2
	1 activity present	1
Size of Watershed (S)	> 1942.35 km2	5	1
	388.47 - 1942.35 km2	4
	155.39 – 388.47 km2	3
	38.85 – 155.39 km2	2
	< 38.85 km2	1
Transportation Avenues (T)	Railway or Interstate avenue through watershed area	5	1
	Highway avenues through watershed area	4
	State highway or other paved avenues through watershed area	3
	Unimproved avenues (dirt roads) through watershed area	2
	No transportation avenues through watershed area	1
Industrial Impact (I)	Industry has a very large discharge or very heavy impact on surroundings	8	4
	Industry has a large discharge or heavy impact on surroundings	6
	Industry has a moderate discharge or moderate impact on surroundings	4
	Industry has minimal discharge and minimal impact on surroundings	2
	No Industry in watershed	1
Vegetative Cover (C)	0 - 5 % Ground Cover	5	1
	6 - 19 % Ground Cover	4
	20 - 34 % Ground Cover	3
	35 - 50 % Ground Cover	2
	> 50 % Ground Cover	1

 
Table 4) Risk classes based on the WRASTIC index

Range of index	Risk classes
10-39	Low
40-69	Intermediate
70-89	High
90-100	Very high

 

 

Results

The results of NSFWQI water quality index
Water quality state of different stations and seasons is presented in table 5 by NSFWQI results.
The results of the risk assessment with WRASTIC index
Seven parameters in WRASTIC Index for Zayandehrud river basin examined and this index was calculated ultimately. Results are presented in Table 6.
Based on WRASTIC index, Zayandehrud basin placed on the class with high risk and this basin is exposed high pollution and vulnerability.
 
 
 
 
 
 
 

Table 5) The results of water quality evaluation at different stations and seasons using NSFWQI

Season stations	spring	water quality status	Summer	water quality status	autumn	water quality status	winter	water quality status
Morkan	57	Moderate	59	Moderate	52	Moderate	58	Moderate
Polkaleh	38	Bad	42	Bad	37	Bad	43	Bad
Falavarjan bridge	35	Bad	44	Bad	35	Bad	43	Bad
Vahid bridge	40	Bad	42	Bad	33	Bad	42	Bad
Khajoo bridge	36	Bad	41	Bad	37	Bad	43	Bad
Choom bridge	32	Bad	36	Bad	29	Bad	35	Bad
Varzaneh bridge	35	Bad	34	Bad	29	Bad	36	Bad

 
Table 6) Calculation of WRASTIC Index for Zayandehrud river basin

studied factors	Determined rate for the study area
Wastewater discharge (W)	Discharge of industrial wastewater into the river network (5)
Recreational impact (R)	Motorized activity allowed on water (in Chadegan and Zayandehrud when the river is full of water) (5)
Agricultural impact (A)	There are irrigation and agricultural development projects in the region (5 agricultural activity) (5)
Size of Watershed (S)	41500 km2 (4)
Transportation Avenues (T)	There are several highways, public roads and railways in the area (5)
Industrial Impact (I)	Industry has a large discharge or heavy impact on surroundings. Wastewater discharge of steel and Dyeing Factory to river network (6)
Vegetative Cover (C)	35 - 50 % Ground Cover (2)
WRASTIC Index for study area	70 (High risk)