This paper aims to turn complex groundwater data into comprehensible information by indexing the different factors numerically comparative to the standards of World Health Organization (WHO) to produce Water Quality Index (WQI). Water Quality Index (WQI) has been used to assess groundwater quality and Geographic Information Systems (GIS) has been used to create maps representing the spatial distribution of groundwater categories in Assiut governorate, Egypt. Water Quality Index has been computed by Un-weighted Arithmetic Water Quality Index (WQIUA) method and applied on 796 wells over eight years from 2006 to 2013. The results showed that WQIUA values for drinking purposes were high and most of them reached higher or close to 100, which indicated that the groundwater was polluted and unsafe for drinking. On the other hand, the quality index of groundwater for irrigation purposes in most of the study area ranges between 55.78 and 78.38 (poor and very poor category); this means that groundwater is moderately polluted and rather suitable for irrigation.
Groundwater quality assessment is considered as a significant topic to make sure possible safe use of this resource. As the population continues to increase, it is necessary to find additional sources of water such as groundwater. Groundwater is deemed one of the major resources for potable water in Assiut governorate especially in rural areas [
This paper aims to assess groundwater quality using Un-weighted Arithmetic Water Quality Index (WQIUA), and display spatial distribution of groundwater quality using GIS in Assiut governorate. In view of the previous studies conducted to assess the quality of groundwater it has been shown that the few number of such studies was interested with groundwater pollution and have been applied on limited regions in Assiut governorate. In 1988, Sobih et al. [
Geographic Information System (GIS) has come into view as “a powerful tool for storing, analyzing, and displaying spatial data and using these data for decision making in several areas including engineering and environmental fields” [
Ahmed and Ali (2009) [
Study area is considered as a part of the Nile Valley, Egypt. It extends south-north between Sohag and El-Minia Governorates from latitude 27˚37'N to 26˚47'N and extends west-east between New Valley and Red Sea Governorates from longitudes 30˚37' to 31˚34'E, as shown in
Un-weighted Arithmetic Water Quality Index (WQIUA) is calculated to diminish the huge data to one numerical value that expresses the overall water quality [
quality parameters numerically comparative to the World Health Organization (WHO) standards (1996) [
While SAR, Na%, PI, MR, and TDS were used to calculate Un-weighted Arithmetic Water Quality Index (WQIUA) of groundwater if used for irrigation purposes.
The un-weighted arithmetic water quality index (WQIUA) or quality rating (q) of ith parameter apart is defined as given in equation (1) [
where:
qi: the quality rating for the ith parameter;
Vi: the observed value of the ith parameter;
Si: water quality standard value.
Un-weighted Arithmetic Water Quality Index (WQIUA) or the average water quality index (Q) for the studied parameters is
Parameter | Unit | WHO Guidelines | Egypt Standards |
---|---|---|---|
Sodium (Na) | Mg/l | 200 | 200 |
Potassium (K) | 12 | - | |
Calcium (Ca) | 200 | 200 | |
Magnesium (Mg) | 125 | 150 | |
Chloride (Cl) | 250 | 500 | |
Sulphate (SO4) | 250 | 250 | |
Bicarbonate (HCO3) | 350 | - | |
Iron (Fe) | 0.3 | 0.3 | |
TDS | 1000 | 1200 | |
TH | - | 500 | |
Manganese (Mn) | 0.4 | 0.4 | |
pH | 6.5 - 8.5 | 6.5 - 8.5 |
Classification pattern | Ranges | Categories |
---|---|---|
Total Dissolved Solids (TDS) [ | <500 | Desirable for drinking |
500 - 1000 | Permissible for Drinking | |
1000 - 3000 | Useful for irrigation | |
>3000 | Unfit for drinking and irrigation | |
Percent Sodium (% Na) [ | 0 - 20 | Excellent |
20 - 40 | Good | |
40 - 60 | Permissible | |
60 - 80 | Doubtful | |
>80 | Unsuitable | |
Sodium Absorption Ratio (SAR) [ | 0 - 10 | Excellent |
10 - 18 | Good | |
18 - 26 | Doubtful | |
>26 | Unsuitable | |
Permeability Index (PI) [ | >75 | Class-I |
25 - 75 | Class-II | |
Magnesium Hazard (MH) [ | >50% | Unsuitable |
<50% | Suitable |
where:
n: number of parameters.
WQIUA or Q classifies groundwater into five categories Based on its value as follows in
Water quality index | Description |
---|---|
0 - 25 | Excellent |
26 - 50 | Good |
51 - 75 | Poor |
76 - 100 | Very poor |
>100 | Unfit or unsuitable |
and 75, it represents that the groundwater is in the poor category. On the other hand, if the average quality index is more than 100, it means that water falls under the fifth category, where groundwater is polluted and not suitable to use [
Interpolation can be defined as “a function used to generate a continuous surface from sampled point values” [
The Inverse Distance Weighted (IDW) is used as interpolation method to create the spatial distribution map of groundwater quality, which infers the grid value for each cell by calculating the average of sample points. The calculated value depends on measured values of phenomenon in wells and the distance between wells and the calculated grid cell [
where:
λi: the weight of point;
Di: the distance between point i and the unknown point;
α: the power ten of weight.
Firstly, the quality rating (qi) was computed by “Equation (1)” for twelve parameters which used to determine validation of groundwater for drinking and purposes as shown in
The calculated values of qi for such parameters have been plotted as illustrated in
The sulfate quality rating (qSO4) is similar with (qK), it is also more than 50 in 2006, 2007 and 2008 and then became below 50 during the next period. It is noted that there is an increase above 50 in the quality rating of K,
Year | Quality Rating Index (qi) | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Na+ | K+ | Ca2+ | Mg2+ | Cl− | Fe | Mn | TDS | pH | TH | |||
2006 | 90.13 | 57.35 | 49.47 | 44.88 | 70.72 | 51.54 | 106.91 | 112.79 | 54.73 | 126.51 | 54.14 | 636.47 |
2007 | 75.26 | 67.80 | 49.63 | 43.12 | 68.70 | 58.51 | 136.67 | 220.00 | 87.13 | 135.84 | 58.66 | 625.46 |
2008 | 57.95 | 28.78 | 47.02 | 41.96 | 75.23 | 68.61 | 93.90 | 17.09 | 10.43 | 126.28 | 50.03 | 600.18 |
2009 | 57.90 | 22.64 | 31.59 | 33.29 | 63.00 | 34.44 | 91.70 | 3.58 | 0.348 | 109.87 | 65.21 | 438.13 |
2010 | 91.62 | 25.22 | 29.61 | 34.22 | 56.78 | 46.65 | 126.97 | 4.76 | 0.518 | 127.16 | 57.61 | 431.23 |
2011 | 76.97 | 16.49 | 33.85 | 37.90 | 63.40 | 48.09 | 114.15 | 3.31 | 0.25 | 143.75 | 53.66 | 484.62 |
2012 | 86.39 | 16.97 | 27.06 | 35.15 | 57.34 | 39.15 | 123.25 | 3.31 | 0.25 | 141.27 | 62.72 | 420.59 |
2013 | 70.67 | 14.99 | 19.74 | 28.07 | 58.41 | 34.36 | 84.42 | 3.46 | 0.256 | 126.97 | 65.81 | 323.40 |
So4 and Mn in the years 2006, 2007, and 2008, but the ratios is changed to less than 50 in the period from 2009 until 2013.,
All quality rating indices (q) of Na and Hco3are limited to between 50 and 100, so sodium and bicarbonates ions have negative effect on groundwater quality. The quality rating index (q) for Cl is high throughout the observed years and it reached over 100, which represented that the water is polluted with high levels of Cl. In other case for Fe, the quality rating (q) rate was low in all observed years except 2006 and 2007. PH rate falls within the permissible limits in almost all wells and its quality rating was less than 100 over all years. According to the point that quality rating of TH reached higher than 100, it indicates that groundwater is classified as hard water. Although the quality rating values of Na, K, Ca, Mg, Hco3, and So4 were less than 100 but the quality rating for TDS reached over 100 in all years. This means the groundwater in Nile aquifer system along Assiut governorate is over saturated with total dissolved salts (TDS).
Therefore, quality rating (q) cannot be relied upon alone; all affected variables must be included to get one representative value of groundwater in each year which called the Un-weighted Arithmetic Water Quality Index (WQIAU) or (Q) as demonstrated in Equation (2).
With regard to quality rating index (q) of the five used parameters to assess the suitability of groundwater for irrigation,
It is obvious from
Year | Quality Rating Index (qi) | ||||
---|---|---|---|---|---|
TDS | SAR | Na% | PI | MR | |
2006 | 42.17 | 13.32 | 68.26 | 76.14 | 99.81 |
2007 | 45.28 | 11.76 | 66.10 | 74.37 | 98.01 |
2008 | 42.09 | 9.82 | 59.14 | 72.19 | 95.68 |
2009 | 36.62 | 10.77 | 72.09 | 81.98 | 105.21 |
2010 | 42.39 | 19.45 | 77.90 | 87.74 | 112.51 |
2011 | 47.92 | 15.72 | 82.59 | 88.40 | 113.41 |
2012 | 47.09 | 20.04 | 94.22 | 99.78 | 130.76 |
2013 | 42.32 | 22.68 | 88.49 | 97.47 | 130.80 |
It is noted that it cannot be judged on the groundwater quality using a single factor alone, thus, it must be combined between five parameters to get one representative value which called Un-weighted Arthmetic Water Quality Index (WQIAU) or (Q).
Data of 796 wells over the eight years have been used to estimate the Un-weighted Arithmetic Water Quality Index (WQIUA) or (Q) yearly during the period from 2006 to 2013.
The Un-weighted Arithmetic Water Quality Index (WQIUA) or (Q) has been calculated yearly by Equation (2) as shown in
The tabulated results in
Secondly, GIS has been used to plot the Un-weighted Arithmetic Water Quality Index (WQIUA) results to create the spatial distribution map of WQIUA for drinking water and irrigation water as shown in
The results revealed that the suitability of groundwater for drinking varies from location to another. Generally, the groundwater quality index for drinking around river Nile is less than the new reclaimed lands at the fringes of study area. The groundwater in most of the study area belongs to unsuitable and very poor categories, however good and poor categories occupy small areas. Accordingly, the majority of groundwater wells in study area
Year | No of Wells |
---|---|
2006 | 86 |
2007 | 101 |
2008 | 98 |
2009 | 102 |
2010 | 83 |
2011 | 113 |
2012 | 129 |
2013 | 84 |
Sum | 796 Wells |
Year | WQIAU for drinking | WQIAU for irrigation |
---|---|---|
2006 | 121.30 | 59.94 |
2007 | 135.57 | 59.10 |
2008 | 101.46 | 55.78 |
2009 | 79.31 | 61.33 |
2010 | 86.03 | 68.00 |
2011 | 89.70 | 69.61 |
2012 | 84.45 | 78.38 |
2013 | 69.21 | 76.35 |
are unsuitable for drinking.
The objective of calculating WQIUA is to find out quality assessment of water by synthesizing different available groundwater data. Samples of 796 groundwater wells have been used to determine the Un-weighted Arithmetic Water Quality Index (WQIUA) during the period from 2006 to 2013. The quality indices are worked out for PH, Na, K, Ca, Mg, HCO3, SO4, Cl, TDS, TH, Fe and Mn to evaluate the suitability of groundwater for drinking. While, SAR, Na%, PI, MR, and TDS were used to calculate WQIUA for assessing the suitability of groundwater for irrigation. It is concluded that the groundwater of this study area is not suitable for drinking water but can be
hardly used for irrigation purposes. The results are also supported by the spatial distribution of the WQIUA map which was generated by ArcGIS 9.3. In case of using groundwater for drinking, the most study area belongs to unsuitable and very poor categories, whereas if groundwater is used for irrigation, the most study area belongs to poor and very poor categories.
Mohamed R. ElTahlawi,Mohamed Abo-ElKassem,Gamal. Y.Baghdadi,Hussein A.Saleem, (2016) Estimating and Plotting of Groundwater Quality Using WQI UA and GIS in Assiut Governorate, Egypt. World Journal of Engineering and Technology,04,59-70. doi: 10.4236/wjet.2016.41007