An integrated DRASTIC model using frequency ratio and two new hybrid methods for groundwater vulnerability assessment

Abstract

Groundwater management can be effectively implemented by mapping groundwater contamination. Intense agricultural activities and land overexploitation have resulted in groundwater contamination, which is becoming a critical issue, specifically in areas where fertilizers are extensively used on large plantations. The goal of this study was to develop an integrated DRASTIC model with a frequency ratio (FR) as a novel approach. Two new hybrid methods namely single-parameter sensitivity analysis (SPSA) and an analytical hierarchy process (AHP) are also implemented for adjusting feature weights to local settings. The FR is used for DRASTIC model rates, whereas both SPSA and AHP are used for DRASTIC weights. The FR-DRASTIC, FR-SPSA and FR-AHP methods are developed; nitrate samples from the same month in different years are used for analysis and correlation (May 2010 and May 2012). The first nitrate samples are interpolated using the Kriging approach. The Kerman plain is used as an example, which is located in southeastern part of Iran. Additionally, the new methods are employed in the study area to compare with each other and the original DRASTIC model. The validation results exhibited that using FR approach improved the correlation between vulnerability index and nitrate concentrations compared with original DRASTIC vulnerability correlation which was 0.37. The results indicated that the new hybrid methods exhibited higher correlation 0.75 in the FR-DRASTIC model. Correlations of the FR-SPSA and FR-AHP approaches were 0.77 and 0.80. Hence, the new hybrid methods are more effective and provide reasonably good results. Furthermore, quantitative measures of vulnerability offer an excellent opportunity to effectively prevent as well as reduce contamination.

Groundwater risk assessment based on optimization framework using DRASTIC method

“…Considering the 5-year record of water level, the average values have been calculated and used for the groundwater vulnerability and risk assessment. Net recharge shows the effect of water that infiltrates into the ground and travels toward the groundwater through the unsaturated zone (Neshat et al 2014a). Therefore, a greater amount of recharge leads to more contamination problems within the aquifer media.…”

“…For discontinued parameters (parameters with discrete classes, e.g., impact of vadose zone and soil media), all categories existing in the area should be maintained, regardless of statistical diversity. Modified rating values were derived using the mean of nitrate concentrations of each class reducing to a ten grade scale (Panagopoulos et al 2006;Huan et al 2012;Neshat et al 2014a). In fact, the highest and lowest rates were assigned to the highest and lowest mean nitrate concentrations, respectively.…”

“…For instance, SadatNoori and Ebrahimi (2015) used statistical methods for optimizing rating scores of the DRASTIC model based on point data chloride concentrations to reduce the subjectivity associated with assigning rates and weights to the DRASTIC model. The vulnerability indices have been correlated with nitrate concentrations and/or controlled with sensitivity analysis in most of the previous studies (Rupert 2001;Huan et al 2012;Neshat et al 2014a;Pacheco et al 2014;Ahmed et al 2015;Vaezihir and Tabarmayeh 2015). Recent researchers made alteration to rating scales to adjust the model by data interpolation (kriging method) using ArcGIS® (Ahmed et al 2015;Vaezihir and Tabarmayeh 2015;Sadat-Noori and Ebrahimi 2015).…”

“…Recent researchers made alteration to rating scales to adjust the model by data interpolation (kriging method) using ArcGIS® (Ahmed et al 2015;Vaezihir and Tabarmayeh 2015;Sadat-Noori and Ebrahimi 2015). In addition, modifying the model with omitting or adding layers such as land use pattern to estimate contamination risk to pollutants mostly nitrate (Panagopoulos et al 2006;Bai et al 2012;Huan et al 2012;Neshat et al 2014a;Ahmed et al 2015;Kazakis and Voudouris 2015;Vaezihir and Tabarmayeh 2015) or applying analytic hierarchy process (AHP), a multiple criteria decision-making (MCDM) technique, to adjust weights of the DRASTIC parameters to local settings have become prevalent (Sener and Davraz 2013;Neshat and Pradhan 2014;Neshat et al 2014a). On the other hand, little attention has been given to identify a suitable compatible approach to be employed in any regions.…”

Assessment of Groundwater Nitrate Pollution Potential in Central Valley Aquifer Using Geodetector-Based Frequency Ratio (GFR) and Optimized-DRASTIC Methods

“…The Geodetector calculates the Power of Determinant (PD) values for each contributing factor (or independent variable) based on the spatial variance analysis, which estimates the degree of influence a variable has on the incidence rate, which is groundwater nitrate contamination in this case. The Frequency-ratio (FR) is a technique commonly used in landslide susceptibility mapping [34,35] and was recently introduced in groundwater vulnerability mapping [36]. The FR measures the percent of area with incidence in each interval of a factor to the percent of area of that interval relative to the whole study area.…”