# The Importance of Incorporating Denitrification in the Assessment of Groundwater Vulnerability
## 3 Results and Discussion
### Application of SINTACS-SVN and DRASTIC-PA to Epanomi Coastal Area  
In this study, to prove how LOSN-P can have a crucial role in the vulnerability assessment, two well-known modified methodology, DRASTIC-PA and SINTACS-SVN, have been applied to the Epanomi coastal zone. Both methodologies were calibrated on different study areas and the complete calibration/validation procedure, together with the weights and classes range are available in [PERSON] and [PERSON] [6] and in [PERSON] et al. [12]. In the case of the Epanomi coastal plain, DRASTIC-PA and SINTACS-SVN will be applied using the original weights and scores without a new specific calibration for this study area. This will further reveal the reliability of the two methodologies in a new study area, without a targeted calibration but as standalone methods. Both SINTACS-SVN and DRASTIC-PA use almost the same parameters, except for the groundwater velocity in DRASTIC-PAand Ks in SINTACS-SVN. Two vulnerability maps were produced overlaying the seven parameters for SINTACS-SVN and DRASTIC-PA, using the weights shown in the following equations:  
\[\text{SINTACS-SVN}=3.60(\text{S})+0.36(\text{I})+0.09(\text{N})+2.52(\text{T})+2.52(\text{A})+0.45(\text{C})+2.25(\text{S}) \tag{3}\]  
\[\text{DRASTIC-PA}=0.5(\text{D})+1.1(\text{R})+1.8(\text{A})+0.7(\text{S})+0.8( \text{T})+4.5(\text{I})+0.6(\text{C}) \tag{4}\]  
The two vulnerability maps divided the domain in 5 vulnerability classes, going from very low to very high. Geometrical interval was used for DRASTIC-PA while quantile classification for SINTACS-SVN. One of the main differences concerning LOSN-P in the two methodologies can be noticed analyzing Equations (3) and (4). In the SINTACS-SVN formula the factor accounting for LOSN-P, namely (N), has a weight of 0.09 while in the DRASTIC-PA formula, its weight is 0.7 (represented by S). So, it is clear how in the DRASTIC-PA, LOSN-P has a much higher weight compared to the SINTACS-SVN. The final maps are shown in Figure 4. SINTACS-SVN (Figure 4b) and DRASTIC-PA (Figure 4a) show a remarkably similar discrimination of the different vulnerability classes: very high vulnerability zones are located along the coastline, especially in the Southern and Northern part of the Epanomi coastal zone, very low and low vulnerability zones instead are more frequent moving towards the Eastern border. Both methods show a positive Pearson's \(\mathbf{r}\) correlation (0.57 for SINTACS_SVS and 0.68 for DRASTIC-PA) with NO\({}_{3}^{-}\) concentrations.  
The nitrate values in the study area ranges from 3 mg/L up to 350 mg/L with more than 50% of the dataset exceeding the World Health Organization (WHO) drinking water limit of 50 mg/L. The higher NO\({}_{3}^{-}\) concentration has been attributed to the fertilizer application as the main land use of the study area is agricultural with wheat and vegetables crops (mainly tomatoes). These two crops usually required a high amount of N as fertilizer that has been estimated around 150 kg N/ha for wheat and 250 kg/ha for tomatoes in agreement with [PERSON] et al. [45]. Compared to the SINTACS-SVN,  
Figure 4: (**a**) DRASTIC-PA application and (**b**) SINTACS-SVN for Epanomi coastal zone.  
the DRASTIC-PA shows a better spatial delineation of the vulnerability zones, due to the difference in classes' rating among the two methods, nevertheless both methods are perfectly comparable with the LOSN-P index for the Epanomi coastal zone (Figure 3b), showing a good correspondence among the areas with the higher N loss and the ones with the higher vulnerability.  
This application further remarked how these new methodologies, that directly involve the role of different NO3- attenuation processes in soil and groundwater in the vulnerability assessment are reliable, easily applicable even without a specific calibration and widely applicable worldwide. Providing that the boundary conditions (climate, hydrological setting, etc.) match the ones for which the new vulnerability approaches were defined.