# Assessing Seismic Vulnerability and Pollution Risks of Wastewater Treatment Plants
## 2 Methodology  
The main focus of this research is the visualization of existing qualitative results regarding estimating the seismic vulnerability of WWTPs using GISs. Previous surveys revealed findings related to structural vulnerability, non-structural vulnerability, operational vulnerability, and other aspects [27]. The current paper utilizes results concerning the ISV and ISV-REF, highlighting their exceedances relative to average values. This study emphasizes the visual presentation of the results, their integration with the SHM of Greece, and their geographic distribution according to regions. This approach makes the findings more useful for authorities, decision makers, implementers, auditors, and civil protection agencies. Additionally, this study attempts to combine the exceedances of the above indicators to assess the potential hazard certain WWTPs pose. Below is the previous data that informed the input for this study. The prior study was conducted from April to November 2021. A prototype questionnaire was distributed via the Internet to a representative sample of 116 operators of Greek WWTPs, and the responses were collected. The representative sample consisted of 38 units from Zone I and 78 units from Zone II of the SHM. Zone III was excluded, as the units of that zone represented only a percentage of 3.7% of the total units [29]. Validity and reliability were adequately investigated. The necessary literature was reviewed through the papers presented as follows. Researchers have proposed an empirical method for estimating the seismic structural vulnerability of WWTPs [44]. That study followed four out of thirteen steps concerning the sample set of this infrastructure. The questionnaire included structural, non-structural, and operational factors. Twenty-one highlighted structural factors were assessed via the questionnaire. Participants were asked to evaluate general characteristics, factors related to seismicity and geotechnical data, factors involving technical data (including structural data), and additional factors concerning the materials used in WWTPs. The questionnaire also included seven (7) factors related to non-structural vulnerability and nine (9) factors related to operational vulnerability [27]. Finally, the questionnaire consisted of 44 closed-type questions using a five-point Likert Scale. These questions were organized into six subsections [45]: demographics, structural vulnerability, non-structural vulnerability, operational vulnerability, chronic evolution of soil-water pollution, and coefficients of the variables [29]. After reviewing past recordings, the total number of WWTPs in Greece was 256 units, while the final number used in the questionnaire was 241 units. The proportional representative sample consisted of 116 units and was stratified into four (4) levels based on the seismic hazard of the WWTPs' area, the degree of sewage treatment, the processing capacity, and the sensitivity of the wastewater disposal recipient [29]. The questionnaire was distributed via the Internet using the Google(r) Forms platform, and the operators of the WWTPs were the recipients. A pilot and primary survey were conducted before implementation to ensure validity and reliability. Descriptive statistics were generated [29] using the statistical program IBM-SPSS v. 26 software for Windows. The open-source program of QGIS v3.14 was used to integrate the results of the previous studies [29; 45]. WWTPs are presented in the territory during the processing stage as point layers (see Figure S1 in the SM). Statistical data in the database are introduced and combined, the SHM is utilized, and maps of the combined results are presented. The maps in all the figures represent the entire territory of Greece, which covers an area of 132,049 km\({}^{2}\) and has a population of 10,482,487 as of 2024 [46].