Non-structural and operational parameters for the estimation of seismic vulnerability of wastewater treatment plants

The seismic vulnerability of public buildings must be estimated using structural or non-structural parameters. Scientists ought to investigate these factors for the estimation and analysis of lifelines such as wastewater treatment plants (WWTPs). Although efforts have been made in the past, the serious non-structural and operational parameters are not enough defined. This study considers the amount of shortening of the supposed factors after the literature retrieval of WWTPs’ damages at sixteen severe earthquake events worldwide and three events from Greece. The corresponding parameters used for “ordinary structures” are taken into account. The most severe factors for non-structural vulnerability are seven while for operational vulnerability are nine, including soil, water and air pollution, respectively. These factors can assist the rapid qualitative estimation of seismic vulnerability. Implementing these agents by introducing them to an empirical estimation method will mitigate the seismic risk against the WWTPs, in parallel with measures adopted.


Introduction
Natural and technological disasters may cause many impacts on infrastructure and human lives.Wastewater treatment plants' (WWTPs') failures may result in environmental degradation, deterioration of water quality (Alexakis 2010) and human diseases development.Earthquakes, floods and fires in a local community are only some disasters that can influence infrastructure as WWTPs, causing physical impacts through the water for many years (Alexakis 2020).The increase in the population produces more vast and complex WWTPs in the cities, multiplying the problems (Murgante et al. 2011).The prevention of seismic impacts needs the calculation of all the parameters involved.After all, an earthquake is a multi-parametric phenomenon that is not easily been thoroughly analyzed because its total appearance is not predictable.
The "Sendai Framework for Disaster Risk Reduction 2015-2030" principles are countries' obligations worldwide (UNDRR 2019).Earthquakes are categorized as the most significant risks (Homeland Security 2015).The goal is to protect public health and the environment by the recognition and reduction of the risk, the maintenance of resilient infrastructure and the increase in communication, public awareness and confidence.Other objectives are to identify the vulnerabilities based on knowledge and information.
According to the above, all the efforts worldwide are oriented to the estimation of structural vulnerability (SV), mainly using fragility curves (Panico et al. 2017;Kassem et al. 2020).Furthermore, many empirical or analytical methods for estimating seismic structural vulnerability exist, based on the vulnerability curves or on the damages matrix (Homeland Security 2003;AUTH 2014;Guerrini et al. 2016;FEMA 2020).Besides seismic structural vulnerability, seismic non-structural vulnerability (NSV) consists of the non-existence of appropriate fastenings at machines and surveillance, monitoring, warning and response.Operational vulnerability (OV) is the vulnerability related to the physical, chemical, and biological process of the pollutants' removal from the wastewater.In addition, the OV of the WWTPs consists of the malfunctioning or the non-operation due to parameters at threshold limits, defined by directives.Furthermore, the goal of maintenance of a resilient infrastructure is specialized to the objective of emergency preparedness, response, and recovery planning, mitigating all the vulnerabilities.
In the past, parameters of NSV of "ordinary buildings" are recorded in the questionnaire of Earthquake Planning and Protection Organization (EPPO) (EPPO 2020).The method based on estimating parameters included a checklist under the umbrella of an inspection as Rapid Visual Screening (RVS).
Researchers that use qualitative methods for estimating the seismic vulnerability of WWTPs use questionnaires consisted of SV, NSV and OV parameters (Kerpelis 2019).The approach is represented by the existence of seventeen (17) structural factors (as the existence of cracks at the bearing structure skeleton), ninety-six (96) for NSV and a hundred forty-four (144) for OV about the seismic vulnerability of WWTPs.Attempts were made in the past to shorten the parameters of structural vulnerability using twenty-one (21) main SV factors under an empirical methodology (Kerpelis et al. 2020;2021a, b, c).Another effort to demonstrate the NSV and OV was recently made (Kerpelis et al. 2021a(Kerpelis et al. , 2021b)).NSV and OV parameters as obtained indices can assist the efforts for evaluating the seismic vulnerability of WWTPs (Kassem et al. 2020).
The European Union (EU) produced an overview of the existing methodologies used worldwide for practical risk assessment of critical infrastructures (Giannopoulos et al. 2013).WWTPs as critical infrastructures having special needs for physical, chemical, and biological operations are not included in this survey.The discussion does not apply to specific vulnerabilities such as NSV and OV.Other efforts for estimating the NSV are performed only for standard buildings (Farokhnia & Porter 2012).
Environment protection agency (EPA) does not require assessments of the seismic risk of WWTPs, but some WWTPs prepare these studies without structural or nonstructural vulnerabilities (Prathivadi 2018).Emission estimation tools are suggested instead (US-EPA 2022).Program HAZUS (Homeland Security 2003;FEMA 2020) from federal emergency management administration (FEMA) estimates the seismic risk of structures by finding the fragility curves for structural vulnerability.RVS of buildings for potential seismic hazards uses a checklist with parameters and can contribute to the qualitative estimation of NSV.However, FEMA does not check the seismic vulnerability of specified structures, such as WWTPs, through that method (FEMA 2015).The buildings' structural characteristics and ground-motion records (following past earthquakes) are used to export the fragility functions of typical buildings (Akkar et al. 2005), but there are not revealed any fragility curves for NSV and OV.
Critical infrastructures such as WWTPs must focus on operational environmental performance, and all this must be evaluated under the principles of SD for water management-wastewater treatment and environmental management (Duić et al. 2015), including an extensive view of different scientific fields (Seifert et al. 2019).Researchers using indicators of the SD of WWTPs (Cossio et al. 2020) investigated technical assets for the operation (Guerrini et al. 2016).As an observation, the operational values examined are most detailed and there is a total lack of non-structural asset approaches for these infrastructures.
Although structural vulnerability is been analyzed in detail (Mahamid et al. 2020) and experience was gained from the structural damages (Arslan and Korkmaz 2007), other vulnerabilities, as NSV and OV, are not included in the agenda of the researchers.The importance of other vulnerabilities (except of the structural) is crucial as an assessment of the earthquakes of Gisborne-New Zealand (2007) proved that non-structural components were among the most vulnerable parts in wastewater pumping stations (Zare et al. 2010).
In recent days, a questionnaire for RVS, at the non-structural and operational values (Kassem et al. 2020) is needed.An example of this approach used in Greece is a questionnaire estimating NSV parameters from EPPO about the variation in the individual seismic non-structural assessment standards of "ordinary buildings" (EPPO 2020).The issue is that the evaluation is not under a comprehensive program; it is not obligatory, and it does not focus in infrastructure as WWTPs.There is no provision for the implementation of a similar project that would refer to the OV of the WWTPs.
The parameters for the estimation of NSV and OV are too many without prioritization (Kerpelis 2019), so the approach of seismic vulnerability is even more difficult.The exception is the efforts of two studies in 2021 (Kerpelis et al. 2021a, 1b).The present research studies seismic impacts of earthquakes on WWTPs and specializes in previous researches (Kerpelis 2019;Kerpelis et al. 2021aKerpelis et al. , 2021b) ) for the seismic evaluation of WWTPs, focusing on NSV and OV issues.It shortens the amount of the estimating parameters needed as these described below in detail.It is defined that the parameters that caused huge seismic impacts (after past severe earthquakes) is the main reason for their problems after the seismic events.The survey highlights the main estimating parameters to facilitate the processes, complement previous parameters, and save time and money, which are essential values for rapidly evolving events, such as the seismic events (Keeney et al. 1996).The research is following the principles of sustainability development (Duić et al. 2015;Rashidi et al. 2015).The estimating factors that affect the NSV and OV assessment of WWTPs are based on similar factors as those used for traditional buildings.
The use of these parameters by an empirical evaluating method will produce more completely icon for the seismic vulnerability.Therefore, any implementation of the proposed main parameters from this study would contribute to further and most focused analyses for evaluating the vulnerabilities.Integrating all relevant parameters and kinds of vulnerability should provide planners with a holistic view, as shown by similar surveys (Bathrellos et al. 2017;Skilodimou et al. 2019).

Materials and methods
The main scope of this research is to reveal the relationship between past seismic impacts of WWTPs worldwide with NSV and OV, and the shortening of the amount of non-structural and operational factors of previous studies, for the estimation of the seismic vulnerability.The survey examines the comparison of actual damages of NSV after severe earthquakes at the period 1989-2021 on, contrary with the estimating parameters that had been investigated at previous studies.
A literature review had been conducted about the seismic impacts of sixteen severe earthquake events worldwide and on three occasions from Greek WWTPs (Panico et al. 2017;Triantafyllou et al. 2020).The emphasis was placed on the non-structural and on operational damages, besides the recorded estimating parameters of previous studies.The next session analyzes these damages.Figure 1 presents the steps of the method for the reduction in these parameters.Contact was done with the authorities of Greek WWTPs for the reveal of the recent seismic impacts which they were concerned with NSV and OV.

Seismic impacts of severe earthquakes on WWTPs, due to NSV and OV (1989-2021)
Domestic sewage needs primary and/or secondary treatment, while wastewater from industries also requires tertiary treatment (Ballay and Blais 1998).Worldwide, severe earthquakes cause seismic impacts at WWTPs because of their vulnerability.In this session, the investigation analyze past earthquake impacts focusing at NSV and OV.
The sewage pipeline network can suffer failures because of the permanent ground deformations (Tierney 2012; Fig. 1 Steps for the reveal of the primary seismic estimating parameters Nishisaka 2018).Pipelines are prone to failure at connections with facilities (as tanks) or at each other connections.In Des Moines, Iowa, due to the 1993 earthquake, an operational problem was produced because floods led to a loss of water (Schwab 2010), which is useful for WWTP facilities.Severe disasters such as the earthquakes of Loma Prieta (1989), Kobe (1995) and Tohoku (2011) suffered damages as the temporary shutdown of the installation (due to the power outage) (Panico et al. 2017).Uncontrolled fires broke out at San Francisco (1906) and during the Loma Prieta earthquake, with the consequence that boats were used to transport water at the WWTPs, near the harbor (Kameda 2000).Emergency plans were not implemented sufficiency during the Northridge earthquake (Suarez-Paba et al. 2019).Researchers noticed the importance of implementing nonstructural measures as flexible pipelines and strong connections (Suarez-Paba et al. 2019).NSV includes these electrical risks (Zare et al. 2010).Other risks are associated with electronic equipment and notification in case of trouble (as the absence / insufficient monitoring of WWTPs processes, either alert system or communication system).
Also, OV caused uncontrolled release of harmful and/or hazardous materials on soil and shallow water, which threatened the public health and safety during the earthquakes of Izmit-Turkey (1999) and Chile (2010) (Tang et al. 2011).Furthermore, OV may exists if the administrative buildings and their facilities suffer an earthquake and cannot been used at post earthquake period.For example, if the automatic system for the operational checks and monitoring 7/24 are not in use, the whole system will be affected (Zare et al. 2010).
Collected data from seismic impacts to WWTPs (from 1989 until 2011) emerged operational problems due to the damages of the digesters at the earthquakes of Loma Prieta (1989), San Simeon (2003), and L'Aquila (2009).Additionally, damage of filters at Kobe earthquake (1995), and aeration units at Kobe (1995), at Atico ( 2001), and at Darfield earthquake (2010) were observed.Sedimentation basins had damaged at Kobe (1995), at Kokaeli-Turkey (1999), at San Simeon (2003), at Niigata (2007), at Chile ( 2010), and at El Mayor-Cucapah earthquake (2010).Similarly, aeration tanks at El Mayor-Cucapah (2010) faced many problems (Panico et al. 2017).It was noticed that components that may be potentially not in use were the electric power (non-existence of back up), the chlorination equipment, the sediment flocculation, the chemical tanks and the pipelines.
More analytically, during the 1989 earthquake in Loma Prieta at California, liquefaction and the vulnerability of buildings affected steel tanks and mechanical equipment, leading to the power outage of the WWTPs (USGS 1998).At East Bay Municipal District, damages of the local digester were recorded.At the Taiwan earthquake (1999), power outage proved to be the most significant effect on WWTPs.In addition, reserves about power were not sufficient.Problems were emerged due to the NSV (Schiff and Tang 2000).
During the 1999 Turkey earthquake, heavy damage to mechanical equipment occurred.Operational problems of the WWTPs produced ocean pollution in Izmit bay (Zare et al. 2010).Although the 1994 Northridge earthquake was the most costly natural disaster in US history (Stewart et al. 1994), it did not cause significant and notable damages at WWTPs.OV due to power outages and electrical problems affected fifty-four (54) WWTPs in the surrounding areas (Zare et al. 2010).An evaluation was the need for the level of preparedness of different industrial facilities (Suarez-Paba et al. 2019).
During the Kobe earthquake in Japan (1995), many WWTPs were quake-stricken (Michael et al. 2013).Twenty (20) out of the twenty-three (23) pumping stations were damaged and rendered useless, primarily due to power outages (Zare et al. 2010).NSV (as electric engineering risks) existed during this earthquake.The appropriate reserves (if they existed) about pumping stations would mitigate the impacts.The earthquake affected facilities such as building equipment, pipes, and other relevant facilities (pumping stations).All the sewage systems were collapsed due to the Thailand's tsunami in 2004.
At New Zealand earthquake ( 2007) non-structural components (as the support for equipment), had produced damages and were fundamental for the NSV of the WWTPs (Zare et al. 2010).Many facilities, such as pumping stations, had destroyed during that earthquake, although the earthquake caused minor damage to mechanical parts.In Christchurch, OV was the causality because untreated municipal wastewater had massively discharged into Avon River, Heathcote River, Avon-Heathcote estuary, and the sea.Shallow water was contaminated for at least two years (ECRC 2013).Also at a previous earthquake in 1931, operational problems emerged due to the accumulation of sewage solids in the harbor (Zare et al. 2010).Damages to large-diameter interceptor pipes and small-diameter connection pipes had been observed during the Chile earthquake in 2010.Obviously, destroys of pipeline connections were relevant to the NSV of WWTPs.
After the Great East Japan Earthquake ( 2011), the failure to implement the emergency plan had recorded.The unsuccessful implementation of the emergency measures (as preventing and preparedness measures) was NSV and OV for these WWTPs (Suarez-Paba et al. 2019).The needs were significantly lot, as a tsunami had been created after the earthquake.Problems existed about the temporary recovery methods that were implemented at the Minami-Gamo and the Sennen purification centers, in Sendai (Qi et al. 2014).In addition, the clearance of municipal sewage was the first priority.There should be emergency measures to disinfect discharged water.These problems about health and safety were part of the OV of that earthquake.
Table 1 shows the recorded damages of WWTPs worldwide from 1989 to 2021 (in terms of NSV and OV).Table 2 also shows the WWTPs impacts on three Greek WWTPs (from a whole of fourteen) after severe earthquakes in the period 2011-2021.At this stage, a telephone communication (at November-December 2021) achieved with the authorities of WWTPs about the consequences of recent earthquakes in Greece (period 2011-2021).The severe earthquakes of that period directs to Table 1.
WWTPs did not exist in the surrounding areas of Goumenitsa, Pyrgos, Egio and Andravida, according to the Special Secretariat for Water (Special Secretariat of Water 2021).No data existed about the impacts on WWTPs from the Gulf of Efesos and Lefkada earthquakes.The seismic effects to the other WWTPs were the following (according to the representatives of the infrastructure): • Arkalohori (2021).The support of the airpipes at pretreatment process dropped down.Some pumping machines stopped operating due to soil sludge that was inserted inside.These machines unblocked immediately or replaced with others that were existed as a reserve.
A water supply issue (due to pipe leakages) occured for about 2-3 days.Other subjects included the electronic issues because the logistics stopped operating (due to the burnt-out of the power supply) and the management took place manually for the first period.The operation of the WWTPs was restored after 2-3 days due to the existence of the large balancing tank, to the reserves and to the new structures (it was constructed about 5 years before).• Elassona (2021).The earthquake did not cause problems with the infrastructure.The network and the pumping stations operated well as usual.• Samos (2020).The main problems to WWTPs of Samos were the non-operation of the pumping machines.Electrical issues were existed, as a result of the burnt-out of these pumping machines.Three to four (instead of the standard conditions) stopped operating due to a voltage drop in electricity.Τhe soil was inserted and mixed with the water inside water pipes in the town due to their cracks, the pipes' age, and to their narrow diameter.
Reserves of pumping machines existed, so the operation problems were eliminated.• Kos (2017).The movement of the liquids inside the tanks caused the stressing of their supporting (it took a waved form).The supporting of the sludge condensate scrape failed, and the partition walls in a meandering tank for phosphorus removal failed, too.A fire broke out in the control panel after one month of the seismic occurrence due to the movement of the wires.Recurrent power outages occurred, having to result in the interruption of automatic processes.The water supply network was damaged while the sewerage network was not destroyed.No reserves existed.• Rodos (2008).The earthquake did not produce problems with the infrastructure.The network, and the pumping stations operated well and reserves were available.• Kithira (2006).The infrastructure of WWTPs in the surrounding areas did not exist until 2010 (for the WWTP of Monembasia).• Parnitha (1999).The WWTPs of Psitallia and Metamorfosi did not face problems as there existed power autonomy, while the infrastructure Psitallia is one of the biggest in Europe.
The consequences analyzed at the paragraphs before lead to Table 2 and to the main cautions that cause problems to WWTPs: • For NSV: The failure of the supporting of the tanks and equipment is the most emerged damage to WWTPs.Fires also can stop the operations of the processes.Power outages occur to these infrastructures.Electrical problems can stop the pumping machines or other processes.These may stop operating due to burnt outs or the entrance of soil into them.Electronic problems such as the stopping of the logistics can also occur (due to the burnt-out of the power supply).

Minimize the parameters included in the RVS of structures and to previous WWTPs' questionnaires and studies
The RVS of prioritized buildings as the public buildings was used to investigate In addition, ninety-six (96) variables are related to NSV in WWTPs.These are walls and long-length walls, electromechanical installations, fuel tanks, pipelines, electrical equipment and lighting.The following belong also to NSV: the "control building" places (doors and exits, windows, parapets, protecting railings-cladding-plates-other decorative elements, fences and walls, attachments, escalators, elevators, PCs, stored materials, fire detection and fire firefighting).Variables on the connection of WWTPs to city networks are also included.
The questionnaire also includes a hundred and forty-four (144) variables about the units that constitute the WWTPs.These variables are about (a) general characteristics, (b) preliminary treatment, (c) primary sewage treatment plant, (d) secondary sedimentation treatment purification, and (e) the WWTPs pipes.The preliminary treatment consists of bar racks, pulping, grit chamber and skimming tank.The primary sewage treatment plant consists of a primary sedimentation tank.The secondary sedimentation treatment purification consists of biological filter, tank of activated sludge, tank of secondary sedimentation, stabilization tanks, chemical precipitation, sludge treatment (hopper-concentration-digestion-conditioning-dewatering and dryingstabilization-final disposal).
Recently, researchers announced seven (7) factors for NSV to be the most serious: the inadequacy of equipment support, and pipeline connections, the existence and operation of fire safety and detection, the risks associated with electrical engineering, the absence / elliptical monitoring of WWTPs' processes, either alert or communication and notification in case of trouble (Kerpelis et al. 2021b).Other emerged parameters of NSV in the same study were the failure to implement the emergency plan, insufficient maintenance of the installation or existing malpractice and the existence of regular inspections-checks.
The same authors also extracted nine (9) main OV parameters: the automatic system for the operational checks and monitoring 7/24, the operation of the pumping station, the applicable health and safety devices, and the water supply network.More OV estimating parameters were the soil pollution, water pollution, air pollution, operation problems, and the reserves available (Kerpelis et al. 2021a).

Results and discussion
The main scope of this study is the reduction in the parameters' amount for NSV and OV, which are useful for empirical estimating analysis of WWTPs' seismic vulnerability (following the relevance of seismic impacts with NSV and OV).The seismic evaluation through the proposed parameters guarantees the protection of public health and the environment.
Below, the study presents the results of shortening the amount of non-structural and operational factors of previous studies (Kerpelis 2019) for the estimation of seismic vulnerability, taking into account the real damages of nineteen cases of that earthquakes affected WWTPs strongly (Tables 1, 2) and the findings of similar studies (Kerpelis et al. 2021a(Kerpelis et al. , 2021b)).The working case is that the damages and misuses in cases of severe earthquakes are the most important as recorded in the past through Questionnaires (Kerpelis et al. 2021a, b), or by the estimation of its variables (Kerpelis 2019) and the investigation of the NSV variables through the "ordinary structures" (EPPO 2020).
The analysis highlights seven (7) factors that may determine the non-structural vulnerability (NSV) of WWTPs (Table 2).These are: (a) the inadequacy of support for equipment and pipeline connections, (b) the existence and operation of fire safety and detection, (c) the risks associated with electrical engineering and (d) the risks associated with electronic equipment (as the absence / incomplete monitoring of WWTPs processes, either alert or communication and notification in case of trouble).The electrical system of a WWTP controls all the parts of the WWTP (as the tanks, pipes, sensors, manual valves, filters, electric motors and much more parts of the installation).
Complementary parameters of NSV for the estimation are: (e) the failure to implement the emergency plan, (f) insufficient maintenance of the installation or existing malpractice and (g) the existence of regular inspectionschecks.Table 2 shows the central values for NSV (FESTO 2013).
The present analysis also highlights nine (9) factors that may determine the operational vulnerability (OV) of WWTPs (Table 3).These are: (a) the automatic system for the operational checks and monitoring 7/24, (b) the operation of mechanical equipment (pipes or pumping stations), (c) the applicable health and safety devices, and (d) the water supply network.
Complementary operational vulnerability parameters are: (e) the soil pollution, using five (5) chemical parameters (NO 3 − , Mg 2+ , Ca 2+ , Cl − , and Na + ) in addition with concentrations of Na 2+ , Mg 2+ and Cl − and toxic indicators of heavy metals as Co, Cr, Ni, Mn and V following the requirements of Directive 86/278/EEC.Continuing about OV parameters: (f) the water pollution, using the analysis of heavy metal elements-indicators as Hg; Cd; Pb; Cr and organochlorine pesticides, (g) the air pollution (which produces odors in the surrounding area), using the suspended particulate matter (SPM), the SO 2, NO x, non-methane volatile organic compounds (VOCs), and CO as pollutant indicators.Other OV parameters are (h) operation problems like the risks of flammable and toxic materials, foaming, overflow, algae, uneven mixing of sewages, and (i) the available reserves.
Results of laboratory tests of water, soil and air elements, including the above indicators, are valuable.The proposed NSV and OV factors can indicate whether the thresholds of the substances' indicies are exceeded or not (declared by directives).The investigation is also essential for seismic vulnerability in order to compare the recordings of their condition before and after an earthquake.Pollution of water, soil and air signs alert and actions for downgrading of indicators' values, below the thresholds of the directives were mentioned.The present empirical survey produces qualitative results according to real WWTPs' impacts.Means of vulnerability records as the historical data, interviews with experienced estimators, and references provided more classified reviewed data.The study examined individual cases of worldwide and Greek severe earthquakes that had impacts to WWTPs.It suggests that a database record or technical reports about the data of previous failures due to NSV and OV in every region can assist the seismic evaluation of WWTPs by the comparison of previous and new data.The preferred method choice of the telephone communication with the responsible personnel of Greek WWTPs produced sincere data but new technologies such as GIS can also assist furthermore the effort of recording the NSV and OV estimating parameters for all the WWTPs, in the future.
The advantages of the qualitative methodology that estimates seismic vulnerability using these NSV and OV parameters are (a) the minimization of estimation time which is very important in case of earthquakes, and (b) the cost saved as the resources needed are less than those needed in other used methods.The disadvantage of the estimation using the main parameters of the present study are (a) the existence of non-educated or non-experienced personnel for the implementation of the parameters and (b) the accuracy of the results as the whole study uses the variables at a holistic view.It suggests that time and cost of detailed surveys can be hindrance for the quick estimation of vulnerability, most of all.Analytical estimations of water indices like fifteen (15) organochlorine pesticides of the surface waters, and soil indices like five (5) chemical parameters (or four factors, including measurements of seventeen elements) must be included at secondary detailed studies.
Many qualitative results are prone to reduced accuracy that disappears after detailed in-depth studies.Other parameters that must be included to these studies (qualitative and quantitative) are the education and experience of the participants.The examination of these ensured during the telephone communication.Problems as the non-recording of seismic impacts to WWTPs caused difficulties to the study and the forgetting of these by the personnel (after some decades) is a fact.Sometimes people that faced the seismic impacts in the past were not present at this time (due to retirement and personnel movement to other services).
Remarkably, these main parameters may have a grade of influence each other.For example, the main parameter "electrical engineering" of NSV has a grade of identical with the main parameter of OV "the automatic system for the operational checks and monitoring."The same happens to the main parameter "insufficient maintenance of the installation" of NSV in contrary to the main parameter "soil pollution" of OV.Also, the related cost depends on the estimation methodology (Juan-García et al. 2017), so it's essential to investigate the optimal parameters.
A proposed strategy to mitigate the impacts of seismic events on the WWTPs is the quick estimation of seismic vulnerability, through RVS checklist and more analytical research performed in a later period.When focusing on the NSV and OV, the parameters revealed by this survey must be used.New data from earthquake impacts must embedded in the existing database of consequences.The results should determine the protective measures that should be implemented.Protective recommendations must be the beginning for new conditions that will arise and must be considered to the next estimation, as described.The most appropriate methods of precautions to be followed are fastenings at machines and performing maintenance of the infrastructure.The operational management imposes 7/24 surveillance, monitoring, recording, of the treatment processes and of the structure.In case of emergency, warning and response are needed (using appropriate alert and communication system), when thresholds of the substances' indices, declared by directives are exceeding.Reserves about power and pumping stations must be sufficient.The existence of large balancing tanks may mitigate seismic impacts on these critical infrastructures.
Further studies using the conjunction of the proposed primary parameters with the seismic SV can produce interesting results under the umbrella of an empirical methodology and the current directives and regulations.Other vulnerabilities of WWTPs such as communication, transport, and financial can also use the same method for searching the influence of their primary parameters.Registration of past impacts in conjunction with a real-time investigation can extract the best estimation indicators to be used for the quick qualitative capture of reality.Progressive adding of these vulnerabilities in the future can drive the scientists and the implementers of WWTPs' policy to more effective actions and protective measures.Another subject for investigation is the contribution percentage of each parameter of the study.The calculation of indicators through weighting factors and gravity coefficients for each of them can increase the resilience of WWTPs, in the future.

Conclusion
The survey methodology suggests research about the consequences on WWTPs, after severe earthquakes and analysis of existing parameters of NSV and OV at existing studies.The impacts of sixteen (16) powerful earthquakes worldwide and three recent catastrophic earthquakes in Greece (from a whole of fourteen) reveal the main proposed parameters of NSV and OV.The recording included worldwide  and Greek impacts on WWTPs (2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020)(2021).The literature review results combined with past qualitative implementations (as EPPO suggests seventy-four (74) NSV parameters for ordinary buildings).Other studies suggested ninety-six (96) variables related to NSV (or seven factors preferred by others) and a hundred and forty-four (144) variables associated with OV (or nine factors selected by others) in WWTPs.
The main result of the study is seven (7) NSV factors: (a) the inadequacy of equipment support and pipeline connections, (b) the existence and operation of fire safety and detection, (c) the risks associated with electrical engineering, (d) the risks associated with electronic equipment, as electrical system controls every part of the WWTPs (the absence / incomplete monitoring of WWTPs processes, either alert or communication and notification in case of trouble), (e) the failure to implement the emergency plan, (f) insufficient maintenance of the installation or existing malpractice, and (g) the existence of regular inspectionschecks.Other main results of the study are nine (9) OV factors:(a) the automatic system for the operational checks and monitoring 7/24, (b) the operation of mechanical equipment (pipes or pumping stations), (c) the applicable health and safety devices, (d) the water supply network, (e) the soil pollution, using five chemical parameters (NO 3 − , Mg 2+ , Ca 2+ , Cl − , and Na + ) in addition with concentrations of Mg 2+ and Cl − and potentially toxic indicators as Co, Cr, Ni, Mn and V. Continuing about OV parameters: (f) the water pollution, using the analysis of fifteen (15) elements indictors for surface water or the essential five elements-indicators as Hg; Cd; Pb; Cr and organochlorine pesticides.Alternatively, four factors using seventeen elements can be used for groundwater pollution, (g) air pollution using the suspended particulate matter (SPM), the SO 2, NO x, non-methane volatile organic compounds, and Co as pollutant indicators, (h) operation problems like the risks of flammable and toxic materials, foaming, overflow, algae, uneven mixing of sewages, and (i) the available reserves.
This study assists the efforts of the seismic estimation of WWTPs, presenting the most suitable main parameters for NSV and OV.These described parameters serve the principles of human life and the environment's protection.It is characterized as a sustainable process because it decreases the negative seismic impacts and elevated emission levels while assists the mitigation of the respective lifecycle of substances discharged into the natural environment.
The main risk of estimating the NSV and the OV through qualitative factors is that vulnerabilities are interactive each other and the existence of a grade of influence among them is possible.Other disasters or other conditions may differentiate these serious values, influencing decisions.The investigation of each part of vulnerability (as structural, social, financial) must follow a holistic view, searching all their relations.
NSV and was implemented by EPPO (based on FEMA method of RSV)(FEMA 2015).The ordinary buildings' questionnaire of EPPO about NSV was recorded 74 values (EPPO 2020).The variables were 27 architectural elements, 26 building facilities and 21 furniture and objects.The architectural elements consist of the filling walls and space dividers of structures, plaster suspended ceilings, lighting, doors and rescue routes, windows, permanent decorations and attachments.The building facilities consist of elevators and escalators, emergency facilities, heating-cooling facilities, electro-mechanical attachments, electrical equipment, fire detection, and fire extinguishing systems.The furniture and objects consist of communication devices, office equipment, files, stored materials, kitchen and laundry equipment, dangerous materials, furniture and indoor decorative elements.The proposed variables for the seismic estimation of Primary and Secondary WWTPs included two hundrend and sixty-five (265) ones, categorizised as SV, NSV and OV variables(Kerpelis 2019).Twenty-five (25) structural vulnerability variables such as Structural factors like identity, technical characteristics, seismological and geotechnical features of the area, and the WWTPs' structural type were recorded.

Table 2
Seven main parameters for evaluating NSV of WWTPs

Grouping of the consequences of earthquakes on WWTPs Worldwide (1989-2011)
The consequences analyzed in the above paragraphs lead to Table1and to the main cautions that cause problems to WWTPs: • These were collectively (for OV): Temporary shutdown of the installation and insufficient reserves about power (Loma Prieta in 1989), floods led to a loss of water (although Directive 91/271/EEC predicts these cases) and of course air / soil / water pollution (Des Moines, Iowa in 1993), operation problems to all the 17 WWTPs (due to the power outage and the misuse because of damages).Uncontrolled release of harmful and/ • For OV: The automatic processes can stop due to the lack of power.The damaged water supply network cannot assist the WWTPs processes.Reserves would be valuable if they existed.Water supply possibly can stop after severe earthquakes due to the entrance of soil inside them.Operational matters exist after seismic activity in the area.Pumping machines stop operating.Balancing tanks are also valuable.

Table 3
Nine crucial parameters for evaluating OV of WWTPs