Assessing intermittent saline inflows in urban water systems.

Urban water drainage systems' primary function is to transport sanitary or stormwater. The intrusion of saline waters has recognized detrimental effects. Especially in coastal areas, saline inflows can compromise performance by increasing the risk of untreated discharges, weakening the structural condition of concrete or metallic components, reducing the effectiveness of wastewater treatment processes and limiting the potential reuse for irrigation. Performance deterioration can be prevented by an early assessment of exposure to saline water, followed by timely actions to control its causes and consequences. The paper describes a procedure for diagnosing undue saline inflows. The procedure is based on the determination of saline inflow's magnitude, acceptance levels, and contribution to the system's performance. Contextual factors and performance indicators, and their reference values, are selected for the assessment. Options to address the problem are proposed, depending on the results. These options can relate to organizational, operational, and structural actions. Application to a case study allowed to validate the method and discuss the results. Here, saline volumes entering the system are quite relevant (almost 30%), posing problems regarding corrosion, treatment plant operation and significant concrete exposure to intermittent saline waters.


INTRODUCTION
The primary function of urban water drainage systems is to transport either sanitary or stormwater flows (in separate systems) or both (in combined systems). Separate sanitary systems, besides foul flows, can accommodate some groundwater infiltration, industry, or commercial effluents. Regardless of the type of system, saline waters are not part of the inflows acceptable in sewers.
Seawater can have a salinity corresponding to total dissolved solids (TDS) of above 35 g/L), depending on water temperature and local conditions, while raw wastewater can have a TDS of 0.4 g/L, varying with the upstream sanitary and industrial inflows (EPA 2004;Monte & Albuquerque 2010). The input of a small portion of seawater into the sewers can significantly affect wastewater salinity.
Saline inflows entering sewer systems can come directly from saline coastal waters (Phillips et al. 2015) or infiltration of brackish or saline groundwater (Osman et al. 2017). These sources are the ones most commonly recognized by water utilities. However, other sources may occur. Domestic or commercial connections, e.g., when brackish water is used in water supply (Tang & Lee 2002), can be an allowed saline water input but still generate deleterious consequences. Industrial activities Classification of typical causes and consequences supports the selection of an effective course of action since the inflow's mechanisms are understood and acted upon. Generically, the existence of undue inflows is recognized; decision on where to act and what to do, to control or solve the problem, is not always clear, as the identification and location of causes are often unknown. Knowledge of causes allows to identify adequately corrective interventions, locate similar anomalies, and prevent future occurrences (Almeida & Cardoso 2010). Analysis and typification of causes and consequences of saline inflows are undertaken from the literature review and processes analysis.
A tailored set of contextual factors, performance indicators, and reference values is proposed. This set aims to assess the magnitude of saline inflows, prevent their occurrence (by monitoring and acting on their causes and mechanisms), and ensure service quality (by monitoring and controlling their consequences), To assess the inflow magnitude, whenever it is more closely related to the tide, representative sampling should be ensured. Nyquist's theorem states that a periodic signal (such as tide) must be sampled at twice the highest frequency component of the signal. As spring and neap tides have an approximate frequency of 2/month and daily extreme and average tides of 2/day or 4/day respectively, data on tides ought to be taken at least 8/day (every 3 h) ensuring that tidal cycles (daily and monthly) are represented.
The assessment uses performance indicators. These translate the aims of the utility in the medium-long term. Performance indicators are typically expressed as ratios between variables. They contribute to expressing the level of performance in a certain area over a period (Matos et al. 2003). By comparing the result of the indicators with pre-set reference values, it is possible to assign a judgment to the result, e.g., good, acceptable, or unsatisfactory (Alegre et al. 2017). The reference values for a metric can be set from the literature review, regulations, standards, available assessment frameworks, benchmarking of a representative sample or expert opinion. Indicators include variables that depend on the utilities' activities and decisions. By monitoring the result of the indicators over time, it is possible to assess whether the implemented actions are having the expected impact. The analysis and interpretation of performance indicators' results need to consider the relevant contextual factors. These are contextual aspects independent of management options, such as climate factors, urban occupation, or topography. A judgement cannot be assigned to contextual factors, and therefore reference values are not assigned to them.
Contextual factors and performance indicators can be used for several purposes. These include the diagnosis of the current situation, the selection of the more effective courses of action, the evaluation of the solutions' expected impact and monitoring of the achieved impact in the planning horizon. A more effective diagnosis is expected if the interrelations between causes and consequences are considered (ISO 2014). Overall, one must look at the results assuming the possible explanations for each performance indicator. The complete diagnosis should integrate the analysis of the contextual factors and of the several performance indicators, which are relevant for the problem under analysis (Matos et al. 2003).
The diagnosis based on the results for the contextual factors and performance indicators supports the selection of options for the problem under analysis, in this case, saline inflows. Improvement options need to consider the location and the magnitude of the problem, be directed towards its causes and consequences and ensure effectiveness. In some situations, it is challenging to act in the reduction of undue inflows. If salinity derives from the use of water supply with brackish water or salt for deicing roads, in combined sewers, the reduction might prove difficult. When the root cause is related to groundwater or coastal water inflows, the action might be to reduce or avoid the inflows; if originating from an industrial process, pre-treatment allows changing the inflow's characteristics. The magnitude of the consequences of the inflows ought to be considered as well. This allows for a more targeted improvement option. For instance, recurrent exposure of concrete can be reduced by applying some protective coating, if the concrete deterioration is the major problem; however, if treatment is also affected because of increased volumes, another solution needs to be selected.
The selection of the solution needs to consider resources and implementation opportunities. Short-term resolution of the root causes is often not workable, since these are often many, and costly or geographically dispersed interventions are required. It is possible to intervene in localized causes to improved performance, and gradually implement good practices, that progressively contribute to system sustainability (Almeida et al. 2018). Options to deal with undue inflows can be classified as organizational, operational, and structural. The first includes management options and is broader in their application. Standardization on asset management (ISO 2014) is a starting point for identifying organizational aspects that promote sustainability, alignment within the internal structures of the organization, consideration of stakeholders' needs and expectations, and data management. Operational options relate to operation and maintenance activities, which can range from operation alternatives, inspection and testing techniques, monitoring, cleaning procedures or implementation of temporary bypasses (Almeida & Cardoso 2010;EPA 2015). Infrastructural options relate to physical interventions, as construction works or equipment replacement. These are more limited in their application, focusing on given assets. A selection of rehabilitation procedures is available for renovation, replacement, or component repair. Examples of such procedures are internal lining with continuous pipe or sprayed material, pipe replacement with an open trench or a trenchless technique, repair by injection sealing or cured-in-place patch (Hyman 2005;Almeida & Cardoso 2010;Melchers 2020).
A case study for testing and validating the method was selected. Prerequisites included location by the coastline; availability of data including flow, precipitation and water quality monitoring data, asset registry and component condition data; and previously acknowledged symptoms of saline inflows in the system.

CASE STUDY
Águas do Algarve is the utility responsible for the bulk water supply, wastewater transport, and water and wastewater treatment in the Algarve region. Located on the southern coast of Portugal, the drainage system serves an area of about 5,000 km 2 , 311,490 households and has a total sewer length of about 447 km, 192 pumping stations (PS), and 76 WWTP. The region extends from a long coast, well known for the many Atlantic Ocean bathing areas, to an inland mountainous area. The coastal area has a high tourism demand and is also the main receiving water for both rivers and drainage systems. Sewer systems are, on average, over 30 years old. While urbanisation is quite dense on the coast, in innermost areas, urban agglomerates are dispersed, and urban streams are the main receiving waters.
The case study, the Faro-Olhão subsystem ( Figure 1) is in the coastal area, being served by one WWTP and 14 PS. Most facilities are close to the Ria Formosa coastal natural park. This subsystem has symptoms of undue saline and excessive stormwater inflows, facing problems of noxious odours, equipment and concrete corrosion ( Figure 2, regarding a pumping reservoir, a floodgate and a WWTP concrete wall), and increased energy consumption during high tides. The upstream collection systems, mostly combined and in developed coastal urban areas, are operated by other utilities and connect to Águas do Algarve's separate wastewater system. Most pipes are under tidal influence. Upstream of the WWTP, night flows are rather high, and variation in minimum flows between dry and wet weather seasons is not relevant. The WWTP does not have capacity issues or annual non-conformities with the discharge license. However, constraints in sludge biological treatment and sedimentation processes have been experienced. Treated wastewater is not reused for irrigation. Looking at flow and salinity variations together with the tides in the area served by this system, the relation is clear, as shown in Figure 3. Hourly flow and salinity data were registered in the incoming pipe into the WWTP. Tidal heights are recorded and made publicly available by the Portuguese Navy. Four daily records on higher and lower tides are presented in Figure 3.

Analysis and typification of causes and consequences
The most common processes for saline waters inflowing to sewers are groundwater infiltration or direct saline or brackish inflows. These are both undesirable inflows, which might result from infiltration from inland aquifers with high salts concentration or because of saline intrusion of coastal aquifers (van Weert et al. 2009). However, saline or brackish waters can also result from allowed water use. These can come from domestic connections, when brackish or seawater is used for public supply, for non-potable uses or cleaning activities in coastal areas (Flood & Cahoon 2011;Tang & Lee 2002;van Weert et al. 2009). Some industrial processes also increase water salinity, such as the food, laundry, petroleum, and leather industry areas (Lefebvre & Moletta 2006;Tang & Lee 2002). In colder climates, salt used for deicing roads can be a considerable saline input into sewers (Osman et al. 2017).  The effects of high salinity water entering the wastewater systems are diverse. These include the degradation of assets materials (especially in concrete and metals), reduction of treatment processes efficiency, the quality of treated wastewater generated and the quality of sewer sludge. The last two are of concern if water reuse or land application of sludge is envisaged.
Corrosion of materials, because of salinity, can occur both inside or outside of sewers and other system components. Corrosion from the inside is a widely studied problem, resulting from chemical or biochemical deterioration (Mori et al. 1991). The corrosion and deterioration from the outside can be because of exposure to a marine environment (Hyman 2005), soil aggressiveness or groundwater contamination (Osman et al. 2017). Sewers, which are generally placed between 2 and 3 m below ground, can be regularly submerged in coastal areas and be affected by saline groundwater. Whenever the groundwater elevation exceeds the sewer invert, there is also the potential for ingress of groundwater through joints, cracks, or corroded walls (Osman et al. 2017).
High salinity inflows in pumping stations (PS) or wastewater treatment plants (WWTP) can also cause corrosion of concrete and metals. In concrete, corrosion can start in localized air-voids, at the interface with the steel reinforcement. Chlorides also cause the acceleration of the long-term loss of concrete alkali material. These effects are both increased when the quality of the concrete is compromised. This often happens because of poor compaction or existing structural damages in the concrete surface (Melchers 2020) and to humidity, atmospheric oxygen, and reduced concrete coverage of the metallic structures. The intermittence of saturation and drying cycles poses an additional risk. A cyclically humid and dry environment is more problematic because it provides both abundant humidity and oxygen, increasing the concentration of chlorides in the concrete in the long term. Values as low as 0.5% of chloride content in the binder can initiate corrosion (Chalhoub et al. 2020). This is a complex issue, and this value depends on several factors. On one hand, the type of reinforcement, the geometry of the bars, the surface structural condition, or the type of concrete. On the other hand, the water temperature, the duration and intermittence of the contact with the saline water, and the deposition and penetration of the marine salts, between others. When reinforced concrete is adequately designed and built, it can endure many years in an immersion, tidal or splash zone, or exposed to a salt-laden atmosphere (Melchers 2020). Saline inflows in coastal areas can also increase gravel and sand volume entering the facilities (sewers, PS or WWTP), contributing to the mechanical deterioration of the weakened materials.
Saline contributions can also substantially increase peak flow and volumes, using available system capacity and increasing the risk of discharges. Large volumes of saline inflows can come from direct connections when the elevation of a system's discharge or weir overflow are below the tidal level in a coastal area. Trends of sea-level rise because of climate change are expected to increase hydraulic pressure to these structures, resulting in increasing saline inflow volumes (Phillips et al. 2015). Reduction in capacity, both in the facilities and in the drainage system upstream, can contribute to increasing untreated wastewater overflows, in wet and dry weather, with subsequent environmental and public health risks. Exceeded capacity can be evaluated from the sewers' hydraulic point of view, as a relation between the income volumes and the crosssection capacity of the pipes, or from the increased risk to public health and property, given by the occurrence of overflows or flooding.
Salinity in wastewater can have a deleterious effect on the WWTP operation. Conventional wastewater treatment technologies as activated sludge (Osman et al. 2017) have been affected, as well as membrane bioreactors, because of a rapid loss in membrane permeability (Reid et al. 2006). The nitrification process can be inhibited (Osman et al. 2017). High percentages of salt have been recognized to compromise the operation of conventional aerobic wastewater treatment processes above chloride concentrations of 5-8 g/L (Lefebvre & Moletta 2006). Sludge settling in WWTP can be compromised for values above 3.5-5 g/L. Salinity can reduce or completely inhibit microbial activity in activated sludge. For salinity below 10 g/L, microorganisms could acclimatize in several weeks and achieve the same initial activity as in raw sludge. For salinity above 30 g/L, the acclimatization process was very slow or impossible (Linarićet al. 2013).
The reuse of wastewater for irrigation requires the control of salinity, as it can cause rapid soil salinization, affecting crops and hence degrading agricultural land (WHO 2006). Salinity is considered the most important parameter in determining the suitability of water for irrigation, as salts affect several processes in plant growth (Ayers & Westcot 1994). For such, treated water quality for reuse has long been established limits for chlorides (Osman et al. 2017). Salinity over 0.45 g/L has been recognized to restrict water use for irrigation, posing severe restrictions above 2 g/L (Ayers & Westcot 1994).
The inflow of saline waters can subsequently lead to higher operation and maintenance costs (Flood & Cahoon 2011). These can be because of effects in the treatment processes, repair, or replacement of concrete or metallic structures, gates, and other mechanical equipment, but also because of longer functioning hours of pumping or other equipment in the WWTP. Many small repairs undertaken by operational staff go unreported as saltwater-related damage (Phillips et al. 2015).
In Table 1, a summary of sources, mechanisms, effects, and consequences is presented.

Contextual factors and performance indicators
Contextual factors (Fi) and performance indicators (Pi) have been selected given the identified sources, causes or mechanisms, effects and consequences. Contextual factors are useful for locating the potential sources, causes or mechanisms and to complement performance indicators. Proposed performance indicators allow to quantify saline inflows' magnitude (P1) and to identify their causes (P2, P3, F1-F3) or consequences (P4-P10 and F4). Contextual information to be collected and aggregated contextual factors are proposed in Table 2. Performance indicators are proposed in Table 3, and a specific note is made for those coming from the literature review. The proposed reference values for each performance indicator derive from the bibliographic research made on each topic, which is synthesized after each equation.
The percentage of saline inflow magnitude (P1) can either be given by a quotient between the volume of saline inflow and the total inflow to a certain installation or, if these are not available, by the mass balance between the sum of the wastewater and saline water and the total inflow, as a quotient of salinities, as in (1).
where: V SI : estimated yearly volume of saline inflow (m 3 ); V T : yearly drained volume (m 3 ), Sal T : total inflow salinity (g/L); Sal WW : wastewater salinity (g/L); Sal SW : saline water salinity (g/L). Representative sampling should be ensured to determine this metric, as it closely relates to tidal cycles. As referred in the method, samples ought to be taken at least 8/day (every 3 h). It is recommended that P1 is given by the 95-percentile of the results.
As referred, wastewater salinity can vary with upstream conditions. Even if coastal water salinity may be rather constant for a location, local monitoring of total and wastewater salinities ought to be made. Alternatively, average values for wastewater salinity (Sal WW ) can be used, and local monitoring of total inflow salinity (Sal T ) ought to be made.
Given the references in the literature review, the Sal T should be lower than 3.5-5.0 mg/L so as not to compromise the treatment processes in the WWTP (Tang & Lee 2002;Reid et al. 2006;Monte & Albuquerque 2010;Linarićet al. 2013;Osman et al. 2017). For standard values of Sal WW of 0.4 g/L and Sal SW of 35 g/L, these limits correspond to 9 and 13% for P1, given (1). If treated wastewater is to be used for irrigation, Sal T should be limited to 0.45-1.92 g/L (Ayers & Westcot 1994;EPA 2004;WHO 2006), corresponding to 0.14-4.40% for P1, given (1). Limitations to Sal T for exposure of concrete structures are less restrictive, provided the adequate concrete class, reinforcement coverage, and surface protection; this context factor was not considered in the determination of reference values for P1. Variables in P1 can also aid in the identification of causes for saline inflows. Monitoring Sal WW and comparing results between drainage basins can support the identification of locations where water uses, or water supply upstream, might contribute to increased salinity in sanitary wastewater (e.g. using saline or brackish water for surface washing or flushing).  Exploring saline inflow causes, infiltration is evidenced in P2 and P3 (either through manholes or along the pipes) as in (2) and (3) (Matos et al. 2003). Exposure of critical sewer components to brackish or saline groundwater, when groundwater level because of tidal variation is above the sewers' invert, is given by F1 and F2, as in (4) and (5). The number of manholes and the sewer length is commonly available in the utilities' registry.
where: Inf: infiltration estimate, as the difference between the 25-percentile of the dry-weather flow in the wet and the dry season (m 3 /day); M up : manholes in the sewers upstream (number); L up : length of sewers upstream (km); M c : manholes in critical condition in the system exposed to saline waters (number); M T : total number of manholes (number); L c : length of pipes in critical condition in the system exposed to saline waters (km); L T : total pipe length in the system (km). Sewer components in critical condition might be those classified in classes 4 or 5 because of tightness anomalies, according to the standard EN 13508-2:2003þA1:2011. A parallel case study of 10 monitoring sites , 25-and 75-percentiles for P2 and P3 were studied, allowing the identification that 0.1-0.2 m 3 /day.manhole can already compromise systems' performance.
Still, regarding causes, direct inflow from coastal waters might be perceived through F3, regarding the emergency discharges which invert level is exposed to tidal influence and that are not equipped with a non-return valve. Mapping this context factor, as well as M c and L c , provides a very useful insight into the location and dispersion of the saline inflow causes.
Exploring saline inflow consequences, in coastal areas, sand in the sewers might be caused by direct inflows. As in (6), P4 might signal this occurrence, but given its larger scope, regarding gravel and sand removal (as this metric comes from Matos et al. 2003, therein designated as wEn14), P4 should be investigated along with F3. If information regarding only sand removal is available, a narrower scope for P4 might be used.
where: Wss: Drained weight of grated solids and sands removed from PS and WWTP (ton); L up : length of sewers upstream the WWTP (km). For parallel case studies of four utilities (Almeida et al. 2018) and eight utilities , 25-and 75-percentiles for P4 were studied, which allowed the identification that 2.5-5.0 ton/km can already compromise WWTP performance. These results were discussed with participants from the utilities for an expert-based opinion.
Pipe surcharge is evaluated by P5, as in (7) (Cardoso et al. 2006). Data used for this metric should be restricted to dryweather flow whenever stormwater contributions are expected. Naturally, a pipe surcharge can occur because of other reasons. Interpreting this metric's result should be accompanied by the evaluation of whether less satisfactory results occur simultaneously to higher tides.
where: DWF max : maximum dry-weather flow in the dry season (m 3 /day); FPF: full pipe flow (m 3 /day), given e.g. by the Gauckler-Manning-Strickler equation. It is recommended that DWF max is given by the 95-percentile of the results. In many countries, sanitary sewers are designed for approximately 50-75% full cross-section capacity (MOPTC 1995;CPHEEO 2013;Water UK 2019).
Increased risk to public health and property is denoted by P6 and P7, as in (8) and (9) (Matos et al. 2003). These indicators should assess pollution prevention, concerning the control of untreated wastewater discharges into the receiving environment and protecting people and goods from floods, understood as the flooding occurrences on public roads and properties originating from the sewer system.
Again, these occurrences might be because of other factors, so less satisfactory results should be read against, e.g., precipitation records.
where: F: number of flooding occurrences of sanitary wastewater (number); L SC : sanitary and combined systems pipe length (km). Given their impact, a result of 0 for both metrics is desired. The Portuguese regulator (Alegre et al. 2017) refers that more than 0.5-2.0 flooding occurrences per 100 km have a noteworthy impact.
The chemical attack of construction materials can be evidenced by P8, as in (10), and signalled by F4, providing the number of facilities where concrete and equipment are recurrently exposed to saline waters.
where: L SI : length of pipes with recurrent exposure to saline water and with surface degradation (km); L T : total pipe length in the system (km). The financial impact might be perceived by the results of P9 and P10, as in (11)   and (12).
where: V T : total yearly drained volume (m 3 ); V WW : estimated yearly volume of sanitary inflow, as the difference between the volumes corresponding to the 75-and the 25-percentile of the dry-weather flow in the dry season (m 3 ); €/V av : average cost (€/m 3 ); € T : total costs (€); V SI : estimated yearly volume of saline inflow (m 3 ), which can be given by (1). Reference values for Equations (10)-(12) were proposed and discussed with participants from eight utilities .
In synthesis, reference values for the performance indicators P1-P10 are given in Table 4.

Identification of improvement options
As referred, undue inflows can be addressed and controlled through organizational, operational, and structural approaches. Organizational options can include internal reorganization of roles, responsibilities, and authorities; planning to address risks and opportunities; allocation of needed resources; improving staff competencies; enhancing stakeholder engagement and awareness; and improving documented information. Operational options concern maintenance activities; data acquisition; system diagnosis and analysis; and evaluation of procedures' implementation. Structural options can include rehabilitation, replacement, or construction activities. The portfolio of options to handle saline inflows is identified in Table 5, coming from the literature review (Hyman 2005;Almeida & Cardoso 2010;ISO 2014;EPA 2015;Melchers 2020), the activities related to data collection required for the contextual information (in Table 2) and validation through expert opinion .  Validation in a case study The results of the application of the contextual factors and performance indicators to the case study are presented in Table 6. It should be noted that each contextual factor allows for a better understanding and zoning (when maps are available) of more exposed areas. Also, performance indicators should not be judged individually, as the indicators proposed complement each other, as each one provides a different point of view on the problem. Results for the case study point out that saline volumes input is quite relevant (P1 of almost 30%), posing problems regarding corrosion, WWTP operation (as the utility reported), and relevant concrete exposure to intermittent saline waters, in PS and WWTP (F4).
Other related possible consequences can be the excessive sand inflow (P4) and augmented costs. Costs associated with saline water (P10) are almost 30%, in alignment with P1 (as, for this case study, the inflow volumes to the sector under analysis coincide with those that inflow the WWTP). Compared to other excessive inflows in the system (P9), saline inflows represent more than a third of the augmented costs.
There might also be a relation to overflows (P6) and flooding events (P7), but these would have to be further analyzed to exclude possible cumulative effects with stormwater inflows, as apparently there is no pipe surcharge downstream in dry weather (P5).
The major causes can be direct inflows from the collection system, as there seem to be no generalized infiltration problems (P2 and P3) and no emergency discharges without non-return valves, of the bulk system, with exposure to saline waters (F3). A small extension of exposed critical pipes and manholes has been identified (F1 and F2). However, as those are geographically concentrated in the downtown areas, it might mean that localized groundwater saline inflows can occur.
In addition, the utility recognizes a lack of knowledge regarding emergency discharges. The collection system is managed by other utilities, resulting in the absence of such information, relevant for the present diagnosis.
Given the presented results, a set of organizational, operational, and structural actions is envisaged. The most relevant options for the case study can be: (i) articulate with local stakeholders, namely by enhancing information exchange with the utilities managing the coastal collection systems; (ii) implement field surveys for undue connection detection, to find out every emergency discharge in the tidal-influenced area and plan for its protection with non-return valves; (iii) execute CCTV or visual inspection of the critical pipes and manholes exposed to saline waters, for condition assessment, and plan the rehabilitation of those vulnerable to infiltration; (iv) analyze the reinforced concrete class (the exposure class should be compatible with tidal cyclical exposure to seawater) and equipment protection used in the facilities and plan for the protection of those vulnerable to corrosion.
The next step would be to prioritize the selected options and plan for their implementation. Priorities ought to be established based on the expected effects on system performance but also considering the resources (financial, technical, and staff), internal articulation (e.g., adjusting the scheduling to other interventions already planned by the utility or considering preparatory activities, such as information collection) and time for consolidating institutional relations with other organizations.

CONCLUSIONS
The paper presents a procedure for diagnosing undue saline inflows, namely its magnitude and, considering both the main causes and consequences, proposes contextual factors, performance indicators, and acceptance levels for the last. The aim is to identify the inflow's contribution to the system's performance, risk, and cost. From an IAM perspective, the method considers infrastructure specificities and interdependencies.
A portfolio of improvement options is given, which can be adopted depending on the assessment results, the information maturity of the organization, and its internal and external contexts.
The availability of a case study, for which previous knowledge and valuable data were accessible, allowed the application of most steps of the method. However, for those utilities with lower information maturity, determination of every context factor and performance indicator can be difficult to achieve. In such cases, an iterative procedure can be recommended: starting with the determination of the contextual factors (F1-F4); following with the determination of P1; concluding with the remaining metrics. This adaptation of the method can be scheduled with intermediate activities for information collection. A few activities identified (in Table 5), as operational options to address saline inflows, are closely related to the recommended contextual information (in Table 2).
Replicability opportunities are envisaged to apply the metrics to different functional areas (to prioritize the worst-ranked) or assess other drainage systems facing the effects of saline inflows.

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.