Multi-criteria evaluation of suitable locations for temporary disaster waste storage sites: the case of Cavite, Philippines

The Disaster Waste Management Guidelines published by UNEP/OCHA provides detailed guidelines that are currently being adopted by different countries. This characterizes hazards and wastes generated by different disasters. The framework for disaster waste management which covers four phases of preparing and responding to disasters is discussed. This provides the tools necessary for disaster waste management including waste needs assessment, waste hazard ranking tool, and waste-handling matrix. It gives detailed general and operational considerations in developing temporary disposal sites, as well as a sample layout for a TSS and the environmental, safety, and logistical guidelines.

Based on the framework of disaster waste management, the establishment of TSS is under the early recovery phase, as well as the collection and transportation of wastes and debris to storage and disposal sites. The second phase also covers the preparation of practical advice and guidance for local authorities on tentative solutions for the minimization of negative environmental and health impacts of disaster wastes.

Since TSS is only for “temporary”, UNEP/OCHA also provides the guidelines for the closure of TSS and restoration of the site to its original condition. According to UNEP/OCHA, a temporary storage site should be used for short periods of time, with an average from zero to 12 months.

Temporary storage site (TSS) was introduced and defined by Takai and Otsuka (2021) in their conference presentation as an area where disaster wastes are stored and separated before they are treated or disposed of [9]. A basic flow or transport scheme of DW treatment begins from collection in damaged areas and transportation to rough and advanced separations in the first and second TSS, respectively, to treatment, utilization, or landfill. Segregation of disaster wastes would help in reducing the disposed wastes.

According to the presentation by Tajima in 2021, the functions and designs of TSS may vary among countries, but the involvement of roles of the government in the operations is presented in the context of TSS in Japan [8]. The need to properly prepare TSS is discussed, wherein the consequences of opening a TSS without proper preparation, such as an opening in unsuitable land and opening before sufficient staff and equipment are readied, were emphasized. A summary of the criteria for the conditions of TSS was provided, including the reasons behind each criterion. These are necessary to be able to identify potential areas for TSS. Moreover, the components that must be prepared, including TSS layout plan, procedures, and resources, were also mentioned. The presentation also included the equation to estimate the total TSS area under three assumptions: (1) DW collection is done in some specific time frame, (2) DW are carried into and out of TSS in parallel, and (3) DW are transported from TSS to disposal sites since the TSS is opened. This equation was adopted in this study to analyze the site capacity (Eq. 1).

The study by Osorio and Tandoc (2016) contains quantitative and qualitative data on disaster waste management in seven cities in the National Capital Region—Malabon, Manila, Marikina, Navotas, Pasig, Quezon City, and Taguig [7]. Responses of each city to disaster waste generation were assessed through site visits and ocular inspections, as well as coordination with stakeholders. Shown in their paper are the recorded amounts of wastes generated due to specific typhoons in each city, and the locations of temporary storage sites. Based on the study, not all of the cities studied have established TSS, directing disaster wastes to landfills without proper segregation and treatment. Some of the cities also did not have proper documentation of their disaster-related operations. It was recommended that a disaster waste management plan should be established with the help of useful tools such as a waste map, waste hazard ranking tool, and waste handling matrix.

Barriga assessed the disaster waste management practices as a response to the generation of disaster wastes caused by the typhoons that hit the Bicol region [10]. The assessment was based on international guidelines as there were no management plans and practices that had been established in the Philippines for the provinces to use. Data were analyzed quantitatively, along with waste characterization, identification and mapping of disposal sites and waste facilities, and documentation and assessment of the entire disaster waste management in the region. The assessment was done according to the four phases—(1) Emergency Phase, (2) Early Recovery Phase, (3) Recovery Phase, and (4) Contingency Planning—of response to and preparedness for disaster waste management. It was observed that many of the DWM guidelines have been practiced in the study area. It was shown that the cities and municipality studied (Legazpi, Naga, and Sto. Domingo) had specific guidelines for temporary disposal sites and transportation of wastes to the sites, but these sites were not outside the materials recovery facilities (MRF), and waste maps were not generated. Essentially, MRFs are solid waste management facilities where recyclables are sorted and recovered. Generally, it was stated that Bicol Region is ahead in terms of disaster waste management in the country, but there is still a need to fill in the gaps identified, including the need to establish further guidelines on contingency planning.

According to a 2015 study on how disaster wastes caused by Typhoon Yolanda were managed in Tacloban, Leyte, there were no proper documentations and records on the wastes generated; hence, data were based on news reports, satellite imagery, interviews three months after the disaster, and ocular inspection in the disposal site [11]. The paper provided the timeline of the responses of the authorities to the damages due to the typhoon. It was stated that three temporary dumpsites were set up to aid in the clean-up operation to hasten the immediate relief operations for the survivors. It was also noted that there was no processing of waste materials implemented on the entire island and that the wastes to be recycled had to be transported to neighboring areas or even to Manila. In general, the study states that due to a lack of disaster waste management plan, (1) the clean-up operation after Typhoon Yolanda did not start immediately; (2) there was no proper waste segregation and recycling done; and (3) waste management practices were not documented. The siting of TSS prior to the occurrence of disasters could help address these problems.

The required TSS area for each city/municipality, based on the collected data on amounts of disaster waste generated, were calculated to ensure that the TSS candidates to be selected are able to accommodate the disaster wastes, the required area for TSS is calculated using the Eq. (1) [4, 8],under the assumptions that:

Tajima [8] presented the acceptable values of variables for the estimation of total TSS area such as the apparent specific gravity which are 0.4 \(t/{m}^{3}\) and 1.1 \(t/{m}^{3}\) for combustibles and incombustibles, respectively. The maximum height for a disaster waste pile is 5 m and the working space area ratio is from 0.8 to 1. Increasing the working space area ratio and reducing the maximum allowable height of the waste pile would maximize the calculated required area, thus the values of 1 for the working space area ratio and 1 m for the height of the disaster waste pile were used in the calculations.

Temporary storage sites must be located at certain distances from surface waters to prevent secondary hazards from occurring in bodies of water. According to Cheng and Thompson, whose study area was the state of Victoria in Australia, the buffer zones for surface waters vary from case to case, with most past studies on landfill siting setting 500 m as a buffer distance from rivers [12]. Based on the Amended Guidelines on the Provision of Buffer Zone around Waste Processing and Waste Disposal Facilities, the minimum siting distance from rivers for identifying suitable land for sanitary landfill sites is 100 m, while a 200-m buffer zone is recommended for lakes, ponds, and other water bodies [18].

Since the areas of interest in this study are municipalities and a city that are relatively smaller than a state in terms of land area, and the locations being sited are for temporary storage sites and not a landfill, the minimum buffer zones were used—100 m for rivers, and 200 m for fishponds and coastline. Two separate shapefiles which are contiguous were available for rivers in the selected study sites and were labeled “River 1” and “River 2” for easier identification.

Similarly, TSS should be located away from built-up areas that include residential zones, schools, infrastructures, and buildings that could be affected by site operations. Since the study sites have large built-up areas occupying the total land area, especially Cavite City, the minimum value was considered. According to the Materials Recovery Facility (MRF) Tool Kit of the Asian Development Bank, a minimum buffer zone of 100 m is used for the areas mentioned above for MRFs [19], which also serve as TSS in the Philippines.

Upon checking the available shapefiles for the study sites, it was observed that there were school points that were located outside the built-up area. Hence, analysis for school points was performed separately.

Accessibility is important to reduce the cost of transportation of disaster wastes to temporary storage sites. The study sites have a high density of housing and high accessibility to roads; hence the locations of temporary storage sites were set to be within 100 m from the road network based on the options mentioned by Cheng and Thompson [12], wherein 500 m was used as inclusion zone since their study site was located in a rural area with less road accessibility.

TSS should not be located in specific types of land uses that are productive and critical. UNEP/OCHA specifically mentioned that TSS must not be located in floodplains or wetlands and agricultural land. Basing on the available data on land use, only grassland and open/barren areas were considered as suitable options, while annual crop, brush/shrubs, built-up, fishpond, inland water, mangrove forest, and perennial crop were avoided. However, potential locations that were generated were still inspected via Google Earth to confirm that the selected sites were not productive or critical.

Since the land use/land cover map also contains fishpond and built-up areas, there was an overlap between the land use/land cover map and two other criteria—C.A-2 Distance from fishponds and C.A-4 Distance from built-up in the generated map. This was addressed by specifying the relaxed criterion/a or the criterion/a in which each selected site failed.

To reduce excavation costs and avoid problems of slope stability, MRFs should be located in relatively flat or gently sloping land [19]. The slope requirement was set to no more than 10% in the study of Cheng and Thompson [12]. However, in the slope map available in the study sites, slopes of land were classified as 0 to 8% (level to undulating), followed by 8 to 18% (undulating to rolling), and so on. In this study, the constraint for the criterion on the slope was set to 0 to 8%.

The Philippines Municipal Boundaries shapefile was first clipped into the areas of interest to be used as a guide in the analysis. This would ensure that only the selected sites were being analyzed. The ModelBuilder tool in ArcGIS Pro was used to analyze the criteria through the development of a TSS siting model shown in Fig. 2. The model was adopted from the flowchart created by Cheng and Thompson [12]. Sequences of geoprocessing tools were built and managed, where the output of one tool was fed as the input of another tool. The first geoprocessing tool used was the Euclidean Distance where buffer distances were the inputs for C-A.1 to C-A.5. After obtaining the buffer zones, the layers were standardized using Boolean Algebra with the assigned values—suitable (1) and unsuitable (0). The criteria maps were overlaid, and the sum of values was obtained. A land suitability map was then generated based on the results of the weighted sum.

Based on the values in the map, the most suitable areas were examined using satellite imagery and street view. Potential TSS candidates were located considering that the study areas have large built-up areas, and the municipalities of Noveleta and Kawit have large agricultural lands. The presence of obstructions was also examined. TSS sizes were then estimated and compared with the calculated required total TSS areas. However, in general, since only Google Earth Pro was used to analyze C-B.2 and C-B.3, the obtained information could have differences from the actual sizes and conditions.

A summary table was created to show the information on the selected TSS candidates including the value, coordinates, area, absence of obstructions, land ownership, and failed criteria if there were any. The existing MRFs in the study sites serving as TSS were also evaluated using the same set of criteria.

The generated suitability map was investigated in Google Earth Pro. The layer for locations of MRFs of Cavite City and Noveleta was overlaid on the suitability map to determine the number of points that correspond to their values. The reclassification maps were used to identify in which criterion/a the MRFs did fail. Then, using the satellite imagery and street view of Google Earth Pro, the presence of obstructions was inspected. The MRF sizes provided by PG-ENRO were then compared to the calculated required areas of TSS in the respective city/municipality.

According to Cavite City CENRO (personal communication, September 28, 2021), their available data on disaster waste estimation is the recorded average amount of disaster wastes in the year 2019 amounting to 20.22 tonnes. They stated that the disaster wastes generated in the city are temporarily stored in their MRF located at Barangay 48A, San Antonio, Cavite City.

In addition, it was shared that the city does not perform segregation of disaster wastes since they consider the disaster wastes as residual wastes. After holding the wastes, they are disposed of at the landfill. The landfill that serves Cavite City is the Rizal Provincial Sanitary Landfill operated by International Solid Waste Integrated Management Specialist, Inc. (ISWIMS) located in Rodriguez, Rizal [23]. Based on the estimation through satellite imagery, it would take more than two (2) hours to travel the shortest distance of 68.3 km from the city, specifically from the MRF, to the landfill. Since it could take that much amount of time, the temporary storage of disaster wastes is necessary to accommodate the volumes prior to transportation.

The Noveleta MENRO (personal communication, August 19, 2021) provided the amounts of disaster waste generated by Typhoon Fabian in July 2021, as well as how these were managed, as summarized in Table 4. It can be observed that the disaster wastes are classified according to type, and are handled depending on their classification. From this documentation provided by Noveleta MENRO, the disaster wastes were not directly disposed of as their uses were maximized. The involvement of the residents in disaster waste management was also observed.

On disaster response, Noveleta MENRO primarily performs the environmental impact assessment after a calamity. It cooperates with the municipality’s Local Disaster Risk Reduction and Management Office (LDRRMO) for the evacuation of the residents, and the Office of the Mayor and the Municipal Engineering Office for the assessment and evaluation of the damaged houses, businesses, and infrastructures. Among the agencies involved in disaster response are the Municipal Social Welfare and Development Office (MSWDO), Philippine Coast Guard (PCG), Philippine National Police (PNP), Bureau of Fire Protection (BFP), and other civil society organizations (CSO) volunteers.

All the wastes hauled or collected during times of flooding are temporarily stored at the transfer station located at their municipal MRF which is situated at Poblacion, Noveleta. The final disposal site is at Navotas Sanitary Landfill operated by Phil. Ecology Systems Inc. located in Navotas in Metro Manila. It would take around two (2) hours to travel the shortest distance of 42.4 km from the Noveleta MRF to the said landfill.

For the municipality of Kawit, Kawit MENRO (personal communication, September 16, 2021) stated that they do not have any available data regarding disaster waste management. Disaster wastes hauled are mixed with household wastes. They only record the amount of daily collected wastes using garbage trucks, and not specifically the disaster wastes. The MRF of the municipality is located at Brgy. Aplaya, Binakayan, Kawit. The solid waste disposal site of Kawit is the Suri Waste Management Landfill operated by Suri Waste Management and Disposal Services in Calamba City, Laguna which is more than one (1) hour of travel from the municipality [15].

From the collected data on disaster waste management of the three study sites, it was observed that there are big differences in how each city and municipality recognizes the need to manage disaster wastes and in how they handle them. Another factor that might have led to the differences in DWM practices is the lack of national guidelines on how to properly manage disaster wastes. Generally, it was observed that there is a lack of attention and action with regard to disaster wastes, and the study sites do not have temporary storage sites specifically for disaster wastes. Moreover, disaster waste management in the city/municipality is also affected by the implementation of the city/municipal solid waste management, as the two are connected, and they could have similarities in handling procedures (e.g. segregation and storage).

To set the constraint for C-B.3. Size, the required total area for each study site was calculated using Eq. (1). A sample calculation is shown below. The calculated values are summarized in Table 5.

Required TSS area for Cavite City:

Table 5 shows that in the calculation of the required TSS area for Cavite City, it was assumed that the total wastes were combustibles since there were no specified amounts for different classifications of wastes. This was done to obtain a larger value of the required area since combustibles have lower apparent specific gravity. Meanwhile, two amounts were considered for Noveleta to account for the different apparent specific gravities of different types of wastes: biodegradable for combustibles, and non-biodegradable for incombustibles. This was based on the descriptions of types of waste displayed in the table. For Kawit, since there was no available data on the amounts of generated disaster wastes, the TSS candidates selected in the municipality were exempted from C.B.3 Size.

In comparison with the rule from Tajima’s presentation which requires TSS area to be more than 3000 m² to accommodate machineries, the calculated areas for the study sites were significantly smaller [8]. While the value presented by Tajima was based on the experiences in Japan, the Philippines does not have established guidelines on the required TSS size. Despite the big difference, the calculated areas were still considered due to existing local situations. Based on the list of Material Recovery Facilities provided by PG-ENRO, the sizes of MRFs in the province have large differences, varying from 68 to 47,000 m². The calculated required TSS areas are within the range but are relatively smaller compared to most of the existing MRFs. It is important to note that the input data on the amounts of disaster wastes generated depend on their availability in LGUs. Hence, these data do not equate to the maximum amount of disaster wastes generated as there could be deficiencies in documentation of the effects of typhoons and flooding. Moreover, the selected study sites have large built-up areas, being mostly occupied by residential, agricultural, and aquacultural zones which makes it unworkable to identify potential locations of size greater than 3000 m². Lastly, the presence of heavy machinery was not assumed to occupy spaces inside the TSS.

The features were assigned to each criterion as shown in Table 2. There were multiple features placed under C-A.1 and C-A.4 since they were unable to be merged due to differences in geometry types. For C-A.4, upon looking at the shapefiles, it was observed that there were schools that were not included in the built-up areas, hence it was analyzed separately. In calculating the sum of the weights of the criteria, C-B.4 was not taken into account since the criterion is not strict to only public land ownership despite it being a priority.

Table 6 specifies the reclassification values for each criterion considered, and the suitable and unsuitable regions were defined. Since there were nine (9) layers, 9 out of 11 points from Table 2 were obtained in ArcGIS Pro.

Figure 3 displays the reclassification map of each criterion analyzed in ArcGIS Pro. The areas with a value of 1 are the suitable areas according to the constraints set while the value of 0 indicates unsuitable land. As seen in the figure, C-A.6 Land Use is the most sensitive criterion since most of the land is not suitable under it. Included in the sensitive criteria are C-A.2, C-A.4, and C-A.5.

Because of the location of the study sites relative to Manila Bay, it can be observed from the figure that the entire study area is largely bounded by coastline and that there are rivers within the study area connecting to Manila Bay. The geographic location of the province allows agriculture and fishing to become the leading industries in its local economy, hence the large areas for fishponds located near the coastline, and agricultural land making up the production area. This can also be observed in the reclassification map for land cover which is mostly made up of production and built-up zones.

Observing the reclassification map for the built-up area, it can be seen that comparing the suitable and unsuitable lands in each city/municipality, Cavite City has relatively larger unsuitable lands because of its urbanization and greater infrastructure. Meanwhile, since the study sites are located in coastal plains, the slope of the land is not much of an issue among the criteria.

Shown in Fig. 4 is the resulting suitability map after overlaying all the layers and getting the weighted sum. The higher the value of the area, the more suitable it is. As observed in the figure, only small portions of land reached the maximum value, or satisfied all the criteria, due to the sensitive criteria. Hence, for the selection of TSS candidates, relaxation of criteria was allowed to be able to identify candidates in each city/municipality.

Overlaying the generated suitability map in Google Earth Pro, TSS candidates were located in areas with values of 7 to 9. The Street View was used to verify the reliability of the values obtained from ArcGIS Pro. Then, the sites were inspected using Google Earth Pro in terms of C-B.2 Distance from obstructions and C-B.3 Size. The final candidates are shown in the appendix table. The codes used to refer to each TSS are as follows: CC for Cavite City, N for Noveleta, and K for Kawit. The table also shows the land ownership classification of each TSS location.

It can be observed from the table that the criteria permitted to relax were the distance from built-up areas and the land use, also due to built-up zones in the land cover of the sites. Observing the selected TSS candidates, it is noticeable that the identified TSS in Cavite City are all open lots located in built-up areas, adjacent to residential and/or commercial structures. For Noveleta, the TSS candidates are also located near built-up areas, but the majority are in grasslands. Finally, for Kawit, vacant lots in built-up areas and grasslands were the typical location of selected TSS candidates.

The plot of the candidates on the suitability map is also shown in Fig. 4, along with the satellite images of some of the TSS candidates. Based on the suitability map, other areas may be considered in the selection and inspection of TSS candidates. A total of 18 TSS candidates were identified. Seven (7), six (6), and five (5) TSS candidates were selected for Noveleta, Cavite City, and Kawit, respectively.

Figure 4 also displays the location of the MRFs of Cavite City and Noveleta over the suitability map.

From the analyses, it can be observed that CC-MRF failed the criteria on distances from built-up areas and coastline, and land use, while N-MRF failed in distance from built-up areas, land use, and size. Both comply with eight (8) out of 11 criteria points. It is important to note that upon locating the said MRFs, it was discovered that they were located within the proximity of cemeteries, which were included in the built-up areas as observed in the gathered shapefiles, and they were not necessarily very close to the residential areas. However, during the inspection of the areas using Street View in Google Earth Pro, it was observed that there were people residing in informal houses inside the cemetery, specifically in Cavite City. Still, it should be noted that this situation may not be exactly the same in actual conditions and current time.