Applying Nuclear Techniques in the Attenuation of Flood and Natural Disaster-Borne Contamination
The Philippine Nuclear Research Institute of the Department of Science and Technology with support from the International Atomic Energy Agency, and the Food and Agriculture Organization of the United Nations (FAO). helped assess the changes in circulation, dynamics and quality of groundwater in Tacloban City and helped to evaluate and monitor the natural attenuation of the pollution brought about by Typhoon Haian/Yolanda. Thiry two (32) monitoring stations for groundwater were setup and used for both conventional and nuclear techniques in the characterization of the water. It was found that in the city’s groundwater, sodium chloride, and nitrate were below the Philippine Standards for Drinking Water (PNSDW 2017 version) – thus, seawater did not enter the aquifer and the biological/biomass contamination are being naturally decontaminated. These potential contaminants probably decayed before they could get to the groundwater. It was also found that the isotopic composition of the water in the aquifer is close to that of today’s rainwater – which meant that the city’s water supply was not in danger of disappearing. However, the wells in the relocation site of more than 2000 people were unfit for drinking, with spikes of arsenic and other pollutants. A database for these hydrological data is now available.
Mr Wilfren Clutario, a PNRI collaborator from Tacloban was also able to conduct a study using Asian Green Mussels (Perna viridis) used as bioindicators of pollution using stable carbon and nitrogen isotope ratios in the coastal ecosystems of Tacloban City
During the fieldwork in 2018, 21 locations were visited, primarily new settlements and Mactan Rock pumping stations. The sampling was conducted following three major objectives:
1. Water quality at Mactan Rock pumping stations to evaluate potential changes in comparison to 2015 (P07 and P08C); additional sampling points at the recharge area (N9C), and the Mactan Rock surface water intake (P12C)
2. Drainage water intake from shallow groundwater in creek beds: P15C, P27C, P3C (potential sites), N62 (under construction), P1C, P2C (small drainage intake at St Helena)
3. Baseline data for shallow water at the new settlements: N2A, N3A (Sofia), N1, P4C, P16C, P16C, P14C, P17C, N27, N4, N5, N6, P5C (sea water)
Groundwater in Tacloban is extracted for drinking in only one location. Mactan Rock, a private company operates two pumping stations (P08 and P09) at this location. This water is used to supply a number of new settlements by trucks that deliver water to local cisterns in the villages. Therefore, these two pumping stations are a valuable resource and are very important locally. The parameters of the water collected from the pumping stations in 2015 are not a subject of direct concern. However, the preliminary sampling from 2015 reveals potentially worrisome indicators. Water at P08 and P09 has a minor addition of saline water , which potentially could be associated with intrusion of saline water from the deeper aquifer. Further study and monitoring of the pumping stations are suggested. If the values and parameters observed in 2015 remain constant, these could be the usual characteristics of water at this location. However, if the parameters show changes over time that suggest an increase in salinity, this could potentially be associated with an intrusion of saline water, that can be potentially very serious problem for future exploration of this used aquifer. A saline water intrusion could possibly be triggered by over-pumping, and if this is the case, then limits on extracted water volumes would need to be considered. If the use of groundwater is contemplated in the future, water recharge zone protection needs to be considered, especially at the Mactan Rock pumping stations (P07 and P08) and upstream sections of the drainage water intakes at N62 (under construction) and P2C (a small drainage intake at St Helena)
The direct influence of flooding associated with Typhoon Yolanda on groundwater quality is rather a minor issue with a limited impact and extent. The potentially impacted areas are located in the center of Tacloban, which does not have a central sewage system. Therefore, groundwater quality at these locations, even prior to the typhoon, was likely low. Groundwater in Tacloban is not used for drinking, and the city is supplied by the water supply network run by a water company (Leyte Metropolitan Water District, LMWD) using a surface water reservoir located 20 km from Tacloban. This reservoir was not impacted by the typhoon. More important are indirect impacts of the typhoon on: (i) city cleanup required quick extension of a dump site at Santo Niño without proper isolation; and (ii) destruction of many houses in low income area required construction of the new settlements/villages for people relocated from Tacloban. These villages are located in the areas where the local water supply was not secured and water is delivered by trucks.
Shallow groundwater from the first level (usually <3–10m) in the Tacloban area and in the new settlements is primarily used for washing and other sanitary purposes. The local users are fully aware that the local shallow groundwater is not potable. The major concern is contamination by wastewater from leaking septic tanks and from direct discharge from households that do not have septic tanks. In some locations, elevated heavy metal concentrations have been observed. Since groundwater is not used for drinking, its low quality is a secondary issue. In the new settlements, the major problem is a lack of a constant water supply, potential sanitation problems of the water tanks used, and a need to rely on bottled water.
Not only fresh water resources were investigated; the marine environment was also covered by the study. Increased levels of nutrients in these aquatic environments cause eutrophication of coastal waters. For the purpose of monitoring coastal waters, classical or traditional approaches were used in conjunction with isotope techniques to obtain an idea about the current status or condition of that particular area. Employing stable isotope techniques as an additional monitoring method expounded environmental data by giving possible pollution sources, which may be used for pollution source management.
By using sessile, hardy invertebrates such as primary consumers represented by mussels, it became possible to spatially assess the extent of anthropological impact for selected coastal marine area. The study provided initial baseline data for the reconstruction of food webs in the coastal marine ecosystems of Tacloban City. Terrestrial inputs in the pollutant source apportionment of selected areas were proven by the study. Asian Green Mussels (Perna viridis) were used as bioindicators of pollution using stable carbon and nitrogen isotope ratios in the coastal ecosystems of Tacloban City. The investigation also measured the nutrient loading of the different sites in terms of: NO3−, NO2−, NH4+, Dissolved Inorganic Nitrogen (DIN); drew correlations between the measured isotope ratio values with the measured nutrient loading; and determined the spatial variability of the bivalve isotope ratios, and mapped the extents of terrestrial and typhoon borne contamination in the area with the infromation obtained from the bivalves.
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