“The groundwater in Barangay San Antonio, Basey, Samar will remain non-potable for the next 5 to 10 years.” This was Dr. Bayani Cardenas’ initial conclusion on a study he conducted in the area, as mentioned in his lecture at the National Institute for Geological Sciences last June 18.
Communities in the Philippines like Barangay San Antonio have the least access to piped clean drinking water. According to local officials, around 20 million Filipinos still rely on their own means for their water supply, including pumps for extraction of groundwater, a method that poses several problems to sanitation and structural safety. The World Health Organization states that unclean drinking water, combined with poor sanitation, is the second biggest killer of children, and that one in nine people around the world still lack access to safe water. This problem was aggravated by the onslaught of Typhoon Yolanda (international name: Haiyan), which brought storm surges that contaminated the groundwater in several communities, particularly in Eastern Visayas. These huge waves caused saltwater to seep into aquifers, some of which were the water supply of certain rural communities in Samar and adjacent provinces.
“A drop of salt water in a glass of drinking water can make it non-potable,” said Dr. Cardenas. He added that according to studies, humans can only drink water with at most 1.5-2% salt concentration in water. More than 2% salt concentration will make the water undrinkable.
During their research conducted in January 2014, merely two months after Typhoon Yolanda struck, Dr. Cardenas and his team of geologists and other scientists established a Flood Height Mapping Team, sampled groundwater from about 300 wells in the vicinity, and constructed their own wells. Their findings showed that after the flood subsided, groundwater in the area was contaminated with saltwater.
Dr. Cardenas and his team identified two kinds of aquifers in the area: the surficial aquifer and the deeper aquifer. The surficial aquifer is a shallow aquifer usually made up of beach sand about 10-15 feet deep. While the deeper aquifer, where groundwater is extracted, lies below the surficial aquifer.
Using the Electrical Resistivity Tomography, Dr. Cardenas and his team were able to develop a model illustrating how seawater infiltrates groundwater. The model explains that seawater moves through the water table like fingers slowly seeping through each layer. According to the model, it would take 5-10 years in order for seawater to be taken in and flushed out. However, the model holds true only to the surficial aquifer.
As with the case of deeper aquifers, the team found out that water pumps (colloquially bomba or poso) acted as injectors—taking the saltwater brought by the storm surge directly into the deeper aquifers, contaminating the groundwater.
The team returned 6 months after their first visit and found that the groundwater had become drinkable. This was due to the natural dilution of the groundwater within the deeper aquifer. Although the salinity level has been greatly reduced, there is still the issue of bacterial contamination within the groundwater in San Antonio.
“Since growing coastal populations will continue to rely on groundwater for their needs, strategies for reducing vulnerability to intense storm surge-caused groundwater contamination and mitigating its effects are needed,” researchers stated in the study.
With the extent of damage found in Barangay San Antonio, Dr. Cardenas reiterates that Typhoon Yolanda was one of the worst typhoons in history. However, this was not the first, nor the last—there have been at least 2 cases of typhoons as strong as Yolanda recorded in 1897, with storm surge heights of at least 7 meters. Dr. Cardenas concludes that ferocious typhoons like Yolanda, though rare events, will certainly happen in the future.
With super typhoons being a repeatable and possible occurrence, Filipinos ought to be more prepared in reducing vulnerability and preventing similar damages. The NOAH Lecture Series aims to enhance and enrich local knowledge on storm surges and other natural hazard events that have remarkable impact on the lives of many Filipinos. Project NOAH, a risk reduction tool for vulnerable communities, provides necessary weather information through the NOAH website and its mobile applications. The Project NOAH website makes use of weather tools, sensors, and hazard and risk assessment tools to provide near real-time weather data and hazard information—tools that are helpful in proper disaster preparation and long-term disaster planning and mitigation.