Standardized Groundwater Resource Assessment on a regional scale (1:250,000 provincial scale) and on a medium scale (1:50,000 scale municipal level) that started in 2011 was completed in 2018. This project was aimed at determining groundwater availability in all types of lithological units found in the Bicol Region. With the completion of the Groundwater Availability Maps, vulnerability of groundwater resources stored in the different lithological units has to be assessed as well.
Groundwater vulnerability assessment aims to define the different vulnerabilities of certain aquifers to potential contamination or pollution. Vulnerability assessment is done on the premise that aquifers do not have the same hydrogeological characteristics and that; certain terrains are more vulnerable than others. Thus, with this project, areas that are more vulnerable in terms of groundwater contamination could be delineated. This would help the policy makers and decision makers in the local government units to formulate groundwater protection strategies for a sustainable use of groundwater resources.
In addition, Rule 19.4 of Chapter 3, Section 19 of the Republic Act No. 9275 or the Philippine Clean Water Act of 2004 provides that, the Department of the Environment and Natural Resources (DENR), through the Mines and Geosciences Bureau (MGB), in coordination with the National Water Resources Board (NWRB), shall publish a national baseline groundwater vulnerability map that will reflect the different degrees of groundwater vulnerability to serve as guide in the protection of groundwater from contamination. The MGB shall likewise publish a standard guide/methodology to groundwater vulnerability mapping and ranking of relative vulnerability of groundwater to contamination together with the maps.
With these in mind, the Mines and Geosciences Bureau launched the project Groundwater Vulnerability Assessment in 2019. Project implementation in the Bicol Region took off with the assessment of the vulnerabilities of groundwater resources in the City of Masbate and the Municipalities of Milagros, Mobo, Uson and Cawayan, all the Province of Masbate. The assessment made use of the DRASTIC model, which is an index overlay method. This index overlay method is based on assembling information on the most relevant characteristics affecting aquifer vulnerability. DRASTIC uses a set of seven (7) hydrogeological key parameters to classify the vulnerability to contamination of an aquifer: Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity of the aquifer. DRASTIC yields a numerical index map of groundwater vulnerability that is derived from ratings and weights assigned to the seven map parameters. The rating scales are values that range from 1 to 10 and weights from 1 to 5. The DRASTIC vulnerability index (DVI) is calculated by linear addition of the weights.
This year, the Municipalities of Balud, Mandaon, Aroroy and Baleno have been targeted for assessment. Municipalities in Masbate have been prioritized since the province has the most problem in terms of groundwater resources.