Recognizing the importance of accessible and potable water in everyday lives of the people, the Mines and Geosciences Bureau (MGB) Region IV (CALABARZON) conducted a Groundwater Resource Assessment in the municipalities of Santo Tomas and Malvar in the Province of Batangas on March 8 – 25, 2019 and March 28 – April 12, 2019, respectively. One of the purposes of the study was to assess the availability and vulnerability of the groundwater resources by recognizing the aquifer systems that contain these resources and its potentials and limitations. Another was to identify the different hydrogeological and formational units present in the study area. Lastly, it aimed to determine the groundwater occurrence, movement, discharge, and recharge, and analyze the existing groundwater issues and situation in the area of concern.

The groundwater resource assessment was spearheaded by the Hydrogeology and Environmental Geology Section of the Geosciences Division under MGB IV. It was supervised by Perlito A. Angeles, Supervising Geologist, and assisted by geologists Alen Clyde A. Canlas and Kate Ashley A. Torrefranca.

A systematic collection of geologic, hydrologic, and meteorological information covering the municipalities of Santo Tomas and Malvar was performed, wherein the primary data collection method used was through well inventory. Global Positioning System (GPS) devices were used to determine the location of the wells. Hanna HI-9813-6 instrument was used to check the water quality parameters including pH, EC, TDS and temperature upon sampling.

Well inventory and geologic study of Santo Tomas and Malvar show that the main source of groundwater in the area belongs to the thick and extensive confined aquifer on the underlying Taal Tuff. Since groundwater was utilized as the main source for municipal water use, the aquifer in which groundwater was contained was considered to be highly productive and sufficient for the present-day situation.

The wide, open, and vegetated spaces scattered around both municipalities as well as the elevated areas such as Mt. Makiling and Mt. Malepunyo for Santo Tomas, and the Northern Lipa Plateau for Malvar, were considered to be the main recharge zones. Rainfall was identified to be the main source of groundwater recharge in both municipalities. Groundwater from elevated areas of both municipalities generally moved to lower elevations where it eventually drained to Laguna de Bay and Taal Lake. Since some portions of both municipalities are starting to be developed, a decrease in the amount of rainwater that percolates into the soil is expected which could significantly affect the recharge of the aquifer that the wells of both municipalities tap on. Eventually, the groundwater extraction rate for both municipalities would surpass the recharge rate of the aquifer they tap on, which means that it will not be enough to meet the demand and could lead to groundwater mining.

It was concluded that the water districts, barangays, businesses, resorts, and private owners tap the groundwater through shallow and deep wells existing in both municipalities. Currently, the amount of groundwater is enough to supply the demand. However, measures should be made by the Local Government Units (LGU) of both municipalities to ensure that the groundwater extraction continues to be sustainable.

It was recommended that the construction of wells for future developments be regulated by the LGUs to prevent possible over extraction of groundwater that could severely affect its availability. However, unless other sources of water are found, both municipalities are expected to continue relying on groundwater extraction use which could become unsustainable in the long run.

Perlito A. Angeles, Supervising Geologist, along with Alen Clyde A. Canlas and Kate Ashley A. Torrefranca, Geologists, conducting a portion of georesistivity survey on Barangay San Fernando, Municipality of Malvar, Province of Batangas

A pitcher well in Barangay San Isidro Sur being utilized by a private residence as a source of domestic water.

Conduct of georesistivity survey on Barangay San Fernando, Municipality of Santo Tomas, Province of Batangas

by: Alen Clyde A. Canlas               |         21 June 2019