Anecdotal survey is usually done with in-situ water analysis to gather more data about the well; e.g., age, well depth, etc. (Photo credits: Mines and Geosciences Bureau)

A team of geologists from the Geosciences Division of the Mines and Geosciences Bureau (MGB) MIMAROPA Region has concluded its groundwater resource assessment in Puerto Princesa City.

In a statement it sent to Palawan News, the MGB in the region said the assessment is part of the 2019 implementation of the second phase of the National Groundwater Resource and Vulnerability Assessment Program (NGRVAP) of MGB which focuses on individual cities and municipalities, and aims to produce hydrogeologic/groundwater availability maps with a scale of 1:50,000.

The groundwater resource assessment was held from July 28 to August 12, it said.

It also sought to supplement the field data gathered by the MGB Central Office in Palawan in 2018 as part of the initial phase (province-wide) assessment which produced hydrogeologic maps with scale of 1:250,000.

Early part of a ground electrical resistivity survey where electrodes are nearer to each other. (Photo credits: Mines and Geosciences Bureau)

The fieldwork included well and spring inventory, and georesistivity survey covering 35 barangays, most of which are rural and are dependent on wells and springs for water source, the statement said.

Well and spring inventory was conducted in the whole city to assess the current availability of groundwater. The wells that were inventoried were mostly owned by individual households or shared by the community.

The location of the well, its age (in years), depth to groundwater (water table level, to be used to establish groundwater contour map), discharge (volume of water extractable/or flowing out per unit of time), and current water use/utilization were determined. For springs, the location, discharge (if applicable), and use/utilization (if being used) were recorded (Photo 1).

In situ analysis of water samples were carried out in conjunction with well/spring inventory. A portable water quality kit (Horiba/Hach) was used for this analysis. The physical parameters measured on site were temperature, pH, total dissolved solids (TDS), resistivity, conductivity, salinity, and dissolved oxygen (DO). The results were used to assess the quality of groundwater to determine its suitability for human consumption and other uses.

The statement said further that the second main activity for the field work is the georesistivity survey, also known as ground electrical resistivity survey (Photo 2). This survey introduces electrical currents underground and an equipment will record the electrical properties of the ground.

This can also be used to determine the presence and depth of groundwater. For this fieldwork the technique employed is Vertical Electrical Sounding (VES).

A total of 88 wells and five springs were inventoried and sampled in 31 barangays, and a total of 26 VES points were laid out in 21 barangays (Figure 1). Field data were not gathered in barangays where relevant data are already collected; ground conditions are not suitable for resistivity survey; and the barangay is efficiently serviced by local water district thus there are no available wells for inventory.

After processing all the field data, a comprehensive report on the groundwater resource assessment of Puerto Princesa City will be prepared.

This report will include discussion on the general geology, hydrogeology (groundwater occurrence, groundwater movement, recharge, discharge, storage), groundwater availability in hydrologic units, physical quality of groundwater, and results of resistivity survey (lithologic resistivity units, sounding curves and resistivity profiles). Relevant data will be used to produce a 1:50,000 hydrogeologic map which showcases the hydrogeologic units, piezometric level, and flow direction, among others.

For 2019, the MGB MIMAROPA Region also completed the conduct of groundwater resource assessment in the municipalities of Romblon and Odiongan in the province of Romblon (March), and in the municipalities of El Nido and Linapacan in Palawan (May).

The National Groundwater Resource and Vulnerability Assessment Program aims to determine groundwater availability and quality in the different rock units and geologic formations in the entire country; and establish the chemical composition of the groundwater in the groundwater basins.

Moreover, the said program seeks to establish potentials and limitations of available groundwater in various groundwater basins; and assess the groundwater vulnerability of aquifers in the country.

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