GEOLOGY AND GROUNDWATER RESOURCES OF SOUTHERN LAGUNA DE BAY BASIN, LUZON, PHILIPPINES

MARIO P. SANDOVA
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ABSTRACT



Alluvial deposits, pryoclastic and volcanic rocks of Quaternary age cover the southern Laguna de Bay basin in roughly concentric fashion reckoned from the different volcanic centers in the region. Movements along the Dipa and Marikina faults which flank the eastern and western shores of the lake resulted in the final geomorphic development of the lake and likewise greatly affected the movement of ground water.

Considerable ground water is available in the alluvial deposits around Laguna de Bay and in the slightly reworked portion of the pyroclastic rocks in the vicinity of Canlubang. The finer pyroclastic rocks with few interlayers of sandy materials, supply the domestic water requirements of some towns at the foothills of Mts. Makiling and Banahao. Coarse pyroclastic rocks at depths exceeding 200 feet, supply little ground water. The volcanic rocks serve mostly as recharge points rather than as water-bearing formations.

Estimates of the coefficient of transmissivity, ranges from about 5,000 gallons per day per foot in the pyroclastic rocks and up to 75,000 gallons per day per foot in alluvial materials and reworked pyroclastic rocks. While slight decline in water level is apparent in some wells, the region as a whole has not experienced any dewatering of aquifers.

Springs provide additional sources of water. They are mostly springs flowing out along faults and (or) fractures in volcanic rocks, or water table springs. Except for a high content of iron, ground water is essentially suitable for domestic use. No deterioration of quality due to excessive withdrawal of ground water has been observed.

 

 

 

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