A geological hazard assessment was conducted by Mr. Fidel V. Zepeda, Senior Geologist of the Geosciences Division at Barangay Mayapa, Calamba City, Laguna last May 8-9, 2014. The said area is the proposed site for DENR and DPWH Regional Office Building. The main objective is to identify and mitigate the probable effects of the existing geological hazards to avoid and/or to minimize their effects on the project.
A view of the proposed site of the DENR and DPWH Regional Office building project looking southwest from the northeast (near the SLEX). The project site has relatively flat topography and sparsely vegetated by few trees by few steps and common grasses
The observation showed that there is no natural drainage system in the area to control the surface water. However, the area is not prone to flooding due to its relatively high elevation. There are no fault lines found within and in the vicinity of the proposed site. Though, according to the unpublished geological map of MGB and the structural map of PHIVOLCS, a trace of a fragment of West Valley Fault is about 10.6 aerial kilometers west-southwest of the project. The West Valley Fault might be an earthquake generator which could cause high to low level ground shaking. As observed, the area is prone to ash fall in the event of eruption of Taal Volcano, which is 26.5 aerial kilometers southwest of the project site. The unpublished geological map of MGB indicated that the base rock of the project site is Taal Tuff.
MGB IV-A proposed the installation of artificial canals directed to the Mayapa River given that the area has no natural drainage system. Since the aerial distance of the project site from the West Valley Fault is 10.6 kilometers, the Bureau advised that the project should have mitigation measures considering the possibility of high to low level of ground shaking that may occur in the area. It also recommended that the design of the roof of the building structure must be competent to carry heavy ash fall in case of Taal Volcano eruption. In as much as the proposed project involves construction of heavy building structure, a geotechnical study must be conducted to determine the appropriate depth of the building’s foundation.