Dr. Saldivar-Sali, chairman of Geotecnica Corp. and lecturer of the University of the Philippines in a recent study revealed that the main source of drinking water from the Greater Metro Manila area is possibly being contaminated by leachates from the defunct Payatas dumpsite in Quezon City.
Saldivar-Sali, along with engineering geologist Rialyn Valdez, noted that their test conducted after the Payatas tragedy showed the "high probability of leakage" of leachates into the La Mesa reservoir, located less than half-a-kilometer north of Payatas.
The survey also noted the electrical resistivity sounding and profiling tests conducted at several strategic points near, as well as far from the dumpsite, indicated groundwater laden with the chemical by-products of leachates leaking towards La Mesa Dam and the Marikina River.
This should, therefore, be immediately investigated by direct subsurface techniques such as drilling, sampling and extensive geochemical testing," the report suggested.
"The leakage was triggered by the tragic slope failure at the mountain of trash in the Payatas last July 10," the report said.
"Leakage towards the north of the dumpsite was induced by the rise in the water table inside the dumpsite from an elevation originally lower than the La Mesa reservoir," it added.
The northward flow of leakage is further enhanced by the movement of faults between the Payatas and the dam.
Geologists noted that results of tests of water samples conducted in the early 1990s from deep wells north of Payatas dumpsite showed "abnormally elevated values of critical chemical elements related to leachates." – Marvin Sy