Benguet Corp., the oldest mining company, denied that its old mining structures caused the ground to sink in Barangay Virac, Itogon, Benguet province.
“The stand of the company is clear. The existence of its old mining structures did not cause, nor was it contributory to the occurrence of the ground subsidence. Rather, the subsidence was the natural effect of the weakening of the ground due to combination of factors,” Benguet said in a statement.
Part of the ground in Barangay Virac, Itogon town on Oct. 22 sank following the onslaught of typhoon Lando, which swept past northern Luzon.
The sinkhole swallowed six houses and caused the evacuation of about 170 families residing in the area.
Initial speculations in the community pointed to the collapse of Benguet’s old diversion tunnel underneath as the cause of the ground subsidence.
The Mines and Geosciences Bureau, Benguet’s technical team and representatives from the community immediately conducted a preliminary joint inspection on the company’s underground structures running parallel to the collapsed area, or the the Vegas tunnel built in the 1940s and located above the Old Diversion Tunnels 1 and 2.
Results of preliminary joint inspection discounted the initial claims because the structures were found to be largely intact and that the outlets of the drainage tunnels showed no signs of clogging.
Aside from these two structures, there are no other existing underground workings of the company in the area since it is not an active mining area.
On Oct. 27 and 29, a multipartite assessment team repeated the inspection of ODT 2 and the Vegas tunnel for more detailed investigation on the insistence of the community.
The second investigation found the structures intact, although a damaged wall in ODT 2 of about 11 meters was noted, along with a portion of the road riprap from the surface.
Benguet said the damaged wall in ODT 2 was likely a result of the subsidence.
The results of the further investigation also discovered the presence of small scale mining adits inside ODT 2.
“To avoid further accidents, sand bagging activities and installation of tarpaulin over the affected area was initiated by the company. Also, the limit of the danger zone was confined to 1.1 hectares so that the other families living outside were allowed to return home,” Benguet said.
The MGB in a report on Oct. 30 to the local government unit and the community declared that the collapse of the ground could not be attributed to the diversion tunnels and the Vegas tunnel, whose structural integrity remained whole.