Because of low level of drilling technology during previous field investigation core recovery and core quality designation were very poor and it was doubtful whether the compressive strength was properly determined and base rock was also not classified as it was required. Because of this, project consulting company recommended drilling of 6 boreholes in the river bed and 2 inclined ones for inspection of faults, fractures and joints.

Scope of new works to be done was determined based on our review and evaluation of studies done during previous stage. The purpose set forth was to update the geological study of the previous Feasibility Study to the level which meets the requirements of international standards and financing organization or make it fundable. For example: There was not drill any boreholes in the river bed, but we drilled new boreholes there. At the same time, distances between previous boreholes drilled on the right floodplain were too far, thus we drilled additional boreholes between them and inter-boreholes distances become less. We drilled inclined boreholes because there were no any inclined boreholes were drilled before. By this way the conclusion on dam foundation rocks was drawn based on better quality of core recovery and drilling.

The general geological set-up of the Egiin Goliin HPP DAM SITE was explained based on the tectonic structure of Mongolia. New works required to be done were determined based on our review and evaluation of reports of previous studies. Geological investigation works were completed jointly by Tractebel Engineering (GDF Suez), France or the project consulting company and Erdenyn Erel LLC, Mongolia. We have prepared 20 more geological drawings and attached to the updated Feasibility Study. It was considered that additional drilling is required, so we selected 8 sites for drilling and 98 boxes of core samples were taken and transported to the Ulaanbaatar. All these samples stored in the commercial center of the Erdenyn Erel LLC. All geological parameters and conditions such as lithology and stratigraphy of the dam site, results of laboratory analyses, water packer tests, and Geological Strength Index system, excavation depth or level, slope stability, river water diversion system, dam body impermeability were attached to the updated Feasibility Study report. In connection with the increase of dam height additional geological studies were done for base rock strength and protective measures. Some additional studies normally required after selection of Contractor, among them grout curtain related studies were also completed. As a result of inclined drilling done in the river bed it was clarified