SOME INDICATORS FOR GROUNDWATER RESERVOIR BY DIGITAL FRACTURE MAPPING

This study aims to provide detail information for planning water well placement in the public installation. We surveyed for the new groundwater well placement in four areas located around different districts. Each area has a different index such as object area, geology and geographical status. Digital fracture mapping was available but no other way was possible because of laying facilities under the ground. To understand fracture system for underground reservoir, structurally classified lineaments from landsat images of IKONOS (1m) overlapped on digital topographic map. Digital fracture mapping (1:5,000) using GPS (resolution: about15cm and 1m) was based on denuding structural episode and fracture grade for the object area. To understand horizontal and vertical fracture geometry, we used programs to lay structural elements accurately on a cross section. Multi-trend cross sections transferred to fence diagram. Finally, fence diagram induced to 3-D block diagram. Area-H has the largest surface with airfield and consists of Proterozoic paragneiss (ca. 2.0 Ga.) and Jurassic granitoids (ca.180 Ma.). NE shearing and superposed folds formed a curved triangular shadow zone. It revealed that a massive granite plug filled up the zone and that its role was a vertical aquifer. We found fractured aquifers along the alternated boundary between the gneiss and the granitoids and seven well sites on triple junctions of fractures within the area-H. Areas C and GO consist of the Proterozoic basement. Two areas have too small surface to investigate new well placement. However, the junction point of three fractures of area-C provided an aquifer at the highest mountain slope and two well sites of 55GPM and 70GPM. Area-GO is located on the west limb of NS synclinal fold. The fold caused flexural brittle fault of N20E. Combination with fold and fault provided three wells. Area-S is composed of Jurassic granite with a lot of pegmatite or quartz veins and acidic dikes. Those fracture zones filled by dikes or veins were barren of groundwater. It revealed that triple junction of fractures, geologic boundary, dike swarm and shear fracture by fold and fault were good indicators for groundwater reservoir.