Features

• Jeju-do is an island created by over 300 volcanic eruptions that took place during the 3rd and the earlier part of the 4th period of Cenozoic Era. It consists with scores of layers of basalt lava erupted in the course of volcanic activities. Such geographical structure displays characteristics to develop groundwater due to water permeability of surface of the earth rather than surface waters to form rivers and water streams.
  
  With the annual rainfall of 1,975mm, Jeju-do records the highest level of rainfall in Korea. 46% of the total rainfall permeates underground, thus forms the groundwater resources of Jeju-do. According to experts� research, the volume of these groundwater resources is estimated to be approximately 70 billion tons or more.
  The vast quantity of groundwater in Jeju-do displays the following characteristics as caused by the typical geological and topographical features of this region.

Characteristics of Resource Form

• Most of groundwater in Jeju-do is underlying water or its equivalent. As a result, it exists in the lens form at a considerable depth from the sea level due to the difference in specific gravity between the fresh and seawater.

Jeju Samdasoo is the heaven-blessed water protected by 'G-H Lens'.

• Samdasoo Water Pocket, the Mysterious Fort Protected by G-H Lens- Groundwater floats underneath the sea level in the lens form due to the reaction of natural osmotic pressure and is protected by the sea from inflows of inland pollutants. Therefore, Samdasoo Water Pocket is in fact a gigantic water tank surrounded by a type of �natural pollution prevention walls�. Such a mysterious phenomenon can also be found in Hawaii. Especially, Jeju-do is well known to have very favorable topographic conditions.

Characteristics of Water Quality

• The weak alkaline groundwater neutralizes acidification and prevents aging of cells. The groundwater of Jeju-do is healthful water of good and soft taste because of its low mineral content and the extremely low level of hardness.

Characteristics in accordance with the Peculiarity of Geological Stratum

• Consisted of porous lava, the geological stratum enables self-purification of rainwater as it permeates underground level. In particular, black volcanic ash contained in the soil displays strong pollutant absorption effect, which is no inferior to that of active carbon used as water purifier. This property enables to maintain clean water quality.