The area subject to the plan, from Hanko to Skogby, is situated in southernmost Finland in the First Salpausselkä end moraine area. Almost the whole length of the area subject to the plan (20 kilometers) is classified as I class groundwater area and it consists of five separate groundwater areas. As there presumably exists free groundwater in the greatest part of the Hankoniemi peninsula, the space between the ground level and the groundwater level is critical with regard to protection. A great hazard to the groundwater is also caused by the fact that in the area of the Hankoniemi peninsula, the groundwater level is mainly close to the ground level, in many places at a depth of only 1 - 3 meters. The Hanko-Skogby groundwater protection project is by far the biggest ever in Finland. Groundwater protections will be constructed over a distance of c. 16.5 kilometers and slopes will be protected over an area of over 300,000 m2. There will be altogether 14 discharge points, 10 of which will be into the sea and 4 into the ground. Three pumping plants will be constructed. A geosynthetic clay linear will be used as protective materials. If we estimate 0.227 million dollars as the price for groundwater protection per kilometer, the protection costs will be as high as 3.8 million dollars (4.2 million EUR).