The supply comes from surface river and reservoirs and from groundwater boreholes. The geothermal system will consist of 4,000 boreholes and two energy stations on campus. It required the drilling of eight boreholes of 3600meter deep. Seabed investigation including boreholes at turbine foundation positions was completed by Fugro by April 2015. The Quarks have begun work on drilling the outer boreholes. Geologists also obtain data through stratigraphy, boreholes, core samples, and ice cores. The water is now supplied by three boreholes drilled into the Upper Chalk. One third of these boreholes have been drilled dry. Foundation piles are usually much shallower than boreholes and have a greater radius. Drilling for boreholes was time consuming and long. The thermal exchange occurs via a cluster of 144 boreholes, drilled into the earth. Hydraulic fracturing has regularly been used to improve the performance of water boreholes. The drilling works lasted about six month for each of the two boreholes. Four of the civilians killed were Kenyan contractors working to drill water boreholes. Moreover, regeneration of boreholes and ground source heat exchangers is possible.