One of the threat with the extraction process of Natural Boreholes & Oil Wells is : D) Pipe casings can leak fossil fuels and fracking fluids into ground water aquifers. Boreholes are drilled and then lined with steel tubes so that a mixture of water and sand with small quantities of chemicals, the fracking fluid, can be pumped into them at very high pressure. Fracturing fluids contain chemicals which are known to be toxic, and widespread concern has been expressed over potential water contamination.