Most of the water used to fracture the shale remains trapped thousands of feet underground after it is injected. However, internal pressure in the geologic formation forces some of the water (around 15-20%) back to the surface through the well bore.
Most of this "flowback" water comes back to the surface within seven days to ten days after it is injected. Flowback water is stored temporarily in lagoons or tanks before being sent off-site for disposal. It is usually transported off-site by truck, although some companies are exploring rail transportation as an option.
Drilling companies send brine and flowback water to disposal facilities that have permits to inject fluids thousands of feet underground into deep injection wells (called class II wells).
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