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XTO Energy Inc., an Exxon Mobil subsidiary, is facing criminal charges in Pennsylvania for discharging 50,000 gallons of fracking wastewater from a storage tank at its facility into state waterways.

Attorney General Kathleen Kane announced Tuesday that the company had been charged over spilling wastewater containing a wide range of chemicals in 2010. The leak was discovered by state officials who inspected the XTO Energy water recycling facility in Penn Township, Pa. Chemicals from the fracking wastewater were found in a nearby tributary of the Susquehanna River, Kane explained in a statement.

The Pennsylvania attorney general claimed that one of the valves on the storage tank had been left open. However, XTO said that the spill was an isolated incident and there was no lasting environmental impact.

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An initial investigation by the U.S. Environmental Protection Agency also found no grounds for criminal charges and both parties reached an agreement in July. Under the terms of the settlement, XTO was required to pay $100,000 and had to upgrade its monitoring systems and wastewater recycling operations in Pennsylvania and West Virginia.

Despite this agreement a grand jury indictment has been filed, charging the company with eight counts of violating state laws regulating clean water and solid waste. XTO Energy stated on its website that it intended to contest the charges, claiming that they were unprecedented and baseless as there was no intentional or negligent misconduct by the company.