US$31.1 million in taxes in 2009 to various local taxing bodies. Two power uprates have been approved by the NRC for each reactor since inception. The first uprate was approved on May 4, 2001 allowing for additional 175.6 MWt for each reactor and the second occurring on February 7, 2014 allowing for an increased 58.4 MWt. These uprates represented a 5% and 1.6% percentage increase in capacity, respectively. Electricity Production Surrounding Groundwater and Elevated Levels of Tritium There are two underground aquifers within the first 230 feet (70.1 m) below the power station: the upper aquifer is known as the Galena-Platteville Aquifer and the lower aquifer is known as the St. Peter Sandstone Aquifer. The two bodies of water are separated by a layer of shale and thus not connected. In February 2006, Exelon reported elevated tritium levels in the groundwater beneath the site. Tritium levels were elevated in two of six test wells, according to an Exelon release in February which noted that tritium concentrations of 86,000 pCi/L (2.3 MBq/L) were detected in standing water in underground concrete vaults along the plant's blowdown line. The company stated that the levels posed no risk to public or employee safety. The report coincided with ongoing tritium concerns at the Exelon-owned Braidwood Nuclear Generating Station near Braceville, Illinois. In September, elevated tritium levels were found at Byron in three monitoring wells adjacent to vacuum breaker vaults along the blowdown line. Two of the areas with elevated tritium were found in the shallow portions of the Galena-Platteville Aquifer, while the third location contained elevated tritium levels at the bottom of the same aquifer. Tritium is a very low level beta emitter with an approximate half-life of 12.3 years and it cannot penetrate the outer dead layer of skin. The main concern with this isotope is inhalation or ingestion. None of the September levels exceeded the 20,000 pCi/L U.S. Environmental Protection Agency drinking water standard. On April 12, 2006 the Illinois Environmental Protection Agency (IEPA) issued a violation notice to Exelon concerning Byron Nuclear Generating Station. The notice cited the company for violations of state environmental laws related to the "impairment of resource groundwater", discharging waste-containing contaminants from areas other than the permitted points, and violations of other requirements of the plant's discharge permit. Due to the tritium contamination at Byron, Braidwood and Dresden nuclear power plants in Illinois, the state government passed a