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 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. None of the September levels exceeded the 20,000 pCi/L U.S. Environmental Protection Agency drinking water standard.