Complex sentence: Tritium has leaked from 48 of 65 nuclear sites in the US, detected in groundwater at levels exceeding the United States Environmental Protection Agency (EPA) drinking water standards by up to 375 times.
Split into simpler sentences: Tritium has leaked from 48 of 65 nuclear sites in the US. In one case it was detected in groundwater at levels exceeding the United States Environmental Protection Agency (EPA) drinking water standards by up to 375 times.