Answer:
By air and water
Step-by-step explanation:
Air: the plutonium separation process at the Hanford site released radioactive isotopes in the air which were carried to several neighbouring states of Washington. These isotopes eventually entered the food chain via dairy cows grazing on contaminated fields.
Water: huge volumes of water from the Columbia river was used to dissipate the heat produced by the nuclear reactors. This water, that contained radioactive isotopes, was returned to the river. Radiation was later measured 200 miles downstream.