Washington County Wcd Sand Hollow

What it means: Gross alpha particle activity is a screening measurement of all alpha-emitting radionuclides in water, excluding radon and uranium (which are regulated separately). If gross alpha exceeds 5 pCi/L, further analysis is required to identify specific radionuclides. Elevated gross alpha typically indicates water drawn from deep aquifers in contact with uranium- or thorium-bearing bedrock.

Health effects: Alpha-emitting radionuclides accumulate in bone and soft tissue, delivering sustained internal radiation doses that increase lifetime cancer risk. There is no established safe threshold for ionizing radiation. Individual contributors such as radium-226 and polonium-210 have their own MCLs; gross alpha serves as a cost-effective screening tool that triggers more specific radionuclide analysis when exceeded.

Limit: 15 pCi/L (excluding radon and uranium)

What it means: Radium-226 is a naturally occurring alpha-emitting radioactive isotope in the uranium-238 decay chain. It dissolves from uranium-bearing bedrock into groundwater and is more prevalent in deep, older aquifers. Wells in granite-rich geology can carry detectable radium-226 levels. It is regulated individually as well as jointly with radium-228.

Health effects: Radium-226 accumulates in bone tissue and delivers a sustained alpha radiation dose internally. Long-term exposure increases risk of bone cancer, and historic occupational data from radium dial painters established the carcinogenic mechanism. Children absorb more radium due to active bone growth, making them most vulnerable to skeletal radiation effects.

Limit: 5 pCi/L (when measured individually; combined Ra-226 + Ra-228 MCL also applies)

What it means: Radium-228 is a naturally occurring beta-emitting radioactive isotope in the thorium-232 decay chain. Like radium-226 it leaches from bedrock into groundwater and is found in deep aquifers in granite-rich regions. It is regulated both individually and as part of the combined radium standard. Its half-life of approximately 5.75 years makes it a persistent groundwater concern.

Health effects: Radium-228 accumulates in bone and delivers a beta radiation dose internally, increasing the risk of bone cancer over time. It also decays to radon-220 and other short-lived isotopes, contributing additional radiation dose. As with all radionuclides there is no established safe threshold — any exposure carries some incremental cancer risk.

Limit: 5 pCi/L (when measured individually; combined Ra-226 + Ra-228 MCL also applies)