Belcourt-Turtle Mtn Rural Water System

What it means: Asbestos enters drinking water primarily from the deterioration of asbestos-cement (AC) pipes, which were widely used in US water distribution systems between the 1930s and 1980s. Some naturally occurring asbestos deposits can also contribute. Corrosive water (low pH, soft water) accelerates pipe degradation and fiber release.

Health effects: Long-term ingestion of elevated asbestos levels is associated with an increased risk of benign intestinal polyps (mesothelioma from ingestion remains uncertain in the scientific literature). Inhalation risk from drinking water is considered minimal. EPA classifies asbestos as a Group B1 probable human carcinogen based on inhalation data.

Limit: 7 million fibers per liter (MFL) — fibers longer than 10 micrometers

What it means: Radium-226 and Radium-228 are naturally occurring radioactive isotopes produced by the decay of uranium and thorium in bedrock. They dissolve into groundwater, particularly in deep aquifers with low oxygen and low pH. Granite bedrock and some deep sandstone and limestone aquifers present conditions where combined radium can reach detectable levels in drinking water.

Health effects: Radium is a bone-seeking radionuclide that accumulates in skeletal tissue after ingestion. Long-term exposure increases the risk of bone cancer and leukemia. There is no safe threshold for ionizing radiation — the MCL is set at a level balancing risk reduction with treatment feasibility. Children are particularly vulnerable due to higher rates of bone growth and calcium uptake.

Limit: 5 pCi/L (combined Ra-226 and Ra-228)

What it means: Uranium is a naturally occurring radioactive heavy metal found in rock and soil formations across the United States. It leaches into groundwater through weathering of uranium-bearing minerals, and is more prevalent in granite-rich and other uranium-bearing geologies. Mining and milling operations can also elevate uranium in nearby water supplies.

Health effects: Uranium poses both radiological and chemical health risks. Chronic exposure is primarily associated with kidney damage due to its chemical toxicity as a heavy metal. The radiological risk — increased cancer probability — is also present but secondary to the nephrotoxic concern at drinking water concentrations. There is no safe threshold for radiation exposure.

Limit: 0.030 mg/L (30 µg/L)

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)

What it means: The 2013 RTCR (effective 2016) replaced the original TCR. It triggers automatic E. coli testing whenever total coliform is found. A single E. coli-positive sample is an acute MCL violation. It also requires systems exceeding 5% total coliform-positive samples to conduct a formal assessment and correct any deficiencies, helping prevent contamination before it escalates.

Health effects: Total coliform bacteria indicate that the disinfection barrier has been breached or fecal contamination is entering the system. E. coli specifically indicates fecal contamination and the possible presence of disease-causing pathogens (norovirus, Salmonella, Shigella, Campylobacter). Illness can be severe in elderly, young children, and immunocompromised individuals.

Limit: Zero E. coli; ≤5% of monthly samples total coliform-positive