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To evaluate health effects, the Agency for Toxic Substances and Disease Registry (ATSDR) has developed Minimal Risk Levels (MRLs) for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily human exposure to a contaminant below which non-cancer, adverse health effects are unlikely to occur. ATSDR has developed an MRL for each route of exposure, such as ingestion, inhalation, and dermal contact, and for the length of exposure, such as acute (less than 14 days), intermediate (15 to 365 days), and chronic (greater than 365 days). ATSDR presents these MRLs in Toxicological Profiles. These chemical-specific profiles provide information on health effects, environmental transport, human exposure, and regulatory status. The U.S. Environmental Protection Agency (EPA) has developed reference doses (RfDs) to evaluate non-cancer health effects resulting from exposure to chemicals at Superfund sites.

To estimate exposure from ingestion of chemicals in drinking water, we made the following assumptions: 1) children drink 1 liter (L) of water per day and weigh 15 kg, 2) adults drink 2 L of water per day and weigh 70 kg, and 3) they were exposed to the maximum concentration measured for each chemical.


The maximum estimated daily dose of arsenic from ingestion of private well water is less than ATSDR's chronic oral MRL for adults, but not for children (18). The dose for children is in the same range as the No Observed Adverse Effect Level (NOAEL) for people exposed to arsenic in water. The NOAEL is the level of exposure at which effects may be produced; however, these effects are not considered signs of illness. The maximum level of arsenic occurred at a place of business where children are not likely to be present on a continuous basis. Therefore, we do not expect any non-carcinogenic illnesses in adults or children from exposure to arsenic in private well water.

Arsenic is a known human carcinogen. Ingestion of arsenic over a period of many years can increase the risk of skin cancer and possibly various types of internal cancers (18). However, the maximum estimated daily dose of arsenic from drinking private well water is about 100 times less than the cancer effect level in humans. This dose is also about 3 times less than the amount provided in a normal diet (18). Therefore, it is unlikely that an increased cancer rate would occur in people exposed to arsenic in the private wells near the Stauffer site.


Manganese is an essential element necessary for normal human growth and maintenance of health. ATSDR has not established an MRL for manganese (19). However, EPA has derived a chronic oral RfD for manganese in food. EPA recommends that a modifying factor be applied to this RfD if it is used for assessments involving nondietary exposures (20). The maximum estimated daily dose of manganese from groundwater is less than EPA's modified RfD for manganese in both children and adults. Therefore, no illnesses are likely in children or adults exposed to manganese in private well water.


There is no ATSDR MRL or EPA RfD for radium (21). A Maximum Contaminant Level (MCL) of 5 pCi/L has been established for radium in drinking water. The maximum level of radium found in private well water is less than the MCL. Based on studies of radium dial painters, the lowest total intake level of Radium-226/228 associated with a malignancy was 1.03 µCi/kg (microCuries per Liter) (21). The maximum lifetime total intake of Radium-226/228 from private well water is about 500 times less than this level. Therefore, we do not expect any illnesses in children or adults from exposure to radium in private well water.


Because children may consume water from these wells, the health effects from exposure to chemicals in young children are a special concern. Children are smaller than adults, resulting in higher doses of chemical exposure per body weight. Children are often more sensitive to the effects of chemical exposures than adults and can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.

As detailed in the discussion section above, children are not likely to be exposed to chemicals in private well water at a level sufficient to cause any illnesses.

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