Dual Guidance for Drinking Water
The Minnesota Department of Health (MDH) calculates the quantity or amount of a contaminant in water that will not harm a person who drinks the water. The amount of contaminant is called “health-based guidance.” MDH lists guidance values in the “Human Health-Based Water Guidance Table.”
Some guidance values for contaminants that have been found in Minnesota groundwater can also be promulgated as a rule (the Health Risk Limits for Groundwater rule). Rulemaking occurs approximately every two years and guidance is developed in-between rulemaking and may update an older rule. As a result, both rules and guidance values may be available for a contaminant (dual guidance) and the two values may be different.
MDH is currently publishing both HRL rule values and newer guidance values (Health-Based Values or Risk Assessment Advice) on the MDH website in the Human Health-Based Water Guidance Table. Both values are available and useful for risk evaluations and risk management. Descriptions of the differences and similarities between values adopted into rules and MDH guidance are described on the MDH website (see MDH Guidance).
Displaying both the old HRL value and new guidance for a chemical is a temporary situation. At the first rulemaking opportunity MDH intends to either replace the old value with a new HRL value or repeal the old value without replacement. Once the new rule is promulgated the guidance table will show only the new HRL value or the guidance if no new HRL was promulgated. This will eliminate dual advice for that chemical. However, as MDH continues to reevaluate existing HRL values for more chemicals, new guidance will be developed and posted. MDH anticipates that the guidance table will always contain a few chemicals that will have information on both an old HRL value and new guidance.
All guidance values (HRLs, Health-Based Values, and Risk Assessment Advice) are available to state programs. Some state regulatory programs may be restricted to using HRLs or prefer to use HRLs because the values are promulgated into rule. MDH guidance is only one of many considerations that risk management programs use to determine appropriate responses to contamination issues. In particular, site specific situations may raise questions for the risk manager regarding which value to apply. Knowing the reason why a newer value was developed or knowing the populations at particular risk and how each value protects those populations may be an important consideration for choosing one value over another. While the selection and use of values is the responsibility of programs that are applying MDH rules and guidance, MDH staff are available for consultation concerning the basis and potential use of MDH values.