If TOC removal percentages cannot be met, a utility can comply with the EPA rule by removing at least ______ of _______, as CaCO3, measured monthly and calculated quarterly as an annual running average.

If TOC removal percentages cannot be met, a utility can comply with the EPA rule by removing at least ______ of _______, as CaCO3, measured monthly and calculated quarterly as an annual running average.

• A. 5 mg/L, magnesium carbonate
• B. 10 mg/L, magnesium hardness
• C. 15 mg/L, magnesium hydroxide
• D. 20 mg/L, magnesium carbonate

Answer: (B)

When TOC removal targets can’t be met, there is an EPA-approved backup approach: remove a minimum amount of magnesium hardness, expressed as calcium carbonate, and monitor it on a monthly basis with the value used for compliance calculated quarterly as an annual running average. The required target is 10 mg/L of magnesium hardness as CaCO3. This provides a defensible way to show continued protection when TOC removal is difficult to achieve. The other options don’t fit because they specify either the wrong substance (magnesium carbonate or magnesium hydroxide) or a different amount. The rule uses magnesium hardness expressed as CaCO3 and sets the target at 10 mg/L.

When TOC removal targets can’t be met, there is an EPA-approved backup approach: remove a minimum amount of magnesium hardness, expressed as calcium carbonate, and monitor it on a monthly basis with the value used for compliance calculated quarterly as an annual running average. The required target is 10 mg/L of magnesium hardness as CaCO3. This provides a defensible way to show continued protection when TOC removal is difficult to achieve.

The other options don’t fit because they specify either the wrong substance (magnesium carbonate or magnesium hydroxide) or a different amount. The rule uses magnesium hardness expressed as CaCO3 and sets the target at 10 mg/L.