Gross Alpha in Well Water: The Public 15 pCi/L Line

By SubcontractorHub Editorial Team·Published October 2026

Dealers meet gross alpha in well water when a lab PDF has a picocurie column next to a metal column. Those columns do not share a unit. Uranium mass is its own page, uranium in well water. Radon in the water is radon in well water. Changing picocuries into becquerels, and nothing else, is the picocurie becquerel converter.

Gross Alpha in Well Water on the Primary Table

The national primary drinking water regulations apply to public water systems. In the radionuclide rows, the contaminant is labeled “Alpha particles.” The MCL is 15 picocuries per liter (pCi/L). The MCLG cell reads “none” and “zero.” The potential health effect listed is an increased risk of cancer. The source listed is erosion of natural deposits of certain minerals that are radioactive and may emit a form of radiation known as alpha radiation.

EPA's small-entity compliance guide for radionuclides uses the name gross alpha for that public MCL. It says the third MCL is for gross alpha, which includes all alpha emitters except uranium and radon. The guide's table prints “Gross alpha particle 15 pCi/L.” The primary table's row name and the guide's name are the same 15 pCi/L figure. Write both names on the ticket if the lab used only one of them, so a later reader does not think they are two tests.

The guide is about community water systems and their monitoring. It is not a private-well code. A dealer can still use 15 pCi/L as the public label beside a household result. That label does not become a pass or a fail for the house.

Three Rows People Mix Up

The same primary table puts three radionuclide results near each other. Only one of them is the alpha line.

Combined radium at 5 pCi/L is a smaller number in the same activity unit. It is not a stricter version of 15. Uranium at 30 µg/L is a mass. Dividing 15 by 1,000 does not produce micrograms. The mass scale of 1,000 is explained in milligrams and micrograms, and it does not move activity.

What the Compliance Guide Says About Substitution

The small-entity guide says that, in some cases, a gross alpha measurement may be substituted for a required radium-226 or uranium measurement at a public system. It says the rules are complex. Generally, it allows gross alpha as a substitute for radium-226 if previous gross alpha results, including analytical error, are less than or equal to 5 pCi/L. It allows gross alpha as a substitute for uranium if the gross alpha result is less than or equal to 15 pCi/L.

The same paragraph says that if uranium is measured as radioactivity, a mass estimate can be made by dividing the result in picoCuries by 0.67, and that the quotient is a conservatively high mass in micrograms. If that estimate exceeds 30 µg/L, the guide says to have the laboratory analyze the mass by a direct method. This page prints that sentence so a dealer does not invent a different divisor. It does not run the division. A private-well PDF is not the public-system substitution the guide is describing.

The activity conversion this site does publish is picocuries to becquerels, using the factor on the radiation-terms page, in the picocurie tool. That tool does not output micrograms. Do not send a gross alpha number through it and call the becquerel a uranium mass.

What to Write on the Ticket

1. The number, the unit (pCi/L or whatever the lab printed), and the name the lab used.
2. Whether you set it beside the public 15 pCi/L alpha line.
3. The uranium mass, if the lab also printed one, left in micrograms.
4. Combined radium, if it was printed, left on its own 5 pCi/L comparison.
5. A note that 15 pCi/L is a public-system line, not a private-well statute.
6. No 0.67 division, unless a lab signed that conversion on this sample.

Where Gross Alpha in Well Water Stops

The fetched primary row does not name a treatment, and it does not name a removal percentage. The compliance guide's pages used here do not add a household percent either. None is invented. A listing that names a model is a different document from this explainer.

Beta particles and photon emitters are another row on the primary table, in millirems per year, not picocuries per liter. This page does not convert a gross alpha result into a dose. The testing guide's place for a radionuclide screen, next to the metals, is the well water testing guide. Whether a private well is inside the public program at all is private well water regulations.

A water treatment dealer who files the picocuries, the public 15, and the separate uranium mass will not reopen the unit argument on the next visit. That note is the job. It is not a medical opinion about cancer risk, and it is not a device size.

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