Thallium in Well Water: The Public 0.002 mg/L Line

By SubcontractorHub Editorial Team·Published October 2026

A metals panel can list several names on one page, and the goal next to this metal is not the same digit as the enforceable public number, nor is it the goal printed on the mercury row. Dealers who sell treatment still have to say which public line they are reading. SubcontractorHub is software for the customer record. This page is the row. It is not a treatment design.

The Public 0.002 mg/L Line for Thallium in Well Water

The national primary drinking water regulations are legally enforceable primary standards and treatment techniques that apply to public water systems. In the inorganic block, this metal shows an MCLG of 0.0005 and an MCL of 0.002. The potential health effects cell says hair loss, changes in blood, and kidney, intestine, or liver problems. The source cell says leaching from ore-processing sites, and discharge from electronics, glass, and drug factories.

Footnote 2 says units are in milligrams per liter unless otherwise noted, and that milligrams per liter are equivalent to parts per million. 0.002 mg/L is therefore 0.002 ppm on that note. 0.0005 mg/L is 0.0005 ppm on the same note. Neither conversion is a second standard hiding under a different name. Moving the same digits to micrograms per liter uses the 1,000-to-1 scale on milligrams and micrograms. 0.002 mg/L is 2 µg/L on that scale. 0.0005 mg/L is 0.5 µg/L on that scale. Write both labels if the lab used the smaller unit, so a later reader does not think 2 is a new limit or think 0.5 replaced the goal.

An MCLG is a goal. An MCL is the enforceable public number. On this row the two cells do not print the same digit. The goal is lower. That gap is the point of reading both cells before anyone quotes a single figure. The definitions of those two words are on MCL and MCLG. A goal is not a fine. A matching pair on a neighbor row is still a different metal.

The 0.002 mg/L Figure in the Inorganic Table

Section 141.62, as printed on the Cornell eCFR page fetched the same day, lists maximum contaminant levels for inorganic contaminants. This metal is item (15), at 0.002 mg/L. Mercury, earlier on that table, is item (6), at 0.002 mg/L. The shared MCL digit is why a hurried note collapses the two names. The mercury row has its own page, mercury in well water. Selenium, which is a different inorganic neighbor, has its own page, selenium in well water.

Paragraph (b) says the levels in items (11) through (16), which include item (15), apply to community and non-transient, non-community water systems. A private well is not named in that sentence. A dealer who copies the 0.002 mg/L line onto a kitchen-tap jug still has to say the jug is not the public-system rule. The difference between a city system and a private well is what is a public water system.

The 0.002 mg/L Line Is Not the Mercury Goal

Mercury (inorganic) prints an MCLG of 0.002 mg/L and an MCL of 0.002 mg/L on the same national table. The health cell says kidney damage. The source cell says erosion of natural deposits, discharge from refineries and factories, and runoff from landfills and croplands. The MCL digit is the one that matches. The goal digit does not. The health sentence does not. The source sentence does not. Quoting 0.002 mg/L without the metal name lets the next reader pick the wrong cell.

The source sentence you are allowed to repeat from this fetch is leaching from ore-processing sites, and discharge from electronics, glass, and drug factories. If the lab header names this metal, that is the source cell. A refinery sentence belongs on the mercury row unless this sheet also printed it. Adding the neighbors together is not the rule this page fetched. Beryllium is a separate inorganic page, beryllium in well water, and its digits are not copied here.

What the Note Holds, and What It Does Not

The table above is the note. It is not a quote, and it is not a removal design. A customer who wants a price still needs a test, a model, and a scope. Those live on the job. This page only stops the wrong digit, or the right digit on the wrong metal, from landing in the scope.

What the BAT Marks Do Not Promise

The BAT table on the same Cornell page marks this contaminant as 1 and 5. The key says 1 is activated alumina. The key says 5 is ion exchange. Those marks identify a technology the rule names for compliance with the MCL. They do not say what percent a cartridge in a basement will remove.

The under-500 service-connection note on that key is attached to mark 2, coagulation and filtration, and to mark 6, lime softening. It is not attached to mark 1 or mark 5. Do not borrow that caveat, and do not drop it, as if it were part of this row. A city plant and a point-of-entry tank are not the same machine. If you sell ion exchange, say you sell ion exchange. Do not say the number 5 is a guarantee on this well. No removal percentage was fetched for this row, so none is printed here.

What Should the Thallium in Well Water Note Say?

Five lines keep the next visit from borrowing mercury. Name the metal the lab printed, show both the goal and the MCL, and say whether the jug is a private well. If a line does not apply, mark it skipped. A blank line looks the same as a step you forgot, and a skipped line is still a line someone can read later.

1. The metal name as the lab printed it, not a panel total and not mercury.
2. The result and the unit. If the unit is µg/L, show the mg/L equivalent on the 1,000 scale before anyone compares it with 0.002 or with 0.0005.
3. The public pair you compared it with: MCLG 0.0005 mg/L and MCL 0.002 mg/L, named as the national row for this metal.
4. Whether the sample is a private well or a public system. Paragraph (b) names community and non-transient, non-community systems for item (15).
5. What you did not claim: no removal percent, no installed price, and no statement that 0.002 mg/L is the mercury goal.

Where the Row Sits on the Job

The lab sheet belongs with the customer, the address, and the date of the sample. A price for equipment is a later page, after someone has read this row and the rows next to it. Mixing the 0.002 mg/L line into a softener quote because the panel listed several metals skips the chemical name and skips the fact that the goal cell is 0.0005 mg/L.

How a dealer reads a full panel, including which tests were actually run, is the well water testing guide. The software that holds the customer file is water treatment contractor software. This article does not size a filter and does not tell a household the water is safe to drink.

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