Toluene in Well Water: The Public 1 mg/L Line

By SubcontractorHub Editorial Team·Published October 2026

A lab sheet can print several solvents on one page. The digit next to toluene is not the digit next to benzene. Dealers who sell treatment still have to say which public line they are reading, and that a private well is not the system the rule names. SubcontractorHub is software for the customer record. This page is the row. It is not a treatment design.

The Public 1 mg/L Line

The national primary drinking water regulations are legally enforceable primary standards and treatment techniques that apply to public water systems. In the organic block, toluene's MCLG cell is 1. The MCL is 1. The potential health effects listed are nervous system, kidney, or liver problems. The source cell says discharge from petroleum factories.

The table notes put those figures in milligrams per liter unless otherwise noted. The notes say milligrams per liter are equivalent to parts per million. 1 mg/L is therefore 1 ppm on that note. It is not a different standard. Moving the same digits to micrograms per liter uses the 1,000-to-1 scale on milligrams and micrograms. 1 mg/L is 1,000 µg/L on that scale. Write both labels if the lab used the smaller unit, so a later reader does not think 1,000 is a new limit.

An MCLG is a goal. An MCL is the enforceable public number. On this row the two cells print the same digit. That match is not true of every neighbor. The definitions of those two words are on MCL and MCLG. A goal is not a fine, and a matching pair is still one line.

The 1 mg/L Figure in the 2025 CFR

Section 141.61 of the 2025 Code of Federal Regulations prints maximum contaminant levels for volatile organic contaminants. Toluene, CAS 108-88-3, is 1 mg/L. Benzene, earlier on that table, is 0.005 mg/L. Those are not one number. The benzene row has its own page, benzene in well water.

Paragraph (a) says those volatile-organic levels apply to community and non-transient, non-community water systems. A private well is not named in that sentence. A dealer who copies the 1 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.

Toluene in Well Water Is Not the 0.005 Row

The same volatile table also prints trichloroethylene at 0.005 mg/L and tetrachloroethylene at 0.005 mg/L. Sharing a page is not sharing a number. If the lab wrote toluene, write toluene. The page that already warns not to borrow this 1 mg/L digit is trichloroethylene in well water. Carbon tetrachloride is also 0.005 mg/L, on carbon tetrachloride in well water. Do not paste a metal-degreasing story or a chemical-plant story onto a petroleum-factory row.

Xylenes (total) print 10 mg/L on the same national table. Ethylbenzene prints 0.7 mg/L. Those rows are not this page. A customer who hears “one” still needs the chemical name. Adding the numbers together is not the rule this page fetched.

What the Note Holds, and What It Does Not

The Consumer-Confidence Sentence

Appendix A to Subpart O of Part 141 is the language a consumer confidence report is told to use. The toluene row is labeled in ppm. The traditional MCL cell is 1 mg/L. The MCL in CCR units is 1. The MCLG cell is 1. The major-source cell repeats discharge from petroleum factories.

The health-effects language on that appendix says some people who drink water containing toluene well in excess of the MCL over many years could have problems with their nervous system, kidneys, or liver. That sentence is the report's wording. It is not a diagnosis of the person holding the jug. How to read the city report, when one exists, is how to read a consumer confidence report. A private-well customer does not have that report. Their sheet is one sample. Say so on the work order. The testing steps for that jug are the well water testing guide.

What the BAT Marks Do Not Promise

Table 2 of the same 2025 section lists best available technology for the organic rows. The columns are granular activated carbon, packed tower aeration, and oxidation. Toluene is marked in the first two columns. The oxidation cell is empty. Benzene, on that same table, is also marked in the first two columns and empty in the third. A matching pair of marks is not a matching MCL.

A mark is not a percent removed in a house. This page did not copy a removal percentage, and it does not name an installed price. A filter conversation still starts with the lab name, the unit, and whether the sample is a public result or a private jug. Primary and secondary standards, and why a secondary number is a different list, are on primary and secondary drinking water standards.

What Should the Toluene in Well Water Note Say?

It should name toluene, CAS 108-88-3 if the sheet has it, the result, the unit, and whether the sample is a public-system result or a private-well jug. It should say the public MCL read here is 1 mg/L, and that 1,000 µg/L is the same line. It should not say the sample violated a rule the CFR did not apply to a private well.

1. The chemical name the lab printed, not a neighbor from the same solvent panel.
2. The result and the unit, with 1 mg/L and 1,000 µg/L labeled as one line if both appear.
3. Public system or private well. Do not leave that blank.
4. The source cell you are using: petroleum factories, not gas tanks and not dry cleaners.
5. A note that no removal percent and no installed price were taken from this page.

Where the Row Sits on the Job

The number is useless if the next visit cannot tell toluene from benzene. Save the lab page, the unit, and the sentence about who the rule names. A water treatment dealer who keeps that note will not quote 0.005 mg/L for a row whose public MCL is 1 mg/L.

This page does not say a house passed or failed. It does not size a carbon tank. It does not tell a person whether to drink the water. Those are decisions outside a software article. The record is the row, the unit, and the sample type.

Frequently Asked Questions