Carbon Tetrachloride in Well Water: The Public 0.005 mg/L Line

By SubcontractorHub Editorial Team·Published October 2026

Several volatile rows print 0.005 mg/L. The name on the lab line is what keeps this chemical apart from benzene, from trichloroethylene, and from tetrachloroethylene. SubcontractorHub keeps the customer file. This article keeps the public number. It does not design a filter.

The Public 0.005 mg/L Line

The national primary drinking water regulations limit contaminants at public water systems. In the organic block, the carbon tetrachloride MCLG cell is zero. The MCL cell is 0.005. The health-effects cell lists liver problems and an increased risk of cancer. The source cell says discharge from chemical plants and other industrial activities.

Footnote 2 puts the organic block in milligrams per liter unless a cell says otherwise, and it says milligrams per liter are equivalent to parts per million. 0.005 mg/L is 0.005 ppm on that note. The smaller unit, micrograms per liter, uses the 1,000-to-1 scale already explained on milligrams and micrograms. 0.005 mg/L is 5 µg/L. A lab that prints 5 is not announcing a new standard if the unit is micrograms per liter.

Zero in the goal cell is not a second MCL under 0.005. The words for those two cells are on MCL and MCLG. This row does not match toluene, where the goal and the MCL are both 1 mg/L. That other row is toluene in well water.

CAS 56-23-5 in the 2025 CFR

Section 141.61, in the 2025 title 40 XML, lists volatile organic maximum contaminant levels. Carbon tetrachloride is item 3, CAS 56-23-5, at 0.005 mg/L. Benzene is the row above it, also 0.005 mg/L, under a different CAS. Trichloroethylene is item 5, again 0.005 mg/L. The shared digit is why the chemical name has to travel with the result.

Paragraph (a) limits that table to community and non-transient, non-community water systems. A private well is outside that sentence. Copying 0.005 onto a kitchen sample without saying so treats a household jug as a utility violation. What the utility sentence actually covers is what is a public water system. A private-well rule, where a state has one, is a different page: private well water regulations.

Carbon Tetrachloride in Well Water Is Not the Petroleum Row

Benzene's source cell names factories, gas storage tanks, and landfills. Its health cell names anemia and blood platelets. That page is benzene in well water. Trichloroethylene names metal degreasing sites. Tetrachloroethylene names factories and dry cleaners. Carbon tetrachloride names chemical plants and other industrial activities. A highlighter on every 0.005 will mix those stories.

Toluene is not even the same digit. Its public MCL is 1 mg/L. Do not “correct” a carbon tetrachloride result by borrowing the toluene line, and do not shrink toluene down to 0.005 because both chemicals showed up on one panel. Write the CAS when the sheet has it. If the sheet says the common name and does not give 56-23-5, say that you did not confirm the CAS.

Five Parts per Billion on the Report Appendix

Appendix A to Subpart O of Part 141 tells a consumer confidence report how to print regulated contaminants. The carbon tetrachloride row is labeled in ppb. The traditional MCL cell is 0.005 mg/L. The convert-for-CCR cell says multiply by 1,000. The MCL in CCR units is 5. The MCLG cell is 0.

Five in that ppb column is the product of 0.005 and 1,000. It is not a looser limit and not a tighter one. The health-effects language says some people who drink water containing carbon tetrachloride in excess of the MCL over many years could experience problems with their liver and may have an increased risk of getting cancer. That is the appendix sentence. It is not a medical finding about one customer. When a city report exists, read the detected value on how to read a consumer confidence report before you quote 0.005 from memory. A private well does not get that annual report. The single sample is the well water testing guide.

What the Note Holds, and What It Does Not

Best-Available Marks Are Not a Percent

Table 2 of section 141.61 names granular activated carbon, packed tower aeration, and oxidation as the columns. Carbon tetrachloride is marked under the first two. The oxidation cell is empty. The same pattern appears on benzene. The MCL cells are also both 0.005 mg/L. The source cells are still different, so the marks do not collapse the two chemicals into one recommendation.

Nothing in the fetched table prints a removal percentage for a cartridge under a sink. This page does not add one, and it does not add an installed price. Primary standards, which this row belongs to, are a different list from secondary standards. That split is primary and secondary drinking water standards.

What Should the Carbon Tetrachloride in Well Water Note Say?

It should carry the name, the CAS if present, the result, the unit, and whether the sample came from a public system or a private well. It should record 0.005 mg/L as the public line read here, and 5 µg/L or 5 ppb only as that same line.

1. The name on the lab line, not “the 0.005 solvent.”
2. CAS 56-23-5 when the sheet prints it.
3. The unit, so 5 ppb is not stored as if it were 5 mg/L.
4. Public system or private well, in words.
5. A note that the chemical-plant source cell was the one used, and that no removal percent was copied.

Where This Row Sits Beside the Others

A dealer who saves only “0.005” will open the wrong page on the next call. Save the name with the number. A water treatment dealer can then tell a chemical-plant row from a dry-cleaner row without re-reading the whole panel.

This article does not say the water is safe to drink. It does not say a particular house failed a county rule. It states the public line that was fetched, the systems that line names, and the unit conversion the appendix already prints. The customer record should be able to show those three things without a second guess.

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