VOCs (Petroleum & Solvents)

If you live within 1,000 feet of a gas station, dry cleaner, or industrial site, you should test for these. Most people never do

EPA MCL

Benzene 5 μg/L; TCE 5 μg/L; PCE 5 μg/L; vinyl chloride 2 μg/L; MTBE no federal MCL (some state actions ~13-40 μg/L)

Health concern

Cancer (benzene leukemia; TCE/PCE liver, kidney, NHL; vinyl chloride liver angiosarcoma); neurological; reproductive

Testing method

EPA Method 524.2 by purge-and-trap GC-MS at certified lab; $80-150; not on standard well panels

Volatile organic compounds — VOCs — are the contaminant category that doesn't fit the geology-driven frame of most of this site. They aren't in your aquifer because of the rock; they're in your aquifer because something specific upgradient leaked. The two biggest sources are petroleum products (leaking underground gasoline storage tanks at gas stations, fuel oil tanks at older homes, refineries, pipelines) and chlorinated solvents (dry cleaners, electroplating shops, semiconductor fabs, machine shops, industrial degreasing operations). The geographic pattern is consequently nothing like the natural-contaminant patterns elsewhere on this site: it's a map of human industrial activity.

The bad news is that VOC contamination is not on standard well-water test panels. The good news is that most VOC plumes are localized and identifiable from public records. If you live near a known leaking-underground-storage-tank (LUST) site, a Superfund or brownfield site, an active or former dry cleaner, an industrial facility with a discharge history, or a refinery — you should test specifically for VOCs. If you live in a rural agricultural area with no industrial neighbors, you almost certainly don't need to.

The two main families

Petroleum-derived VOCs ("BTEX" and friends):

• Benzene — the most regulated and most carcinogenic. EPA MCL 5 μg/L, but the carcinogenicity is well-established at lower exposures. Causes leukemia.
• Toluene, ethylbenzene, xylenes (the rest of "BTEX") — less carcinogenic but neurotoxic at higher exposures.
• MTBE (methyl tert-butyl ether) — gasoline oxygenate phased out around 2005-2010 but persistent in groundwater. No federal MCL but some state action levels around 13-40 μg/L. Distinctively unpleasant taste and smell at very low concentrations.
• Naphthalene — present in some petroleum products and as a degradation product.

Chlorinated-solvent VOCs:

• Trichloroethylene (TCE) — historic industrial degreaser; EPA MCL 5 μg/L. Causes kidney cancer, non-Hodgkin lymphoma, and probably liver cancer.
• Tetrachloroethylene (perchloroethylene, PCE, "perc") — historic dry-cleaning solvent; EPA MCL 5 μg/L. Causes bladder cancer, NHL, kidney cancer.
• 1,1,1-Trichloroethane (TCA) — historic solvent; EPA MCL 200 μg/L. Less aggressively carcinogenic than TCE/PCE.
• Vinyl chloride — degradation product of TCE and PCE under reducing conditions; EPA MCL 2 μg/L (lowest of any VOC). Causes liver angiosarcoma — a rare but distinctive cancer.
• Carbon tetrachloride (CCl₄) — historic solvent and pesticide carrier; banned in consumer products 1970 but persistent. EPA MCL 5 μg/L.
• 1,1-Dichloroethylene (1,1-DCE), cis-1,2-DCE — TCE/PCE breakdown products.

The chlorinated solvents are particularly insidious because they're denser than water (they're called DNAPLs — dense non-aqueous-phase liquids). When they leak into groundwater, they sink to the bottom of the aquifer, pool against impermeable layers, and slowly dissolve into passing groundwater for decades. A single dry-cleaner spill from 1970 can contaminate downgradient wells in 2026.

Where they show up

The geographic pattern follows industrial activity, not geology. Specific source categories worth identifying near your well:

• Active or former gas stations — every state has a LUST (Leaking Underground Storage Tank) program with public site lists. Plumes from these typically extend 1,000-3,000 feet downgradient.
• Active or former dry cleaners — particularly small-strip-mall dry cleaners from the 1960s-1990s, which used PCE without containment. State environmental agencies maintain partial inventories.
• Industrial sites and machine shops — manufacturing facilities, electroplating, semiconductor fabs, automotive repair operations.
• Superfund and brownfield sites — the EPA's Superfund Site Information database is searchable by ZIP code; state programs maintain similar lists.
• Old fuel-oil home heating tanks — buried tanks from pre-1970s construction often leaked; some states have abandoned-tank registries.
• Pipelines and refinery vicinities — particularly in TX/LA Gulf coast, parts of the Midwest, the Northeast.
• Military bases (independently of PFAS) — TCE was the standard aircraft and equipment degreaser for decades; many bases have legacy TCE plumes.

If your well is more than about a mile from any of these source categories and you have no specific reason to suspect contamination, VOCs are likely a low-probability test to run. If you're closer, particularly if you're downgradient (uphill source, downhill well), test.

Health effects

VOC health concerns vary by compound but the pattern is consistently chronic exposure causes cancer:

• Benzene — leukemia (Group 1 carcinogen). The clearest dose-response data.
• TCE — kidney cancer, NHL, liver cancer; also cardiac defects from prenatal exposure (the strongest non-cancer concern).
• PCE — bladder cancer (strong evidence), NHL, kidney cancer.
• Vinyl chloride — liver angiosarcoma (a rare cancer that VC causes distinctively).
• Carbon tetrachloride — liver and kidney damage; possible hepatocellular carcinoma.
• Toluene, xylenes, ethylbenzene — neurological effects at occupational exposures; less concern at typical drinking-water concentrations.
• MTBE — possibly carcinogenic; mostly an aesthetic concern (very low taste and smell threshold).

The other reason VOCs are a special category: many of them off-gas during showering, dishwashing, and cooking. Inhalation exposure from contaminated water can be larger than ingestion exposure — and most pitcher and POU filters handle the water without addressing the indoor-air burden.

Testing

• Method: EPA Method 524.2 by purge-and-trap GC-MS at a certified lab. Tests for ~60 VOCs simultaneously. The standard "VOC panel."
• Cost: $80-150 per sample at most certified labs. Higher than basic mineral panels because of analytical complexity.
• Sampling: VOCs evaporate easily. The lab will provide specific 40 mL VOA vials with septum caps and acid preservative; fill them completely with no headspace, cap immediately, refrigerate, and ship overnight. Standard well-water collection technique does not work for VOC sampling.
• Frequency: at well purchase if you're in a high-risk area; every 3-5 years thereafter for ongoing risk areas; annually after any nearby industrial event (spill, demolition, redevelopment).

Treatment

VOCs are one of the contaminant categories where filtration does work well — VOCs are organic and adsorb readily to activated carbon:

• Granular activated carbon (GAC) — the standard treatment. Highly effective for the full BTEX and chlorinated-solvent panel. Whole-house POE installations are common. Cost: $1,000-3,000 installed; carbon replacement annually depending on load.
• Air stripping — used at municipal scale for high-VOC raw water; impractical for residential.
• Reverse osmosis — works for most VOCs; less effective than GAC for the most volatile ones (which can pass through RO membranes with the water).

The catch: GAC also removes chlorine, fluoride, and other beneficial water-quality components, and the spent carbon is technically hazardous waste depending on what it accumulated. Most residential systems handle this by sending spent media to municipal waste, which is technically fine but worth knowing about if you're contaminated to high levels.

Aquifers where this is a concern