Chlorinated solvents
Trichloroethylene and tetrachloroethylene from degreasing and dry cleaning. Denser than water, so they sink through aquifers rather than floating — which makes them among the hardest contaminants to remediate.
Key facts
- Contaminant group
- Industrial
- World Health Organization — guideline
- 20 µg/l trichloroethylene; 40 µg/l tetrachloroethylene
- European Union — legal limit
- 10 µg/l for the sum of tri- and tetrachloroethylene
- United Kingdom — legal limit
- 10 µg/l for the sum
- United States — legal limit
- 5 µg/l trichloroethylene; 5 µg/l tetrachloroethylene; 2 µg/l vinyl chloride
Where it comes from
- Metal degreasing operations
- Dry cleaning, historically using tetrachloroethylene
- Manufacturing and electronics
- Disposal to ground before modern controls
How it behaves in water
Denser than water, so they sink to the base of an aquifer as a separate phase and pool on low-permeability layers. From there they dissolve slowly for decades, acting as a long-term source. Anaerobic degradation produces vinyl chloride, which is considerably more toxic than the parent compounds.
How it is measured
Micrograms per litre by GC-MS. Vinyl chloride requires separate analysis and is often the compound that determines the risk.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 20 µg/l trichloroethylene; 40 µg/l tetrachloroethylene | guideline | — |
| European Union | 10 µg/l for the sum of tri- and tetrachloroethylene | legal limit | — |
| United Kingdom | 10 µg/l for the sum | legal limit | — |
| United States | 5 µg/l trichloroethylene; 5 µg/l tetrachloroethylene; 2 µg/l vinyl chloride | legal limit | — |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
Trichloroethylene is classified by IARC in Group 1 as carcinogenic to humans. Vinyl chloride, a degradation product, is also Group 1 and is regulated at a much lower concentration than its parents.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Air stripping | Boiling in an enclosed space |
| 2 | Granular activated carbon | Sediment filtration |
| 3 | Advanced oxidation | Water softening |
| 4 | In-situ remediation of the source zone, which is slow and expensive | Conventional coagulation and filtration |
Occurrence
Dense solvent plumes are the classic long-tail groundwater contamination problem. Source zones persist for decades and full restoration of a contaminated aquifer is frequently not achievable at any realistic cost.
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted