Chlorinated VOCs
Hepure supplies the three proven chemistries for chlorinated volatile organic compounds (CVOCs) in soil and groundwater: abiotic reduction with zero valent iron, in situ chemical oxidation with permanganate and persulfate, and the electron donors for enhanced anaerobic bioremediation.
About chlorinated VOC contamination
Chlorinated volatile organic compounds are the most common groundwater contaminants in the United States. The family includes the chlorinated ethenes, tetrachloroethene (PCE) and trichloroethene (TCE) and their degradation products dichloroethene (DCE) and vinyl chloride; the chlorinated ethanes, such as 1,1,1-trichloroethane (TCA); and the chlorinated methanes, carbon tetrachloride and chloroform.
They were the workhorse solvents of twentieth-century industry, used for degreasing, dry cleaning, electronics and metal finishing, and released through floor drains, leaking tanks and routine handling at former industrial sites, dry cleaners, military installations and manufacturing plants. Most are dense non-aqueous phase liquids (DNAPLs): heavier than water, they sink through the aquifer and pool on low-permeability layers, where a small volume of product can sustain a dissolved plume for decades.
The chlorinated ethenes also degrade into one another. Under reducing conditions PCE loses chlorine atoms one at a time, PCE to TCE to cis-DCE to vinyl chloride to ethene, and each step is slower and harder than the last. A site that treats the parents without finishing the sequence can end up with a vinyl chloride plume that is more toxic and more strictly regulated than what it started with. That is the single most important fact in CVOC remediation, and it shapes which chemistry fits which site.
Regulatory limits
| Compound | Federal MCL |
|---|---|
| Tetrachloroethene (PCE) | 5 µg/L |
| Trichloroethene (TCE) | 5 µg/L |
| cis-1,2-Dichloroethene | 70 µg/L |
| trans-1,2-Dichloroethene | 100 µg/L |
| 1,1-Dichloroethene | 7 µg/L |
| Vinyl chloride | 2 µg/L |
| 1,1,1-Trichloroethane | 200 µg/L |
| Carbon tetrachloride | 5 µg/L |
| 1,2-Dichloroethane | 5 µg/L |
State groundwater standards and vapor intrusion screening levels are frequently stricter than these federal drinking-water values.
CVOCs treatable with Hepure products
The following chlorinated compounds can be addressed with Hepure’s product line, based on the documented treatment capabilities of zero valent iron, permanganate and activated persulfate. See what ZVI treats for the full iron list.
Tetrachloroethene (PCE)
Also known as perchloroethylene
Trichloroethene (TCE)
Common industrial degreaser
cis-1,2-Dichloroethene
TCE degradation product
trans-1,2-Dichloroethene
TCE degradation product
1,1-Dichloroethene
Vinylidene chloride; TCA degradation product
Vinyl Chloride
Final chlorinated degradation product
Tetrachloromethane
Carbon tetrachloride
Trichloromethane
Chloroform
1,1,1-Trichloroethane
Methyl chloroform
1,1,2-Trichloroethane
Vinyl trichloride
Hexachloroethane
Industrial chemical
1,2,3-Trichloropropane
Industrial solvent
Treatment technologies for CVOCs
Three chemistries cover the family. The right one depends on the compound, the mass, the geology and how long the remedy needs to keep working.
Zero Valent Iron (Ferox ZVI)
ZVI powders reduce chlorinated solvents at the iron surface. For the ethenes the main pathway is beta-elimination, which skips the DCE and vinyl chloride steps entirely; for the ethanes and methanes it is sequential dechlorination at the metal. Since 2000, Hepure’s Ferox iron powders have documented successful outcomes at more than 150 sites across North America. A placement stays reactive for 3 to 15 years, is not consumed by soil oxidant demand, and conditions the aquifer for follow-on bioremediation.
View ZVI Products →Permanganate (ISCO)
Potassium permanganate (KMnO4) and sodium permanganate (NaMnO4) attack the carbon-carbon double bond and oxidize PCE, TCE, DCE and vinyl chloride to carbon dioxide, chloride and manganese dioxide, with no chlorinated intermediates. Permanganate persists for weeks to months and needs no activation. It does not react with the saturated compounds (chlorinated ethanes and methanes), so a mixed plume needs ZVI or persulfate for those.
View Permanganate Products →Activated Persulfate
Activated sodium persulfate generates sulfate radicals that oxidize the full CVOC family, including the ethanes and methanes permanganate leaves alone, as well as co-mingled BTEX and petroleum hydrocarbons. Activation by alkali (Hepure supplies the sodium hydroxide), heat, chelated iron or peroxide is required, and the oxidant persists for days to weeks.
View All Oxidants →Enhanced Anaerobic Bioremediation
Electron donors feed the reductive dechlorination that native bacteria, chiefly Dehalococcoides, carry out one chlorine at a time. Emulsified vegetable oil provides years of slow-release hydrogen; sodium lactate provides a fast start. The remedy succeeds when the sequence is driven all the way to ethene, which is why donors are often paired with ZVI (Ferox Plus, or separate placements) so the abiotic pathway backs up the biological one.
View Bioremediation Products →Which chemistry for which situation
| Situation | Usual choice |
|---|---|
| Source zone, high mass, DNAPL suspected | Sodium permanganate for concentration; Ferox Target for soil mixing; often both in sequence |
| Dissolved plume needing years of control | Ferox PRB barrier or injected Ferox Flow; EVO where biology is established |
| Daughter products (DCE, vinyl chloride) accumulating | ZVI, which does not produce them, or permanganate to destroy them outright |
| Chlorinated ethanes or methanes (TCA, carbon tetrachloride, chloroform) | ZVI or activated persulfate; permanganate is not effective |
| CVOCs mixed with petroleum hydrocarbons or BTEX | Activated persulfate, or ZVI plus an oxygen or donor program |
| Receptor at risk while source treatment proceeds | ZVI barrier or colloidal carbon barrier to arrest migration |
Common questions
Can an oxidant and ZVI be used at the same site? Yes, in sequence, not together. Oxidant first for the source, then ZVI or donor downgradient or after the oxidant is spent. A reductant placed into a freshly oxidized zone is consumed by the residual oxidant.
How much product will a CVOC site need? For oxidants, the contaminant mass times its stoichiometric demand plus the natural oxidant demand of the soil, which usually dominates. For ZVI, the mass, the flow through the treatment zone and the design life. For donors, the competing electron acceptors (oxygen, nitrate, sulfate, iron) as much as the CVOCs. Send us the site data and we will give you a quantity estimate.
Do these products work in fractured bedrock or clay? The chemistry does; delivery is the challenge. Liquids (sodium permanganate, persulfate solution, EVO, lactate) travel further in tight formations than solids; ZVI is placed where it can be mixed, injected in a slurry, or set in a trench. Your contractor’s delivery method will shape the product choice, and we are glad to talk with them directly.