BTEX Remediation

About BTEX Contamination

BTEX is the shorthand for four aromatic hydrocarbons that come out of the ground together wherever gasoline or other light petroleum products have been released: benzene, toluene, ethylbenzene and the three xylene isomers. They are found at service stations, fuel storage terminals, refineries, pipelines and industrial sites, usually as the most mobile and most regulated part of a larger petroleum hydrocarbon plume. Of the four, benzene drives most cleanups: it is a known human carcinogen, it is the most soluble, and its federal drinking-water limit is 5 parts per billion, two to three orders of magnitude tighter than the limits for the other three.

The good news about BTEX is that it is one of the easier contaminant groups to destroy. The aromatic ring is vulnerable to strong oxidants, and the compounds are readily biodegradable under both aerobic and anaerobic conditions. The usual difficulty is not the chemistry but the setting: free product in the source area, low-permeability soils, and the volume of oxidant or oxygen a hydrocarbon plume can consume.

Regulatory limits

Compound	Federal MCL (drinking water)	Notes
Benzene	5 µg/L (0.005 mg/L)	Known human carcinogen; usually the driver
Toluene	1 mg/L	Readily biodegradable
Ethylbenzene	0.7 mg/L	Often persists longest in anaerobic plumes
Xylenes (total)	10 mg/L	Ortho-, meta- and para- isomers combined

State groundwater standards are frequently stricter than the federal values, and many sites are driven by benzene vapor-intrusion thresholds rather than the drinking-water number. Check the standard that applies to your site before sizing a remedy.

Treatment Options for BTEX

Chemical oxidation (ISCO)

Activated sodium persulfate. The most common ISCO choice for BTEX. Persulfate on its own is a modest oxidant; activated with alkali, heat, chelated iron or peroxide it generates sulfate radicals that open the aromatic ring and carry the molecule through to carbon dioxide. It persists in the subsurface for days to weeks, which gives it time to spread through a treatment zone. Hepure supplies the sodium persulfate and, for alkaline activation, the sodium hydroxide.

Hydrogen peroxide (Fenton’s chemistry). Catalyzed with iron, hydrogen peroxide produces hydroxyl radicals that destroy BTEX very quickly, which makes it a good fit for hot spots and source zones. It is short-lived, so it is applied close to the mass it is meant to treat, and the oxygen it leaves behind feeds aerobic biodegradation afterward. Ferrous sulfate is the usual iron catalyst.

Permanganate. Permanganate oxidizes BTEX, but slowly compared with its reaction with chlorinated ethenes; benzene in particular resists it. It is rarely the first choice for a BTEX-only site, and we will say so if asked.

Enhanced bioremediation

Aerobic (oxygen release). BTEX degrades fastest where oxygen is available, and oxygen is almost always the limiting factor in a hydrocarbon plume. Calcium peroxide releases dissolved oxygen slowly over months as it reacts with water, sustaining the aerobic bacteria that do the work. For scale: complete aerobic degradation of benzene consumes about 3 grams of oxygen per gram of benzene, and pure calcium peroxide yields about 0.22 grams of oxygen per gram of product, so the quantity needed follows directly from the hydrocarbon mass in the treatment zone.

Anaerobic (electron donor). Where the aquifer is strongly reducing, BTEX, especially toluene and the xylenes, can be degraded under sulfate-reducing or methanogenic conditions. Emulsified vegetable oil and sodium lactate supply the carbon and hydrogen that sustain those populations. Benzene and ethylbenzene are the slow ones anaerobically, which is why most BTEX programs that reach closure lean on oxygen.

Sequencing

Many sites use the oxidant for the source and the oxygen release for the plume: a persulfate or Fenton’s injection to knock down mass, then calcium peroxide to keep the plume aerobic while the bacteria finish the job. Oxidants and oxygen release are compatible; oxidants and anaerobic donors are not, so a site should not be fed EVO and persulfate in the same zone at the same time.

Common Questions

Persulfate or peroxide for a BTEX source?

Peroxide is faster and cheaper per pound but spends itself within hours; persulfate costs more and lasts weeks, so it reaches further from the injection point. Tight, well-defined hot spots favor peroxide; larger or less accessible source zones favor activated persulfate.

How much oxidant will the site consume?

More than the contaminant alone would suggest. Natural organic matter, reduced iron and manganese in the soil all consume oxidant before it reaches the BTEX. A natural oxidant demand test on site soil, run by your laboratory, is the only reliable way to size an injection; we can supply bench quantities for it and help turn the result into a product quantity.

Can calcium peroxide be used alone?

For dissolved plumes with no free product, yes. Oxygen release alone has closed many fuel sites. Where free product or high concentrations remain in the source, an oxidant first is usually the faster path.

Related contaminants: petroleum hydrocarbons and PAHs.