BTEX and fracking

-What are BTEX chemicals?-

BTEX in gasoline-001The acronym “BTEX” actually refers to four separate chemicals with similar properties—Benzene, Toluene, Ethylbenzene, and Xylene.  BTEX chemicals are naturally occurring components of crude oil, meaning that they are found in small concentrations in refined oil products such as diesel, gasoline, and aviation fuel.  BTEX compounds are also used individually as raw materials and additives in commercial manufacturing.  Due to its versatility in chemical synthesis, benzene is used extensively as a base material for products like plastics, nylon, insecticides, and paint4.  Toluene is a common solvent found in paints, gums, oils, and resins4.  Ethylbenzene may be found in paints, inks, and plastics4.  Xylene is another solvent widely used in the printing, rubber, and leather industries4.

In terms of the fracking debate, BTEX chemicals have drawn concern due to their potential health effects.  While small levels of BTEX exposure—such as limited handling of paint or pumping gasoline—are not harmful, constant or high concentration exposure can have negative effects on the skin, central nervous, respiratory, liver, and kidney systems4.

BTEX exposureExacerbating these concerns is the fact that BTEX chemicals are easily spread through the environment.  BTEX chemicals are examples of volatile organic compounds or VOCs.  “Organic” simply means that the chemical is carbon based.  The area of concern for BTEX is the “volatile” characteristic.  A “volatile” chemical is one that easily converts from a liquid to a gas state.  This means that volatile organics like BTEX may easily contaminate liquids like oil and water as well as air, and readily travel between these mediums.  As such, it is important to track and contain BTEX chemicals during the fracking process.

Where are BTEX chemicals found in the fracking process?

BTEX and frackingBTEX chemicals can enter the hydraulic fracturing process from two main sources.  The first of these is in the fracking fluid.  Although this is the main concern of many activists and environmental groups, fracking fluid is actually not a common BTEX source.   Some early fracking processes experimented with diesel and petroleum gel fluids but this practice is no longer common today.  While BTEX chemicals are still used as dilute chemical additives, this practice is hardly widespread.  A search of records on the chemical disclosure site, FracFocus , shows 532 well sites currently using BTEX chemical additives1.  This search also included petroleum raffinates and light petroleum distillates, which may or may not contain BTEX components.  Even with this inclusion, these 532 cases make up only 1% of the 50,135 well sites whose chemical data is recorded on FracFocus1.   Furthermore, these additives are found in only miniscule amounts in standard fracking fluid.

A more common entry point for BTEX into the fracking process is underground.  Crude oil and natural gas are naturally occurring mixtures of various types of hydrocarbons—and BTEX compounds are often among these.  When oil and natural gas are released from impermeable rock, so are BTEX organics.  BTEX is more often a contaminant of produced water than an additive in fracking fluid.  While release of BTEX is an inevitable byproduct of oil and natural gas extraction, it is important to focus on where these chemicals go next.

Sources of BTEX contamination

To be specific, it is imperative that sources of BTEX contamination inherent to the fracking process are identified so that contamination of drinking water and air near populous areas may be avoided.

Contamination from fracking fluid?

While the injection of BTEX chemical additives into the earth may sound alarming, it is not a direct source of contamination.  Let’s take a look at the journey made by fracking fluid.  First, this fluid travels into the earth through a wellbore.  This wellbore is lined with casing—concentric layers of pipe and cement that, when properly constructed, are completely impermeable to the fluid and all chemical additives. The fluid then reaches the targeted rock formation.  This bedrock is also impermeable to fluid and natural gas.  After all, this is the reason why it is being fractured in the first place.  Fracking fluid and chemicals may flow into the new fractures, but will not travel further through the rock.  At this point, there is nowhere else for the fluid to go and it flows back up the impermeable casing.  Overall, this process is extremely contained.

Casing failure

After examining this process, it is clear that poor casing construction or casing failure is a key culprit in BTEX contamination.  A recent Duke University study showed increased methane content in groundwater near drilling sites.  These elevated levels are a result of methane leaking out of faulty well casings on its journey to the surface and migrating into aquifers through permeable rock.  When casing integrity is compromised, volatile organics like BTEX are capable of similar migration.

Produced water

untreated produced water pond

Open air produced water pond.

Although BTEX chemicals are often found in produced water, responsible treatment and handling can eliminate risk.   In most states, these precautions are ensured by regulatory requirements.  As air contamination can occur from holding produced water in open air ponds, this practice has been banned or restricted in many areas.  While produced water is most often reinjected in underground disposal wells, BTEX contamination can occur when wastewater is discharged into local water bodies.  As a result, states require and strictly enforce high standards cleaning and water treatment before issuing permits for such discharge.

Surface Spills

Between on-site flow streams and holding tanks for both produced water and oil and gas, fracking sites undoubtedly handle a lot of BTEX containing fluids—and these fluids can spill.  While historically, there has not been wealth of research examining the frequency and effects of BTEX surface spills, a recent study by ChemRisk attempts to fill this gap.  Completed in the spring of 2013, the study examines surface spills of BTEX in Weld County, Colorado over the course of a year.  The area is the densest drilling region in the United States, containing 18,000 active wells within county lines3.

During the year in question, 368 BTEX containing spills were documented in the area.  Less than .5% of all active wells reported a spill during the study period3.  However, 110 of these spills were determined to effect either nearby surface or groundwater.  In addition, this percentage shows that 368 spills occurred at only 90 sites, indicating that some wells or some operators are repeat offenders.

BTEX MCLsOf the 110 spills determined to effect water sources, 60 were tested for BTEX levels3.  On average, BTEX levels in the tested spills exceeded acceptable government limits for potable water.  Average benzene levels were observed to be 90% above the limit with toluene at 30% above, ethylbenzene at 12% above, and xylene at 8% over3.

BTEX spill sourcesThe most common cause of spills was found to be equipment failure rather than human error with spills most often occurring at on-site tank batteries and production facilities3.  While the ChemRisk study represents only an initial assessment of BTEX spill effects, results show that proper maintenance and repair of drilling equipment is essential to prevention of BTEX contamination associated with fracking.




1)       FracFocus. (2013).

2)       Hammer, R., VanBriesen, J., & Levine, L. National Resources Defense Council, (2012). In fracking’s wake: New rules are needed to protect our health and environment from contaminated wastewater

3)       Sahmel, J. (2013, January). Analysis of btex groundwater concentrations from surface spills associated with hydraulic fracturing operations in colorado.

4)       Technical Outreach Services for Communities. (n.d.). Informally published manuscript, Department of Engineering, Michigan State University, East Lansing, .



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