Total Petroleum Hydrocarbons in Vapor: Seeing the Forest for the Trees

An Overview and Laboratory Perspective of Air-Phase TPHSuzie Nawikas & Kristin Beckley for H&P Mobile Geochemistry, Inc.

Overview• General Review of TPH

– Why Worry About TPH in Vapor

– Carbon Ranges and Fractions

• Analytical Methods

– GC/FID and GC/MS Methods

– In Depth Look at MA APH Method

– Method Selection

• Summary

By John, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=4081809

What are Total Petroleum Hydrocarbons?

• Complex mixture of hundreds of distinct compounds with unique environmental considerations

• Range from very light gas products (natural gas) to heavy fuel oils and asphalt

• Can impact soil, water, soil vapor, and air

• May be present at a single site from a combination of sources

• Weathering and biodegradation can impact the analytical result and fuel identification

Sources of Petroleum Hydrocarbons

Photos by Branork - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3811632

Combustion

• Vehicles, Airplanes, etc.

• Cooking and Heating appliances

Industry

• Leaking USTs (gas stations, homes, commercial, etc)

• MGPs, Refineries

• Dry Cleaners

Household Goods

• Cleaning Products

• Toiletries

• Unexpected Products (Silly String, Candles, etc)

Natural Sources

• Seeps

• Natural Gas

• Naturally occurring organic matter in soil (peat)

Why do we care about TPH in Vapor and Air?

• EPA does have generic RSL values for TPH fractions in the air matrix, which can be considered in supplemental noncancer health risk assessments.

• Very few regional agencies regulate based on TPH, but the ones that do use individual criteria, making it very challenging as a lab and as a consultant.

• As an environmental laboratory, we are asked to report TPH in vapor and air on a weekly basis, and the data often generate more questions than answers.

• Language across work plans is often confusing and without consistent definition of the range to be reported, method to be used, or screening levels to be targeted (i.e. GRO, TPH as gasoline, etc)

EPA RSLs Resident – Air (Nov 2015)

Why is it so confusing?• Many regional guidelines do not reference specific carbon

ranges (or maybe they do), and the guidelines also provide a range of methods that are available, but not easily compared

• Very few methods are written specifically for TPH, leading laboratories to modify methods in a variety of ways

• General lack of mutual knowledge/communication between all parties involved (regulators, consultants, and labs)

“Total” Petroleum Hydrocarbons

• No single analysis can truly report all components of petroleum products.

– Although named “total,” all methods are limited to a specific range and type of analyte.

– Petroleum hydrocarbon analysis can vary greatly by method, from reporting a simple bulk concentration, to reporting fractions and individual compounds

TPH Carbon Ranges• Carbon Range refers to the number of carbons in the compound

• There is some uncertainty in carbon chain breakdown ranges since many methods are based on “marker” compounds such as basic alkanes (butane, hexane, heptane, etc)

• Branched hydrocarbons, or additive compounds (fuel oxygenates), may elute before or after their respective marker. For this reason, the carbon range of a particular product is best thought of as an estimated range for that product

• The achievable carbon range varies with each method, type of instrumentation, different laboratory, etc.

– For example, when requesting “TPH as gasoline” this could refer to C4-C12, C5-C12, C6-12, etc. Results for this test can vary greatly based on the defined carbon range and the product being evaluated

TPH Carbon Ranges

Volatile and Semi-Volatile Ranges in Soil Vapor and Air

Significant Overlap in the C8-C16 Range

Bulk Ranges (Default Ranges for H&P,

for example)TPH Gasoline C5-C12TPH Diesel C12-C22

Aliphatic and Aromatic Hydrocarbon Fractions

U.S. EPA 2009. PPRTV for Complex Mixtures of Aliphatic and Aromatic Hydrocarbons (CASRN). U.S. EPA, Superfund Technical Support Center, ORD, Cincinnati, OH.

Aliphatic and Aromatic Hydrocarbon Fractions

ALIPHATIC• C5-C8

– Pentane, Hexane, Cyclohexane, 2,3-Dimethylpentane, Heptane, Octane

• C9-C12– 2,3-Dimethylheptane,

Nonane, Undecane, Dodecane, Butylcyclohexane, Decane

AROMATIC• C9-C10

– Isopropylbenzene, Trimethylbenzenes, 1-Methly-3-ethylbenzene, isopropyltoluene

• Target Aromatic analtyes are often evaluated as individual compounds: BTEXN

“Air-Phase Petroleum Hydrocarbons are defined as collective ranges of hydrocarbon compounds eluting from isopentane to n-dodecane, excluding Target APH Analytes. APH is comprised of C5- C8 aliphatic hydrocarbons, C9-C12 aliphatic hydrocarbons, and C9-C10 aromatic hydrocarbons.”

APH, Rev1, Massachusetts DEP, December 2009

Aliphatic and Aromatic Hydrocarbon Fractions

Various APH Ranges offered by H&P, by request:

Review of TPH in Vapor and Air• TPH, in general, can be expected at a large number of sites,

whether or not it is included in the evaluation• Although regulations are inconsistent and TPH is not often a

driver for risk investigations, it is still being requested for certain states and projects

• Important to understand the complexity of the carbon ranges and associated fractions

• Putting “TPH” on a chain of custody is not enough – the lab needs additional information in order to meet the objective

Moving on to discuss various analytical methods available for TPH analysis…

Analytical Methods For TPH in Vapor and Air

GC/MS Methods

• EPA TO-3

• EPA TO-12

• EPA TO-14

GC/FID Methods

• IR Devices (Screening)• Tenax with Thermal Desorption (various detectors)• Other Sorbents with Solvent Extraction (various detectors)• Regional Methods

• 8015B/C• 8260SV (B/C)

• 8270C/D

• EPA TO-15 • EPA TO-17• MADEP APH

(and other state modifications)

EPA Toxic Organic (TO) Compendium Methods

SW-846 Methods

Other Methods

GC/FID Based Methodology• Detector responds to C-H (carbon-hydrogen bonds), making GC/FID methods responsive to

petroleum hydrocarbons and other compounds containing C-H bonds• Straight-chain hydrocarbons respond linearly and allow for methods based on the predictable

response• Instrumentation is easy to use and maintain, resulting in laboratory methods that may be more cost

effective than GC/MS based methods• Excellent for previously characterized sites with very high TPH concentrations and no presence of

chlorinated solvents (or other non-petroleum interference)• GC/FID methods can report individual compounds when set up to do so, but positive identification

of compounds is impossible without secondary method confirmation (GC/MS or second column confirmations)

• Selection of a GC/FID method should be done with care since going back to obtain additional information is not always possible: Many labs use shortened run times designed to only report a single TPH number without any ability to distinguish compounds or finite carbon ranges

• GC/FID results may bias false high by including non-petroleum concentrations indistinguishable from the TPH detection

Analytical Methods For Volatile & Semi-Volatile TPH

GC/FID Methods

EPA TO-3 (m)

EPA TO-12

EPA TO-14

8015B/C (m)

In general, GC/FID Methods are unable to distinguish aromatic/aliphatic breakdowns, and may only provide very limited carbon chain information

These are the two most commonly

used, and the method names are technically

interchangeable

Written for air, but rarely run as written, TPH reporting is a modification of the method

Written for TPH in soil and water, easily modified for vapor/air analysis

GC/MS Based Methodology• Detector responds to a wide variety of compounds (by mass), including petroleum

hydrocarbons• TPH concentrations are typically reported from an average response of the fuel

product (gasoline, diesel, etc) and provide the most representative concentrations when closely matching the unweathered fuel used in calibration

• Calculations and assumptions may be defined (APH) or undefined in the method (general TPH)

• Library search functionality allows the identification of unknown compounds that may be impacting overall TPH results

• The more sophisticated GC/MS instrumentation allows separation of TPH concentrations from other non-petroleum components (particularly chlorinated compounds)

• Methods are generally more costly than GC/FID, but may be run concurrently with other tests for VOCs and SVOCs, making the TPH analysis a less expensive “add on”

Analytical Methods For Volatile & Semi-Volatile TPH

GC/MS Methods

• EPA TO-15 • EPA TO-17• MADEP APH

(and other state modifications)

• 8260SV (B/C)

• 8270C/D

GC/MS Methods are designed for targeted VOC reporting, which in turn allows for targeted APH or TPH reporting with valuable interpretation and

insight as to what is contributing to the TPH concentrations.

Only method(s) ACTUALLY WRITTEN FOR PETROLEUM

FRACTIONS IN AIR!

TO-15, MA APH, 8260 = TPH GRO, TO-17, 8270 = TPH GRO & DRO

For all methods on this list, they are designed for VOCs but are

readily adapted for TPH reporting

Air Phase Petroleum Hydrocarbons (APH) Approach• Not to be confused with EPH or VPH, both intended to describe

soil/water matrices (although VPH is often used incorrectly for Vapor rather than Volatile)

• GC/MS based methods can report aliphatic and aromatic ranges. • Methods (MADEP-APH, etc) provide laboratories with specific

guidance for reporting aromatic & aliphatic ranges while omitting chlorinated solvents and other non-petroleum compounds

• Target alkanes and aromatics are used to calculate a response factor for similar compounds and define carbon ranges for reporting

• Ion scans are used to separate aromatic hydrocarbons from aliphatic during data processing

• Often run in conjunction with traditional EPA TO-15, since much of the APH method QC is adopted from TO-15. The MADEP method specifies a short volatiles list in addition to the APH fractions, but this is often substituted for the full TO-15 reporting to maximize the reported information

• MADEP-APH method provides a conservative approach to account for late/early eluting branched and cyclic hydrocarbons (takes into consideration limitations of using carbon range markers)

APH, Rev1, Massachusetts DEP, December 2009

Method Selection ConsiderationsWhen using a GC/MS Method instead of or in addition to a GC/FID Method, it allows the analyst to think critically about the concentrations contributing to the TPH values.

The laboratory can subtract and/or identify non-fuel hydrocarbons. Natural products such as limonene, pinene, and camphene elute in the higher gasoline range and can dramatically impact results.

Soil Vapor: Environmental

Sample Chromatograph

(8260SV Soil Vapor Analysis by GC/MS

for VOCs and TPHg)

8260SV TPH gas (C5-C12) Analysis

C5-C12 = 2,400 ug/LHowever…PCE = 1,600 ug/L

PCE was removed from the TPH value, yielding a TPH gas result of 800 ug/L

GC/FID would not show this detail

Method Selection Considerations

• GC/FID Methods definitely have their place – the intent is not to lure people away from GC/FID – just to be aware of the limitations.

• Is the suspected fuel product in the carbon range achievable by the method?

• Does the method meet reporting limit objectives for screening, given the expected concentrations of the sample?

• Is historical data available for the site to indicate the range of detected hydrocarbons?

• Is historical data available for other site contaminants (especially chlorinated solvents)?

• Is Risk Assessment being performed? Are aromatic/aliphatic breakdowns of interest?

The laboratory can be a great source of information when determining the appropriate approach. Discuss your objectives and site history with them.

In Summary

• Instrumentation and method selection are critically important to data objectives• Involving your lab in the discussion early can help match services to your site• Every method has a purpose, and there is no one right or wrong answer (it will vary

by site and by objective)• BE AWARE of the vast differences in TPH reporting across labs, methods, etc – don’t

always assume that you are comparing apples to apples• Ask questions and be informed

Much like someone evaluating a forest, it is important to consider whether you are looking at the forest as a whole, the types of trees, or the impact of each type. Further, at what point does the overwhelming size of the forest negate

the need to look at a single tree? This is the type of discussion that is necessary for TPH evaluations. - Kristin Beckley

Questions?Suzie.Nawikas@handpmg.comKristin.Beckley@handpmg.com