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

Transcription

1 Total Petroleum Hydrocarbons in Vapor: Seeing the Forest for the Trees An Overview and Laboratory Perspective of Air-Phase TPH Suzie Nawikas & Kristin Beckley for H&P Mobile Geochemistry, Inc.

2 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,

3 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

4 Sources of Petroleum Hydrocarbons 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) Photos by Branork - Own work, CC BY 3.0,

5 Why do we care about TPH in Vapor and Air? EPA RSLs Resident Air (Nov 2015) 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)

6 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)

7 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

8 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

9 TPH Carbon Ranges Bulk Ranges (Default Ranges for H&P, for example) TPH Gasoline C5-C12 TPH Diesel C12-C22 Volatile and Semi-Volatile Ranges in Soil Vapor and Air Significant Overlap in the C8-C16 Range

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

11 Aliphatic and Aromatic Hydrocarbon Fractions 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. 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 APH, Rev1, Massachusetts DEP, December 2009

12 Aliphatic and Aromatic Hydrocarbon Fractions Various APH Ranges offered by H&P, by request:

13 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

14 Analytical Methods For TPH in Vapor and Air GC/MS Methods GC/FID Methods EPA TO-15 EPA TO-17 MADEP APH (and other state modifications) 8260SV (B/C) 8270C/D EPA Toxic Organic (TO) Compendium Methods SW-846 Methods Other Methods EPA TO-3 EPA TO-12 EPA TO B/C IR Devices (Screening) Tenax with Thermal Desorption (various detectors) Other Sorbents with Solvent Extraction (various detectors) Regional Methods

15 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

16 Analytical Methods For Volatile & Semi-Volatile TPH GC/FID Methods 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 EPA TO-3 (m) EPA TO-12 EPA TO B/C (m) These are the two most commonly used, and the method names are technically interchangeable In general, GC/FID Methods are unable to distinguish aromatic/aliphatic breakdowns, and may only provide very limited carbon chain information

17 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

18 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 TO-15, MA APH, 8260 = TPH GRO, TO-17, 8270 = TPH GRO & DRO Only method(s) ACTUALLY WRITTEN FOR PETROLEUM FRACTIONS IN AIR! For all methods on this list, they are designed for VOCs but are readily adapted for TPH reporting 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.

19 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)

20 Method Selection Considerations When 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. APH, Rev1, Massachusetts DEP, December 2009

21 8260SV TPH gas (C5-C12) Analysis C5-C12 = 2,400 ug/l However PCE = 1,600 ug/l Soil Vapor: Environmental Sample Chromatograph (8260SV Soil Vapor Analysis by GC/MS for VOCs and TPHg) PCE was removed from the TPH value, yielding a TPH gas result of 800 ug/l GC/FID would not show this detail

22 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.

23 In Summary 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 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

24 Questions?