1、 Risk-Based Methodologies for Evaluating Petroleum Hydrocarbon Impacts at Oil and NaturalGas E all 14 of the gas condensates contained benzene atconcentrations above 300 mg/kg. At benzene concentrations above thisthreshold, a simple, conservative Tier 1 analysis indicates that benzenecontrols the ri
2、sk at the site, where the limiting exposure pathway is notdirect contact with soil but leaching of the benzene from soil to ground-water. As such, the Tier 1 TPH RBSLs that are derived for ground-water protection purposes at an E present theequations for the calculation of risk-based screening level
3、s (AppendixB); and discuss the effect of hydrocarbon-saturated soil conditions onrisk-based screening levels (Appendix C). Lastly, a list of references, aglossary, and a list of abbreviations can be found at the end of the docu-ment.Several organizations are addres-sing the risk-based managementof h
4、ydrocarbon-impacted media:Gd8 American Petroleum Institute(API)Gd8 Total Petroleum HydrocarbonCriteria Working Group(TPHCWG)Gd8 Petroleum EnvironmentalResearch Forum (PERF) andGd8 GRI (formerly the GasResearch Institute, currently,GTI)Purpose of Document:Describe recent advances inrisk-based decisio
5、n-making andtheir use in establishing clean-up concentrations for E however, it may also be dictated bythe governing regulatory body.6At most E 1,000; or5,000Gd8 Texas: 10,000Gd8 Wyoming: 1,000 to 10,000Gd8 Alberta (Canada): 1,000Cost-benefit analysis will deter-mine if the more detailed Tier 2 orTi
6、er 3 analysis is warranted.Timing is also likely to be an im-portant factor.7manager must evaluate the potential reduction in site remedial coststhat may be realized by conducting the Tier 2 analysis and compare thatreduction to the additional cost of conducting the risk analysis. If thepotential sa
7、vings outweigh the potential cost, it would be in themanagers best interest to move forward with the analysis. In somecases, it is not the cost that drives the decision but the schedule. If thetime required to conduct the next tier of risk analysis is not acceptableto regulatory agencies or the publ
8、ic, then the decision to proceed withsite remediation is essentially made for the site manager.8PART IIICHARACTERISTICS OF CRUDE OILS,REFINED PETROLEUM PRODUCTS,CONDENSATES, AND E Kerr, et al., 1999a; Kerr, et al.,1999b; Magaw, et al., 1999a; Magaw, et al., 1999b; McMillen, et al.,1999a; McMillen, e
9、t al., 1999b. A summary of these chemical,physical, and toxicological data is presented here.CHEMICAL CHARACTERISTICSWHAT ARE THE CHEMICAL CHARACTERISTICS OF CRUDE OIL AND ITSREFINED PRODUCTS?In the broadest sense, petroleum hydrocarbons can be divided into twoclasses of chemicals, saturates and uns
10、aturates. The saturates, alsoreferred to as alkanes or paraffins-, are comprised of three main sub-classes based on the structure of their molecules: either straight chains,branched chains, or cyclic. Straight-chain compounds are known asnormal alkanes (or n-alkanes). The branched chain compounds ar
11、edesignated isoalkanes and the cyclic compounds, cycloalkanes. Petro-leum geologists typically refer to alkanes as paraffins and cycloalkanesas cycloparaffins or naphthenes. Within the unsaturates, there are twomain subclasses, aromatics and olefins. This classification of petro-leum hydrocarbons is
12、 summarized in Figure 1. The compounds encom-passed by the classification, aliphatic hydrocarbons, include all of thenon-aromatic compounds shown at the bottom of Figure 1 (i.e., n-alkanes, isoalkanes, cycloalkanes or naphthenes, and olefins). Aro-matic hydrocarbons are comprised of one or more unsa
13、turated cyclicstructures, or rings. Benzene contains one such ring, while polycyclicaromatic hydrocarbons contain two or more rings (e.g., phenanthrenehas three unsaturated rings).Crude OilFigure 2 describes the major classes of petroleum hydrocarbons that arepresent in crude oil. The primary satura
14、ted and unsaturated hydro-carbons consist of n-alkanes, isoalkanes, cycloalkanes, and the mono-,Chapter Overview:Gd8 Presents chemical, physicaland toxicological character-isticsGd8 Compares and contrastscharacteristics of differentmaterialsn-Alkane:Isoalkane:Cycloalkane:Unsaturates:Olefins:Aromatic
15、s:CH|HCH|HCH|HCH|HCH|HCH|HCH|H|C|HH HHHCH|HCH|HCH|HCH|HCH|HCH|HCH|HHHCCCCCH HHHHHHHH HCHHCHH=Saturates:(alkanes or paraffins)CH|CCHHHH|C|CC|HDoubleCa rbonBond9di-, and tri-aromatics; there are no olefins in crude oil. In addition tothese saturated and unsaturated hydrocarbons, there are also two non
16、-hydrocarbon fractions (i.e., fractions that contain compounds inaddition to carbon and hydrogen such as nitrogen, sulfur, and oxygen).These non-hydrocarbon fractions are the asphaltenes and resins.Crude oil is composedalmost entirely (i.e., 93% to99%) of hydrogen andcarbon, in the ratio ofapproxima
17、tely 2:1. Theseelements form the hydro-carbon compounds that arethe backbone of crude oil.Minor elements such assulfur, nitrogen, and oxygenconstitute less than 1 per-cent, to as much as 7 per-cent, of some crude oils.These elements are found inthe non-hydrocarbon com-pounds known as asphal-tenes an
18、d resins.FIGURE 1. CHEMICAL CLASSIFICATION OF PETROLEUM HYDROCARBONSPetroleumHydrocarbonsSaturates (alsoknown as paraffinsor alkanes)Unsaturatesn-alkanes(straightchain)isoalkanes(branchedchain)cycloalkanesor naphthenes(cyclic)Aromatics OlefinsFIGURE 2. MAIN GROUPS OF CHEMICAL COMPOUNDS IN CRUDE OILN
19、on-HydrocarbonsHydrocarbonsCrude OilLight DistillateFraction withBoiling Point210oCHydrocarbonsand ResinsSaturatedHydrocarbonsUnsaturatedHydrocarbonsaromatichydrocarbons (e.g.,mono, di-, Magaw, etal., 1999b; Kerr, et al., 1999a; Kerr, et al., 1999b. The analysis ofPAHs in 60 crude oils revealed that
20、 the mean concentrations of sevencarcinogenic PAHs were quite low for six of the seven compounds,ranging from 0.06 (indeno(1,2,3-cd)pyrene) to 5.5 (benz(a)anthracene)mg/kg oil. The mean concentration for chrysene was 28.5 mg/kg oil.Naphthalene accounted for as much as 85% of the total PAHs detected.
21、For the metals analyses of 26 crude oils, the mean concentrationsdetected were less than 1.5 mg/kg of oil for all metals except nickel,vanadium, and zinc. The mean concentrations of these three metalswere 20, 63, and 3 mg/kg of oil, respectively.Refined ProductsSince crude oil is comprised primarily
22、 of highly complex mixtures ofhydrocarbons, it follows that the products refined from crude oil arealso complex hydrocarbon mixtures. Indeed, they are even moreenriched in hydrocarbons than crude oil since the refining processesFIGURE 3. GAS CHROMATOGRAMSFOR TWO CRUDE OILSComposition of normal crude
23、 oilis bounded as follows:Gd8 40 to 80% saturatesGd8 15 to 40% aromaticsGd8 0 to 20% resins andasphaltenesCarbon-Number Range:Hydrocarbon mixtures are oftendefined in terms of the range ofthe number of carbons that arepresent in the individual com-pounds that make up the mix-ture. For example, gasol
24、ine iscomprised of hydrocarbons thathave anywhere from four to tencarbons in their chemical struc-ture. As such, the carbon-num-ber range for gasoline is C5-C10.11Range of concentrations forcarcinogenic PAHs and metalsin crude oils (mean concentra-tions, mg/kg):Gd8 Carcinogenic PAHs: 0.06for indeno(
25、1,2,3-cd)pyreneto 28.5 chryseneGd8 Metals: 1.5 except fornickel (20), vanadium (63),and zinc (3)used for their production either destroys nearly all of the non-hydro-carbons (i.e., asphaltenes and resins) or concentrates them in otherproducts. Since it is extremely difficult to identify all the comp
26、onentsof crude oils and its refined products, these materials are oftencharacterized in terms of boiling range and approximate carbon numberranges as previously discussed. To illustrate this point, Figure 4 showsboiling points and carbon number ranges for six common crude oilproducts ASTM, 1989. Not
27、e that the carbon number ranges for therefined products are much narrower than that of the crude oil itself.Note also that the boiling points of the products increase as their carbonnumber range increases.Blending agents and additives are also added to refined products. Thenature and quantity of the
28、se materials that are added vary substantiallyon a regional basis throughout the United States.Blending agents and additivesare also added to refinedproducts. Examples of theseinclude:Gd8 Anti-knock agents (methyl-tert-butylether)Gd8 Anti-oxidants(aminophenols)Gd8 Metal activators (aminopropane)Gd8
29、Lead scavengers (ethylenedibromide)Gd8 Anti-rust agents (sulfo-nates)Gd8 Anti-icing agents (alcohols)Gd8 Detergents (amides)Gd8 Ignition improvers (nitrates)Gd8 Combustion catalysts (MnO,MgO)Gd8 Cold flow improvers (poly-olefins)The addition of these materialsand the amounts used vary sub-stantially
30、 on a seasonal orregional basis throughout theUnited States.FIGURE 4. BOILING POINT AND CARBON NUMBER RANGES FOR SIX COMMON CRUDEOIL PRODUCTSTemperatures in C54049545040536031522518013590450Gasoline (C5-C10)30-200 CNaphtha (C8-C12)100-200 CKerosene and Jet Fuels (C11-C13150-250 CDiesel and Fuel Oils
31、 (C13-C17)160-400 CHeavy Fuel Oils (C19-C25)315-540 CLubricating Oils (C20-C45)425-540 C12WHAT ARE THE CHEMICAL CHARACTERISTICS OF CONDENSATES?Gas condensates are extracted with natural gas in a liquid form. Theyhave a narrower carbon number range than crude oil, typicallyextending from C6to C30.Gas
32、 chromatograms of the saturated and aromatic hydrocarbon frac-tions of two condensates are shown in Figure 5. These fingerprintsillustrate the large degree of variability that can exist for these hydro-carbon mixtures. In particular, it is clear that Condensate A encom-passes a much broader range of
33、 hydrocarbons than does Condensate B.Also, the ratio of the saturated hydrocarbons to the aromatichydrocarbons is quite different for these two condensates, increasingfrom 3.2 for condensate B to 5.8 for Condensate A.The chemical composition of fourteen gas condensates was determinedby the Petroleum
34、 Environmental Research Forum and GRI Hawthorne,et al., 1998; Rixey, 1999. From these studies, the following generali-zations regarding the detailed chemical composition of the condensatescan be made:Gd8 Major chemical components are the straight-chained andbranched saturated and unsaturated hydroca
35、rbons.Gd8 Benzene concentrations ranged from approximately 0.15 to3.6% by weight.Gd8 Only three of the seven carcinogenic PAHs were detected incondensates (benzo(b)fluoranthene, chrysene, and benzo(a)-anthracene). The highest mean concentration was that ofchrysene, 1.8 mg/kg oil. The concentrations
36、of the 16priority pollutant PAHs ranged from 200 to 6,000 mg/kg oil,with more than 95 percent of the total being naphthalene.From a somewhat broader perspective, the carbon number ranges thatwere represented by the condensates varied from a minimum range ofC5to C9to a maximum range of C6to C30.WHAT
37、ARE THE CHEMICAL CHARACTERISTICS OF E&P WASTES?There are a variety of wastes that are generated during each step of theoil and gas exploration and production process. An extensive listing ofthese wastes is provided in a publication by the American PetroleumInstitute, Environmental Guidance Document:
38、 Waste Management inExploration and Production Operations American Petroleum Institute,1997. These listings are tabulated based upon the specific phase ofexploration and production operations which include: (1) exploration,(2) drilling, (3) well completion and workover, (4) field production, and(5)
39、gas plant (including gas gathering) operations. A summary of theprimary wastes that are identified with each operation is provided inAppendix A.Typical Characteristics ofCondensates:Gd8 Typical carbon numberranges: (1) Minimum: C5toC9and (2) Maximum: C6toC30Gd8 Benzene concentrationsranging from 0.1
40、5 to 3.6%Gd8 Only three of seven car-cinogenic PAHs (benzo(b)-fluoranthene, chrysene, andbenzo(c)anthracene) weredetected in condensateswith chrysene having thehighest mean concentrationof 1.8 mg/kg oil.Gd8 Total priority pollutant PAHconcentrations: 200 to6000 mg/kg (mostlynaphthalene)FIGURE 5. GAS CHROMATOGRAMS OFGAS CONDENSATESCondensate BAromaticSaturateAromaticCondensate ASaturate* * Internal Standard
