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Environmental ForensicsPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713770863

On Methods for Age-Dating Diesel Fuel Released in the Near-SurfaceEnvironmentYakov Galperina; Isaac R. Kaplanba Environmental Geochemistry Consulting, Moorpark, CA, USA b Institute of Geophysics andPlanetary Physics, University of California, Los Angeles, CA, USA

Online publication date: 16 March 2011

To cite this Article Galperin, Yakov and Kaplan, Isaac R.(2011) 'On Methods for Age-Dating Diesel Fuel Released in theNear-Surface Environment', Environmental Forensics, 12: 1, 3 4

To link to this Article: DOI: 10.1080/15275922.2011.547436URL: http://dx.doi.org/10.1080/15275922.2011.547436

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Environmental Forensics, 12:34, 2011

Copyright C Taylor & Francis Group, LLC

ISSN: 15275922 print / 15275930 online

DOI: 10.1080/15275922.2011.547436

On Methods for Age-Dating Diesel Fuel Released in theNear-Surface Environment

Yakov Galperin1 and Isaac R. Kaplan2

1Environmental Geochemistry Consulting, Moorpark, CA, USA2Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA

The editorial by Oudijk and Wade in this issue of the journal

demonstrates that confusion still exists regarding the applica-

bility of Christensen and Larsen (1993) method (C&L) for age-

dating middle-distillate fuels in the near-surface environment.

The general comments in the editorial suggest a misunderstand-

ing regarding a fundamental difference between the approach to

this method developed by Hurst and Schmidt (2005), which they

called the middle distillate degradation (MDD) model, and our

interpretation based on the basic Monod model for microbial

substrate utilization kinetics (Galperin and Kaplan, 2008).

The C&L method established an empirical linear correlation

between the time since occurrence of a diesel fuel release and

the corresponding values ofn-C17/Pr ratio. This correlation was

ascertained for vadose (unsaturated) zone soil contamination

occurring from a sudden fuel release at sites with specified sets

of environmental conditions (e.g., geographic location, hydro-

carbon concentration, sampling depth). Because of the empir-

ical nature of this correlation and the absence of descriptionsof certain environmental parameters, no objective criteria can

be developed on acceptable values of these parameters (i.e., soil

characteristics, site hydrology, moisture content, and availability

of oxygen and nutrients) for establishing the applicability limits

of the C&L age-dating approach. An attempt to account for dif-

ferent environmental conditions through the matrix of weath-

ering regimes (Oudijk, 2009) is based on subjective values and

therefore is unreliable. In addition to the absence of criteria for

site-specific environmental conditions, application of the C&L

approach is confounded by uncertainties introduced by variabil-

ity of the initial n-heptadecane to pristane ratio, (n-C017 )/(Pr0).

The MDD model (Hurst and Schmidt, 2005) was proposed

as an extension of the empirical C&L correlation, which inaddition to hydrocarbon-contaminated soil, includes separate-

phase petroleum products and a broad range of environmental

settings. Evaluation of the MDD model reveals inconsistencies

in its experimental base and theoretical premise (Galperin and

Kaplan, 2008a). The extension proposed by Hurst and Schmidt

Address correspondence to Yakov Galperin, Environmental Geo-chemistry Consulting, 13543 Bear Valley Road, Moorpark, CA, 93021,USA. E-mail: [email protected]

(2005) assumes the uniform rate of alkane biodegradation un-

der typically aerobic conditions in vadose zone soil and un-

der predominantly anaerobic conditions of the separate-phase

product, which contradicts published analytical data and the

body of information accumulated in the literature on biodegra-

dation of petroleum hydrocarbons. Due to the lack of a ba-

sic model for hydrocarbon biodegradation in the near-surface

environment, Hurst and Schmidt (2005) also misinterpret the

effect of the initial (n-C017 )/(Pr0) values on the release age

calculation.

The Galperin and Kaplan (2008) approach describes the em-

pirical linear correlation established by C&L in terms of the

Monod model with zero-order kinetics. This model accounts for

variations in the initial (n-C017 )/(Pr0) values and allows for de-

veloping criteria for evaluating applicability of this age-dating

method in different environmental settings. For example, be-

cause the Monod model relates the rate of substrate metabolism

to the concentration of a single growth-controlling substrate(Alexander, 1994), it implies an adequate supply of oxygen and

nutrients, so that they do not limit bacterial metabolism. Accord-

ingly, the C&L approach can only be applied to hydrocarbon

contamination in the vadose zone soil where the availability of

sufficient concentration of O2 favors aerobic biodegradation. In

contrast, a much slowerdegradation occurs under predominantly

anaerobic conditions that commonly develop in the groundwa-

ter (saturated) zone or in a body of non-aqueous phase liquid

(NAPL).

The unsaturated zone soil water content is also a major fac-

tor affecting hydrocarbon biodegradation. The degree to which

the soil pore space is filled with water affects the exchange of

gases through the soil. The optimal water saturation is typicallyassumed to range from 30% to 70% of the total soil porosity,

depending on the soil texture. In practice, however, soil water

content hasbeen found to directly limit biodegradation rates only

in very dry desert environments. A more common influence, is

that excess of soil water has led to significant reductions in soil

gas permeability and therefore deficiency of O2 required for

hydrocarbon mineralization. As in the case with water, the pore

space can be filled with NAPL, which will also restrict the move-

ment of gases, so that O2 can be rapidly depleted and aerobic

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4 Y. Galperin and I. R. Kaplan

degradation is severely inhibited. Residual NAPL concentration

in the vadose zone soil should be considered as being close to the

upper concentration limits of applicability of the model. In order

to sustain microbial growth, certain nutrients must be available

at minimum levels. Primary nutrients, nitrogen and phosphorus,

are required in thegreatest concentrations andare themost likely

to be limiting, whereas the rest are considered micronutrients

and generally are available in excess in soil. However, because

nutrients are not destroyed, but recycled in an ecosystem, un-

like O2, a steady input of nutrients is not required (Leeson and

Hinchee, 1996).

Attempts to use this model outside of its applicability lim-

its lead to mistakes in the calculated age of the fugitive fuel

in the subsurface environment (Stout et al., 2002; Wade, 2002;

Galperin and Kaplan, 2008, 2008a). It should be mentioned

that in most environmental investigations, the variability in the

main parameters affecting the rate of biodegradation typically

allow for only semi-quantitative estimating age of a fuel release

(typically within 5-year intervals). It is also widely accepted

that because of the multiple variables involved, the n-C17

/Pr

ratio is only one of many factors that typically need to be rec-

onciled for a reliable estimate of a fuel release age (Kaplan,

2003).

References

Alexander, M. 1994. Biodegradation and bioremediation. New York: Aca-demic Press.

Christensen, L. B., and Larsen, T. H. 1993. Method for determining the ageof diesel oil spills in the soil. Ground Water Monitoring and Remediation23(4): 142149.

Galperin, Y., and Kaplan, I. R. 2008. Zero-order kinetics model for theChristensen-Larsen method for fugitive fuel age estimates. Ground Water

Monitoring and Remediation 28(2): 9497.Galperin, Y., and Kaplan, I. R. 2008a. Age significance of n-C 17/Pr ra-

tios in forensic investigations of refined product and crude oil releases:Discussion. Environmental Geosciences 15(2): 8586.

Hurst, R. W., and Schmidt, G. W. 2005. Age significance of nC 17/Pr ra-tios in forensic investigations of refined product and crude oil releases.Environmental Geosciences 12(3): 177192.

Kaplan, I. R. 2003. Age dating of environmental organic residues. Environ-mental Forensics 4(3): 95141.

Leeson,A., andHinchee, R.E. 1996. Principles and practicesof bioventing.Volume I: Bioventing principles. Battelle Memorial Institute, Columbus,OH, pp. 184.

Oudijk, G. 2009. Age dating heating-oil releases, Part 2. Assessing weath-ering and release time frames throughchemistry, geology and sitehistory.Environmental Forensics 10(2): 120131.

Stout, S. A., Uhler, A. D., McCarthy, K. J., and Emsbo-Mattingly, S. D.

2002. Invited commentary on the Christensen and Larsen technique. En-vironmental Forensics 3(1): 911.

Wade, M. J. 2002. Invited commentary on the Christensen and Larsentechnique. Environmental Forensics 3(1): 13.

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