Luc Paul Tousignant -
Environmental Engineering Services (LPT)
540, boul. De l’Hopital
Suite 404
Gatineau, Quebec J8V 3T2
Ph: (819) 243-5853
Fax: (819) 243-9130
E-mail: lpt@qc.aira.com

Philip Augustine
Augustine, Bater, Polowin
Suite 1100, 141 Laurier Steet
Ottawa, Ontario K1P 5J3
Ph:(613) 569-9500
Fax:(613) 569-9522
E-mail: pwa@abplaw.com

The relationship (if any) between the age of petroleum found in the subsurface and its non-weathered condition was considered during a recent environmental arbitration. The arbitration involved a major petroleum company (vendor) and a commercial wholesale distributor (purchaser). At stake was the legal and financial responsibility for approximately $2,600,000 in soil and groundwater remediation. The petroleum company took the position that because the petroleum product encountered within the subsurface had a non-weathered gas chromatographic (GC) profile, the petroleum was of recent origin. On this basis, the petroleum company denied legal and financial responsibility for the clean-up of contaminated soil and groundwater at the subject site. The wholesale distributor argued that while, superficially petroleum product exhibiting a non-weathered GC profile would appear to imply that the petroleum product was of recent origin, that conclusion is not necessarily correct and is subject to numerous local conditions. The following paper will present a case study of the arbitration, a description of the various factors affecting weathering of free petroleum product, a discussion on the effectiveness of age dating of hydrocarbons and the arbitrators ruling/conclusion.

Case Study

The subject site consisted of two (2) former bulk petroleum storage facilities which were situated side by side (one immediately north of the other) on a 14 hectare piece of property, located in the City of Ottawa, Ontario (Photo 1). In the mid 1980s, a major petroleum company acquired the two petroleum facilities and subsequently decommissioned them both during the late 1980’s.

Geological Conditions

The northern and southern portions of the site is underlain by a brown, fine-to-medium grained sand of post glacial origin (Richard et al., 1967). Thin, grey, silty sand and silty clay units are found interbedded within the sand throughout the site. The local groundwater table is at an average depth of 5 metres below grade. A perched water table was also encountered in one area of the southern
portion of the site at a depth of approximately 2 metres below grade. The local groundwater regime was calculated to have an average hydraulic gradient of approximately 0.01 m/m in a northeasterly direction.

Northern Site

Upon decommissioning the petroleum storage facilities on the northern portion of the site, the petroleum company retained an environmental consultant to assess whether the underlying soil and groundwater regimes had been adversely impacted from the past operation of the facility. After several subsurface investigations were undertaken, the consultant concluded that the site met provincial standards. Based on their conclusions, the petroleum company sold the northern portion of the site to a third party. Subsequently, this portion of the site was found to have extensive groundwater contamination, which was characterised by both dissolved phase and free phase petroleum product. The petroleum company gave the new purchaser assurances that it would remediate the site. In the fall of 1990, the petroleum company conducted a major remediation program involving a major excavation to remove the free petroleum product from the surface of the groundwater. At the conclusion of the excavation, the consultant for the petroleum company concluded that all free product had been removed from the subsurface of the site. In order to treat the dissolved phase groundwater contaminant plume, the consultant installed, operated and monitored a groundwater pump and treat system.

In 1991, while the groundwater pump and treat system was still being operated and monitored by the petroleum company’s consultant, the northern site was sold by the third party to the commercial wholesale distributor (purchaser).

In 1992, free petroleum product was discovered in an existing monitoring well on the northern portion of the site (hereinafter referred to as monitoring well N1). This monitoring well was located beneath the northern former bulk petroleum storage facility and was situated immediately adjacent a former above ground diesel storage tank.

The petroleum company immediately claimed that the petroleum product in N1 was a result of vandalism for which it was not responsible. The petroleum company claimed that the petroleum product was introduced into the subsurface sometime after it completed its remediation attempts. The petroleum company claimed that the petroleum product negated all of its past remedial efforts and thus it was no longer responsible for any further on-site remediation and ceased dissolved phase remediation on the northern portion of the site.

Southern Site

The petroleum company had an initial investigation completed of the southern site by their same consultant. Based on the results of their investigations, the consultant concluded that the southern portion of the site met acceptable provincial criteria.

Prior to the wholesale distributor (purchaser) completing the purchase of the southern property, Trow Consulting Engineers (Trow), was retained to verify the subsurface conditions of the site on behalf of the purchaser. Trow found free petroleum product floating on the surface of the groundwater regime and heavily contaminated soil beneath portions of the site. Faced with these facts, the petroleum company acknowledged that the site did not meet acceptable provincial criteria and accepted responsibility for the remediation of the site. With this commitment in hand, the commercial purchaser completed the purchase of the southern site in 1991, but held back approximately 50% of the purchase price pending successful completion of the remediation by the petroleum company.

In the summer of 1991, the petroleum company completed a major soil excavation program on the southern portion of the site. The primary focus of the remediation program was to recover the free petroleum product from the surface of the groundwater table and remediate the soil and groundwater regimes to acceptable provincial criteria. In an attempt to reduce costly landfill disposal fees, the petroleum company’s consultant attempted to treat the contaminated soil on-site using enhanced volatilization techniques.

Over the next 5 years, the petroleum company performed no less than four additional remediation attempts to bring the southern portion of the site into compliance with provincial regulations. All of these additional remedial attempts focused on near surface (< 3-4 m) soil contamination. Verification studies performed by OMM/Trow and others showed each time that the remedial attempts failed to attain the desired remediation objectives.

In 1996, free petroleum product was encountered in a newly constructed monitoring well on the southerly site (hereinafter referred to as monitoring well S1) which was located beneath a part of the southern former bulk petroleum storage facility. Once again, the petroleum company claimed vandalism was the source of the free product discovered in S1 and terminated all site remedial efforts.

The petroleum product in both the N1 and S1 monitoring wells was measured, at times, to be up to 0.4 m in thickness. A free product sample was collected by Trow from monitoring well S1 and submitted to an environmental laboratory for characterization. The laboratory found the petroleum product to have a chromatographic profile similar to that of non-weathered diesel fuel.

Remediation by Purchaser

In order to proceed with the development of the site, the commercial purchaser took it upon itself to remediate both the northern and southern portions of the site. Trow was retained to design and supervise the construction of an innovative, partially subgrade bioremediation facility which was used to treat the contaminated soil from both portions of the site in two separate batches. The bioremediation facility, or bioreactor, incorporated the use of the A.M.O.E.B.A.TM Process - a bioremediation technology developed by Trow for the federal government in 1994. The system also incorporated an elaborate on-site groundwater treatment system to treat the dissolved phase groundwater contaminant plumes underlying both the northern and southern former bulk petroleum storage facilities.

Arbitration

The commercial purchaser sought monetary reimbursement from the petroleum company for the cost of the final site remediation programs, which it undertook. The petroleum company refused to reimburse the commercial purchaser and the parties agreed to submit the matter to arbitration.

Petroleum Company’s Position

The petroleum company took the position at the arbitration that the free petroleum product discovered in the northern portion of the site in 1992 and in the southern portion of the site in 1996 was unrelated to the sites previous use as bulk petroleum storage facilities. As a result, it denied liability for the site remediation costs incurred by the commercial purchaser. The petroleum company relied on the following arguments in support of their position. It claimed:

1. That the non-weathered nature of the petroleum product indicated that the product was recently introduced into the subsurface. The petroleum company retained the services of a well-known forensic chemist who supported the company’s contention that the product was recent in age. The forensic chemist even went as far as claiming that the product was between 3 and 5 years old (i.e. after the commercial purchaser had purchased the property).

2. That prior to the discovery of petroleum product in monitoring well N1 in 1992, free product had not been previously detected in this well. Furthermore, it claimed that the dissolved groundwater concentrations within this well had been improving as a result of the ongoing groundwater pump and treat system installed in the vicinity of this well.

3. That all of the free petroleum product had been successfully recovered during the 1990 and 1991 initial remedial excavations, thus the 1992 and 1996 occurrences had to be unrelated to past site use.

Since no obvious source for the free petroleum product existed on-site, the petroleum company simply attributed the presence of the product to possible acts of vandalism.

Commercial Purchaser’s Position

The commercial purchaser claimed that the petroleum company failed to achieve an acceptable level of soil and groundwater remediation on this site and thus, the petroleum company was still financially responsible for the final site remediation program, which was undertaken by them. In essence, the position of the commercial purchaser was that the discovery of free petroleum product in 1992 and 1996 was simply residual product which remained on the surface of the groundwater regime due to the incomplete remedial efforts undertaken by the petroleum company. The product was drawn into the monitoring wells by the operation of their groundwater pump and treat systems. Arguments made in favour of their position included the following:

1. Free product was historically used on-site and was found to be present on the surface of the groundwater regime, prior to initial clean-up attempts undertaken by the petroleum company in 1990 and 1991;

2. Initial and subsequent remediation programs undertaken by the petroleum company between 1990 and 1996 were incomplete and unsuccessful due to: i) the lack of proper initial site characterization studies to delineate the full extent of the free petroleum product plumes, ii) the failure to collect soil verification samples of the walls and base of the remedial excavations, iii) the failure to obtain an adequate number of soil verification samples of the treated soil prior to it being used as backfill material, and iv) the failure, in at least one situation, to establish the remedial objective criteria prior to undertaking the remediation program.

3. Prior to the occurrences of free product in N1 and S1, the petroleum company’s own consultant documented the presence of petroleum product on the surface of the groundwater table at several locations after the major attempt at recovering the free petroleum product was undertaken in 1990 and 1991;

4. No evidence of vandalism existed to support the presence of the product in N1 or S1 originating from the introduction of petroleum product onto the ground surface or into existing monitoring wells (which were always locked);

5. No off-site sources of petroleum product existed hydraulically up-gradient from this location;

6. Field notes taken by the petroleum company’s consultant indicated that free petroleum product was sporadically present in monitoring well N1 with the first observations being made before the 1990 remedial attempt;

7. Field notes taken by the petroleum company’s consultant also indicated that free petroleum product was in fact present on the surface of the groundwater table in the area of the 1990 excavation after it was backfilled (i.e. after they claimed to have recovered all of the product);

8. The non-weathered chromatographic profile of the petroleum product was attributed to:

a) The relatively deep groundwater table (>5m) which would limit fresh, oxygenated surface water from reaching this zone. Without this source of oxygen, biological processes would likely have been inhibited or greatly reduced;

b) The presence of low conductivity zones (i.e., silty sand and silty clay lenses) within the native soil which could have served as a confining layer - effectively minimizing or preventing volatilisation of the more volatile fractions of the petroleum product; and,

c). The silty sand and clay lenses may have also served to deflect any surface water infiltration and groundwater away and/or around the petroleum product plume further preserving it from weathering processes.

Factors Affecting Petroleum Product Degradation

The degradation (weathering) of hydrocarbons in the subsurface is affected by three main processes. These processes are biological, chemical and physical.

Biological Processes

Hydrocarbons will be most significantly degraded by biological processes in conditions which permit the proliferation of biological organisms. These conditions can be affected by the following:

1. Contaminant Concentration

When the concentration of contaminants reaches a certain level it inhibits microbial growth. The level of microbial inhibition varies from one contaminant to another. For example, when free petroleum product is encountered in the subsurface, the concentration of the contaminant is usually so high that it is often toxic for the microorganisms. Although biodegradation of free petroleum product can occur in these circumstances, it would most likely be restricted to the interface of the petroleum product and the groundwater. At that location the hydrocarbon will usually be present in the dissolved phase and therefore be more readily available for microbial uptake (Stout and Lundegard, 1998).

2. Temperature

Temperature can have profound effects on the biodegradation rates of hydrocarbons in the subsurface (McNicoll and Baweja, 1995). Temperature affects the metabolic rate of microorganisms, the volatilization rates of hydrocarbons (the higher the temperature the higher the volatilization rate), the solubility of the compound and the composition of the microbial community (Leahy and Colwell, 1990). As a rule-of-thumb, the rate of biodegradation is halved for every 10 oC decrease in temperature (this is known as the Q10 rule - Metcalf and Eddy, 1979). From the above rule-of-thumb it is apparent that an increase in temperature (up to the microorganisms preferred range) increases the biodegradation rate. Likewise, a decrease in temperature decreases the rate of biodegradation.

3. Nutrients

The level of nutrients in the host soil and/or groundwater can affect biodegradation rates of hydrocarbons. Low levels of nutrients such as nitrogen and phosphorus in soil (ie sands) or groundwater can significantly reduce the rate of biodegradation (Leahy and Colwell, 1990).

4. pH

Most bacteria and fungi prefer near neutral pH conditions with fungi being more tolerant of acidic conditions. Extremes in pH will generally have a negative impact on the availability of microorganisms, which degrade hydrocarbons. Typically a pH between 6 and 8 is preferred by microorganisms (Leahy and Colwell, 1990).

5. Oxygen

Most biodegradation of hydrocarbons and other organic contaminants occurs aerobically and this, by definition, requires oxygen. Due to the hydrophobic nature of hydrocarbons, it is likely that no water will be present in free product found in the subsurface and therefore no dissolved oxygen will be present. In aerobic degradation systems, oxygen is usually the rate??? limiting parameter affecting biodegradation (Leahy and Colwell, 1990).

Physical and Chemical Processes

Physical and chemical processes can also affect the degradation or weathering of petroleum product. These processes include:

1. Solubility

The solubility of hydrocarbons in water is a very important parameter when studying the movement and degradation of a petroleum product plume. Volatilization and biodegradation rates of hydrocarbons are strongly affected by their solubility. For instance, microorganisms must first produce enzymes to dissolve hydrocarbons in order to biodegrade them. If the product is partially dissolved, the task of assimilating them is made easier for the microorganisms. As well, the more soluble hydrocarbons will more readily travel in the groundwater thus reducing the concentration of the product plume and increasing the rate of degradation. The aqueous solubility of hydrocarbons decreases with an increase in the carbon number.

2. Soil Organic Matter and Adsorption

Organic contaminants tend to adsorb onto organic matter. Adsorption controls the quantity of free organic chemicals in solution thus governing a contaminants mobility, persistence and bio-availability. This results in a removal of mass from the free product plume.

3. Volatilization

Volatilization can remove mass from the product before other processes even commence (Tousignant, 1990). This is especially the case when dealing with hydrocarbons (such as gasoline) which have a relatively high percentage of volatile compounds (i.e., Benzene). Volatilization rates are affected by soil properties (such as soil type and permeability), local environmental conditions (such as soil moisture content, temperature, etc); and the chemical and physical properties of the petroleum product.

4. Moisture Content

Moisture content plays an important role in adsorption mechanics since water molecules compete with organic molecules for adsorption sites on soil particles. An increase in moisture content decreases the adsorption of hydrocarbons. Water molecules compete poorly with non-polar molecules for hydrophobic surfaces in soil organic matter. In other words, despite the moisture content, hydrocarbons (which are non-polar hydrophobic molecules) will readily adsorb on the hydrophobic sites of soil organic matter thus making these hydrocarbons unavailable for microbial uptake.

In summary, due to the toxic nature of petroleum product to biological processes, the physical and chemical processes are often the predominant mechanisms, which affect free petroleum product degradation, or weathering, in a subsurface environment.

Age Dating

Hydrocarbons encountered in the subsurface are often analyzed using a gas chromatograph (GC). The GC provides a profile of the hydrocarbon which when equated (i.e. area under curve is calculated), the concentration of the hydrocarbon can be determined. The GC profile can also provide some indications as to whether hydrocarbon is weathered or non-weathered. Non-weathered hydrocarbons have a profile, which is characterized by a series of long spikes extending above a bell shaped curve or “hump”. Weathered hydrocarbons show fewer long spikes on the hump or, in extreme cases, just the hump. The theory which underlies the age dating of hydrocarbons is that the more weathered the hydrocarbon GC profile (i.e. the fewer the long spikes), the older the petroleum product.

The fallacy of this theory is apparent if one considers the dramatically different weathering pattern which would be experienced by two samples of petroleum product if one were kept away from oxygen in a dark cool place and another which was exposed to oxygen, warm temperatures and sunshine. Clearly, after a period of time the two samples, despite being the same age, would show marked differences in weathering. Notwithstanding the obvious unreliability of co-relating weathering and age there seems to be a wide spread misconception that if petroleum with a fresh or non-weathered GC profile is found in the subsurface it must be of recent origin. This was the theory advanced by the petroleum company in the above noted case study.

According to Senn and Johnson (1987), the presence of high concentrations of light end compounds would be indicative that the product has not been in the soil for an extended period of time. However, this paper is only intended as a general guide to the interpretation of gas chromatograms. It would be fair to say that the absence of light end compounds from a gas chromatogram indicates that a certain degree of weathering has occurred. This, in effect, demonstrates that the site conditions favor weathering (biological, physical and/or chemical). However, the presence of light end hydrocarbons or fresh product by no means implies that the spill is recent (Christian and Larsen - 1993). The Senn and Johnson (1987) paper warns against the erroneous interpretation of gas chromatograms without due consideration of the site conditions.

According to Stout and Lundegard (1997) when free product above the groundwater is present, biodegradation appears to be greatest in the zones below the oil-water interface where pore saturation with diesel is lowest. They suggest that bioremediation is favored in this zone since contact with flowing groundwater occurs (i.e. delivery of dissolved oxygen is made possible and dissolved hydrocarbons may thus be degraded). Curtis and Lammey (1998) go on to suggest that the presence of fresh free product in an old plume can be explained by an “insulating effect” occurring around the core of the plume. They explain that the fringes of the plume suffer some degree of weathering and thus have their viscosity affected which in turn creates a “shell” around the core of the plume thus preventing the mixing of the shell and core products. Therefore, the middle of the plume remains unaffected. Christian and Larsen (1993) describe other reasons for the preservation of the plume freshness. They explain that the conditions generally found inside an oil affected body inhibit microbial growth. These conditions include low nutrient concentrations, low levels or complete absence of oxygen and high contaminant concentrations that may be toxic to soil microorganisms. The effect that these conditions can have on a product freshness is well described in Wang et al. (1998) were relatively fresh product was encountered in 25 year old contaminated soil.

To summarize, free product in a soil column above the water table can remain relatively unchanged due to a variety of factors. The most important ones being: 1) the concentration of the product may be toxic to the microorganisms, 2) the presence of free product saturated soil means that the soil pores are filled with free product and, because of the hydrophobic nature of hydrocarbons, dissolved oxygen present in the groundwater and infiltration water cannot reach these areas, 3) the weathering of the plume fringes cause a difference in product viscosity thus creating a protective “shell” around the core of the plume thus isolating it.

Arbitrator’s Ruling

During the lengthy arbitration process, the petroleum company spared no expense at trying to support their “non-weathered means recent” argument including the calling of evidence from 4 expert witnesses. Upon examining all of the evidence, the arbitrator concluded that the most likely source of the petroleum product was the historical petroleum storage tank facilities. The presence in 1992 and 1996 of free product (some of which was non-weathered) was, he concluded, simply the result of incomplete remedial efforts by the petroleum company. The arbitrator did not concur with the argument that the non-weathered nature of the product meant that it was recent. He cited with approval the evidence of two of the experts called for the purchaser. Commenting on one such expert, the arbitrator stated:

The arbitrator concluded that the petroleum company did not prove that the unweathered petroleum product was of recent origin. In fact, the arbitrator went on to state:

This finding (and others) by the arbitrator ultimately led to his decision that the petroleum company was legally and financially responsible for the contamination on the sites and ordered that it pay the commercial purchaser approximately $2,600,000 for the remediation of the property. In addition, the petroleum company ultimately paid a substantial portion of the commercial purchaser’s legal fees in this matter.

Conclusions

Based on the facts of the case study and the arbitrator’s ruling, it is evident that one cannot assume that non-weathered free petroleum product found in the subsurface means that the product is recent in age. There are some scientific references available suggesting that under certain conditions old product can remain unweathered for many, many years (Stout and Lundegard, 1998; Wang et al, 1998). These articles however all suggest that this phenomena tends to occur in the centre of a relatively thick (i.e. several metres) petroleum column. In this particular case, the product thickness did not exceed 0.4 m of thickness and thus would appear to be markedly different from case studies that have been previously noted in literature.

Based on the results of this case study, it is evident that an environmental investigator cannot simply look at the chromatographic profiles of a petroleum product to assess its relative age. Rather, one must carefully consider all factors ranging from product type to host conditions and carefully weigh all of these factors before making any age-related statements pertaining to free product in the subsurface.

References

Christensen, L.B., Larsen, T.A., Method for Determining the Age of Diesel Oil Spills in the Soil, Groundwater Monitoring Review, Fall 1993, pp. 142-149.

Curtis, F. and Lammey, J. Intrinsic Remediation of a Diesel Fuel Plume in Goosebay, Labrador, Canada, Environmental Pollution 103( 1998) pp. 203-210.

Leahy, J.G.; Colwell, R.R. Microbial Degradation of Hydrocarbons in the Environment, Microbiological Reviews, 1990, 54, pp. 305-315. McNicoll, D.M.; Baweja, A.S. 1995. Bioremediation of Petroleum Contaminated Soils: An Innovative, Environmentally Friendly Technology, Environment Canada Publication EN40-491/1995.

Metcalf & Eddy, Inc. Wastewater Engineering: Treatment/Disposal/Reuse, McGraw-Hill Book Company, 2nd edition, New York, 1979.

Richards et al., Surficial Material and Terraine Features, Ottawa-Hull, Map 1425A, 1974.

Senn, R.B. and Johnson, M.S., 1987. Interpretation of Gas Chromatographic Data in Subsurface Hydrocarbon Investigations, Groundwater Monitoring Review, 7, 1:5863.

Stout, S.A. and Lundegard, P.D., Intrinsic Biodegradation of Diesel Fuel in an Interval of Separate Phase Hydrocardons, Applied Geochemistry, Vol. 13 Number 7, pp.851-859, 1998.

Tousignant, L.P. “Disappearance of Polyciclic Aromatic Hydrocarbons from a Soil Using Biostimulation Techniques”, Masters Thesis, McGill University, Montreal (Quebec), 1990.

Wang, Z. et al. A Study of Twenty-Five Year Old Nipising Oil Spill: Persistence of Oil Residues and Comparisons Between Surface and Subsurface Sediments, Environmental Science and Technology, Vol. 32 Number 15, 1998, pp. 2222-2232.

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