Presentation on the use of petroleum biomarkers for delineation of petroleum impacts in a high organic soil area (muskeg). Phytogenic hydrocarbons are natural compounds that are misidentified by standard analytical methodologies of high organic content soils as petroleum hydrocrabons. This artificially biases the measurements high for organic rich soils. Petroleum hydrocarbon products have distinct petrogenic biomarkers that can be used to identify if a sample contains petroleum or not. These biomarkers were used in this presentation to determine where petroleum impacts in the soil end and limit the unnecessary excavation of a muskeg chasing samples that were above guidelines due to the presence of natural hydrocarbons. Presentation shows how environmental forensics and petroleum forensics investigations can be used in an environmental site assessment.
Presented as part of the INEF conference held in Calgary, Alberta in 2009.
A typical problem faced by environmental consultants is petroleum hydrocarbon releases in soil as the result of oil and gas activities.
Normally these are easy to identify and characterize with routine laboratory analysis, but some organically rich soil soils pose additional challenges.
These types of soils often contain high concentrations of naturally occurring phytogenic compounds that may be reported as petroleum hydrocarbons by routine analytical methods.
Though both types of materials may have originated from organic matter, it is the conditions of their formation that determine the end product.
Phytogenic – milder conditions, shorter time period
Petrogenic – harsher conditions such as diagenesis & catagenesis
Biomarkers are very resistant to weathering and degradation. Over time, the basic structures remain intact giving scientists an indication of the source material.
Bacteriohopanetetrol – distinctive ring structure remains.
Organically rich soil have the potential to interfere with the delineation of petroleum hydrocarbon impacts.
Diverse ecosystem – all parties involved wanted to ensure that minimal disturbance was created and that the least possible amount of natural vegetation and habitat was removed.
Most of our background samples were above guidelines, indicating the need for a different approach.
Each sample showing hydrocarbon exceedances underwent additional cleanup to remove extraneous, polar compounds eluting and being included in the petroleum hydrocarbons concentrations.
Polar compounds tend to obscure the petroleum hydrocarbons in chromatograms, making identification difficult and giving elevated concentrations.
As we can see, the baseline seems to be running away and the chromatogram is very busy, showing large interferences from the numerous compounds in the sample.
Difference is very apparent – shows a large contribution of polar compounds (organic matter) to the petroleum hydrocarbons chromatograms.
This is an approved clean-up technique, as the treatment only removes polar components. The petroleum hydrocarbon guidelines do not apply to these polar components.
Lab standard, shown in black, contains about twelve biomarkers (hopanes) found in crude oil.
Weathered sample, shown in red, most compounds have been degraded to low levels but several persistent biomarkers remain, identifying this sample as containing petrogenic sources of hydrocarbons.
For additional assurance, the mass-spectra from suspected biomarker peaks were compared to library spectra.
Spectral match confirmed the presence of the petroleum biomarkers providing a secondary identification in addition to retention time match.
Figure shows all 15 samples that exceeded the petroleum hydrocarbon F3 fraction guideline (300 mg/kg)
Figure shows black bars (containing petroleum biomarkers) and green bars (identified as natural hydrocarbons since no petroleum biomarkers were present).
The15 samples showing F3 exceedances would result in a very large excavation would be required.
The area removed would extend beyond the north and south boundaries of the site, including large, naturally forested areas.
Positive petroleum biomarker identification was made in these 5 samples, confirming impacted soils.
The remaining 10 samples did not contain the petroleum biomarkers and were therefore considered unimpacted, thus representing natural hydrocarbons.
A map of the site shows all 15 of the sample locations having the initial F3 exceedances – anything in yellow, orange or red was over guidelines.
Hatched areas shows the area that was excavated.
As can be expected, the five samples that showed the presence of petroleum biomarkers were all located within close proximity of the former well head.
The lack of petroleum biomarkers helped the client save these circled areas (and possibly more) from being excavated.