I mentioned in a previous blog how an expert’s investigation relies on Observation compared to laboratory and field testing. (Refs 1, 2) That blog described an investigation that contained many examples of observation and no examples of lab and field testing.
The following investigation contained many examples of laboratory and field testing – I will spare you the eye-glazing-over details – and one main observation that showed up at the end.
***
I was retained to investigate the cause of a fuel oil contaminated site in Cape Breton. It was an old spill from a fuel oil delivery truck that resulted in the evacuation of a home because of the fumes. A business on the property was also closed. The site was in a rural area on ground sloping down to a small lake.
Main question: Where did the fuel oil go?
The main question was the extent of the contamination – how far did the oil flow from the spill location. This involved sampling the soil at a number of locations beneath the house and testing for oil in a laboratory. This work found the limits of the contamination just beyond the house.
Previous work by others concluded that the ground beneath the business was not contaminated. This was based on one laboratory test of a sample of the ground some distance downhill of the business and excavation of contaminated soil at the spill location just uphill. This was forensic investigation light in my opinion – an observation.
Fuel oil rides along quite nicely on the surface of groundwater. This means that the depth to the groundwater and where it flows are important in cleaning up a contaminated site. I knew that the water table was at the lake surface and usually rose with the ground beyond a lake. But what depth was it at the spill site?
A topographic map of the area suggested that the groundwater was within 5 to 8 feet of the ground surface just uphill of the business. This was my subjective assessment, an observation after doing this kind of engineering work for years.
The owners of the property said later that the water in an old dug well just downhill of the business was at the ground surface so cows could drink there in the past. This reinforced my assessment of the depth of the groundwater at the spill site. Also that fuel oil contaminated the cow’s drinking water in the past downhill of the business and likely the soil beneath the business.
Tidying up
By way of tidying up and finishing my forensic investigation, I arranged for drone video of the site for record purposes. It also facilitated telephone discussion of my forensic investigation with my client – sort of like Zoom meetings today. I was taking this kind of video of all my sites by this time then distributing copies of the video to my client and interested parties. Sometimes these videos contained surprises at the end of the day, as you will see below.
I had the drone pilot sweep across the site at an altitude of 300 to 400 feet on the four points of the compass for the big picture then low at several 10s of feet over points of interest.
Studying the video later I was surprised to see a tongue of dark soil extending from beneath the rear of the business down hill beyond the cow’s water well. This indicated that the groundwater was at a shallow depth and that the soil beneath the business was probably contaminated with fuel oil. Also, that the test location by others was beyond the contaminated area. This was my main, almost single Observation during this forensic investigation – Example #2 – compared to many Observations in Example #1.
References
- Observational Method: Example #1 Posted July 31, 2023
- One forensic observation does not a cause make. Posted July 18, 2023
(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada, August 29, 2023. ejorden@eastlink.ca)