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Tasks for the tailings project
To learn what is needed about the subsurface at our
site, the following four specific tasks were identified:
- Locate an old buried gas pipeline.
- determine the volume of calcine (a by product of the mining process that was dumped in pits at our site);
- map the topography of the bedrock horizon underlying sediments and calcine;
- find out if a plume of contaminated ground water exists.
We also learned that there are several types of information that will
tell us about the subsurface. This
table is a summary:
Finally, there was a summary of expected physical properties:
Unit |
Comments |
Possible electrical resistivity (ohm-m) |
Possible density (gm/cc) |
Possible velocity (m/s) |
bedrock |
Granite (see outcrops). |
> 3000 |
2.67
|
2300-3300 |
Surficial cover |
Pebbly soil with some grass. |
20 to 100 (variable owing to wide range of grain size, presence of organics, and existance of a vados zone. |
1.5 - 1.8
|
450-650 |
Natural sediments |
Sandy till (porosity around 18%). |
50 - 80 dry, 20 - 40 wet |
2.2 - 2.4
|
1000-1400 |
Calcine |
An iron-oxide compound. |
1 - 10 wet |
2.75 - 2.85
|
600-800 |
Pipeline |
Likely metal, and it could be up to 10 m deep owing to calcine and soil cover added since emplacement. |
High if metal (which it will be for gas), but clay or plastic pipes can be hard to detect |
N/A
|
N/A |
Backfill materials |
Roads, places where construction occured, trenches with utilities. |
Likely higher conductivity than natural sediments. |
1.5 - 1.8 |
500-700 |
Water |
Natural groundwater at this site will be mainly fresh rain water that has had a relatively short residence-time in the ground. |
The actual effect of groundwater resistivity depends upon porosity. |
N/A |
N/A |
Contaminated water |
The plume. |
Water from tailings can be acidic, and hence conductive. As above, the actual resistivity of ground depends upon the resistivity of this water. |
N/A |
N/A |
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