#197 - Borehole and soil gas analysis- Part 2

A while back, we posted some information about analysis of boreholes at decommissioned mine sites. Here is Part 1 of the discussion.

At the time, we mentioned that we have frequently sold the Model 309 Portable O2 / CO2 analyzer for this application. Because some of the samples will be pulled up from deep into the borehole, we can install a heavy duty pump into the instrument. This solution has been great for this application.

One mining company recently contacted us requesting a solution to a problem they were having with water accumulation in their analyzers. In the standard instrument we supply to this company, we incorporate a bowl filter of some kind at the sample inlet to capture any water that may come up with the gas. This approach has usually been adequate for the brief period that they have sampled at each point. However, at some boreholes, water accumulation in the interstices between the back-fill material and the liner has been significant. The analyzer has to pull out a large volume of water from each of the tubes in the bundle before the gas analysis can begin.

To cope with this reality, we proposed a closed catch-pot arrangement that isolates the water while maintaining the extractive suction. In operation, the sample pump pulls on the borehole tube. The entrained water comes up first and simply falls to the bottom of the clear bowl. When the water is evacuated from the tube, the gas sample passes into the detectors for measurement.

This arrangement is nothing new; it’s an old trick that has been around for years. We just haven’t implemented it in such an overt style with a portable analyzer. If you are monitoring soil gas from a tube bundle in a mine tailings borehole, let us know. We can offer a solution.

For information on these and other gas analyzer systems, give Mike or Dave at Nova a call, or send us an e-mail.

1-800-295-3771

sales at nova-gas dot com

websales at nova-gas dot com

http://www.nova-gas.com/

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#123 - Borehole and soil gas analysis - Part 1

Borehole Gas Analysis

A borehole is basically a thin shaft that extends into the ground vertically or horizontally. There are numerous purposes for drilling boreholes including water, petroleum, or gas extraction. A borehole may be required for environmental or geological investigations.

We have had numerous requests in the past from mining companies who want to test the gas atmosphere in boreholes extending vertically into the ground. The site may be a prospective mine, a depleted mine, or a critical area of interest near the mine. A portable instrument is required because there may be several boreholes on a site. The technician travels to each hole to obtain a series of gas analysis readings.

For gas analysis, there will usually be a tube bundle extending to different depths into the shaft. By attaching a gas analyzer to each of the tubes, an atmosphere vs. depth profile can be obtained of the shaft. This information can be indicative of soil condition, microbial activity, or some other investigated parameter.

We have frequently sold the Model 309 Portable O2 / CO2 analyzer for this application. Because some of the samples will be pulled up from deep into the borehole, we can install a heavy duty pump into the instrument. We usually incorporate a bowl filter of some kind at the sample inlet to capture any water that may come up with the gas.

Ore Sample Gas Analysis

In some cases, analysis might be required for a rock or ore sample that is brought to the surface for study. Because gas does not normally come off of a rock sample in large constant volumes, the sample will be sealed into a canister.

Inlet and outlet ports on the canister allow the gas analyzer to be connected via flexible tubing. The outlet port on the canister is connected to the inlet port of the analyzer. The inlet port of the canister is connected to the vent of the analyzer. The gas flows in a closed loop as shown in the picture below.

Valves and tubing can be arranged to minimize the amount of diluting air that is introduced into the canister atmosphere.

Ground Level Gas Analysis

We have also had requests for analyzers for ground level gas analysis. The procedure may consist of a domed and sealed cover over a section of soil. The cover has a tube fitting which may be connected to a gas analyzer.

The gas analyzer will pull a sample from the airspace between the cover and the soil. Because a limited volume of air exists between the cover and the soil, a pressure reduction will develop as the analyzer pulls more sample. The heavy duty pump can continue to pull so that a small sample of soil gas can eventually be obtained. We suspect that these conditions of sample extraction are not ideal for high accuracy readings. However, some users have reported that the resulting readings are enough to satisfy the requirements of their soil investigations.

Link to the Model 309.

Other interesting links:

http://en.wikipedia.org/wiki/Tailings

https://en.wikipedia.org/wiki/Borehole

https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

NOVA Analytical Systems

1-800-295-3771

sales at nova-gas dot com

websales at nova-gas dot com

http://www.nova-gas.com/

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http://www.linkedin.com/company/nova-analytical-systems-inc-

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