Seasonality to Mine Inflows

[CJ@RESPEC]

I am curious as if anybody has tracked or observed when new inflows occur into mines. One mine I have examined suggests new inflows or large increases in old inflows predominately occur in the fall and spring seasons. I have approached in a statisical manner and is supportive. I have read published literature on a few other mines that had large inflows in the winter. Has anyone else observed if there is any seasonality to when inflows occur?

Cheers,
CJ

[Chris Wolkersdorfer]

Yes, I encountered that several times at different mines. Two main reasons are the case: rain events and snowmelt.

The time delay depends on the overlaying strata and might vary from several hours to a week or two. In one mine the delay (proven by tracer tests) was several minutes and in another case roughly a day. In deeper mines we found a week delay. In general: the deeper the mine or the lower the hydraulic conductivity the lower will the seasonal fluctuation be.

Where I am working now the seasonal variation is really big: in Summer time it might happen that no pump runs and in winter time up to 10 pumps are running to prevent the mine water table from rasining.

Some explanations are in my book and some other are in a paper that you can download here:

[CJ@RESPEC]

Chris,

Thanks for the link to the paper and I look forward to reading it. However in the cases I state, it is not a function of climatic seasonality. The specific case I am involved with is at a depth of 1,000 meters. I have great confidence in saying there is no nearby "source" to the surface and is not a function of "wet" seasons. The water has been tested for tritium and has not been detected in samples. Isotopic sampling indicates the water is of older origin. These inflows are long term and such isn't a function of haven't flushed out connate water. So, this is why I can state with relative confidence that when inflows start or increase it is not a function of climatic variables. I can understand and have seen climatic varability in mines with better connections to surface "sources".

Basically, a connection develops from the mine opening to the aquifer and then inflows occur. In other words, an area is dry, or may have drips, and then an inflow occurs. And what I am saying is that this process statisically tends to occur more in the winter and spring. If real and not an artifact, this is where it is a bit confusing as what seasonal variable could act as "trigger" for these inflows. The only things I can think that impart some stress (admittedly quite small though) into the rock with seasonality may be earth tides or barmotric loading. For example, barometric swings and variations are larger in the winter months. Water tides are also greater in the winter and suspect same is true for earth tides because same controlling forces.

Regards,
Cj

[Chris Wolkersdorfer]

What do you mean with "Tritium indiactes"? Tritium can't be used any more to evaluate if the water's residence time is long or short. Tritium concentrations in precipitation are back to "normal". Or do you have time series of current samples in the mine and compared them with time series in precipitation?

Even at depths of 1000 m you can have seasonal variations - their pattern is just high pass filtered and might have a longer time lack. To evaluate the mean residence of that water in the mine you must use 85Kr or CFCs. That's your ony chance to evaluate your hypothesis that the water is not of vadose origin.

Concerning your other comments: no idea as I don't have enough experience with tidal effects and deep mine water. What about the frequency of the "seasonal fluctuation". What did FFT or wavelet analyses tell you? Dou you also encounter seasonality of chemical parameters. Look into Zn and Cu. There is a nice paper from Alpers and Nordstrom about Cu/Zn seasonality. This investigation might help.

[CJ@RESPEC]

In terms or tritium, it is not detected within the resolution of lab analysis. There is not enough tritium data to do a time series to compare to natural precipitation. Again, there is a fair amount of isotopic data (O18 and deuterium) of the inflow brine. O18 and deuterium are well characterized in current precipitation and such is a valid test to say there is no direct recharge from current precipitation (current in time scale of geologic age). However that is not to say that it may be on the mixing line of an older brine member and surface water.

That is an interesting question on the seasonality of chemical parameters. I haven't specifically tested this, but I conjecture there aren't any seasonal changes. As best we can tell, all chemistry analytes have been pretty stable over almost the last 30 years.

I don't think I previously pointed out that this a brine inflow and not a freshwater inflow. Off hand, I don't know the levels of zinc, but is very low because zinc is used as tracer. I can't comment on copper levels as don't know off hand.

Regards,
CJ

[Chris Wolkersdorfer]

Your case becomes more and more interesting ...

Just to summarize: you have brines flowing into a 1000 m deep mine and they show seasonality (Spring and Fall) of the flow Q and you would like to know if others have seen that before and how this observation could be explained.

In case it is a brine I would not expect that you could see any indications from the Cu or Zn analyses. What about Sr or EC (I assume several thousand to 10thousands of mg/L) ? Any indication that it could be sea water - I would assume not.

What about the amplitude and frequency of the seasonality? Amplitude seems to be 3 months. Could you send a graph of the inflow? How do you measure the inflow?

Would this paper help a little bit:

Martel, A. T., Gibling, M. R. & Nguyen, M. (2001): Brines in the Carboniferous Sydney Coalfield, Atlantic Canada. – Appl. Geochem., 16 (1): 35-55, 12 Abb., 2 Tab.; Oxford.

At the moment I don't have a clue why you have seasonality. Is the chemistry at least a little bit seasonal as well. Did you conduct multivariate statistics, is there a correlation of Q with any chemical parameter?

[CJ@RESPEC]

You are correct that mine is 1000 meters deep, is located inter-continental, and has brine inflows. You partially correct on the way you describe the seasonality of the inflows, but not sure if completely on the same “wavelet”. For example, let’s say there are 5 inflows flowing at x gallons per minute at generally consistent rates for a period of time. Then a new inflow develops in a new area where flow was not previously occurring. In terms of seasonality, these new inflows seem to occur in fall and spring. Let’s go forward a period of time and one of the original 5 inflows suddenly increases by ten fold. Again in terms of seasonality, this tends to occur in fall and spring. So if one was to look at inflows every year by season, it wouldn’t show every spring and fall has larger total inflow rates. However when the step-increases occur, the data is suggestive that they occur predominately in the fall and spring.

Perhaps where my scenario maybe a bit different is that these inflows are a function of a mechanical breakdown of the “aquifer” seal. In other words, the rooms weren’t wet when mined and not a function of drilling into. So do you encounter inflows where they are, for lack of a better time, spontaneous and weren’t mined or drilled into. And if so, I am asking about the time of the year they broke out.

I will follow up on getting permission to share or show data.

There is no chance these inflows are tapped into pre-existing oceans.

Inflow is measured manually (known volume and time to fill) and totaled. Additionally, the inflow brine is pumped out of the mine and totalizers are located on the lines.

Again, the inflow increases don’t occur every year so I don’t think it is a 3 to 6 month frequency as I interpret you are pondering.

I hope this clears up things rather than confuses.

Cheers,
CJ