Estimate the evaporation and groundwater seepage rates for a material pile

[rconway91]

I have a material that is piled and stored until it is dry enough to transport. I know the initial water content when it is placed and I know the water content when it is dry enough to transport, so I can estimate the amount of water lost by the pile as a whole while its drying.

Conceptually, some of the water is lost to evaporation and some water is lost from infiltration to groundwater. I am interested in the proportion lost to groundwater for site water quality reasons. I am guessing that estimating the amount lost to evaporation will be easier than estimating the amount lost to groundwater. I can then estimate the amount lost to groundwater by subtracting the evaporation losses from the total losses (there is no overland flow from the material pile).

So my question is, is there a way to estimate evaporation losses from a material pile? I know the initial water content, final water content, field capacity (aka specific retention) climate data, average pile geometry.

 

[oldestguy]

Take a pail and punch a lot of holes of diameter much less than the material size. Do periodic test with material in pail. If you don't mind leaving a trail of water along the road, then that is more liberal than if you don't want to leave a trail. When a test results in your leakage "spec" haul it.

 

[rconway91]

The material is classified as a silt based on USC, so I would not be able to drill holes smaller than the particle size.

Also, I do not think this would provide me the information I am after (the seepage to groundwater). Even if I were able to measure the seepage through the bottom of the bucket, I would need to do it an environment where there was no evaporation or any water that seeped out would just be evaporated. I want to know what portion of the pore water is evaporated and what portion percolates downward and infiltrates into groundwater.

 

[oldestguy]

Shudda stated that to begin with along with the initial moisture content. I suspect that pile will sit there for a long time if moisture content is much above the liquid limit.
Edit: In my experience, this sort of study is quite unusual. The more you lose by evaporation, the higher contaminant concentration of the seepage water. Check out vacuum lycimeters since that method may help.

 

[GeoEnvGuy]

I think there is an astm for pan evaporation.

 

[rconway91]

There is an ASTM for pan evaporation, but this is pore water so I would need to come up with some factor to related evaporation at depth to pan evaporation. I have looked into the pan evaporation rate, and if I apply it at its full value, I get that there is enough evaporation to completely evaporate all the excess water in the pile in a couple days. However, based on site observations I know that some of the pore water is getting into groundwater, so application of the full pan evaporation is not correct.

 

[GeoEnvGuy]

Did you consider filling the pan with the material and comparing a moisture content of the pan material to that of the pile.

 

[chicopee]

whatever the size of a small size sample you select, the results will differ remarkably from a large size sample. I see a viable field experiment in the making. To reduce evaporation you'll need to cover the test piles with plastic sheething. Then reduce seepage loss the bottom of the piles will need plastic sheething. Then you'll need numerous silt piles for each condition that I mentioned to get some statistical results.
Now another approach which may be beneficial is to visit quarries involved in rock crushing operations and probe the brain of the managers so they can lead you in the right direction.

 

[BigH]

What is the unsaturated coefficient of permeabiliy of the ground - with groundwater level at depth? What is the unsaturated coefficient of permeability of the 'pile'. As evaporation occurs at the "edge" of the pile it will take longer, in my view, to eavporate into the pile (presuming the pile is large and not a few front end loader buckets) so it is most likely that downward drainage will be more. This is where the type of "ground" becomes important.

 

[fattdad]

Somewhere in this discussion is the topic of specific storage. If you take a dry pile and let it get wet, the water may never, "Drain" out of it. There are capillary forces that will just keep it locked up!

I'll also direct you to the Thornthwaite equation. That may offer some guidance.

Regarding permeability and first-principals, just recall that as saturation decreases, so does permeability. Having air in the way of water flow restricts movement, again, owing to surface tension.

You may have to haul a smaller load?

You may have to turn the pile?

You can always turn the pile until the water content is reduced?

f-d

ípapß gordo ainÆt no madre flaca!