Gday All

I would greatly appreciate any feedback/encouragement on my methods for a mine seepage investigation I am conducting. cheers!!

[b]Background Info[/b]:  I am investigating a tailings pond seepage 3D transient model. This pond is using a perimeter interception well scheme to capture seepage and recycle back to the pond. The underling aquifer setting is mainly a fine to coarse-grained sand aquifer up to 60m thick and 200km2. I am utilizing up to 100 4th type BC's to represent the wells in the sand aquifer and am using minimum head constraints equivalent to 4m above base of screen interval. I am using a 2nd type flux boundary to represent the pond ( to avoid 1st type BC in close proximity to high number of wells) with flux volumes into the model calculated off the mine water balance and divided into the area of the pond's surface area. I have set a max head constraint on this flux boundary to represent the tailings pond maximum elevation, so that groundwater cannot mound above the pond elevation. Pond is initially about 40m above phreatic surface and thus will drain into the aquifer and develop a "mound". The pond has a massive open pit situated 1km to the side and I have run my first simulation representing this open pit as a 1st type CHB using a head that is equivalent to the base of the aquifer. This boundary has aggressively dewatered the sand aquifer and appears to be preventing mounding from occurring beneath the tailings pond flux zone.

[b]Questions[/b]:
1) Are 4th type wells the best boundaries to represent wells in this case? I read a post by Eladd about using a 2nd type boundary (Max = 0) and very high Kz.
2) Is there a better way to simulate the seepage from the pond so that the head elevation and water flux into the model are honoured?
3) Is the open pit dewatering best represented as a series of 4th type wells simulating a typical drawdown zone? Or can I modify the constraints on a 3rd type BC to represent a "drain" type scenario (similar to Dwain edington post on March 08, 2007)?

Any feedback would be sweet!

I am working in a Open Pit too, I try to modelizy the influence zone.

I think the best to model the mine, is constant HEAD ( 1 firs condition) with the value of the bottom of the pit

Cheers

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