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I'm designing a village school toilet for about 500 students using a VIP seepage pit design. The toilet will be built on a hillside, which brings up my question.

Is there a means of predicting the underground effluent flow path?

Specifically, will the effluent surface at some level below the seepage pit?

If so, where and how?

I'm designing a village school toilet for about 500 students using a VIP seepage pit design. The toilet will be built on a hillside, which brings up up my question.

Is there a means of predicting the underground effluent flow path?

Specifically, will the effluent surface at some level below the seepage pit?

If so, where and how?

EDIT: in response to both of the comments received, here’s a little more siting information. 

There are 2 possible toilet sites:  one on the edge of a steep slope (~40-50%) with the foundation being within 1 meter of the beginning of the slope (top of the hill).  There’s no well within several hundred meters of this site, but a streambed at the bottom of the slope, maybe 15 meters below the toilet site.  The soil is a loam with some clay mixed in places.

The second site is also on a slope, but much more gradual (~10-15%) and in the middle of the sloping hillside rather than on the top.  This site also has no well within several hundred meters, but has farm fields beginning at about 30 yards downhill of the building site.  There are no visible springs in the areas below either sites (other than the flowing stream below site #1).  The soil here is also a loam/clay mix.

I’m concerned that the toilet subsoil effluent might surface in either the stream in site #1 or the farm fields below site #2.  It would appear that from one response received that the effluent, if mostly flowing downward due to gravity, might surface at the stream level below site #1, or might not surface at all in site #2.  I’m also concerned that the subsurface soil in site #1 might become saturated due to the volume of liquid (which I’m calculating to be about 1.5 liter/person/day or about 750 liter/day with a dry pit, no flush, VIP toilet over a 30 square meter pit area) and become unstable.  What affect would that volume have on the subsoil stability?

I hope this provides the additional information needed.  

I'm designing a village school toilet for about 500 students using a VIP seepage pit design. The toilet will be built on a hillside, which brings up my question. Is there a means of predicting the underground effluent flow path? Specifically, will the effluent surface at some level below the seepage pit? If so, where and how?

EDIT: in response to both of the comments received, here’s a little more siting information. 

There are 2 possible toilet sites:  one on the edge of a steep slope (~40-50%) with the foundation being within 1 meter of the beginning of the slope (top of the hill).  There’s no well within several hundred meters of this site, but a streambed at the bottom of the slope, maybe 15 meters below the toilet site.  The soil is a loam with some clay mixed in places.

The second site is also on a slope, but much more gradual (~10-15%) and in the middle of the sloping hillside rather than on the top.  This site also has no well within several hundred meters, but has farm fields beginning at about 30 yards downhill of the building site.  There are no visible springs in the areas below either sites (other than the flowing stream below site #1).  The soil here is also a loam/clay mix.

I’m concerned that the toilet subsoil effluent might surface in either the stream in site #1 or the farm fields below site #2.  It would appear that from one response received that the effluent, if mostly flowing downward due to gravity, might surface at the stream level below site #1, or might not surface at all in site #2.  I’m also concerned that the subsurface soil in site #1 might become saturated due to the volume of liquid (which I’m calculating to be about 1.5 liter/person/day or about 750 liter/day with a dry pit, no flush, VIP toilet over a 30 square meter pit area) and become unstable.  What affect would that volume have on the subsoil stability?

I hope this provides the additional information needed.