How to simulate outflow rate out of saturated fill

[Muluadwa]

Hi all',

I would like to simulate the outflow rate out of a saturated compacted fill material 120 m by 60 m pit area (1.8 m depth) with 4 layers units (clay/gravel). Leakage is detected at the leachate extraction and detection sumps. The fill material- could be saturated during time of placement (since there was 160 mm of rainfall during this time). Therefore, there has been no recharge/rainfall since capped. It is well capsulated with clay liners (sidewall/ bottom of the pit)in place. The water table in the area is deep 12 m below surface.

The task is to figure out if the outflow/leakage is coming out of the saturated fill material or it is leakage from surface (which is unacceptable).

I am planning to simulate the outflow rate and match with the observed flow rate at the leachate extraction sump (coming out after 3 months since placement, this could be due to delayance effect?. Do we expect a constant outflow rate through out or varies exponentially with time? How long do we need to pump out if the leakage is coming out of the filled mataerial. How can I simulate this problem this using MODFLOW?

regards

Muluadwa