Retention Pond Recovery

[Engcv]

I am designing a retention pond on a hillside where the natural grade is 5%. It is falling from an elevation of 14 to 6, with the groundwater 5.5 feet below existing grade and the confining layer 9.5' below existing grade. The pond will have a top elevation of 12 and a bottom elevation of 8, the bottom of the pond sloping maintaining a 1.5' distance between the groundwater profile. There will be a 5' berm at the back of the pond with a weir structure discharging into adjacent wetlands.

Does anyone have any suggestions as to how to model the recovery of the pond, when the groundwater profile is homogenous to the existing ground but not to the bottom of the pond? Most application I am aware of assumes a homogenous, isotropic of the unconfined aquifer layer in respect to the pond bottom. The soil is sandy, with a lateral saturated hydraulic conductivity of 35 ft/day.

Thanks for any help,