Peter Schätzl Grundwassermodellierer

One option would be to intersect the selection you have (all nodes) with nodes on slice 1 (e .g., by using the 'Select by expression' tool) - assuming that you have a layered model.

I think you should find what you are looking for on http://www.feflow.info/html/help73/feflow/09_Parameters/Material_Properties/time_varying_materials.html.

From only looking at the images it is hard to tell what is going on. I'd recommend that as a next step you plot the rate budget on all the transfer nodes to see where the inflow occurs.

You can use "Select by map line" in the selection tools. Please note that for 3D selection, the settings defined in Problem Settings - Map settings apply.

These quesions you'll have to answer yourself based on what the targets of your simulation are - the forum members can help you with technical questions, but the conceptual basis required knowledge than cannot easily be conveyed in a couple of lines.

As a first approximation, you can use a constant head node with the approximate well level that you target. FEFLOW gives you the balance on the node, corrresponding to the pumping rate. There are, however, a few more conditions to consider: The balance depends on spatial discretization, so you should use the so-called ideal element size around the well if you want to get the budget right (depending on the radius of the planned well). There is also an optimum water level in the well that gives you maximum inflow (in case your aquifer is unconfined) as with too much drawdown, the inflow reduces due to reduced transmissivity while with not enough drawdown, the low head gradient limits the inflow. FEFLOW will not calculate that ideal drawdown for you, but you can estimate it in advance from analytical equations or simply do some tests with different levels in FEFLOW.

As a head-type BC will fix the hydraulic head at the node, the resulting head can never be higher or lower. Thus a constraint using the head value would never actually constrain the BC. You can, however, achieve something similar with a transfer-type BC, but please take a minute to read the documentation about the meaning of a min/max head in this case.

Yes, it does.

As I said, I'm not very familiar with the Leapfrog - FEFLOW interface, but one option could be to re-generate the mesh for the different volumes in FEFLOW using TetGen. Whether this helps to reduce the number of elements significantly will, however, depend on the geometry of the volume-bounding interfaces which cannot be changed in FEFLOW.

Yes, it is - see http://www.feflow.info/html/help73/feflow/09_Parameters/Material_Properties/mass_parameters.html for details.