We are thinking of adding an addition to our house. Right now it's a 2
section split level/rambler where half of the house is a split 2 level,
and the other half is a rambler style at ground level with a full basement.

The addition will be adding on to the section with the full basement.
We are being asked if we think adding a full basement to the addition is
something we want to do.

On one side I say yes... we can then add an egress window and make it
another bedroom, so the extra cost for excavation and foundry work would
be worth the added value for sq. feet and another bedroom.

On the other had, I believe we have drain tile running around our house
that channels into our sump pump in the basement. We do have 3 "pipes"
entering the sump hole. One is a floor drain, another is for the beaver
system, and the 3rd I believe is for the drain tile around the house.

We pump water from spring until mid-June on a good year. Unless the
sump pump goes out, there's no issue.

But, the question is, will adding another full basement (it would extend
out past the corner the sump hole is in) be trouble with:

1. Water in the ground during excavation and foundation work
2. Moving the sump hole or adding another sump hole (we would prefer
to fill in the current one and move it to the new section).
3. General water issues with the house as it is. (ie will a larger
basement cause more issues)

One idea I had was we just had to have a mound septic put in. This
means right now we have 3 runs of about 100' of drain tile in our back
yard from the old septic tank not being used. Right now I am pumping
the sump water into it. (pumps about 3 gallons every 5 minutes right
now, but slows to every hour or so when it starts to warm up).

And idea we had was to channel the drain tile from around the house to
this tile instead of into the basement. Is this feasible? Ground in
the area is mostly clayish. Wells are around 400' deep.