I have bought a small area of undeveloped land (3/4 acre) in the
suburb of Granbury Texas about 1/2 mile from Lake Granbury.  I dream
of having a basement under the house to keep cool in the summer.
Having grown up in North Dallas, I know how hot August can be.  I now
live in Washington State and basements are everywhere. Now I wish to
build a second home in the Granbury area and want a basement.  In
addition to putting a basement under the house, my dream home will
include a large water holding tank (underground) approx 750 gallons
for rainwater and or gray water. I wish to incorporate a geothermal
water exchange system to keep the utilities cost down and utilize the
passive temperature regulation of the earth.  Finally, the housing
development requires a septic not city sewer system.  So.....on 3/4
acre how much underground construction and building will the law of
physics allow if I am only 1/2 mile from the lake. I do not know very
much about how deep a hole can be dug when that close to water and I
don't know how large an area under the ground can be used. The land
has many trees (most likely Pecan since this is an old pecan
plantation). I wouldn't want to hurt the root system of the trees
which are on the periphery of the lots.  Thank you very much for your
attention. redding6

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Clarification of Question by redding6-ga on 24 Jul 2004 15:18 PDT

Thank you for your response. I also asked about how busy the
underground of an area can be without being detrimental to the
existing trees. Does a rule of thumb exist regarding how far from the
trees an underground item can be such as a large plastic enclosed
water storage tank or a basement.  Also I asked about the geothermal
pipes existing with the other items, do they need to be a certain
distance apart from the basement or the septic system.  The only fact
I know about the residental development where the lots are located is
that they require a septic sewage system.  The area is not yet
developed enough for city water. Answers to the questions posed would
be greatly appreciated.

Your lot may be more 6 feet above the surface of the lake, in which
case the lake won't flood your basement, unless you want more than 6
feet of your basement below the surface. A topograhic map wiil help
you determine that the floor of your basement is higher than the lake
surface. 1/2 mile may be more than enough to protect you from the
Lake. On the negative side the water table could be ten feet above the
lake level after one of those very hard rains that occur several times
per decade, if not oftener. Talk to your neighbors, if any, and the
seller. Someone may have spent a lot of money determining the flooding
potential. The county agent (of agriculture) may have some information
or can point you to a cheap source.
 It is possible to build a basement that won't flood even if the water
table rises 6 feet above the floor, but it will be costly, especially
if you ask for a 5 year guarentee of no water on the floor.
 It may not matter much that your grey water tank is covered with
water except it needs to have a concrete slab or other weight on top
to prevent it from floating to the surface when it is not full.
 An underground potable water tank is risky as you may not realize
conciderable surface water is leaking into the drinking water. One
solution is to have back up electric power to insure the potable water
is always under at least 10 psi of pressure.
 In many locals, you can not get a permit for a septic tank if
community sewage is available reasononably close. Big fines are levied
if they can prove you built a septic tank without a permit.  Neil