Based on your description of the problem, your would have to be crazy
to expect your solution to work.

1) 6mil plastic won't do anything for you. Over time, it will develop
holes and tears. This is unavoidable. Water will go under, around, and
through it.

2) trying to lower a water table is not a simple matter of draining
into a leach field. You are talking about millions of gallons of water.
You need to figure out what flow rate will be needed to lower the table
an adequate amount. What you have described (porous soil, rapid
seeping, very high water table) sounds like you would basically be
tring to drain an underground river with a few plastic sheets and some
4-inch pipes.

3) you described your "trench" as 5 feet wide and 10 feet deep, filled
8 feet deep with water. That is just plain crazy, and dangerous, and
undoable for "a few hundred dollars" in a "few days". That close to
your house, your foundation would crumble, the fence would fall in, the
neighbor kid and the mailman would fall in, drown, then sue you, your
backhoe would fall in and you'd go bankrupt, loose your house, not to
mention being dead. All unpleasant things.

4) Can I say again that this plan is crazy. You can't dig a trench in 8
feet of water. You didn't even mention pumping during construction.

5) Lowering the water table may cause cave-ins and sink holes, perhaps
under your house, under the street, under your neighbors house. Google
Images for "water table sink hole" to find some really amazing photos
of what can happen when water tables drop significantly. Locally, I
have seen sinkholes form after water mitigation was done wrong.

Since you don't seem likely to hire anyone to fix this problem, you are
going to have to go back to the drawing board. But before you start
thinking up plans and fixes, you really need to do some more research.


Try to figure out where the water is coming from, how much there is,
etc. Is it seasonal? Is it fed by surface water, a spring, etc? Do your
neighbors have water problems? Where will all the water go?

Just to give you some ideas for alternatives that might be more
appropriate (depending on what your research turns up):
- A sump-pump or three might be all you need, either under your house,
or near the house, to lower the table just a bit right around the
house.
- Diverting surface water somewhere upstream/uphill might be enough.
Water might be pooling up somewhere uphill from you, for example,
soaking the ground.
- You might have a non-porous layer of soil (clay?) a few feet down,
keeping the water too close to the surface. It might be enough to just
bore down through this layer in a few places, to let the water seep
down to a lower level.

All these ideas might be much cheaper, easier, and more effective than
what you want to do. Or they might be worse, or might even cause even
bigger problems. I don't konw, and it sounds like you don't either yet.
Good luck on your research and your project.

-Kevin