A moisture mitigation company can come in and seal the slab and the walls of the basement. To do this properly, they really would like to have access to the raw concrete barrier walls (remove drywall, studs, etc).

They will come in a clean the concrete, shot blast it, clean it again and then apply 2 coats of moisture barrier. If you want them to, they can then "cap" the barrier with a new coat of concrete so that you have a beautiful flat subfloor to work with.

I've heard the "moisture mitigation" alone is about $5/sf. If you want them to add a concrete topping it will add another $2/sf onto the job.

Now you are ready to use your basement without any worry for moisture intrusion. This is the "real" way to do it. I'm sure others will chime in with cheaper options, but the basement specialists will tell you stories about how much of the "other fixes" they have to remove so that they can get their work done.

Your situation is double precarious. Seattle alone is WET. An underground river is SWIMMING POOL wet. Add the two together and you have SERIOUS moisture penetration issues.

A friend had a house that had an underground water problem under the basement floor/foundation. Hydraulic pressure on the water kept forcing water into her basement. There were stains 18" high on the interior wall sheet rock.

She finally had a company come out and jack hammer a trench completely around the interior of the basement floor, down to the footings. A collection system(plastic tubing mush like drain tile) was installed in the trench and connected to a sump and pump. The exhaust piping for the water was installed to exit the foundation above the yard level(freeze proof) and a line buried in the yard to move the water out to the curb(permissible because it was 'natural' water, not household generated).

Then concrete was poured to fill the trench with a lip installed to allow water penetrating the basement walls to drain into the collection piping.

I glued thick plastic sheeting to the walls(in strips to allow water a path), tucked the plastic into the lip and then framed walls about 3" away from the plastic covered walls, sheet rocked added insulation, and finished out the basement.

10 years later, no problems. The company was a local franchise of the Dry Basement Company. I've read bad reviews of this process, but when it was done by knowledgeable and competent people, it works. Cost in about 2004 was $8,000 and took one prep and one work day. She had a really large basement as it took 50 4' by 8' sheets of sheet rock to finish about 3/4 of the walls and replace the damaged interior wall sheet rock.

Start with a calcium chloride cake test. Can't do wood over any result over 7 lbs.

Thank you all,

I feel a little more knowledgeable to be able to discuss with a basement contractor.