I can't answer your technical question, but reading your post is raising all kinds of red flags for me. I wonder if there might be something else going with the builder - such as money issues. Maybe the answers (or lack thereof) is his way of stalling.

Either way, it doesn't sound like a good start to your project. Be careful with payments to the builder.

There is no way for me to know for sure but I suspect the contractor found organic or otherwise usuitable material and removed it. I suspect he must have additional concerns if he has asked a geo tech eng for a recommendation. Perhaps he doesn't want to discuss the situation with you until he has enough information. In the end, he will probably want more money.

So here is the informal report from the GeoTech Eng. and we now have to run cost estimates to see which are even feasible. Developer is saying we can't switch lots either. I don't want to be impatient, but it could be August is we wait for the watertable to recede. We are think Option #4 is we can afford it. Builder is running costs.

Based on my visit to the site ant test pits performed this lot has a groundwater problem along with soft alluvial soils on the back 2/3 of the building area. The back line of the house was located along a drainage way for the subdivision and the water is flowing in from the west on top and below the surface through this area. The soft soils on the rear portion of the lot in the building area need to be removed and replaced if the house is to be built on this lot and the drainage will need to be permanently directed around the back of the lot away from the house. To deal with the soil and groundwater conditions, OMI has comprised the following approaches to proceeding with construction:

1. If wanted done Immediately- Undercut the soft soil and place 1-ft of opengraded stone in the wet areas. Then place a filter fabric over the stone and put in compacted fill up to subgrade elevation for the house pad. The footing will be normal construction bearing in the fill.
2. If can wait for a window of opportunity- Undercut the soft soil. Let the lot drain naturally until the lot starts to dry out to the point the water is outside the building area. Place fill up to the subgrade elevation for the house pad. The footing will be normal construction bearing in the fill.
3. Wait until the driest season of the year and allow the water table to subside. Undercut 2-ft and compact the surface soils before placing 3 to 4-ft of soil over the back of the building area. The footing will be normal construction bearing in the fill. This approach may not work if the groundwater has no outlet.
4. Alternate Immediate approach-Place fill on the lot as needed to provide the proper elevation for building area and proper surface drainage. Dig the footings down to firm residual soil and pour flowable fill up to planned bottom of footing depth. Normal foundation bearing on the flowable fill in the back and stiff residual soil on the front.
5. Select a new lot that does not have a drainage area running through the building area

You've got to plan a big draingage path for the whole subdivision to dran through your lot and your house is right in the middle? That doesn't translate into a buildable lot IMHO. Option #5 would be my pick. Subsurface moisture issues are a big question mark and even if repaired, can come back to haunt you later if you have a 100 year rain event.

I would want the engineer to be working for me and I would be talking to him rather than strangers on the internet. I would also want my own structural engineer to be reviewing the foundation design. Option 4 sounds expensive but you don't have much choice if you are in a hurry and already own the lot.

I would be interested to know if there is information about the "drainage way" that the developer knew about but did not disclose to you. A lawyer should be looking at the documents very carefully before you commit more money to the project.

Good luck with the site.

I wouldn't build on that lot if the subdivision drainage is through the building site (or even if it wasn't - your yard will be a disaster). I agree with Renovator - that is a defect that should have been disclosed before sale. I would have an attorney get involved - if the owner knew and didn't disclose, he could be in real trouble. That would give you leverage to switch lots - which is what I would do. Now that you know of the defect, you would need to disclose it, which would make the lot unsaleable I would think.

Option 5 without a doubt. Compacting all that fill does nothing unless the subdivision's grading is also addressed to at least move the creek to the rear of the property. You might be talking wetlands here, with Federal regulations. And then if you have a big old trash moving gully washer, the rain might rise above the swale and flood your house.

Did the builder not have to file a drainage plan when this subdivision was planned? That's the place to start.

Look on the bright side: A waterfront lot.