etd, i'd like to have viewed all yer pics but (apologetically) dont have the time on dial up, and probably cant add anything of great significance anyway. just wanted to chime in and thank you for providing such a detailed posting.
my thoughts just from the text:
you described the soils really well, and it sounds like the shale zone (a glacial till?) has confined water (water under pressure). the mushy clay you initially hit at 7 feet sounds like the natural level (water table for the water emanating from the shale). it sounds like in yer area once the upper soils are soaked in, the pond should be fine. lining would hasten the filling so it sounds like it just depends on yer patience. for insurance, how easily could you doze up some clay rich soils to compact over the sandy loam?
i wouldnt worry about rocks in a clay matrix (if its a true clay matrix).
it also sounds like the amount of pressure underwhich the water flows out from the shale exceeds the back pressure exerted by yer pond on the shale, which is awesome, cause if it was the other way around, you'd never fill up.
i wish i had gushing ground water.....yer lucky!
