B Relan, I may have jumped the gun with my first reply. I now have looked at all of your previous posts and I see you have had an engineer out to the site. Let me just say that engineers (as well as NRCS technicians) are not generally comfortable with making guarantees about whether a particular site will hold water. This is one of those CYA situations for them.

I have looked at and evaluated hundreds of pond and lake sites in the past twenty-seven years, and I can tell you that it would be very unlikely that a site with good clay in the bottom and which extends high up in the sides, such as in the knoll you describe, is going to lose it's water through what sounds like pockets of sandy material on the sides. If the parent soil material at your site is clay, as it seems from your description, then I would say the sandy material up on the sides is of no particular concern except where it may underlay the embankment. That material will be taken care of through the standard site preparation and/or coring as appropriate for construction of the embankment.

If I were you, I would be very encouraged by the existence of the several other good lakes in close proximity to your site, since that is always one of the better indicators for a feasible pond or lake site. I seriously doubt that any of those other lakes in the vicinity were clay-lined as a seperate construction procedure since that is such a cost-prohibitive factor for a lake of any appreciable size.

My suggestion would be to get someone who knows what they are doing in terms of designing and staking out the embankment, spillway, and water impoundment areas. Then find a reputable local dirt contractor with pond or lake building experience to do the work, according to prepared drawings and construction specifications.

Good Luck