i dont really know ewest. flyash can also be a product of thermal remediation of contaminated soils, so I would probably want a chemical analysis (tox screen) of it to review before i put it in pond. residual refractory toxic compounds (those highly resistant to heat) would be of concern.
as far as being a sealing agent, i could see it helping to bind soils if blended and compacted well....sounds like it might be a really useful alternative.
