I am not a pond expert, but I am not sure it is practical to evaluate the dam core once the dam is completed. It has been record-breaking dry here in west-central Indiana, at least where I am at, and we got nothing from the last wave of storms. If it were me, I'd wait and see how it fills. I am not sure of any way to be sure about the dam integrity without a real test, unless you can see the water seeping out the dam on the far side (away from the pond).