I am guessing the borrow pits and quarry have very deep areas meaning their is a lot of water volume that is harder to warm or cool. This fact means the temperature of these water bodies does not change as rapidly as a shallower pond would. This means RES which are more sensitive to this do better. Also, I think the waters have higher alkalinity levels supporting more diverse and larger numbers of molluscs like snails and clams and crustaceans like shrimp and crayfish which RES love to eat.
What he said. With regards to stocking the gravel quarry, I think if you could use a block-off net to raise a goodly number (i.e. 200 or so per acre) of RES to maturity and release them into the pond at the same time. I don't know if a smaller amount of fish released into the pond will ensure a naturally reproducing population. Since RES don't readily take to pellets, I'd look into blocking off an area very early after ice-out and concentrate on improving the habitat in that area to make it very habitable to forage that RES will target, then boost that area with shrimp, crayfish and snails.
If that wasn't an option, and I had a forage pond available, I'd run a test for a year trying to cage raise RES using FHM and shrimp based pellets. With your contacts, you should be able to find someone who has the pellets in a commercial sized bag. They are made for aquarium raised tropical fish.
