I had a low spot in my yard with lush grass but no standing water. I took a skid steer and dug down 3 feet. It filled with water and stayed full all summer. This is ground water in sand. There is 8 feet of sand on top of good clay in all the surrounding area. So I dug a 100x180ft and (12 feet at the deepest) pond with a 300 excavator while the pond was full of water. It is a challenge and dangerous to dig unless you have a good pump to keep it low. You might need to dry out the spoil piles for a day or 2 before you try landscaping it out. I had to move my dirt about 150feet with my excavator. It took me 40hrs to finish the project but less then half that time was actually digging.
