what happened in my front lawn 2 years ago. I started having a lush green grass plot growing and upon a real close look, found that the soil was always damp, which in turn caused the grass to grow really well there. Come to find out that my leech bed was full (it's about 20 years old). Four thousand dollars later, I had a new filter bed and 250 feet of new pipe to the storm drain at the road. I'm not positive that you may have the same exact problem, but your post caused a raised eyebrow on my part. Good Luck....