we had our septic system pumped this past July for the first time since we purchased the house 10 years ago because the drain field was area was wet and there was an awful stench around the house. All has been fine until approx. one week ago. I noticed that my dogs have dug 3 to 4 holes in the yard right where the drain field is. Each of these holes in filled with sewage and the stench is back. Any idea what the problem could be?