In need of a plumbers advice. The owner of the house we moved into had it supposedly converted from septic to sewer. We moved in in Aug. Since then we've had plumbing issues, the ground in the backyard over the septic tank is sinking in as well as the concrete slabs for the patio. The green plate covering the pipeline has popped off and will no longer fit back on. We also have had a sink hole in the side driveway adjacent to the back yard. There is a very gross sewage odor in the back yard and the grass has died off. I've posted pics. Any thoughts, suggestions or imput would be greatly appreciated. Thanks.