We live in a ranch style house with a finished lower level. I have a septic tank and laterals. (lateral field is only 3 years old) I just had a plumber replace all the old 4" cast iron pipe from septic tank into house for waste and venting to roofline. We also have a sump hole with pump, which does not connect to the septic system. The problem we are having is we have a terrible sewer gas smell coming from the lower level whenever someone takes a shower or we are running are fireplace upstairs. I have exhausted my resources. I have know where else to turn please help. We are tired of living with this.