Septic systems should not be used immediately after floods. Drain fields will not work until underground water has receded. Septic lines may have broken during the flood (especially after the good shaking in this week’s earthquake). Whenever the water table is high or your septic drain field has been flooded, there is a risk that sewage will back up into your home. The only way to prevent this backup is to relieve pressure on the system by using it less. Basically, there is nothing you can do but wait, do not use the system if the soil is saturated and flooded. The wastewater will not be treated and will become a source of pollution, if it does not back up into your house, it will bubble up into your yard. Conserve water as much as possible while the system restores itself and the water table fails.
Do not return to your home until flood waters have receded. If there was significant flooding in your yard, water will have flooded into your septic tank through the top. The tops of septic tanks are not water tight. Flood waters entering the septic tank will have lifted the floating crust of fats and grease in the septic tank. Some of this scum may have floated and/or partially plugged the outlet tee. If the septic system backs up into the house check the tank first for outlet blockage. Remember, that septic tanks can be dangerous, methane from the bacterial digestion of waste and lack of oxygen can overwhelm you. Hire someone with the right tools to clear your outlet tee.
Do not pump the septic tank while the soil is still saturated. Furthermore, pumping out a tank that is in saturated soil may cause it to “pop out” of the ground. (Likewise, recently installed systems may “pop out” of the ground more readily than older systems because the soil has not had enough time to settle and compact.) Call a septic service company (not just a tank pumping company) and schedule an appointment in a few days. Do not use the septic system for a few days (I know) have the service company clear any outlet blockage, or blockage to the drain field, check pumps and valves and partially pump down the tank if your soils are not dry enough or fully pump the tank if the soil has drained enough. The available volume in the tank will give you several days of plumbing use if you conserve water to allow your drain field to recover. Go easy the septic system operates on the principals of settling, bacterial digestion, and soil filtration all gentle and slow natural processes that have been battered by the storm.