Rain, High Water and Your Septic System

A wet place to treat wastewater

NOAA's climate normals show the Pensacola area as humid subtropical, with rain spread through the year and a wetter summer (NOAA NCEI U.S. Climate Normals). The National Weather Service office that covers Pensacola tracks the heavy rain, flash floods and tropical systems that hit the area (National Weather Service Mobile/Pensacola). In late April 2014, the National Weather Service estimated about 20 inches of rain at Pensacola over two days (NWS Mobile/Pensacola, April 29-30, 2014 flash flood event), and Hurricane Sally flooded much of the region in September 2020. Events like these raise groundwater for days or weeks.

Why rain slows a septic system

A drain field depends on unsaturated soil. When the ground is full of water, effluent cannot soak away, so it backs up into the tank and then the house. The U.S. EPA notes that flooding and saturated soil can keep a system from working until the ground drains (U.S. EPA, SepticSmart and septic systems). On low lots, the field may be underwater.

Before a storm

• Know where the tank, field and any pump and alarm are.
• Make sure lids are secured so floodwater does not pour in.
• Move roof downspouts so roof water does not land on the field.
• If the system has a pump, know where its breaker is.
• Check FEMA's flood maps to see whether the property is in a mapped flood zone (FEMA flood maps).

During and right after

• Cut water use: fewer flushes, short showers, no laundry or dishwasher if drains are slow.
• Do not pump the tank while the ground around it is flooded unless someone checks conditions first. A high water table can push on an empty tank.
• If the power is out on a pump system, the alarm may sound when power returns. Keep water use low until the pump catches up.
• Stay out of floodwater, which may carry sewage.

When the water goes down

If drains return to normal as the yard dries, the system may be fine. Signs it needs a check:

• Backups continue after the ground dries.
• Odor or wet spots stay over the field.
• The pump alarm keeps coming on.
• Floodwater covered the tank lids or electrical parts.
• Soil washed away over the field or tank.

Silt and debris can get into a flooded tank, so pumping after the ground drains is common.

If it happens after every rain

A field that backs up with each storm may be too low, undersized or failing. A raised or mound replacement is sometimes the long-term answer. See drain field repair and replacement and what shapes a drain field scope.

Related pages: drain field repair & replacement, septic system repair, septic tank pumping, and what shapes an estimate.

Sources: National Weather Service Mobile/Pensacola; NOAA NCEI U.S. Climate Normals; U.S. EPA, SepticSmart and septic systems; FEMA flood maps.