The short answer
A sump pump that smells like rotten eggs or sewage in a Northern Virginia basement is usually stale water. When water sits in the bottom of the pit for weeks without the pump running, bacteria in it make hydrogen sulfide, the gas that smells like rotten eggs, and an open or loose lid lets it into the house. Pour clean water into the pit until the pump runs and swaps out the old water. If the smell comes right back, it’s something else: a washer or sink draining into the pit, a lid that isn’t sealed, or a pit that’s really a sewage ejector basin.
First, rule out gas
Natural gas has a rotten-egg smell added to it on purpose. If the smell is strongest near the furnace, the water heater or the stove rather than the pit, or it keeps getting stronger, leave the house and call your gas company from outside. Don’t flip switches on the way out.
$697 Sump Pump Replacement
A new cast iron pump in your existing pit, a quiet check valve, new pipe to the discharge, the old pump hauled away and a bucket test before we leave. See the offer
The usual causes
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Swipe to see all columns →
| What you notice | The likely cause | The fix |
|---|---|---|
| Rotten eggs, strongest right at the pit, after a dry spell | Stale water sitting under the float | Pour in clean water until the pump runs. Repeat after a few dry weeks. |
| The smell shows up after laundry | A washer or utility sink drains into the pit | That water belongs in the sewer. A plumber moves the line. |
| Sewage smell, and the pit has a bolted lid and a vent pipe | It’s a sewage ejector basin, not a sump | The seal, the vent or the pump needs a look. |
| A damp, earthy smell from an open pit | Air from the soil under the slab coming up through the pit | A sealed lid with gaskets around the pipes |
| Sewer gas near the pit, but the pit water is clean | A dry floor drain nearby | Pour a bucket of water down the floor drain to refill its trap. |
| The water is high, dark and still | The pump has stopped | Check the power and the float. Sump pump not working has the steps. |
Stale water, the usual one
A sump pump only runs when the water lifts its float. Between storms, a few inches of water can sit in the bottom of the pit for weeks with nothing fresh coming in, and that’s where the rotten-egg smell comes from. Running clean water through it is the fix: pour slowly until the float lifts and the pump empties the pit. If the smell keeps coming back in a finished basement, a sealed lid keeps it in the pit.
Laundry and sinks in the pit
In a lot of older basements, somebody ran the washer hose or the utility sink drain into the sump pit because it was close. Soap, lint and food scraps in water that sits still will smell, and the pump sends that wastewater out into the yard. It belongs in the sewer. Moving the line to a drain, or to a laundry pump, is a plumbing job we price at the visit.
Seal the lid
A loose or open lid lets whatever is in the pit into the basement. A sealed lid, with gaskets around the pipes and the cord, keeps it in. An open pit is also one of the ways radon gets into a basement, and radon has no smell at all, so a sealed lid is worth having either way.
When it’s really an ejector basin
If the pit has a heavy, bolted lid and a vent pipe running up from it, and it sits near a basement bathroom or laundry, it’s probably a sewage ejector basin, not a sump. A sewage smell there means the lid seal, the vent or the pump. Our ejector pump page explains how it works, and what to do when the ejector alarm goes off covers the urgent version.
When the pump is the problem
A pump that stopped running leaves the pit full of standing water, and that smells fast. What a silent or humming sump pump means goes through the checks, and the sump pump alarm guide covers the beeping. If the pump is done, our sump pump replacement is $697 installed, normally $997: a new cast iron pump in your existing pit, a quiet check valve, new pipe to the discharge, the old pump hauled away and a bucket test before we leave. A water alarm is included.
What sump pump work costs in Northern Virginia has the rest of the prices, and our sump pump repair page has the battery backups.
Smell coming from somewhere else?
If the pit checks out, the smell is coming from somewhere else: a dry trap, a loose toilet, a cracked vent. Our guide to a sewer smell in the house walks through every one.
Book it
A plumbing diagnosis visit is $49, or $250 after hours, and you get the price of the fix before we start. Call (703) 997-9757, day or night, or book online with the problem already filled in. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why does my sump pump smell like rotten eggs?
Water sitting in the pit for weeks grows bacteria that make hydrogen sulfide, the rotten-egg gas. Pour clean water into the pit until the pump runs and empties it. If the smell comes back fast, check whether a washer or sink drains into the pit, and seal the lid.
Why does my basement smell like sewage near the sump pump?
The pit may really be a sewage ejector basin with a bad seal or vent, a floor drain nearby may have dried out, or wastewater from a washer or sink may be draining into the pit. Pour water down the floor drains first. If the smell stays, call a plumber.
How do I get rid of the smell from my sump pit?
Run clean water through it until the pump cycles, seal the lid with gaskets around the pipes, and move any washer or sink drain out of the pit and into the sewer. If the pit already has a sealed lid and a vent, it’s likely an ejector basin, and that’s a plumber’s job.
Is a sump pump smell a problem?
Most of the time it’s stale water, and fresh water and a sealed lid end it. A real sewage smell means wastewater or sewer gas is getting somewhere it shouldn’t, so have it found. If the rotten-egg smell is near a gas appliance instead of the pit, leave and call your gas company.
