Do you have a septic system? That smell indicates anerobic bacteria, usually caused by overwet soil or compost. Caused by the bacteria working on superwet organic material.
hortster

I used to have this acacia tree, it made the soil smell like poop. I used to think it was my cats pooping in the soil, but then after we cut down the foul tree, the smell went away, so I knew it was the tree.

We've been on the sewer line since we moved here 18 years ago. If they hit an old septic tank while digging wouldn't it have been apparent to them?

If, for some reason your soil is wet; i.e., underground spring, heavy rains, neighbor's overwatering of lawn and drainage into your yard, etc., and it saturates highly organic soil you will get anerobic bacteria working on it. Stenchola. Drying (oxygenation) can relieve that, so your contractor may be correct if he is uncovering a situation like this.
At a place I lived (30+ years ago) my neighbors decided to line their 10' diameter, wire fence enclosed compost pile with a double layer of visqueen plastic (still don't know why), then water the heck out of it to get it to break down. Created a miasmiatic swamp. Whoa. Same severe stenchola. I snuck over with an icepick and pummelled the whiz out of their plastic at the bottom for drainage. Then I was able to breathe and leave my windows open at night. I'm sure they still think they did the right thing - oops, true confessions...;)
hortster

Soils lacking air, anaerobic soils, often will have an aroma reminiscent of sewage. That has nothing to do with having a septic tank or drain field nearby, it is the odor the anaerobic bacteria emit. Wet soils can smell the same.

We've never had a drainage problem on our property, but it's understandable that wet soil piled up in mounds with rain puddles in low spots could create swampy, sewer like conditions. Hopefully as the soil dries out and is redistributed the odor will go away. Thank you all for your input.
5

Horster,they're probably bragging how effective that compost was to this very day.lolo

bon

My backyard smells like sewage. I am on city sewer system with pipes at front of house. inside there is only bedrooms at back of house. no toilets/ plumbing at all.

Gail, can you tell us about your soil: sandy, silty or clay, typically wet or dry?

Is there grass, what is the surrounding terrain and plant life like?

Does it smell only when you dig it up, or can you smell it just walking over the ground?

Is your back yard higher or lower than the front and the other yards around it?

Do any of your neighbors have this problem?

How old is your house?

I bought 3 bags of topsoil from Home depot and it has that sewer smell. I was planning to plant some veggies (seeds) but now im not sure if its a good idea to use this soil. What would you do?

I'd use it, now that I have it.

If it dries out it will lose that unpleasant aroma. As noted, the smell come from anaerobic conditions - closed bag/lack of oxygen and wet.

The smell won't hurt any any seed germination, seedlings or plants but the overly wet conditions could.

If it's not raining, spread it out on a bare area or a tarp for a couple of days and it will be re-oxygenated and the smell will dissipate. Once mixed into soil, it'll be just fine.

I'd return it if it really did smell like sewage. If it just smelt like damp potting mix, I'm fine with that.

Not on a sewage line. Smells up whole yard after a rain. Takes several days to dry out. One corner of 2 acre lot. Mushy. Grass won’t grow in that area

Other than move,there's not much you can do about living in a swamp Gail.