What should I do to rescue grass from a petrol spill?

Question

We had some less than stellar workmen do some work a few weeks ago, and one of them spilled a substantial amount of petrol onto our front lawn. There is now an area about 100cm in diameter where the grass is completely dead.

I was not able to do anything about it until now (about 3 weeks later), so I have dug up the entire dead area, down to about 30cm. This is as far as I can reasonably dig, because we live in a clay area (Sydney Australia - almost all of the west is just clay).

The clay still stinks of petrol though, as did all of the dirt and grass I dug up.

Is there any way I can repair this? Do I just leave it dug out for a few weeks to "dry"? (It's summer at the moment, so lots of long, hot 30°C days and hotter)?

If I throw some fresh dirt from another part of the yard into the hole and plant new grass seeds, will the petrol that's in the clay just re-contaminate it? Or is that area going to be dead forever?

Answer 1

I can't really answer this other than to say that you probably need to remove more depth of soil, and it would obviously have been best to deal with it when it happened rather than this much time later. Soil treatment with hydrated lime reduces leaching of hydrocarbons, but it still means you'd have to wait a good while before attempting to plant, because it's not just the grass that's been killed, there will be knock on effects on soil organisms.

I don't know about Australia, but I imagine you must have some kind of Environmental Health department of the local authority, or a separate department, who might be able to give you some advice as to how to deal with this. They may, though, want to know exactly how much petrol was involved to determine whether it will affect the groundwater or local water table. Really, the builders who caused the problem are responsible for effecting remedial works, and I'd talk to the Environmental people about that too.

Answer 2

You can dig out the soil and get rid of it but it's considered hazardous waste so you need to find a suitable place to dispose of it. For a fairly small area like this that's probably the best way to go though.

You're going to have a really hard time planting grass and keeping it alive (even sod) with the heat you're having. Wait until the fall to repair the grass.

You're probably going to leave some fuel behind though.

There are microorganisms in compost that break down petroleum hydrocarbons. See this publication from the US EPA on Bioremediation and Pollution Prevention (pdf). One application metioned was of an Air Force Base. They used to haul off the contaminated dirt to be incinerated but then started to mix the contaminated soil with yard trimmings and turkey manure and then compost the whole mix. That got rid of the contamination and saved them a lot of money.

I would at least fill the hole up with either straight compost or a mix that's 50% of more compost and wait until temps are better for establishing grass.

I have a quick list on my site showing some of the problems compost can solve.

Answer 3

It seems reasonable to wait a 6 months for the petrol to further wash away, dig as much more soil around the site as you would like and fill with new topsoil. Grass should grow back on the new soil. Spilled petrol isn't good for the groundwater but that small quantity is likely bound in the surrounding clays.

Answer 4

I have had great success by removing the dead sod. I then take a large enough of charcoal to fill the heaping. By burning the charcoal I believe it raises the contamination back up and burns it. I remove the ash and fill the area with new topsoil and seed. I’ve used this method 3 times and been successful. Grass started fine and continued to grow. I the past I found that it started to grow but as it rooted it died right away.