If she is growing the pumpkins to use as jack o lanterns and not to eat then you can let her go ahead and plant. If the area is going to be used to grow food plants, then you will need to have the soil tested to see if it is contaminated, how deep the contamination goes and what remediation is needed. Plants will take up various chemicals and store them in their tissues. If you then eat the plant, you get the toxins.

Adding clean soil is not adequate as the plant roots will go below it. After one season worms will mix the bad soil into the good. The bad soil must be removed, the depth to be removed depends on the depth of the contamination.

There's a guy in New Orleans who's planting turnip greens on an area that was contaminated with arsenic:
After each crop is harvested & safely disposed of-not eaten!-he'll get the soil re-checked until it's proved to be safe to use for an ordinary garden.

You might ask on the Soil Compost & Mulch Forum if there's a crop that will bind up petroleum;
there are lots of helpful & knowledgeable people over there.

Hi WSgirlygirl,

Here are two URLs for you to check out. The first is the dogpile search for Bioremediation with Mushrooms linked below.

http://www.dogpile.com/info.dogpl/search/web/Bioremediation%2Bwith%2Bmushrooms

The second is to a sight from that search.
http://www.fungi.com/mycotech/mycova.html

From the Mycotech / Mycova home page.

..."After several years, and redundant experiments to prove to naysayers that our data was valid, we have made some astonishing discoveries. (I am continually bemused that humans "discover" what nature has known all along.) The first significant study showed that a strain of Oyster mushrooms could break down heavy oil. A trial project at a vehicle storage center controlled by the Washington State Dept. of Transportation (WSDOT) enlisted the techniques from several, competing bioremediation groups. The soil was blackened with oil and reeked of aromatic hydrocarbons. We inoculated one berm of soil approximately 8 feet x 30 feet x 3 feet high with mushroom spawn while other technicians employed a variety of methods, ranging from bacteria to chemical agents. After 4 weeks, the tarps were pulled back from each test pile. The first piles employing the other techniques were unremarkable. Then the tarp was pulled from our pile, and gasps of astonishment and laughter welled up from the observers. The hydrocarbon-laden pile was bursting with mushrooms! Oyster mushrooms up to 12 inches in diameter had formed across the pile. Analyses showed that more than 95% of many of the PAH (polycyclic aromatic hydrocarbons) were destroyed, reduced to non-toxic components, and the mushrooms were also free of any petroleum products.

After 8 weeks, the mushrooms had rotted away, and then came another startling revelation. As the mushrooms rotted, flies were attracted. (Sciarid, Phorid and other "fungus gnats" commonly seek out mushrooms, engorged themselves with spores, and spread the spores to other habitats). The flies became a magnet for other insects, which in turn brought in birds. Apparently the birds brought in seeds. Soon ours was an oasis, the only pile teeming with life! We think we have found what is called a "keystone" organism, one that facilitates, cascade of other biological processes that contribute to habitat remediation. Critics, who were in favor of using plants (as in "phytoremediation") and/or bacteria, reluctantly became de facto advocates of our process since the mushrooms opened the door for this natural sequencing."...

Terran

Here is a link that might be useful: Dogpile search > Bioremediation with Mushrooms

Bioremediation with any type of compost is the fastest and most economical way to go and does not require the removal of large quantities of existing soil. We often underestimate the ability of soil microbial life to return manmade problems to their proper condition and it is well-documented how the applications of composted organic matter will remediate all manner of contaminates, including heavy metals and petrochemicals. The EPA has a fact sheet published on this issue, including the time frames involved, that should prove useful. The process, under proper conditions, should take only weeks rather months, but raised beds are certainly an option as well and can be used to plant and grow the pumpkins or any other edible crop virtually immediately.

To locate the EPA fact sheet just Google "soil remediation, compost". It is a .pdf file that doesn't link.

Before spending any money and time on remediation, I think you should get the soil tested. Most sites that need remediation have been used to store chemicals or are industrial sites.

If your yard has just been used for parking cars, maybe it isn't bad and can be used as is.

I did a search at http://www.epa.gov for soil remediation with compost. The search is linked below, if it works.

The first option that came up wasn't pdf, so it is not the one that garden gal had in mind. Maybe, she'll check back and relate the URL to the pdf that she had read.

http://www.epa.gov/epaoswer/non-hw/compost/analysis.txt

Terran

Here is a link that might be useful: EPA Search

Attached is the html version of the EPA fact sheet. It is not as readable as the .pdf file and any diagrams contained in the .pdf file will be lacking but it contains the gist of the article. And it should provide a link to the original file in the .pdf format you can access if you use Adobe Reader.

Here is a link that might be useful: EPA fact sheet