Problem is greater if it also involves contamination of ground/well water for the property, which can make the job hit $100,000.Besides the testing, excavate the contaminated soil, recover pooled oil from the area, other biological or chemical additives used to help remove oil contamination.

Contaminated soil can leach out chemicals every time the water table gets high or even when stormwater travels thru the soil on its way down to the water table.

Don't mean to sound harsh but that's business.

Hope I wasn't too harsh.

This may sound harsh, but it sounds like you may have some more work to do on mastering personal finance ... yes, you may be frugal and be able to manage expenses ... that is great, you are half way there ... but yet, you have no capital, so you are not all the way there yet IMO.

Recently looked at a 100k sq ft building that was 10% full and the chemicals used in the chiller were not monitored.  

I told him he needs to keep pets off the lawn for an hour after the gardener comes for the first time, and he asked if they would be spraying "toxic chemicals." 

I was trying not to be too harsh, but you nailed it.

Be overly cautious and harsh with your analysis.

You can find out the amount of water used by taking pool measurement and checking on line,, they'll have the info because this is used to calculate chemicals needed to maintain the pool.Was the well disclosed on your purchase of the property,, If it's listed and now in your name then your the sole owner..