I wanna get in on this. Been doing groundwater remediation for a quarter century this year.
You all are both right and both wrong. It all depends and there are no absolutes. Sandy vs clayey soils, temperature outdoors, depth to water table, groundwater velocity.
Gasoline? Nature quickly degrades it. With MTBE in it? MTBE doesn't degrade and moves fast. Oil mix? Degrades slower.
Got a shallow private well on a small property? Try not to dump gas for your own good.
I've got sites that I took over that have been in remediation since the early 1980s that won't be clean before 2050s. It took a snapshot in time to contaminate, it'll take decades to remediate.
I have chemicals that have regulatory groundwater concentration limits that are almost unattainable. Equivalent to about 1 sugar packet in 100 Olympic size swimming pools. Ridiculously small.
Soapbox time: the regs in the US and a few other developed countries got us to where we are with clean air and water, but more and more regs are not helpful, diminishing returns. I've been responsible managing for a dozen and a half chemical plant closures and demolitions. In only one instance did we bring jobs back to the US. Pollution is bad, clean environment is good, overkill is wasteful*.
Just like flying, there are a spectrum of risks; just be smart and don't go to either extreme.
*One last ranty-rantish rant - in this country there are extremists that are looking for the n'th degree of clean, looking for parts per quadrillion of chemicals in our food and water and lobbying to ban certain (all?) chemicals. Wouldn't that effort and dollar be better spent on improving health in other parts of the world? In last 25 years, I've spent millions on remediating soil and groundwater, burning through $1-2MM per month, managing liabilities of over $100MM. Last year I went on a mission trip to Honduras for Living Water International with 11 other people and installed a drinking water well at an elementary school that only had raw river water piped to the school; attendance rates were 50% due to water borne illness. I spent 1 week there and we collectively spent less than $20k to bring clean water to 500 kiddos. I did more good for human health and wellbeing in 1 week and $20k than I have 25 years and over $10MM spent in my career. WTF are we doing in our stupid bubbles? I laid off of my PPL training for 3 months after that trip cuz it just seemed pointless after seeing all that over there.
I've been a little cranky on POA lately, haven't I?
Hope I didn't lead this thread into a future lock.