Question
Denver,CO 5000sqft treeless backyard facing South. Hot sun all day, Yard was literally woody weeds/chickweed field, 5yrs ago at move-in. Finally established a yard from seed. The only tree in yard was old dying cottonwood 40"dia trunk. Removed tree in March. 3 months later long deep crevices appeared in soil over half the yard. 4'-10'long x 36"deep x 2"-4"wide,metal yardstick easily slides down 36" and comes out dry. All grass died off around cracks. (tree stump sprouted up regrowth from stump.)Major Remedial VOC ground contamination clean-up (TCE,etc)project going on 5yrs now at building site located about 1/2 mile away. Site ground water flow slopes downhill from site to 3'drain tunnel at edge of property. Drain tunnel cuts under major street across empty lot on other side and exits at mouth of mile-long drainage ditch running about 15' out from my back fence line. Pipe length is about 200' with a drop from property toward my end of about 15'-20'.
Maps of contamination movement confirm the contamination
is moving from the source,dwnhill with the leading edge running directly over my backyard (the lowest elevation). Is there any other explanation (tree root system)etc. that could be causing cracks? It is critical for me to know if I can eliminate the tree removal as a possible cause. Curious about the cost of a soil test, too. This really is a copy of the movie Erin Brokovich (same chemical,same mode of contamination, same health concerns from exposure AND personal risk from revealing what is now only my knowledge of the problem. @ weeks ago a 6'long crevice 32"deep appearing on the front side of house next to front door 20" out from foundation. I lease the house and landlord continues to evade any response to my concerns. I am not interested in a lawsuit or movie contract... I just want to know if I should be running for my life or I am overreacting. Thanks for your opinion on the soil.

Answer
Hi BC,  I think you can eliminate the tree.  When trees die and roots decompose, you see some slight settling in certain types of soils, but this is usually evident over a couple of years. At the same time, I'm fairly certain that surface runoff is not the culprit.
Cracks the size you mention, are usually associated with subsoil settling from areas filled for construction (which can be suddenly started by excessive rain or extensive drought) or broken water/sewer lines or an unstable mountain slope.
Obviously you are very concerned, so the first think I would do is rule out the possiblilities and contact your local utility company to check for water main or sewer leaks.  If neither, then... I'd look for a local geologist.  Your county may have one on staff that you could get to come by for free.  You may have to hire one or see if your local college or university has someone who could come by for an opinion, not a study.
You might even ask the company doing the cleanup to take a look.  Depending on who you talk to, some are very willing to help, some are afraid to talk to anyone.
Then relay what ever info you get to your landlord because the cracks are probably under the foundation also, which may damage the house. I would think he would care.
The contamination is another issue.  If it is indeed documented that the property is contaminated, I think your landlord would have a difficult time holding you to a lease.  Only you can determine the risk based on the groundwater information which I would think your landlord should also have to supply if he know's the land is contaminated. Jim