I know of a fellow with an open loop system that has a giant drain like return in his yard. It's basically a 10'x10' hole several feet deep filled with stone that the water dumps into. Gradually smaller gravel up until about a foot from the surface where it's dirt and grass again. This allows the water to leech back into his well all the while being filtered through the ground and picking up the heat it lost in the heat pump. It also filters the water should there be any contaminate and keeps the water source from being stirred up by water entering with velocity.

If you get oil in your well you are going to have major problems. Cleaning the well will not be fast or easy. But, I can not really see a reasonable pathway for the oil to enter the well. The water is under pressure so any oil leak would likely go to the outside of the unit instead of through an exchanger and into a positive pressure water line.

If cleaning ground water were as simple as Judd makes it appear, I would not be overseeing millions of dollars in groundwater cleanup right.

I think inline loop pumps are generally 1/6 to 1/12 of a horse power and take about 250-ish watts (going off memory).

The coaxial heat exchanger that my system and many others use(s) is just a coil of one copper tube within another.  The inner tube contains freon and oil so that, if the copper failed, contaminants would make their way into the water supply via the return line. 

I've done some groundwater cleanup myself and you're right, once something gets in the ground its not easy to get out.  If the contamination stayed within the well casing/screen then it would be relatively easy.  Unfortunately the very flow we depend upon to make these HP systems work is the same flow that contaminates the surrounding aquifer when oil is released to the well.

Thanks for the pump info.

Now if I can just find an inexpensive way to measure the water level in my well while I experiment with bleeding some return flow off to a sinkhole. I seem to remember someone building an electrical device that hung on the end of a long measuring tape. It would beep when it was submerged in water.

Edit: I just realized that will be even harder with water from the HP return line splashing down into the well...