What is that awful smell around the John Muir Medical Center area in Walnut Creek?

I've heard the theories. It's hospital sewage. It's from the pond in nearby Heather Farms park. But I want to know what it really is and why it smells so darn bad!What is that awful smell around the John Muir Medical Center area in Walnut Creek?
There are sulfur deposits around that area.It is naturally occurring.It poses no danger but it does drive the property values down around that area because no one wants to deal with the stanch,especially around the summer months.I have worked there and I know first-hand.What is that awful smell around the John Muir Medical Center area in Walnut Creek?
it is sewer gas not hospital sewage. I read it once in the local paper ages ago. It has been going on for at least 10 years that I can recall.