I'll add this to my list of hazardous regions.
I know there's an area in Costa Mesa, near Newport Harbor High School that had a high occurrence of a rare cancer. A few families contracted and their kids were diagnosed in there early 20s. Oddly enough, the researcher from UCI that did the case study passed away from cancer (not sure if it was the same cancer) a few years ago. My friend's 28 year old boyfriend is in remission for the second time.
When my parents house hunted in the early 90s, they had their eyes set of Huntington Beach. They bought in Huntington Harbor. My dad by profession was an engineer and somehow knew something wasn't right with the area near Edison High School. He said they did a lot of toxic waste handling in the 40s-50s. An old article in OC Weekly reported that a neighborhood of young children were contracting an extremely rare cancer in the 80s-90s. I'm not sure if this is still a problem today, but I'd stay away.
It seems to me that in the less developed areas of Orange County might have been used as a dumping zone in the past (whether accidental or not). Years pass by, industry closes, pressure mounts from regulators, residence and schools are built, and the no one is away of the potential hazards in their environment. When I studied Sociology, I took a few classes on medical sociology that focused on social, cultural, and environment reasons for high occurrences of disease. I hope people can use this knowledge for good and not just profit. A buddy of mine from college studies environmental samples for JP Morgan Chase and evaluates the samples to assess the risk for their potential investments. While this is important to run a successful business, I wish there were more professionals looking out for the people...before profits. Unfortunately, we're left with the fast and efficient EPA to investigate, study, and blow the whistle.