Can anyone else share some info about this? 

I just recently read about the carcinogens in the air around the Roseville Railyard - apparently a study has been done by CARB, Union Pacific and other local agencies that shows the high levels of diesel particulate matter that can adversely affect peoples' health depending on the direction of the wind. The result is an elevated cancer risk.

More info here:
http://www.sactaqc.org/resources/literature/airquality/locomotive_roseville_yard.htm
http://dwb.sacbee.com/content/news/story/12704219p-13556689c.html