Is there scientific evidence that living within a certain proximity to
an ordinary transformer (the usual ones seen on poles on city streets)
can affect certain people so that they develop leukemia over time.

"In the past, some studies suggested exposure to electromagnetic
fields as another possible risk factor for leukemia. Electromagnetic
fields are a type of low-energy radiation that comes from power lines
and electric appliances. However, results from recent studies show
that the evidence is weak for electromagnetic fields as a risk
factor."

http://www.cancer.gov/cancertopics/wyntk/leukemia/page6