Generating a random list of (x, y) points that satisfy a condition?

So I need to generate a matrix of x and y points given that they meet the condition that at these (x,y) points concentration is greater than 10. Note that I first run a code that gives me concentration at each location, and now I need Matlab to "randomly" pick (x,y) points with the above condition.

Would appreciate any suggestions on how to go about this.