What would be necessary to defend the adequacy of the recruitment/testing methods against a possible challenge?

Assuming that, despite your best efforts, the success rate for recruiting minority applicants is less than 80% of the success rate for non-minority applicants.  What would your advice be to the Fire Commission when it had to determine whether to certify the results?  What would be necessary to defend the adequacy of the recruitment/testing methods against a possible challenge?  What steps could be taken to enhance the likelihood of a successful defense of the recruitment/testing methods in the unfortunate event that minority applicants did much worse than non-minority applicants on the test?