Can my employer deny a vacation I planned to take within the 30 days notice I have given to leave the company?

An employer almost always has the right to deny a request for vacation leave when it is to their advantage to do so.  The more important question is whether you must be paid for the unused vacation time upon termination.  That is a more complicated question and depends on what the agreement is between the employer and employee regarding payment of unused vacation upon termination.  When there is no express agreement or policy, then it is not often easy to determine whether the employer has any obligation to pay.  Past history and other relevant information can be used to present to a judge in small claims court if a claim for unpaid vacation time is filed.