These standards shall not be applied to an existing site development approved prior to the adoption of this chapter unless such site development is enlarged or expanded, in which case the standards of this chapter shall apply to the areas of enlargement or expansion. However, these standards shall apply in all cases where the existing conditions are found to be hazardous to pedestrian or vehicular traffic or where a specific parking or drainage problem can be relieved by their application. In such case, the Board shall require that revisions be made, but only to the extent necessary to alleviate the problem, as a condition for approval of the enlargement or expansion of the use.