A nonconforming soil mining operation may expand by mining within the boundaries of the original parcel on which the mine was legally permitted, only to the extent allowed by an existing DEC permit or as otherwise provided by the laws of New York State. Such an operation may not begin to process materials mined off-site by crushing, screening, sorting, washing, drying, or otherwise, unless the Planning Board grants a special permit to allow such processing. This shall not prevent the continuation of any nonconforming soil mining operation which was processing materials mined off-site at the time it became nonconforming, nor shall it prevent the continuation of any nonconforming industrial use of a property where soil mining products mined off site are used as a raw material.