Any lawfully existing hazardous waste facility, use or activity, holding a valid operating permit or license and operating in conformance therewith, which engages in the processing, treatment, or disposal of on-site-generated hazardous wastes, as defined in N.J.A.C. 7:26-1.4, may continue within the zone in which it is located, subject to the provisions of §
31-36 and other provisions of applicable laws, local, state and federal. Nothing herein shall preclude changes in or additions to existing facilities engaged in the treatment, storage or disposal of hazardous waste, provided the facilities are lawfully approved and operating, if required by applicable state or federal law, administrative orders, or in order to protect public health and safety.