The department may approve amendments to public groundwater permits for lands located within the Quincy subarea, including changes in points of withdrawal, purpose, and places of use, only if it believes, after investigation, that the activities proposed in the amendment or amendments will not:

(1) Impair existing rights;

(2) Prove detrimental to the public interest;

(3) Cause the tapping of a different body of groundwater (as defined herein or as determined by the department);

(4) Adversely affect the comprehensive scheme of water management adopted for the Quincy subarea.

In addition, with regard to holders of permits or certificates for the use of public groundwaters in the Quincy subarea, said permits and certificates shall represent "a valid right to withdraw public groundwaters," as that term is used in RCW 90.44.100, only to the extent of beneficial use actually made under the permit or certificate.