The director may authorize variances or exemptions from the regulations adopted pursuant to this chapter under conditions and in such manner as he or she deems necessary and desirable; provided, however, that the variances or exemptions are permitted under conditions and in a manner which is not less stringent than the conditions under, and the manner in which, variances and exemptions may be granted under the federal Safe Drinking Water Act, P.L. 93-523, and any amendments thereto, 42 U.S.C. § 300f et seq.