(1) The local health officer:

(a) Shall apply this chapter to OSS for treatment, siting, design, installation, and operation and maintenance measures treating sewage and dispersing effluent from residential sources with design flows up to 3,500 gallons per day;

(b) May apply this chapter to OSS for nonresidential sources of sewage if treatment, siting, design, installation, and operation and maintenance measures provide treatment and effluent dispersal equal to that required of residential sources;

(c) May not apply this chapter to industrial wastewater.

(2) The department shall apply the requirements of this chapter for the registration of proprietary treatment and distribution products.

(3) A valid OSS design approval, or installation permit issued prior to the effective date of these rules:

(a) Shall be acted upon in accordance with the requirements of this chapter in force at the time of issuance;

(b) Remains valid for a period of not more than five years from the date of approval or issuance, or remains valid for an additional year beyond the effective date of this chapter, whichever has the most lenient expiration date; and

(c) May be modified to include additional requirements if the health officer determines that a serious threat to public health exists.

(4) This chapter does not apply to facilities regulated as reclaimed water use under chapters 90.46 RCW and 173-219 WAC.