(1) The following discharges are not subject to permits under this chapter:

(a) Discharges to municipal sewerage systems of domestic wastewater from residential, commercial, or industrial structures.

(b) Any industrial or commercial discharge to a municipal sewerage system for which authority to issue permits has been granted to the municipality under RCW 90.48.165.

(c) Any industrial or commercial discharge to a municipal sewerage system operating under, and in compliance with, the applicable requirements of a local pretreatment program approved under section 307 of FWPCA and WAC 173-216-150. In the event of noncompliance, this exemption no longer applies and the discharger is immediately subject to enforcement action under chapter 90.48 RCW for discharging without a waste discharge permit.

(d) Discharges to municipal sewerage systems of wastes from industrial or commercial sources whose wastewater is similar in character and strength to normal domestic wastewater: Provided, That such discharges do not have the potential to adversely affect performance of the system. Examples of this type of discharge sources may include hotels, restaurants, laundries and food preparation establishments.

(e) Discharges for which an NPDES permit from the department is required pursuant to chapter 173-220 WAC.

(f) Discharges which are otherwise subject to the permit requirements of this chapter but which are covered under a general permit issued pursuant to chapter 173-226 WAC.

(g) Discharges of domestic wastewater from a septic tank with subsurface sewage treatment and disposal and an ultimate design capacity less than or equal to fourteen thousand five hundred gallons per day. These systems are governed by on-site sewage disposal systems, chapter 246-272 WAC which is administered by the Washington state department of health.

(h) Discharges of domestic wastewater from a mechanical treatment system or lagoon followed by subsurface disposal with an ultimate design capacity less than or equal to three thousand five hundred gallons per day. These systems are governed by on-site sewage disposal systems, chapter 246-272 WAC which is administered by the Washington state department of health.

(2) A permit is required for any source subject to pretreatment standards promulgated under section 307 of FWPCA, unless exempted under subsections (1)(b) and (c) of this section.

(3) These exemptions shall not relieve any discharger from the requirement to apply all known, available, and reasonable methods to prevent and control waste discharges to the waters of the state, nor the requirement to obtain approval of plans and reports for the construction of wastewater facilities. Nothing herein shall limit the authority of the department to take enforcement action for any unlawful discharge of waste materials or other violations of the Water Pollution Control Act, chapter 90.48 RCW.