Declares that the purpose of this act is to establish, in a single state agency, comprehensive regulation of the design, operation, and maintenance of large on-site sewage systems, and their operators, that provides both public health and environmental protection.

Declares the permitting and continuing oversight of large on-site sewage systems.

Directs the state department of health to establish standards and rules for the siting, design, construction, installation, operation, maintenance, and repair of large on-site sewage systems, and to enforce the standards and rules established.

Amends chapters 70.118 and 70.05 RCW to enhance local health officer enforcement authority regarding on-site systems.

Exempts operators certified by the department of health.

Amends RCW 36.94.010 to clarify its applicability to large on-site sewage systems.