(1) Ecology recognizes three basic phases of planning:

(a) Water pollution control and abatement plan (for sewage drainage basins)

(b) Preliminary engineering report

(c) Construction plans and specifications

(2) These phases are defined as given in WAC 372-68-030. The water pollution control and abatement plan, which covers all water pollution sources, is wider in scope than the other two phases, which deal primarily with the design and construction of wastewater collection and treatment works. The last two phases are progressively more detailed than is the water pollution control and abatement plan. Preliminary engineering reports for proposed wastewater collection and/or treatment facilities must comply with the water pollution control and abatement plan for the sewage drainage basin in which they are located. Construction plans and specifications for a proposed facility must comply with the preliminary engineering report for that facility.

(3) It is acceptable to combine the other phases of planning for proposed water pollution control facilities with the water pollution control and abatement plan subject to limitations as specified in WAC 372-20-030. Such a combined plan will receive as many certifications of approval as the phases of planning which it satisfied.