(1) By the anniversary date of its sewage treatment plant NPDES permit, in conjunction with its annual assessment for prevention of facilities overloading where applicable, a municipality shall submit an annual CSO report to the department for review and approval that:

(a) Details the past year's frequency and volume of combined sewage discharged from each CSO site, or group of CSO sites in close proximity. Field monitoring is necessary to estimate these parameters. The report shall indicate whether a CSO site or group of sites has increased over the baseline annual condition. If any increase has occurred, the municipality shall propose a project and schedule to reduce that CSO site or group of sites to or below its baseline condition;

(i) When a CSO site has been reduced to an average of one overflow per year through use of storage or separation, the department may consider reducing the monitoring requirement to frequency verification;

(ii) If the selected CSO control project is at-site treatment and discharge, the department may issue a modification to the applicable sewage treatment plant permit or issue a separate NPDES permit for that discharge. The permit or permit modification must include effluent limits, flow capacity limits, and reporting requirements. The total treated and untreated annual discharge from an at-site treatment plant may not increase above the baseline annual;

(b) Explains the previous year's CSO reduction accomplishments; and

(c) Lists the projects planned for the next year.

(2) In conjunction with its application for renewal of its applicable NPDES permit, the municipality shall submit an amendment to its CSO reduction plan. The amendment shall include:

(a) An assessment of the effectiveness of the CSO reduction plan to date; and

(b) A reevaluation of the CSO sites' project priority ranking; and

(c) A list of projects to be accomplished in the next five years, based upon priorities and estimated revenues. The department of ecology may incorporate such a schedule into an administrative order or the applicable NPDES permit.