2022 marked the 20th anniversary of the Technology Assessment Protocol – Ecology (TAPE), Washington State’s rigorous stormwater control measure (SCM) evaluation protocol and peer-reviewed regulatory certification process that is nationally recognized. In recent years, many TAPE filtration SCMs have been seeking approval at higher hydraulic loading rates, while during that same time period, many SCMs have required more frequent maintenance. Proponents are required to report the SCM hydraulic performance relative to the design flow rate and report all maintenance activities during TAPE evaluations. However, to date, TAPE has not had a formal process to assess maintenance requirements or hydraulic performance of approved devices. The absence of robust maintenance information has led to some municipalities adding their own restrictions or requirements on top of TAPE certification. In 2019, Ecology convened a subgroup of the TAPE Stakeholders Advisory Group and Board of External Reviewers to brainstorm ideas of how TAPE could better assess SCM maintenance needs. Through surveys of municipalities, manufacturers, and other user groups, the subgroup developed a draft maintenance and hydraulic assessment protocol for stormwater treatment filtration devices. The protocol, which is still in development, will provide a way to assess how much of a water year an SCM can treat before failing. Results from the assessment may be used to adjust an SCM’s approved hydraulic loading rate. This presentation will highlight the process that was followed to develop the protocol, the successes, and challenges of that process, provide details on the new maintenance/hydraulic assessment protocol, and describe how the results from the assessment will be used. The presentation will conclude with a discussion of the differences between monitoring and testing requirements for proprietary and non-proprietary stormwater treatment solutions.