The County of Clackamas has enacted a Stormwater Ordinance in order to establish minimum stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within this jurisdiction. The County of Clackamas is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The County of Clackamas will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The County of Clackamas, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The County of Clackamas has the authority to inspect stormwater facilities and practices in order to ascertain that they are properly maintained and functioning.
SECTION 5 – STORMWATER MANAGEMENT PLAN
This Section of the Stormwater Management Design Standards describes the methods and criteria necessary to integrate infiltration, water quality, and flow control stormwater facilities into a comprehensive stormwater management plan.
5.1 PLAN REVIEW REQUIREMENT THRESHOLDS
5.1.1 Stormwater Management Plan ≥ 5,000 sqft of Impervious Area
All development that results in 5,000 square feet or more of new impervious surface and/or a modification of existing impervious surfaces is subject to these Standards including: stormwater management, natural resource protection, and erosion control requirements.
5.1.2 Stormwater Management Plan ≤ 5,000 sqft of Impervious Area
All development that results in less than 5,000 square feet of new impervious surface and/or a modification of existing impervious surfaces which is not being phased or segmented in such a manner to avoid the requirements of these Standards is required to meet all provisions herein, including Section 4 – Natural Resources and Vegetated Buffers. All development per Section 5.1.2 that results in less than 5,000 square feet are exempted from the following Sections:
5.1.3 Erosion Control Plan and NPDES 1200-C Permits
Within the boundaries of the District, any grading or soil disturbance associated with a development activity which disturbs 800 square feet or greater is required to obtain an Erosion Control permit from the District. For erosion control requirements see Section 6 of these Standards. Any development activity in unincorporated Clackamas County not governed by a local authority will be required to obtain a National Pollutant Discharge Elimination System (NPDES) 1200-C Permit for any grading or soil disturbance associated with a development activity which disturbs 1 acre or greater area. The District has an agreement with DEQ to serve as the Agent of DEQ for these permits in the unincorporated area of Clackamas County. This includes plan review, permitting, inspection and enforcement of NPDES 1200-C permit requirements.
5.5.10 Maintenance
Maintenance is required for all on-site surface water facilities. A commercial or industrial user having ownership or control of onsite detention facilities shall maintain such facilities in compliance with these Standards and provide documentation of annual maintenance. The maintenance program must be approved by the District. All surface water facilities shall be maintained as needed and as approved by the District. Proof of maintenance shall be annually submitted in accordance with a schedule approved by the District. If the facility is not maintained, the District may perform the maintenance and charge the owner of the facility.
5.1 PLAN REVIEW REQUIREMENT THRESHOLDS
5.1.1 Stormwater Management Plan ≥ 5,000 sqft of Impervious Area
All development that results in 5,000 square feet or more of new impervious surface and/or a modification of existing impervious surfaces is subject to these Standards including: stormwater management, natural resource protection, and erosion control requirements.
5.1.2 Stormwater Management Plan ≤ 5,000 sqft of Impervious Area
All development that results in less than 5,000 square feet of new impervious surface and/or a modification of existing impervious surfaces which is not being phased or segmented in such a manner to avoid the requirements of these Standards is required to meet all provisions herein, including Section 4 – Natural Resources and Vegetated Buffers. All development per Section 5.1.2 that results in less than 5,000 square feet are exempted from the following Sections:
a) Section 5.3 - Stormwater Water Quality Treatment Standards;
b) Section 5.4 - Stormwater Infiltration Standards;
c) Section 5.5 - Stormwater Quantity / Flow Control Standards.
5.1.3 Erosion Control Plan and NPDES 1200-C Permits
Within the boundaries of the District, any grading or soil disturbance associated with a development activity which disturbs 800 square feet or greater is required to obtain an Erosion Control permit from the District. For erosion control requirements see Section 6 of these Standards.
Any development activity in unincorporated Clackamas County not governed by a local authority will be required to obtain a National Pollutant Discharge Elimination System (NPDES) 1200-C Permit for any grading or soil disturbance associated with a development activity which disturbs 1 acre or greater area. The District has an agreement with DEQ to serve as the Agent of DEQ for these permits in the unincorporated area of Clackamas County. This includes plan review, permitting, inspection and enforcement of NPDES 1200-C permit requirements.
5.3 STORMWATER INFILTRATION STANDARDS
Infiltration/Retention Systems
Infiltration systems are required for all new developments and redevelopments to infiltrate all runoff from storm events up to one-half inch of rainfall in 24 hours. Treatment shall occur prior to or concurrent with infiltration systems in accordance with Section 5.2. Infiltration system capacity may be incorporated into the detention system design, in order to reduce the required detention volume with appropriate professional on-site infiltration rate testing. Infiltration facilities shall be sized to infiltrate the design runoff volume within a maximum of 96 hours for the one-half inch requirement and 36 hours for the detention requirement.
Infiltration requirements may be waived, or reduced, if it can be demonstrated by a registered professional engineer that infiltration will destabilize the soil, cause adverse structural or environmental impacts, or due to site constraints such as high groundwater, springs, or impermeable soils.
Stormwater Permit Application Forms and Fees