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(1) Purpose. The purpose of EC 9.6792 is to reduce runoff pollution and mitigate the volume, duration, time of concentration and rate of stormwater runoff from development by implementing stormwater management techniques that promote the use of natural and built systems for infiltration, evapotranspiration and reuse of rainwater and that use or mimic natural hydrologic processes while capturing and treating approximately 80% of the average annual rainfall.

(2) Applicability and Exemptions.

(a) The standard in EC 9.6792(3)(a) applies to all land use applications submitted after March 1, 2014, that do not propose construction of a public street, private street or a shared driveway.

(b) The standards in EC 9.6792(3)(b), (e)-(g) apply to all land use applications submitted after March 1, 2014, that propose construction of a public street.

(c) The standards in EC 9.6792(3)(c), (e)-(g) apply to all land use applications submitted after March 1, 2014, that propose construction of a private street or shared driveway.

(d) Except as exempt under EC 9.6792(3)(e), the standards in EC 9.6792(3)(d)-(g) apply to applications for all development permits submitted after March 1, 2014.

(e) The standards in EC 9.6792(3)(d)-(g) do not apply to development permit applications:

1. For the construction of less than 1,000 square feet of new or replaced impervious surface within a 12 month period;

2. For interior alterations of an existing structure;

3. For the construction of more than 1,000 square feet of impervious surface that replaces existing impervious surface for purposes of maintenance or repair for the continuance of the current function, providing that as part of such maintenance and repair the applicant is replacing less than 50% of the length of the stormwater drainage system (including pipes, drainageway catch basins and drywells) on the development site;

4. For the construction of new or replaced impervious surface where all of the stormwater runoff from the impervious surface will discharge into an on-site, privately maintained underground injection control system that is registered and approved by the Oregon Department of Environmental Quality;

5. For the construction of a one or two family dwelling on a lot or parcel that was created by a land division application submitted and approved by the City prior to March 1, 2014, that is consistent with the approved land use application and the City’s stormwater quality (pollution reduction) standards in place at the time of the land division application; or

6. For the construction of a one or two family dwelling on a lot or parcel that was created by a land division application that included the construction of a public or private street or shared driveway submitted and approved by the City after March 1, 2014, if the lot or parcel adjoins the public or private street or shared driveway and the facility within the public or private street or shared driveway is an infiltration or filtration facility designed and sized to accommodate stormwater runoff from the adjoining lots or parcels at full buildout of the lots or parcels.

(f) The standards in EC 9.6792(3) do not apply to land use applications or development permit applications within the S-DR Downtown Riverfront Special Area Zone. Instead, the standards at EC 9.3155(17) apply.

(3) Standards.

(a) For land use applications not proposing the construction of a public or private street or shared driveway, the applicant shall submit a site development plan that delineates the following conditions existing on the development site:

1. Infiltration rates less than 2 inches per hour;

2. Bedrock less than 5 feet below the ground surface;

3. Groundwater elevations less than 6 feet; or,

4. Ground surface slopes greater than 10%.

(b) For land use applications proposing the construction of a public street, stormwater quality facilities to treat the stormwater runoff from the proposed public street shall be selected from the Stormwater Management Manual and shall be based on the following priority order: infiltration, filtration, mechanical treatment.

1. If selecting an infiltration or filtration facility to treat the stormwater runoff from the public street, the facility can be sized to also treat the stormwater runoff from the one and two family dwelling lots or parcels adjoining the public street based on full buildout of those lots or parcels.

2. If using a mechanical facility to treat the stormwater runoff from the public street or if the infiltration or filtration facility is not sized to also treat the stormwater runoff from the adjoining lots or parcels at full buildout, all lots or parcels created by the land division application shall comply with EC 9.6792(3)(d)-(g) at the time of development permit application.

(c) For land use applications proposing construction of a private street or shared driveway, stormwater quality facilities to treat the runoff from the proposed private street or shared driveway shall be selected from the Stormwater Management Manual and shall be based on the following priority order: infiltration, filtration.

1. An infiltration or filtration treatment facility to treat the stormwater runoff from the shared driveway or private street can be sized to treat the stormwater runoff from the proposed one and two family dwelling lots or parcels that adjoin the shared driveway or private street based on full buildout of those lots or parcels.

2. If the infiltration or filtration facility is not sized to treat the stormwater runoff from the adjoining lots or parcels at full build out, all lots or parcels created by the land division application must comply with EC 9.6792(3)(d)-(g) at the time of development permit application.

(d) For development permit applications, stormwater quality facilities shall be selected from the Stormwater Management Manual and shall be based on the following priority order: infiltration, filtration, off-site stormwater quality management.

1. If selecting a filtration treatment facility, the applicant shall submit a report that demonstrates at least one of the following development site conditions exist: a. Infiltration rates are less than 2 inches per hour; b. Bedrock is less than 5 feet below the ground surface; c. Groundwater elevations are less than 6 feet; or, d. Ground surface slopes are greater than 10%.

2. If selecting off-site stormwater quality management by contributing to the public off-site stormwater quality facilities, through payment of a higher stormwater system development charge adopted as part of the City’s system development charge methodology, the applicant shall submit a report that demonstrates there is insufficient land area to construct an approved infiltration or filtration facility by setting forth the required size of the smallest infiltration or filtration facility needed for the development’s impervious surface area and a site plan demonstrating that an approved infiltration or filtration facility cannot be located on the development site without reducing the size of the proposed development which is otherwise consistent with all other applicable lot and development standards.

(e) The selected stormwater quality facilities shall treat all stormwater runoff from all new or replaced impervious surface areas, or an equivalent on-site area, that will result from the water quality design storm except that the selected the stormwater quality facility does not need to treat the stormwater runoff from new or replaced impervious surface that is 500 sq. feet or less and does not gravity-feed into the selected treatment facility.

(f) All stormwater quality facilities shall be sited, designed and constructed according to the water quality provisions and the facility design requirements set forth in the Stormwater Management Manual.

(g) The standards in EC 9.6792(3) may be adjusted pursuant to EC 9.8030(24).

(Section 9.6792 added by Ordinance No. 20369, enacted June 14, 2006, effective July 14, 2006; amended by Ordinance No. 20521, enacted January 13, 2014, effective March 1, 2014; and by Ordinance No. 20619, enacted July 22, 2019, effective August 25, 2019.)