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17.38.035 Drainage Management Policies and Standards.

A.  Stormwater must be managed in as close proximity to the development or redevelopment site as is practicable, and stormwater management must avoid a net negative impact on nearby streams, wetlands, groundwater, and other water bodies.  All local, state, and federal permit requirements related to implementation of stormwater management facilities must be met by the owner/operator prior to facility use. Surface water discharges from onsite facilities must be discharged to a receiving system approved by BES.

1.  The City may enter into agreements with property owners to manage stormwater flows through methods other than onsite controls:

a.  In joint facilities where public and private property flows co-mingle.

b.  In offsite areas that are “traded” for required onsite management areas related to new development and redevelopment.  The City may require more than a 1:1 exchange on the amount of required management area.

2.  All discharges from a site must be routed through a discharge point to a receiving system as approved by the Director. Approval of discharge points  is subject to the following:

a.  The discharge must be conveyed along a route of service approved by the Director.

b.  The discharge point must comply with the following:

(1)  The Sewer and Drainage Facilities Design Manual and the Source Control Manual, for sanitary, wastewater, or other discharges to the sanitary or combined system.

(2)  The Stormwater Management Manual and the Source Control Manual, for stormwater and other discharges to the City’s storm and drainage system, groundwater, or surface water.

B.  The quality of stormwater leaving the site after development or redevelopment must be equal to or better than the quality of stormwater leaving the site before development or redevelopment, to the extent practicable, based on the following criteria:

1.  Except as allowed under Subsection B.2. below, the development or redevelopment will fully treat all stormwater:

a.  Onsite;

b.  Within the original parcel from which the new parcel was created; or

c.  In an approved offsite facility with sufficient capacity, as determined by the Bureau.

2.  The owner of a development or redevelopment with a stormwater discharge that cannot practicably comply with Subsection B.1. above may, with written BES approval, meet stormwater requirements by:

a.  Managing stormwater in an offsite facility designed to treat flows from the subject property and managed by the site developer/owner or another legal agent:

b.  Managing stormwater in an offsite facility designed to treat flows from the subject property and operated by the City; or

c.  Paying a stormwater offsite management fee as required by the Stormwater Management Manual. The stormwater offsite management fee collected will be placed in a mitigation account to be used to mitigate the impacts that arise from offsite discharge of stormwater.

3.  Stormwater management facilities required for development or redevelopment must be designed, installed and maintained in accordance with the Stormwater Management Manual.

4.  Land use activities of particular concern as pollution sources may be required to implement additional pollution controls and source controls including but not limited to those management practices specified in the Stormwater Management Manual and the Source Control Manual.

5.  Development or redevelopment in a watershed that drains to streams with established Total Maximum Daily Load limitations, as provided under the Federal Clean Water Act, Oregon Law, Administrative Rules and other legal authorities,  must ensure that stormwater management facilities meet the requirements for pollutants of concern, as stated in the Stormwater Management Manual.

6.  The Director is authorized to exempt land uses, discharge locations or other areas of the city from the requirements of this Subsection if onsite pollution reduction or pollution control is not needed or desirable due to limited pollutant loads or offsite methods of pollution control are available.  All exemptions are specified in the Stormwater Management Manual and the Source Control Manual.

C.  The quantity and flow rate of stormwater leaving the site after development or redevelopment must be equal to or less than the quantity and flow rate of stormwater leaving the site before development or redevelopment, as much as is practicable, based on the following criteria:

1.  Except as allowed under Subsection C.2. below, stormwater will be fully managed:

a.  Onsite;

b.  Within the original parcel from which the new parcel was created; or

c.  In a privately developed offsite facility with sufficient capacity, as determined by the Bureau.

2.  The owner of a development or redevelopment with stormwater discharges that cannot practicably comply with Subsection C.1. above may, with written BES approval, meet stormwater requirements by either:

a.  Managing stormwater in an offsite facility designed for the volume and rate of flows from the subject property and managed by the site developer/site owner or another legal agent;

b.  Managing stormwater in an offsite facility designed for the volume and rate of flows from the subject property and operated by the City; or

c.  Paying a stormwater offsite management fee as required by the Stormwater Management Manual. The fee collected will be placed in an account to be used to mitigate the impacts of offsite discharges of stormwater. 

3.  Development and redevelopment must mitigate all project impervious surfaces through retention and on-site infiltration to the maximum extent practicable.  Where on-site retention is not possible, development and redevelopment must detain stormwater through a combination of measures that prevent an increased rate of flow leaving a site during a range of storm frequencies as specified in the Stormwater Management Manual.

4.  The Director is authorized to exempt areas of the city from the quantity control requirements if flow control is not needed or desirable because there is sufficient capacity and limited impacts to the receiving drainage system.  All exemptions will be specified in the Stormwater Management Manual.

5.  Any development or redevelopment that discharges to a tributary of the Willamette River, other than the Columbia Slough, must design stormwater management facilities to minimize hydromodification impacts from storm events as determined by the Director.

6.  Site drainage facilities must be designed to safely convey less frequent, higher flows through or around stormwater management facilities and to an approved discharge point with adequate capacity without damage to the receiving system, whether natural or constructed.

D.  The pumping and discharge of groundwater to a City receiving system may be allowed only after a BES Discharge Authorization has been obtained, as required in the Source Control Manual. The application for that authorization must demonstrate that groundwater discharges must meet the associated requirements in the Source Control Manual and Chapters 17.34 and 17.39, which govern both quality and quantity of groundwater discharges.

E.  All conveyance systems must be analyzed, designed and constructed for existing tributary offsite stormwater and developed onsite stormwater from the proposed project in compliance with the City's Sewer and Drainage Facilities Design Manual.  The general goal of these standards is to convey both onsite and offsite waters in a way that meets the capacity needs of the City conveyance system, is protective of public health and safety, and minimizes environmental impacts in the downstream receiving system.

F.  All stormwater management facilities, source controls, and drainage systems must comply with the standards of the Stormwater Management Manual and the Source Control Manual and may require permit review and approval before commencement of work.  Public systems must be reviewed and approved by BES in compliance with the sizing and location standards in the Stormwater Management Manual.  Private onsite systems must be reviewed and approved by BES for compliance with the stormwater hierarchy and other guidance specified in the Stormwater Management Manual and the Source Control Manual, and may be reviewed by Bureau of Development Services for compliance with the plumbing code regulations in Section 25.01.020.  Installation or modification of any stormwater system or source control, whether it involves structural changes, changes to planting schemes, or the management of drainage area in addition to what was previously approved, may require a permit from or review by the BES Chief Engineer.

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