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17.38.035 Drainage Management Policies and Standards.

(Amended by Ordinance Nos. 174745, 176561, 176783, 176955, 180037, 182144, 185397, 186902 and 187904, effective August 19, 2016.)

A.  Stormwater shall be managed in as close proximity to the development site as is practicable, and stormwater management shall 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 shall be discharged to an approved drainage facility.

1.    The City may initiate individual agreements with property owners to manage stormwater flows through alternative methods to 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 and redevelopment.  The City may require more than a 1:1 exchange on the amount of required management area.

2.  All discharges must be routed to a discharge point approved by the Director. Approval of discharge points must meet the following standards:

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)  Sanitary, wastewater or other discharges to the sanitary or combined system must comply with the Sewer and Drainage Facilities Design Manual and the Source Control Manual.

(2)  Stormwater or other discharges to the City’s storm and drainage system must comply with the Stormwater Management Manual and the Source Control Manual.

B.  The quality of stormwater leaving the site after development shall be equal to or better than the quality of stormwater leaving the site before development, as much as is practicable, based on the following criteria: 

1.  Stormwater management facilities required for development shall be designed, installed and maintained in accordance with the Stormwater Management Manual, which is based on achieving at least 70% removal of the Total Suspended Solids (TSS) from the flow entering the facility for the design storm specified in the Stormwater Management Manual.

2.  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.

3.  Development 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 mechanisms shall assure that stormwater management facilities meet the requirements for pollutants of concern, as stated in the Stormwater Management Manual.

4.  Stormwater discharge which is not practicable to fully treat to the standards of this Section and the Stormwater Management Manual, shall be either:

a.  Managed in an offsite facility or

b.  Given the option of paying a stormwater offsite management fee. The Bureau will employ a methodology for calculating the fee that is based upon an average unit cost of onsite facilities where such facilities would be effective and establish the calculation method and fee by rule. The stormwater offsite management fee collected shall be placed in a mitigation account to be used to mitigate the impacts that arise from offsite discharge of stormwater runoff.

5.  Not withstanding Subsection 17.38.035 B.4., for any parcel created after the effective date of this Chapter, the development shall fully treat all stormwater:

a.  Onsite, or

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.

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 shall be equal to or less than the quantity and flow rate of stormwater leaving the site before development, as much as is practicable, based on the following criteria:

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

2.  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 shall be specified in the Stormwater Management Manual.

3.  Any development that discharges to a tributary of the Willamette River, other than the Columbia Slough, shall design stormwater management facilities such that the rate of flow discharging from such facilities for up to a two-year design storm event does not lengthen the period of time the tributary channel receiving the discharge sustains erosion causing flows, as determined by the Bureau.

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

5.  Stormwater discharge which cannot be practicably managed for quantity or flow rate control as defined in this Subsection and the Stormwater Management Manual shall either be:

a.  Managed in an offsite facility designed for the pollutant load, volume and rate of flows from subject property and managed by the site developer/site owner or another legal agent, or

b.  Managed in an offsite stormwater management facility operated by the City subject to paying a stormwater offsite management fee. The Bureau will employ a methodology for calculating the fee that is based upon an average unit cost of onsite facilities where such facilities would be effective and establish the calculation method and fee by rule. 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 runoff.

6.  Not withstanding Subsection 17.38.035 C.5., for any parcel created after the effective date of this Chapter,  stormwater shall be fully managed:

a.  Onsite, or

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.

D.     The Director is authorized to establish requirements for the pumping and discharge of groundwater as a waste (discharge to waste).  The Source Control Manual regulations govern both quality and quantity impacts of pumping and discharging groundwater to City receiving systems.  The regulations may exempt, establish discharges as deminimus, or provide for and limit the permanent or temporary discharge of groundwater.   Temporary groundwater discharges may be authorized through the batch discharge processes described in Title 17.34 and 17.39.  In establishing rules to regulate the pumping and discharge of groundwater as a waste, the Director shall, at a minimum, incorporate and implement the following standards.

1.  Authorizations for discharge.  Unless the Director’s rules establish exceptions or determines discharges are de minimis, any pumping and discharge to waste of groundwater may proceed only after a groundwater specific discharge authorization by the Director.  This authorization shall establish volume, flow rate and pollutant load limits for the discharge. 

2.  Limiting flow volume and flow rate.  Pumping and discharge of groundwater as a waste will only be allowed where the proposed discharger has first reduced the rate and volume of groundwater requiring discharge to a City system to the greatest extent practicable. Examples include:

a.  Limiting the pumping and discharge of groundwater to rates not exceeding those rates that would be required for a building designed and engineered to minimize ground water intrusion and necessary ground water pumping; and

b.  Requiring management techniques implemented by the property developer and operator to assure continued effective use of structures in the presence of groundwater infiltration; and

c.  When there is sufficient capacity in the City receiving system.  Capacity shall be defined by rule and will consider providing capacity for other and future anticipated and primary uses of the systems.

3.  Onsite management a priority.  Pumped ground water shall be managed first by onsite methods, such as infiltration, to the greatest extent practical. Thereafter private conveyance facilities shall discharge through infiltration offsite or to surface water bodies.  Offsite discharge to City systems shall be approved only after onsite alternatives are evaluated.

4.  Prohibited discharges.  Offsite discharges meeting the following criteria are prohibited:

a.  Discharge to City-owned underground injection controls (UICs).

b.  Discharges meeting the tests for prohibited discharges in Chapters 17.34 and 17.39.  Notwithstanding this limitation, the City may allow discharge of contaminated ground water that has been treated to meet standards set by the Director to ensure that any groundwater discharges do not cause or threaten to cause a public nuisance, groundwater or surface water pollution, cause or threaten to cause the City to violate its own discharge permits granted by the Department of Environmental Quality.

(1)  The Director may establish rules to limit or prevent the pumping and discharge of contaminated groundwater and may require one-time or on-going testing or monitoring of water quality by the applicant for discharge authorization approval.

E.    All conveyance systems shall be analyzed, designed and constructed for existing tributary offsite runoff and developed onsite runoff 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 that minimizes environmental impacts in the downstream receiving system.  The Director reserves the right to determine the appropriateness of combination facilities in meeting these standards.

F.    All stormwater management facilities, source controls, and drainage systems must comply with the standards set forth in 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.