Redwood City Municipal Code Art. II Stormwater Treatment Measures and Maintenance Program

This Article is necessary to protect the health, safety and general welfare of the people of Redwood City and the surrounding region from water quality degradation caused by stormwater run-off. This Article has been enacted and shall be implemented in a manner consistent with the requirements of the California Regional Water Quality Control Board (RWQCB) applicable to the City of Redwood City. This Article shall be supplemental to the requirements of Article I, of Chapter 27A, of this Code, with respect to stormwater.

(Ord. No. 2269, § 2, 8-9-04)

(Ord. No. 2465, § 4(Exh. B), 8-26-19)

The following words and phrases, whenever used in this Article, shall be as set forth below:

GREEN INFRASTRUCTURE: Means the construction and retrofit of storm drainage to reduce runoff volumes, disperse runoff to vegetated areas, harvest and use runoff where feasible, promote infiltration and evapotranspiration, and use bio-retention and other natural systems to detain and treat runoff before it reaches our creeks and Bay. Green infrastructure facilities include, but are not limited to, pervious pavement, infiltration basins, bio-retention facilities or "raingardens," green roofs, and rainwater harvesting systems. Green infrastructure can be incorporated into construction on new and previously developed parcels, as well as new and rebuilt streets, roads, and other infrastructure within the public right-of-way. Green Infrastructure may apply to any type of infrastructure or land development project.

C.3 REGULATED PROJECT: Shall mean development projects as defined by Provision C.3.b.ii of the Municipal Regional Stormwater NPDES Permit (MRP), Order No. 2022-0018, NPDES Permit No. CAS612008, or its successor. This includes public and private projects that create and/or replace five thousand (5,000) square feet or more of impervious surface, or as may be amended in the future.

IMPERVIOUS SURFACE: Shall mean a surface covering or pavement of a developed parcel of land that prevents the land's natural ability to absorb and infiltrate rainfall/stormwater. Impervious surfaces include, but are not limited to: Roof tops; walkways; patios; driveways; parking lots; storage areas; impervious concrete and asphalt; and any other continuous watertight pavement or covering. Landscaped soil and pervious pavement, including pavers with pervious openings and seams, underlain with pervious soil or pervious storage material, such as a gravel layer sufficient to hold at least the volume of rainfall runoff, as defined in Provision C.3.d of the MRP, are not impervious surfaces. Open, uncovered retention/detention facilities are not considered impervious surfaces for purposes of determining whether a project is a Stormwater Treatment Project as defined under Provisions C.3.b and C.3.g of the MRP. Open, uncovered retention/detention facilities shall be considered impervious surfaces for purposes of runoff modeling and meeting the hydromodification standard as defined in Provision C.3.g.ii of the MRP.

PERMANENT STORMWATER POLLUTION PREVENTION MEASURES (PSPPM): Shall mean any source control measures, site design measures, and/or stormwater treatment measures, or combinations thereof that reduce stormwater pollution as required by Order R2-2015-0049 in NPDES Permit No. CAS612008 issued by the RWQCB, San Francisco Bay Region, as it may be amended from time to time. The design and implementation of the PSPPM must be in accordance with the guidelines and technical specifications provided by the City or other City-approved authority and the requirements of Order No. R2-2015-0049. The design and implementation of the PSPPM must also incorporate green infrastructure designed to limit contributions of urban runoff pollutants to San Francisco Bay per the MRP.

SITE DESIGN MEASURES: Shall mean site planning techniques to conserve natural spaces and/or limit the amount of impervious surface at new development and significant redevelopment projects in order to minimize runoff and the transport of pollutants in runoff.

SOURCE CONTROL MEASURES: Shall mean any schedules of activities, structural devices, prohibitions of practices, maintenance procedures, managerial practices or operational practices that aim to prevent stormwater pollution by reducing the potential for pollution at its source.

STORMWATER TREATMENT MEASURES: Shall mean any engineered system designed to remove pollutants from stormwater by simple gravity settling of particulate pollutants, filtration, biological uptake, media adsorption or any other physical, biological, or chemical process.

STORMWATER TREATMENT PROJECT: Shall mean all C.3 Regulated and Green Infrastructure projects, where Green Infrastructure projects are defined by resolution of the City Council.

(Ord. No. 2269, § 2, 8-9-04)

(Ord. No. 2465, § 4(Exh. B), 8-26-19; Ord. No. 2542, § 5(Exh. B), 10-14-24)

A. All Stormwater Treatment Projects shall include permanent stormwater pollution prevention measures in order to reduce water quality impacts of stormwater runoff from the entire site for the life of the project.

1. C.3 Regulated Projects that result in an increase of, or replacement of, more than fifty percent (50%) of the impervious surface of a previously existing development shall include permanent stormwater pollution prevention measures sufficient to reduce water quality impacts of stormwater runoff from the entire site for the life of the project.

2. C.3 Regulated Projects that result in an increase of, or replacement of, fifty percent (50%) or less of the impervious surface of a previously existing development shall include permanent stormwater pollution prevention measures sufficient to reduce water quality impacts of stormwater runoff from the increased or replaced portion of the site for the life of the project.

B. Stormwater treatment measure proposed as part of a project's permanent stormwater pollution prevention measures shall be designed in accordance with the following hydraulic sizing criteria to treat stormwater runoff.

1. Volume Hydraulic Design Basis: Stormwater treatment measures that detain stormwater for a certain period and treat primarily through sedimentation and infiltration, whose primary mode of action depends on volume capacity, such as detention/retention units, green roofs, or infiltration structures, shall be designed to treat stormwater runoff equal to:

a. The maximized stormwater quality capture volume for the area, based on historical rainfall records, determined using the formula and volume capture coefficients set forth in Urban Runoff Quality Management, WEF Manual of Practice No. 23/ASCE Manual of Practice No. 87 (1998), pages 175—178 (e.g., approximately the eighty-fifth (85th) percentile twenty-four (24) hour storm runoff event); or

b. The volume of annual runoff required to achieve eighty percent (80%) of more capture, determined in accordance with the methodology set forth in the California Stormwater Best Management Practices Handbook for New Development and Redevelopment (2003), using local rainfall data.

2. Flow Hydraulic Design Basis: Stormwater treatment measures that treat pollutants from a moving stream of water through filtration, infiltration, sedimentation and/or biological processes, whose primary mode of action depends on flow capacity, such as bio-retention areas, flow-through planters, tree well filters, or media filters, shall be sized to treat:

a. Ten percent (10%) of the fifty (50) year peak flow rate;

b. The flow of runoff produced by a rain event equal to at least two (2) times the eighty-fifth (85th) percentile hourly rainfall intensity for the applicable area, based on historical records of hourly rainfall depths; or

c. The flow of runoff resulting from a rain event equal to at least 0.2 inches per hour intensity (also known as the "4 percent method").

3. Combination Flow and Volume Design Basis: For projects on sites where infiltration should be avoided, or that are planned to maximize density at a redevelopment or infill site, a combination flow and volume design basis may be used for bio-retention areas and flow-through planters. These treatment measures shall be sized to treat at least eighty (80) percent of the total runoff over the life of the project, using local rainfall data and the methodology set forth in the C.3 Stormwater Technical Guidance, written by the San Mateo Countywide Water Pollution Prevention Program.

C. Stormwater treatment measures proposed as part of a project's permanent stormwater pollution prevention measures shall be designed in accordance with the City's Green Infrastructure Plan established by resolution of the City Council, which may be amended from time to time.

D. All plans and construction of stormwater treatment measures are subject to inspection and approval by the City Engineer.

E. No final building or occupancy permit shall be issued without the written certification of the City Engineer that the requirements of this Chapter have been satisfied. Such certification shall be in the form prescribed by the City Engineer and shall not be issued without payment of all applicable fees which may be imposed for administration of this Chapter.

(Ord. No. 2269, § 2, 8-9-04)

(Ord. No. 2465, § 4(Exh. B), 8-26-19; Ord. No. 2542, § 4(Exh. A), 10-14-24)

A. The property owner(s), its administrators, successors, or any other persons, including any homeowners association, of a Stormwater Treatment Project shall take all necessary actions to ensure that the permanent stormwater pollution prevention measures ("PSPPM") are properly maintained so that they continue to operate as originally designed and approved. The maintenance of the control measures shall be in accordance with the terms and conditions of a maintenance agreement and shall be in the form of a covenant running with the land, environmental mitigation measures, a use permit, enforceable conditions of approval, or other legal agreement. The agreement shall provide access to the extent allowable by law for representatives or agents of City for the purpose of verification of property operation and maintenance of the specific PSPPM. The agreement must be signed by the City Clerk and shall be recorded in the office of the County Recorder, shall remain in force until ownership of the developed property has been transferred, and upon transfer, shall be binding on the new owner(s).

B. Any property owner that has been required by this Chapter to construct or install and maintain PSPPM shall upon transferring ownership of such property provide the new owners with a current copy of this Chapter, and shall inform the new owners in writing of their obligation to properly operate and maintain such PSPPM.

C. It shall be unlawful to alter, modify or change any components of the PSPPM without first obtaining the written certification of the City Engineer that the requirements of this Chapter have been satisfied.

(Ord. No. 2269, § 2, 8-9-04)

(Ord. No. 2465, § 4(Exh. B), 8-26-19; Ord. No. 2556, § 5(Exh. B), 12-22-25)

A. As a condition of approval, the City Engineer may require the owner of a C.3 Regulated Project to establish a self-monitoring and reporting program to ensure all PSPPM are in compliance with the provisions of this Chapter. The self-monitoring report must be in accordance with the guidelines published by the San Mateo Countywide Water Pollution Prevention Program.

B. The City Engineer, or his or her authorized representatives, may conduct all inspection, surveillance, and monitoring procedures necessary to assure compliance with applicable sections of this Chapter or with state regulations.

C. Representatives of the City Engineer shall be authorized to enter, without unreasonable delay, any premises of any project subject to the requirements of this Chapter to carry out inspections and monitoring to assure compliance with this Chapter and applicable State of California regulations. Records shall be available to City personnel for inspection and copying.

D. In addition to any other remedy available to the City, City Inspectors may issue compliance directives at the time of the inspection to require the owner to implement actions that will correct violations of this Chapter.

(Ord. No. 2269, § 2, 8-9-04)

(Ord. No. 2465, § 4(Exh. B), 8-26-19)