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O 690 ORDINANCE NO. 690 AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF ARROYO GRANDE AMENDING SECTION 16.08.010 OF TITLE 16 REGARDING DESIGN REQUIREMENTS FOR POST CONSTRUCTION REQUIREMENTS WHEREAS, the City is required to adopt regulations in order to comply with the requirements of the Federal Clean Water Act, the implementing regulations for the National Pollutant Discharge Elimination System, and the California Porter-Cologne Water Quality Control Act; and WHEREAS, the City implements these requirements through the Storm Water Management Program approved by City Council Resolution 3708; and WHEREAS, the City Council adopted Ordinance 660, which incorporated Design Requirements for Post Construction Stormwater Compliance into the Arroyo Grande Municipal Code, by reference; and WHEREAS, the Design Requirements for Post Construction Stormwater Compliance include project exemptions, which are not permitted by the California Regional Water Quality Control Board Central Coast Region Resolution No. R3-2013-0032; and WHEREAS, an amendment to the City's Design Requirements for Post Construction Stormwater Compliance is required to remove the allowance for exemptions; and WHEREAS, the Planning Commission of the City of Arroyo Grande has reviewed the proposed amendments to the Design Requirements for Post Construction Stormwater at a Public Hearing on January 16, 2018 and recommended adoption of the regulations; and WHEREAS, at its meeting of February 13, 2018, the City Council duly considered all evidence, including public testimony from interested parties and the evaluation and recommendations by the Planning Commission and has determined that the following Development Code Amendment findings can be made in an affirmative manner: A. The proposed revision to this title is consistent with the goals, objectives, policies and programs of the general plan, and is necessary and desirable to implement the provisions of the general plan. The City is required to adopt regulations in order to comply with the requirements of the Federal Clean Water Act, the implementing regulations for the National Pollutant Discharge Elimination System, and the California Porter-Cologne Water Quality Control Act and the proposed revisions to the Design Requirements for Post Construction Stormwater Compliance are consistent with the requirements of the California Regional Water Quality Control Board Central Coast Region ORDINANCE NO. 690 PAGE 2 Resolution No. R3-2013-0032 regarding post-construction controls for MS4 stormwater discharges, and are also consistent with the goals, objectives, policies and programs of the City's General Plan, and are necessary and desirable to implement the provisions of the General Plan. B. The proposed revision to this title will not adversely affect the public health, safety, and welfare or result in an illogical land use pattern. The proposed revisions to the Design Requirements for Post Construction Stormwater Compliance are consistent with the requirements of the California Regional Water Quality Control Board Central Coast Region Resolution No. R3-2013-0032 regarding post- construction controls for MS4 stormwater discharges, and will not adversely affect the public health, safety and welfare, or result in an illogical land use pattern. C. The proposed revision to this title is consistent with the purpose and intent of the title. The proposed revisions to Design Requirements for Post Construction Stormwater Compliance remove the identification of exemptions from post construction requirements, are consistent with the requirements of the California Regional Water Quality Control Board Central Coast Region Resolution No. R3-2013-0032 regarding post-construction controls for MS4 stormwater discharges, and is considered consistent with the purpose and intent of Title 16. D. The potential environmental impacts of the proposed revision to this title are insignificant, or there are overriding considerations that outweigh the potential impacts. The proposed revisions to this title that require projects to comply with the Design Requirements for Post Construction Stormwater Compliance, are Categorically Exempt from CEQA review per Section 15308 of the CEQA Guidelines applicable to actions taken to protect the environment, and therefore the potential environmental impacts of the proposed revisions to Title 16 are insignificant. THE CITY COUNCIL OF THE CITY OF ARROYO GRANDE DOES ORDAIN AS FOLLOWS: SECTION 1: The above recitals are true and correct and incorporated herein by this reference. SECTION 2: Section 16.08.010.T. (Design Requirements for Post Construction Stormwater Compliance) of the City of Arroyo Grande Municipal Code is amended to reference a new document, a copy of which is attached to the Ordinance and incorporated herein by this reference as Exhibit A. ORDINANCE NO. 690 PAGE 3 SECTION 3: If any section, subsection, subdivision, paragraph, sentence, or clause of this Ordinance or any part thereof is for any reason held to be unlawful, such decision shall not affect the validity of the remaining portion of this Ordinance or any part thereof. The City Council hereby declares that it would have passed each section, subsection, subdivision, paragraph, sentence, or clause thereof, irrespective of the fact that any one or more section, subsection, subdivision, paragraph, sentence, or clause be declared unconstitutional. SECTION 4: Within fifteen (15) days after passage of this Ordinance, it shall be published once, together with the names of the Council Members voting thereon, in a newspaper of general circulation within the City. SECTION 5: This Ordinance shall take effect and be in full force and effect thirty (30) days after its passage. On motion of Council Member Barneich, seconded by Council Member Brown, and on the following roll call vote to wit: AYES: Council Members Barneich, Brown, Ray, and Mayor Hill NOES: Council Member Harmon ABSENT: None the foregoing Ordinance was adopted this 27th day of February, 2018. ORDINANCE NO. GAO PAGE 4 JIM ILL, MAYOR ATTEST; dp- / (ple(kAte-z. KELLY T �,RE, CITY CLERK APPROVED AS TO CONTENT: 1114k WalawJAMES -- AN CITY MANAGER APPROVED AS TO FORM: HEATHER K. WHITHAM, CITY ATTORNEY Exhibit “A” City of Arroyo Grande Design Requirements for Post Construction Stormwater Compliance Purpose The purpose of this document is to provide guidance and direction on how to comply with Post- Construction Stormwater Requirements (PCR's) within the City of Arroyo Grande. This document is intended to be used by developers, contractors, builders, designers, engineers, architects, planners, homeowners, and all others interested in learning how to address stormwater quality during the planning, design, construction and maintenance phases of a project. It is meant to be used as an aid for both onsite and public improvement projects. Project applicants should use this document to: • Determine which performance requirement apply • Understand how each performance requirement will be applied within the City • Obtain direction regarding means of demonstrating compliance Impact of Development on Water Resources Undeveloped natural landscape areas such as forests and grasslands act like sponges for rainfall. When natural landscape areas are covered with impervious (nonporous) surfaces like roads, parking lots, and roofs, this “sponge-like” function is lost and the amount of rainfall that can be absorbed is considerably reduced. The percentage of impervious surface area of a site influences how much stormwater is infiltrated into the ground, evapotranspirated back into the atmosphere, or leaves the site as stormwater runoff. See figure 1. When the amount of impervious surface area of a site is altered the normal watershed processes is also altered. This can lead to a significant host of problems including:  Increased loads of chemical pollutants;  Increased toxicity;  Changes to flow magnitude, frequency, and seasonality of various discharges;  Physical changes to stream, lake, or wetland habitats;  Changes in the energy dynamics of food webs, sunlight, and temperature;  Changes in biotic interactions between native and exotic species. Changes in impervious surface area can also alter the amount and quality of stormwater that infiltrates and recharges our groundwater aquifers. Figure 1. The relationship between impervious surface area, runoff, infiltration and evapotranspiration. (Stream Corridor Restoration: Principles, Processes, & Practices, FISWG 1998) The loss of infiltration from urbanization has also resulted in significant groundwater changes. As more surface area becomes covered with impervious surfaces, less water is able to seep back into the ground. Reduced groundwater recharge rates may result in lower base flows during dry weather as less groundwater is available to move through the soil and into stream channels and aquifers. See Chapter 13.05 of the City's Municipal Code for more on City's regulations regarding Water Conservation. To protect surface water quality and groundwater resources, new development and significant redevelopment projects should be designed, constructed, and maintained to minimize the interruption of natural watershed processes and to treat storm water as a resource and an asset, instead of a waste product. Post Construction Requirements The Central Coast Regional Water Quality Control Board recognizes that it is necessary to protect watershed processes so that beneficial uses of receiving waters are maintained and, were applicable, restored. The primary objective of these Post-Construction Stormwater Management Requirements is to ensure reduction of pollutant discharges to the Maximum Extent Practicable and preventing stormwater discharges from causing or contribution to a violation of receiving water quality standards in all applicable development projects that require approvals and/or permit is issued under the planning, building or other comparable authority. To address the impacts of development on water quality, the National Pollutant Discharge Elimination System (NPDES) Small Municipal Separate Storm Sewer System (MS4) General Permit requires the City of Arroyo Grande to develop and implement a Guidance Document that includes specific Best Management Practices (BMPs). Regulated projects include all new development or redevelopment projects that create and/or replace greater than or equal to 2,500 square feet of impervious surface (collectively over the entire project site). A list of projects impacted by the post construction storm water requirements can be found Resolution No. R3-2013-0032 Section B Post Construction Requirements 1. A list of projects not included as Regulated Projects can be found in Resolution No. R3-2013-0032 Section B Post Construction Requirements 1b. Examples of non-regulated projects include routine overlays and slurry seals, the installation of an ADA ramps, or solar panels on rooftops, or repair of roads or aerial utilities. Non-Regulated Projects are still encouraged to implement practices that will reduce stormwater impacts associated with their proposed development. Performance Requirements If the project is considered to be a Regulated project, the regulated project will be required to meet Performance Requirement 1 (PR 1). Many regulated projects are required to meet additional performance requirements. To determine if the project must meet additional requirements, you must determine the Net Impervious Area. The Net Impervious Area is the total (including new and replaced) post-construction impervious areas, minus any reduction in total imperviousness from the pre-project to post-project conditions. Permeable pavements may only be excluded from the impervious surface area calculation if they are designed to infiltrate. Net impervious area = New and replaced impervious area - Pre-project to post-project reduction in impervious area, if any Pre-project impervious areas consists of all hard, non-vegetated surface area that prevents or significantly limits the entry of water into the soil mantle, as would occur under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, surfaces which impede the natural infiltration of stormwater. Open, uncovered retention/detention facilities shall not be considered as impervious surfaces for purposes of determining whether the thresholds for application of Performance Requirements are exceeded. However, for modeling purposes, open, uncovered facilities that retain/detain water (e.g., retention ponds, pools) shall be considered impervious surfaces. Total Project Site Area is the area defined by the legal boundaries of a parcel or parcel s of land which the new development or redevelopment takes place. Post-project Impervious surface areas is the total (including new and replaced) impervious areas on the development site once the project is completely constructed. They include, but are not limited to: roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, surfaces which impede the natural infiltration of stormwater. It does not include open, uncovered retention/detention facilities. New (%) is the portion of the post-project impervious area that did replace an existing pervious surface area. Replaced (%) is the portion of the post-project impervious area that replaced an existing impervious surface area. Total Disturbed Area is the portion of the total project site area that will be subject to construction, used as a staging or storage area, or whose vegetation and soils are otherwise directly impacted by the project. An applicant will be required to provide supporting documentation regarding permeable paver (or alternate surface) areas excluded from impervious area calculations. The five Post-Construction Requirements (PCRs) developed by the State Regional Water Quality Control Board are summarized below: Performance Requirement 1: Site Design and Runoff Reduction All regulated projects, projects creating and/or replace ≥ 2,500 square feet of impervious surface (collectively over the entire project site), including detached single-family home projects, are subject to PR 1 and must minimally incorporate the following Low Impact Development (LID) design strategies into the project. 1. Limit disturbance of creeks and natural drainage features 2. Minimize compaction of highly permeable soils 3. Limit clearing and grading of native vegetation at the site to the minimum area needed to build the project, allow access, and provide fire protection 4. Minimize impervious surfaces by concentrating improvements on the least sensitive portions of the site, while leaving the remaining land in a natural undisturbed state 5. Minimize stormwater runoff by implementing one or more of the following site design measures: i. Direct roof runoff into cisterns or rain barrels for reuse ii. Direct roof runoff onto vegetated areas safely away from building foundations and footings, consistent with California building code iii. Direct runoff from sidewalks, walkways, and/or patios onto vegetated areas safely away from building foundations and footings, consistent with California building code iv. Direct runoff from driveways and/or uncovered parking lots onto vegetated areas safely away from building foundations and footings, consistent with California building code v. Construct bike lanes, driveways, uncovered parking lots, sidewalks, walkways, and patios with permeable surfaces The developer shall provide appropriate documentation certifying that project complies with Site Design and Runoff Reduction Performance Requirements. Certification Statement shall clearly identify the level of compliance with each of the applicable performance requirements the project is subject to. All certification shall be signed and stamped by the engineer of Record and shall include qualify and quantify identified deficiencies, per performance requirements. Performance Requirement 2: Water Quality Treatment Projects subject to PR2 are projects with a Net Impervious Area ≥ 5,000 square feet that are not single family homes, and detached single family homes ≥15,000 square feet of Net Impervious Area. These projects shall treat stormwater runoff to reduce pollutant loads and concentrations using physical, biological and chemical removal. Developer shall provide and include net impervious area calculations. Regulated projects subject to PR2 must treat a defined minimum volume or maximum surface loading rate of runoff using onsite measures. Allowable onsite measures are listed in the order of preference (highest to lowest):  Low Impact Development - implement harvesting and use infiltration, and evapotranspiration measures that collectively retain stormwater runoff equal to the volume of runoff generated by the 85th percentile 24-hour storm event, based on local rainfall data.  Biofiltration Treatment Systems - implement biofiltration systems using facilities that must be demonstrated to be at least as effective as a biofiltration treatment system that meets the following parameters: i. a max surface loading rate of 5" per hour based on a rain intensity of 0.2 inches or two times the 85th percentile hourly rainfall intensity for the applicable area, ii. Surface minimum reservoir volume of equal to the biofiltration area times a depth of 6 inches, iii. Proper plan selection with a minimum depth of 24 inches and an infiltration rate of 5 in/hr, iv. Subsurface drain/storage layer with an area equal to the biofiltration surface area and having a minimum depth of 12 inches.  Non-Retention Based Treatment Systems - implement stormwater control measure that achieve at least one of the following: i. a volume capacity designed to treat stormwater runoff equal to the runoff generated by the 85th percentile 24-hour storm event ii. a flow capacity sized equal to at least two times the 85th percentile hourly rainfall intensity for the applicable area and equal to at least 0.2 in/hr intensity. Design alternatives will only be considered if the applicant can demonstrate that ALL of the following measures of equivalent effectiveness are demonstrated: 1. Equal or greater amount of runoff infiltrated or evapotranspired; 2. Equal or lower pollutant concentrations in runoff that is discharged after bio-filtration; 3. Equal or greater protection against shock loadings and spills; and 4. Equal or greater accessibility and ease of inspection and maintenance. Technical guidance for designing bio-retention facilities is available from the Central Coast LID Initiative web site: http://www.centralcoastlidi.org/Central_Coast_LIDI/LID_Structural_BMPs.html The guidance includes design specifications and standard plans. It also includes plant lists appropriate for installation of LID and Bio-filtration Systems on the Central Coast. Project subject to PR2 shall include a Stormwater Control Plan (SWCP) containing the following: 1. Project type and address and name of applicant 2. Calculations for total new, replaced and net impervious area pre/post development 3. Applicable requirement for both PR 1 and PR 2 4. Description of all post construction structural stormwater control measures including calculations 5. Documentation certifying that the selection, sizing and design of measures meet requirements Performance Requirement 3: Runoff Retention Performance Requirement 3 shall apply to projects, except detached single family homes, that create and/or replace ≥ 15,000 square feet of impervious surface (collectively over the entire project site), and detached single family homes ≥ 15,000 square feet of net impervious area, WMZs 1, 2. Regulated projects subject to PR3 must retain a designated design storm volume. Applicants of regulated projects subject to this requirement must: 1. Watershed Management Zone 1: a) Retain 95th Percentile Rainfall Event – Prevent offsite discharge from events up to the 95th percentile 24-hour rainfall event as determined from local rainfall data.4 b) Compliance must be achieved via infiltration 2. Watershed Management Zone 2: a) Retain 95th Percentile Rainfall Event – Prevent offsite discharge from events up to the 95th percentile 24-hour rainfall event as determined from local rainfall data. b) Compliance must be achieved via storage, rainwater harvesting, infiltration, and/or evapotranspiration. PR3 regulated projects shall use the following LID development standards: 1. Site Assessment Measures – each Regulated Project shall identify opportunities and constraints to implement LID Stormwater Control Measures. Provide documentation of the following, as appropriate to the development site: a) Site topography including hydrologic features b) Seasonal high groundwater c) Geological analysis including geotechnical hazards d) Soil type and hydrologic soil groups e) Run-on characteristics and existing drainage infrastructure 2. Site Design Measures – Regulated Project shall optimize the use of LID site design measures, as feasible and appropriate at the project site. Regulated Projects subject to Performance Requirement No. 3 must augment design strategies required by Performance Requirement No. 1 with the following: a) Define the development envelope and protected areas, identifying areas that are most suitable for development and areas to be left undisturbed b) Conserve natural areas, including existing trees, other vegetation, and soils c) Limit the overall impervious footprint of the project d) Construct streets, sidewalks, or parking lot aisles to the minimum widths necessary, provided that public safety or mobility uses are not compromised e) Set back development from creeks, wetlands, and riparian habitats f) Conform the site layout along natural landforms g) Avoid excessive grading and disturbance of vegetation and soils 3. Delineation of discrete Drainage Management Areas (DMAs) – Regulated Project shall delineate DMAs to support a decentralized approach to stormwater management. A map or diagram dividing the entire project site into discrete DMAs shall be provided. Each Regulated Project shall account for the drainage from each DMA using measures identified as follows: a) Undisturbed and Natural Landscape Areas –each Regulated Project shall implement appropriate Site Design and Runoff Reduction Measures in Performance Requirement No. 1, to reduce the amount of runoff for which retention and treatment is required. Runoff reduction measures that can be used to account for this reduction also include as follows: i. Undisturbed or areas planted with native, drought-tolerant, or LID appropriate vegetation that do not receive runoff from other areas may be considered self-treating and no additional stormwater management is required. ii. Runoff from impervious surfaces, generated by the rainfall events identified in Section B.4.c, may be directed to undisturbed or natural landscaped areas. When the applicant can demonstrate that this runoff will be infiltrated and will not produce runoff to the storm drain system, or a surface receiving waterbody, or create nuisance ponding that may affect vegetation health or contribute to vector problems, then no additional stormwater management is required for these impervious surfaces. b) Structural Stormwater Control Measures – Where it has been demonstrated in the Stormwater Control Plans, that the use of Site Design measures listed above, Runoff Reduction measures listed in Performance Requirement No.1, and undisturbed and natural landscape has been maximized to the extent feasible, Structural Stormwater Control Measures designed for water quality treatment and/or flow control shall be used to comply with Performance Requirement No. 3. 4. Ten Percent Adjustment for Sites with Technical Infeasibility – Where technical infeasibility, as described in Section C.1.c., prevents full on-site compliance with the Runoff Retention Performance Requirement, on-site retention of the full Retention Volume per Section B.4.d.vi. is not required and the Regulated Project is required to dedicate no less than ten percent of the Regulated Project’s Equivalent Impervious Surface Area5 to retention-based Stormwater Control Measures. 5. Off-Site Mitigation – Off-site mitigation is required when Regulated Projects do not retain the full Retention Volume, and 1) fail to demonstrate technical infeasibility of full retention; or 2) demonstrate technical infeasibility of full retention AND fail to dedicate at least ten percent of the Regulated Project’s Equivalent Impervious Surface Area to retention-based Stormwater Control Measures. 6. Reporting Requirements – For each Regulated Project subject to the Runoff Retention Performance Requirement, provide the following information in a Stormwater Control Plan. Final project approval shall not be granted until the Stormwater Control Plan for the Regulated Project sufficiently demonstrates the Regulated Project design meets the Water Quality Treatment and Runoff Retention Performance Requirements. Performance Requirement 4: Peak Management All Regulated Projects that create and/or replace >22,500 square feet of impervious surface (collectively over the entire project site) in Watershed Management Zones 1 and 2 shall manage peak stormwater runoff to ensure that post-development peak flows, discharged from the site, do not exceed pre-project peak flows for the 2- through 10- year storm events and shall meet Water Quality Treatment and Runoff Retention Performance Requirements. Reporting Requirements – For each Regulated Project subject to the Peak Management Performance Requirement a Stormwater Control Plan shall be required. Final project approval shall not be granted until the Stormwater Control Plan for the Regulated Project sufficiently demonstrates the Regulated Project design meets the Water Quality Treatment, Runoff Retention, and Peak Management Requirements. Performance Requirement 5: Special Circumstances There are no Special Circumstance designations in the City of Arroyo Grande. Alternative Compliance The City will only consider alternative compliance for projects able to demonstration technical infeasibility and who cannot satisfy the 10% adjustment criteria on site. Alternative Compliance may be allowed under the following circumstances: 1. Technical Infeasibility - applicant must submit a site-specific hydrologic and/or design analysis conducted and endorsed by a registered professional engineer, geologist, architect, and/or landscape architect, demonstrating that compliance with the applicable numeric Post- Construction Stormwater Management Requirements is technically infeasible. 2. The Regulated Project applicant must submit a description of the project(s) that will provide off - site mitigation. The proposed off-site projects may be existing facilities and/or prospective projects that are as effective in maintaining watershed processes as implementation of the applicable Post-Construction Stormwater Requirements on-site. The description shall include: c) The location of the proposed off-site project(s) must be within the same watershed as the Regulated Project. Alternative Compliance project sites located outside the watershed may be approved by the Central Coast Water Board Executive Officer d) A schedule for completion of offsite mitigation project(s), where the off-site mitigation project(s) has not been constructed. Technical infeasibility may be caused by site conditions, including: a) Depth to seasonal high groundwater limits infiltration and/or prevents construction of sub- grade stormwater control measures b) Depth to an impervious layer such as bedrock limits infiltration c) Sites where soil types significantly limit infiltration d) Sites where pollutant mobilization in the soil or groundwater is a documented concern e) Space constraints (e.g., infill projects, some redevelopment projects, high density development) f) Geotechnical hazards g) Stormwater Control Measures located within 100 feet of a groundwater well used for drinking water h) Incompatibility with surrounding drainage system (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning treatment or flow control facility). Operational and Maintenance Plans The developer shall submit an Operation and Maintenance Plan and Maintenance Agreements (O&M Plan) that clearly establish responsibility for all structural Water Quality Treatment, Runoff Retention, and/or Peak Management controls for all Regulated Projects. The Regulated Project applicant shall develop and implement a written O&M Plan. The O&M Plan shall be submitted for approval prior to final approval/occupancy. The O&M Plan must include: a. A site map identifying all structural Stormwater Control Measures (SCM's) requiring O&M practices to function as designed b. O&M procedures for each structural stormwater control measure including, but not limited to, LID facilities, retention/detention basins, and proprietorship devices. c. The O&M Plan will include short-and long-term maintenance requirements, recommended frequency of maintenance, and estimated cost for maintenance. Maintenance Agreement and Transfer of Responsibility for SCMs: Prior to issuing approval for final occupancy the owner of the Regulated Project subject to these Post-Construction Requirements shall provide verification of ongoing maintenance provisions for Structural Stormwater Control Measures, including but not limited to legal agreements, covenants, CEQA mitigation requirements, and or conditional use permits. Verification shall include, at a minimum: a. The project owner’s signed statement accepting responsibility for the O&M of the installed onsite and/or offsite structural treatment and flow control SCMs until such responsibility is legally transferred to another entity; and either i. A signed statement from the public entity assuming responsibility for structural treatment and flow control SCM maintenance and stating that the SCM meets all local agency design standards; or ii. Written conditions in the sales or lease agreements or deed for the project that require the buyer or lessee to assume responsibility for the O&M of the onsite and/or offsite structural treatment and flow control SCM until such responsibility is legally transferred to another entity; or iii. Written text in project deeds, or conditions, covenants and restrictions for multi-unit residential projects that require the homeowners association or, if there is no association, each individual owner to assume responsibility for the O&M of the onsite and/or offsite structural treatment and flow control SCM until such responsibility is legally transferred to another entity; or iv. Any other legally enforceable agreement or mechanism, such as recordation in the property deed, that assigns responsibility for the O&M of the onsite and/or offsite structural treatment and flow control SCM to the project owner(s). Reporting The Central Coast Regional Board requires two types of reporting.  Project applicant reporting to the City Applicants of regulated projects subject to Runoff Retention Requirement (PR 3) are required to demonstrate compliance with a decentralized approach to stormwater management through a Stormwater Control Plan. Additional supporting information is required if the project is subject to additional Performance Requirements. Determine Watershed Management Zones Projects creating or replacing 15,000 square feet or more of impervious surfaces, that are not a detached single family residence, and do not qualify for a special circumstance designation, will need to know their Watershed Management Zone (WMZ). Watershed management zones (WMZs) are based on common key watershed processes and receiving water type. They are the basis for determining if the project is subject to Runoff Retention Performance Standards, or Runoff Retention and Peak management Requirements Performance Standards. There are two Watershed Management Zones located within the City of Arroyo Grande. For a copy of the Watershed Management Zone map please visit the Engineer's office at City Hall. If the project is located on part of the two WMZs, the applicant shall satisfy the requirements of each zone proportionately. The City’s Engineering Division can assist if the maps do not clearly identify the watershed management zone the project is located in. Determine Applicable Rainfall Event The performance criteria for post-construction retention standards is the percentile storm that best represents the volume that is fully infiltrated in a natural condition, and thus should be managed onsite to maintain the pre-development hydrology for duration, rate and volume of stormwater flows. The percentile rain event is the 95th percentile rain event and shall be achieved by infiltration, rainwater harvesting and/or evaporation for Watershed Management Zones 1 and 2. To obtain exhibits for the 85th and 95th percentile, 24-hour storm exhibits go to http://www.swrcb.ca.gov/rwqcb3/water_issues/programs/stormwater/docs/lid/lid_hydromod_c harette_index.shtml OFFICIAL CERTIFICATION I, KELLY WETMORE, City Clerk of the City of Arroyo Grande, County of San Luis Obispo, State of California, do hereby certify under penalty of perjury, that the attached Ordinance.No. 690 which was introduced at a regular meeting of the City Council on February 13, 2018; was passed and adopted at a regular meeting of the City Council on the 27th day of February 2018; and was duly published in accordance with State law (G.C. 40806). WITNESS ray hand and the Seal of the City of Arroyo Grande affixed this 1st day of March 2018.. KELLY W TM RE, CITY CLERK