CC 2018-02-27_09f Adopt Ord_DCA Post Construction Stormwater Requirements
MEMORANDUM
TO: CITY COUNCIL
FROM: TERESA MCCLISH, COMMUNITY DEVELOPMENT DIRECTOR
BY: ROBIN DICKERSON, CITY ENGINEER
SUBJECT: CONSIDERATION OF ADOPTION OF ORDINANCE FOR
DEVELOPMENT CODE AMENDMENT CASE NO. 18-001;
AMENDMENTS TO TITLE 16 OF THE ARROYO GRANDE MUNICIPAL
CODE REGARDING DESIGN REQUIREMENTS FOR POST
CONSTRUCTION STORMWATER COMPLIANCE; LOCATION-
CITYWIDE; APPLICANT – CITY OF ARROYO GRANDE
DATE: FEBRUARY 27, 2018
SUMMARY OF ACTION:
Adoption of the Ordinance would modify the Design Requirements for Post Construction
Stormwater Compliance to eliminate project exemptions consistent with State
requirements implemented by the Regional Water Quality Control Board (RWQCB).
IMPACT ON FINANCIAL AND PERSONNEL RESOURCES:
No financial impacts have been identified.
RECOMMENDATION:
It is recommended that the City Council adopt an Ordinance amending Title 16 of the
Arroyo Grande Municipal Code (AGMC) regarding Design Requirements for Post
Construction Stormwater Compliance.
BACKGROUND:
The Storm Water Guidance Document (SWGD) is a requirement of the California
Environmental Protection Agency State Water Resources Control Board Phase II Small
Municipal Separate Storm Sewer System (MS4) Permit. On February 25, 2014, City
Council approved the Design Requirements for Post Construction Storm Water
Compliance and passed Ord. No. 660, which incorporated the design requirements into
the AGMC by reference. On January 16, 2018, the Planning Commission unanimously
approved Resolution No 18-2293 recommending the City Council approve modifications
to the Design Requirements for Post-Construction Stormwater compliance to eliminate
project exemptions consistent with State requirements implemented by the Regional
Water Quality Control Board (RWQCB). On February 13, 2018, the City Council
unanimously introduced the Ordinance, without modification.
Item 9.f. - Page 1Item 9.f. - Page 1
CITY COUNCIL
CONSIDERATION OF ADOPTION OF ORDINANCE FOR DEVELOPMENT CODE
AMENDMENT CASE NO. 18-001
FEBRUARY 27, 2018
PAGE 2
ANALYSIS OF ISSUES:
The ordinance is now ready for adoption. The ordinance will become effective thirty
days after final page of the ordinance.
ALTERNATIVES:
1. Adopt the Ordinance;
2. Modify and re-introduce the Ordinance; or
3. Provide other direction to staff.
ENVIRONMENTAL REVIEW:
In accordance with the California Environmental Quality Act (CEQA) Guidelines, it has
been determined that the project is Categorically Exempt per Section 15308 of the
CEQA Guidelines, which governs actions by regulatory agencies for the protection of
the environment.
PUBLIC NOTIFICATION AND COMMENTS:
The Agenda was posted at City Hall and on the City’s website in accordance with
Government Code Section 54954.2. At the time of report publication, no comments
have been received.
Item 9.f. - Page 2Item 9.f. - Page 2
ORDINANCE NO.
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
Item 9.f. - Page 3
ORDINANCE NO.
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.
Item 9.f. - Page 4
ORDINANCE NO.
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: A summary of this Ordinance shall be published in a newspaper
published and circulated in the City of Arroyo Grande at least five (5) days prior to the
City Council meeting at which the proposed Ordinance is to be adopted. A certified
copy of the full text of the proposed Ordinance shall be posted in the office of the City
Clerk. Within fifteen (15) days after adoption of the Ordinance, the summary with the
names of those City Council members voting for and against the Ordinance shall be
published again, and the City Clerk shall post a certified copy of the full text of such
adopted Ordinance.
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 , seconded by Council Member , and
on the following roll call vote to wit:
AYES:
NOES:
ABSENT:
the foregoing Ordinance was adopted this day of , 2018.
Item 9.f. - Page 5
ORDINANCE NO.
PAGE 4
JIM HILL, MAYOR
ATTEST:
KELLY WETMORE, CITY CLERK
APPROVED AS TO CONTENT:
JAMES A. BERGMAN, CITY MANAGER
APPROVED AS TO FORM:
HEATHER K. WHITHAM, CITY ATTORNEY
Item 9.f. - Page 6
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.
Item 9.f. - Page 7
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.
Item 9.f. - Page 8
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
Item 9.f. - Page 9
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
Item 9.f. - Page 10
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.
Item 9.f. - Page 11
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:
Item 9.f. - Page 12
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
Item 9.f. - Page 13
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.
Item 9.f. - Page 14
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
Item 9.f. - Page 15
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
Item 9.f. - Page 16
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
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