HomeMy WebLinkAbout47-19RESOLUTION 47-19
RESOLUTION OF THE CITY COUNCIL
OF THE TOWN OF LOS ALTOS HILLS
APPROVING A GREEN STORMWATER INFRASTRUCTURE PLAN
IN ACCORDANCE WITH PROVISION C.3.J
OF THE MUNICIPAL REGIONAL PERMIT
WHEREAS, the Town of Los Altos Hills is a permittee under the San Francisco Bay Regional
Water Quality Control Board's Municipal Regional Permit (MRP) that regulates stormwater
discharges from municipal storm drain systems throughout Santa Clara Valley; and
WHEREAS, the Town of Los Altos Hills is a member of the Santa Clara Valley Santa Clara
Valley Urban Runoff Pollution Prevention Program (SCVURPPP), and implements the MRP in
collaboration with other members of the SCVURPPP; and
WHEREAS, Provision C.3.j of the MRP requires each permittee to develop a Green Stormwater
Infrastructure Plan that demonstrates how permittees will gradually shift from traditional "gray"
storm drain infrastructure to a more resilient and sustainable storm drain system comprised of
"green" infrastructure, which captures, stores and treats stormwater using natural processes; and
WHEREAS, the MRP also requires that Green Stormwater Infrastructure Plans of Permittees
should achieve specific reductions in pollutants discharged by stormwater to local creeks and San
Francisco Bay within certain time horizons; and
WHEREAS, all permittees under the MRP are required to submit by September 30, 2019 a Green
Stormwater Infrastructure Plan to the Regional Water Quality Control Board; and
WHEREAS, the attached Green Stormwater Infrastructure Plan guides the identification,
prioritization, design, implementation, tracking, and reporting of green stormwater infrastructure
projects within the Town of Los Altos Hills; and
WHEREAS, the Town of Los Altos. Hills is committed to complying with requirements of the
MRP and implementing a more sustainable approach to stormwater management that provides
multiple benefits to the community and environment; and
WHEREAS, it is the intent of the Town of Los Altos Hills to evaluate and pursue funding sources
and allocate available resources to implement the Green Stormwater Infrastructure Plan;
NOW THEREFORE BE IT RESOLVED, the City Council of the Town of Los ,Altos Hills
approves, passed and adopted the attached Green Stormwater Infrastructure Plan at a special
meeting held on the 21 st day of August 2019 by the following vote:
AYES: Spreen, Wu, Corrigan, Tankha, Tyson
NOES: None
Resolution 47-19 Page 1
ABSENT: None
ABSTAIN: None
ATTEST:
Deborah Padovan, City Clerk
BY: �-
Roger Veen, yor
Resolution 47-19
Page 2
Attachment 2
Approved on: August 21, 2019
Approved by: Town of Los Altos Hills City Council
Prepared by:
Town of Los Altos Hills
26379 Fremont Road CALIFORNIA
Los Altos Hills, CA 94022
(650) 947-7222
In compliance with Provision C.3.j.1.(2) of Order No. R2-2015-0049, NPDES Permit No. CAS612008
Resolution 47-19 Page 3
Cover: View of Los Altos Hills from local walking trail (Source: Town of Los Altos Hills)
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ACKNOWLEDGEMENTS
The Town of Los Altos Hills gratefully acknowledges the following individuals and organizations that
contributed to this Green Stormwater Infrastructure Plan:
Town of Los Altos Hills
• Nichol Bowersox
• Kaho Kong
EOA, Inc.
• Jill Bicknell, P.E.
• Vishakha Atre
• Liesbeth Magna
The Town would also like to thank and acknowledge the City of Palo Alto and the City of San Jose for
sharing text from their Green Stormwater Infrastructure Plans.
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Table of Contents
EXECUTIVE SUMMARY.............................................................................................................................:....1
1. INTRODUCTION.....................................................................................................................................2
1.1 Purpose and Goals of the GSI Plan................................................................................................2
1.2 Town Description..........................................................................................................................
2
1.3 Regulatory Context.......................................................................................................................
5
1.3.1 Federal and State Regulations and Initiatives.......................................................................5
1.3.2 Municipal Regional Stormwater Permit................................................................................5
1.4 GSI Plan Development Process.....................................................................................................6
1.4.1 GSI Plan Development and Adoption....................................................................................6
1.4.2 Regional Collaboration..........................................................................................................7
1.4.3 Education and Outreach.......................................................................................................7
1,5 GSI Plan Structure and Required Elements...................................................................................8
2. WHAT IS GREEN STORMWATER INFRASTRUCTURE?............................................................................9
2.1 Green Stormwater Infrastructure.................................................................................................9
2.2 Benefits of Green Stormwater Infrastructure...............................................................................9
2.3 Types of Green Stormwater Infrastructure Facilities..................................................................10
2.3.1 Biotreatment/Bioretention.................................................................................................10
2.3.2 Stormwater Tree Well Filters and Suspended Pavement Systems.....................................10
2.3.3 Pervious Pavement.............................................................................................................11
2.3.4 Infiltration Facilities............................................................................................................12
2.3.5 Green Roofs.........................................................................................................................12
2.3.6 Rainwater Harvesting and Use............................................................................................13
2.4 Existing GSI Facilities...................................................................................................................13
3. INTEGRATION WITH OTHER PLANNING DOCUMENTS.......................................................................14
3.1 Town Planning Document Review..............................................................................................14
3.1.1 General Plan (2007-2015)...................................................................................................14
3.1.2 Pavement Management Plan Report (2018)......................................................................15
3.1.3 Storm Drainage Master Plan (2004)...................................................................................15
3.1.4 Workplan for Integration of GSI Language into Existing and Future Town Planning
Documents..........................................................................................................................................15
3.2 Regional Plans.............................................................................................................................16
3.2.1 Santa Clara Basin Stormwater Resource Plan.....................................................................16
In
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3.2.2 Santa Clara Valley Water District's One Water Plan...........................................................16
3.2.3 Bay Area Integrated Regional Water Management Plan....................................................17
4. GSI DESIGN GUIDELINES, DETAILS, AND SPECIFICATIONS..................................................................18
4.1 Design Guidelines........................................................................................................................18
4.2 Details and Specifications...........................................................................................................18
4.3 Incorporation of SCVURPPP Details and Specifications into Town Standards ............................19
5. GSI PROJECT PRIORITIZATION AND IMPERVIOUS TARGETS...............................................................20
5.1 Project Types............................................................................................................................... 20
5.1.1 Early Implementation Projects............................................................................................20
5.1.2 Regulated Projects..............................................................................................................20
5.1.3 LID Projects.........................................................................................................................20
5.1.4 Regional Projects.................................................................................................................20
5.1.5 Green Street Projects..........................................................................................................21
5.2 Identification and Prioritization Process.....................................................................................21
5.2.1 Step 1: Stormwater Resource Plan Prioritization...............................................................21
5.2.2 Step 2: Town -Specific Prioritization....................................................................................23
5.2.3 Prioritization Results...........................................................................................................24
6. GSI IMPLEMENTATION PLAN..............................................................................................................26
6.1 Town GSI Strategy.......................................................................................................................26
6.2 Process for Identifying and Evaluating GSI Project Opportunities..............................................27
6.3 Workplan for Early Implementation Projects.............................................................................27
6.4 Legal Mechanisms for GSI Implementation................................................................................27
6.5 Evaluation of Funding Options....................................................................................................28
6.5.1 Current Funding Sources for GSI Program Elements..........................................................28
6.5.2 Potential Future Funding Options....................................................................................... 28
6.6 Impervious Area Targets.............................................................................................................32
6.7 Project Tracking System........................................................:.....................................................35
6.7.1 Town Project Tracking System (Regulated and GSI)........................................................... 35
6.7.2 SCVURPPP Project Tracking System....................................................................................35
vi
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TABLES
Table 1-1 Summary of GSI Plan Elements required by Provision C.3.j.i of the MRP....................................8
Table 3-1 Workplan for Integration of GSI Language into Existing Town Planning Documents.................16
Table 5-1 Screening factors for parcel -based and right-of-way project opportunities..............................23
Table 6-1. Predicted extent of impervious area to be retrofit via GSI implementation on privately- and
publicly -owned parcels in the Town of Los Altos Hills by 2020, 2030, and 2040 .......................................34
FIGURES
Figure 1-1 Slope map of the Los Altos Hills Area..........................................................................................4
Figure 2-1 Stormwater curb extension, Rosita Park, Los Altos...................................................................10
Figure 2-2 Stormwater planter, Hacienda Avenue.....................................................................................10
Figure 2-3 Stormwater tree well filter conceptual examples.....................................................................11
Figure 2-4 Permeable Pavers, Mayfield Playing Fields, Palo Alto...............................................................11
Figure 2-5 Infiltration trench, San Jose.......................................................................................................12
Figure 2-6 Subsurface infiltration system...................................................................................................12
Figure 2-7 Green Roof at Fourth Street Apartments, San Jose...................................................................12
Figure 2-8 Rainwater Harvesting cistern, Environmental Innovation Center, San Jose .............................13
Figure 2-9 Subsurface vault under construction.........................................................................................13
Figure 5-1 Town of Los Altos Hill Public Parcels and Street Segments with GSI Opportunities .................25
Figure 6-1. Parcels within the Town of Los Altos Hill's jurisdiction that are planned for development or
redevelopmentwith GSI.............................................................................................................................33
APPENDICES
Appendix A — Prioritization Metrics for Scoring GSI Project Opportunities
Appendix B — Potential Parcel -based and Green Street Project Opportunities
Appendix C — Guidance for Identifying Green Infrastructure Potential in Municipal Capital Improvement
Program Projects
vii
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LIST OF ACRONYMS
BASMAA
Bay Area Stormwater Management Agencies Association
Caltrans
California Department of Transportation
CIP
Capital Improvement Program
DOF
Department of Finance
EPA
United States Environmental Protection Agency
FY
Fiscal Year
GI
Green Infrastructure
GIS
Geographic Information System
GSI
Green Stormwater Infrastructure
IRWMP
Integrated Regional Water Management Plan
LID
Low Impact Development
MRP
Municipal Regional Stormwater NPDES Permit
MS4
Municipal Separate Storm Sewer System
NPDES
National Pollutant Discharge Elimination System
0&M
Operation and Maintenance
PDA
Priority Development Area
PICP
Permeable Interlocking Concrete Pavers
PP
Permeable Pavers
SCVURPPP
Santa Clara Valley Urban Runoff Pollution Prevention Program
State Water Board
State Water Resource Control Board
STORMS
Strategy to Optimize Resource Management of Stormwater
SWRP
Storm Water Resource Plan
Valley Water
Santa Clara Valley Water District
Regional Water Board
San Francisco Bay Regional Water Quality Control Board
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EXECUTIVE SUMMARY
J u to e 1C1, 2 i j .l
Urban development has traditionally involved replacing natural landscapes with solid pavements and
buildings, and using storm drain systems to carry increased amounts of stormwater runoff and
pollutants directly into local streams. To reduce the impact of urban development on waterways, Bay
Area municipalities are augmenting traditional stormwater conveyance systems with Green Stormwater
Infrastructure (GSI) features. GSI features mimic nature, and use plants, soils, and/or pervious surfaces
to collect stormwater, allowing it soak into the ground, and be filtered by soil. This reduces the quantity
of water and pollutants flowing into local creeks.
The Town of Los Altos Hills has prepared this GSI Plan to guide the siting, implementation, tracking, and
reporting of GSI projects on Town -owned land over the next several decades. Development of the GSI
Plan is required by the Town's Municipal Regional Stormwater National Pollutant Discharge Elimination
System (NPDES) Permit.
The GSI Plan describes the Town's methodology to identify and prioritize areas for implementing GSI,
and estimates targets for the extent of the Town's area that will be addressed by GSI through 2040. The
Plan includes maps of the Town's prioritized areas for potential GSI projects, and lays out the Town's GSI
implementation strategy. Preservation of the Town's current semi -rural atmosphere is a key part of that
strategy, as is working within the constraints of the topography and geology associated with the Town's
location within the foothills of the Santa Cruz mountains. The Plan contains guidance and standards for
GSI project design and construction, and describes how the Town will track and map constructed GSI
projects and make the information available to the public. Lastly, it explains existing legal mechanisms to
implement the GSI Plan, and identifies potential sources of funding for the design, construction, and
maintenance of GSI projects.
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1. INTRODUCTION
Urban development has traditionally involved replacing natural landscapes with solid pavements and
buildings, and using storm drain systems to carry increased amounts of stormwater runoff and
pollutants directly into local streams. Green stormwater infrastructure (GSI), however, uses plants and
soils to mimic natural watershed processes, capture stormwater and create healthier environments. Bay
Area cities and counties are required by State and regional regulatory agencies to move from traditional
(gray) stormwater conveyance systems to GSI systems over time. This GSI Plan serves as an
implementation guide for the Town of Los Altos Hills (Town) to incorporate GSI into storm drain
infrastructure on public and private lands where feasible over the next several decades.
1.1 Purpose and Goals of the GSI Plan
The purpose of the Town's GSI Plan is to demonstrate the Town's commitment to incorporating GSI into
storm drain infrastructure on public and private lands where feasible over the next several decades. The
GSI Plan will guide the identification, implementation, tracking, and reporting of green stormwater
infrastructure projects within the Town. The GSI Plan will be coordinated with the General Plan and
other Town plans to achieve multiple potential benefits to the community, such as improved water and
air quality, reduced flooding, increased water supply, traffic calming, safer pedestrian and bicycle
facilities, climate resiliency, improved wildlife habitat, and a more pleasant urban environment.
Specific goals of the GSI Plan are to:
• Align the Town's goals, policies and implementation strategies for GSI with the General Plan and
other related planning documents;
• Identify and prioritize GSI opportunities throughout the Town;
• Establish targets for the extent of Town area to be addressed by GSI over certain timeframes;
• Provide a workplan and legal and funding mechanisms to implement prioritized projects; and
• Establish a process for tracking, mapping, and reporting completed projects
1.2 Town Description
Incorporated in 1956, the Town of Los Altos Hills is located in Santa Clara County, in the foothills of the
Santa Cruz Mountains. The Town has a jurisdictional area of approximately 5,760 acres (9 square miles),
making it one of the smallest incorporated towns in Santa Clara County, and is characterized by rolling
hills, rugged mountains, extensive open spaces, and semi -rural lifestyle. Up to the decade of the 1950's,
land ownership in the Los Altos Hills was in relatively large holdings, which had been held as ranches and
estates. As the Town has developed, residents have continued to support the preservation of low-
density residential development and the semi -rural character of the community through one -acre
zoning and the protection of open space, creek corridors, wildlife habitat and heritage oak trees.
According to the 2010 Census, the Town has a population of 7,922, with a population density of 900
people per square mile and average household size of 2.78. As of January 2019, according to the
California Department of Finance (DOF)1, the estimated population is 8,785.
1 Source: State of California, Department of Finance, E-1 Population Estimates for Cities, Counties and the State with Annual
Percent Change — January 1, 2017 and 2018. Sacramento, California, May 2018. Online at
http://www.dof.ca.gov/Forecasting/Demographics/Estimates/E-1/.
2
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The Town is unique for the region, in that it consists mainly of low-density single-family residential
development, with a minimum lot size of at least one acre. According to the Housing Element of the
General Plan (Town of Los Altos Hills, 2015), uses other than semi -rural residential, such as retail and
medical services and employment centers, are readily available in adjoining, suburban communities, and
their duplication in the Town, especially to serve a relatively small population, are unnecessary. Thus,
there are no commercial or industrial uses within the Town limits. The only non-residential uses within
the Town are open space, parks and recreation facilities, a unique pathways system including miles of
well-maintained roadside and off-road paths, and public and private institutions such as schools,
religious facilities and governmental buildings.
Three major faults traverse the Town of Los Altos Hills:
• Berrocal Fault, which runs from west to east.
• Altamont Fault, parallel to Berrocal Fault.
• Monte Vista Fault, running from northwest to southeast.
All of these fault lines are categorized by the state as potentially active.
The seismic faults and steep slopes (Figure 1-1), unstable soils, and other natural hazards place
significant constraints on development of the Town and surrounding area.
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iw USG U.S. Department of the Interior
"Q"""i i<z, 2019
San Francisca Bay Area, California
1:35,862
Figure 1-1 Slope map of the Los Altos Hills Area (Source: USGS. Online at https://pubs.usgs.gov/of/2001/of02-
351/of02-351_5b. pdf)
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The Town maintains approximately 500 trees, 80 linear miles of public pathways and 77 linear miles of
streets. The Town's recreational areas and facilities encompass approximately 151 acres and include the
Westwind Community Barn; Purissima and Edith Park; the Byrne, Juan Prado Mesa, O'Keefe, and
Murietta Open Space Preserves; and the Little League Fields and Riding Arena. In addition to the Town -
owned facilities, there are four educational facilities located in or near the Town — Gardner Bullis
School, Pinewood School, Saint Nicholas School, and Foothill Community College. Other large properties
with nonresidential uses include the Daughters of Charity and Congregation Beth Am.
The Town's drainage system consists of a combination of primarily roadside drainage ditches, cross
culverts, and a limited number of underground pipes. These drainage systems discharge to Matadero,
Deer, Barron, Adobe, Hale, and Permanente Creeks. The creeks and tributaries intersect open space and
residential areas in natural channels throughout the Town.
1.3 Regulatory Context
1.3.1 Federal and State Regulations and Initiatives
The U.S. Environmental Protection Agency (EPA) has authority under the Clean Water Act to promulgate
and enforce stormwater related regulations. For the State of California, EPA has delegated the
regulatory authority to the State Water Resources Control Board (State Water Board), which in turn, has
delegated authority to the San Francisco Bay Regional Water Quality Control Board (Regional Water
Board) to issue National Pollutant Discharge Elimination System (NPDES) permits in the San Francisco
Bay Region. Stormwater NPDES permits allow stormwater discharges from municipal separate storm
sewer systems (MS4s) to local creeks, San Francisco Bay, and other water bodies as long as they do not
adversely affect the beneficial uses of or exceed any applicable water quality standards for those waters.
Since the early 2000's, the EPA has recognized and promoted the benefits of using GSI in protecting
drinking water supplies and public health, mitigating overflows from combined and separate storm
sewers and reducing stormwater pollution, and it has encouraged the use of GSI by municipal agencies
as a prominent component of their MS4 programs.
The State and Regional Water Boards have followed suit in recognizing not only the water quality
benefits of GSI but the opportunity to augment local water supplies in response to the impacts of
drought and climate change as well. The 2014 California Water Action Plan called for multiple benefit
stormwater management solutions and more efficient permitting programs. This directive created the
State Water Board's "Strategy to Optimize Resource Management of Stormwater" (STORMS). STORMS'
stated mission is to "lead the evolution of storm water management in California by advancing the
perspective that storm water is a valuable resource, supporting policies for collaborative watershed -
level storm water management and pollution prevention, removing obstacles to funding, developing
resources, and integrating regulatory and non -regulatory interests."
These Federal and State initiatives have influenced approaches in Bay Area municipal stormwater NPDES
permits, as described in Section 1.3.2.
1.3.2 Municipal Regional Stormwater Permit
The Town is subject to the requirements of the Municipal Regional Stormwater NPDES Permit (MRP) for
Phase I municipalities and agencies in the San Francisco Bay area (Order R2-2015-0049), which became
effective on January 1, 2016. The MRP applies to 76 municipalities and flood control agencies that
discharge stormwater to San Francisco Bay, collectively referred to as permittees.
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Over the last 13 years, under Provision C.3 of the MRP and previous permits, new development and
redevelopment projects on private and public property that exceed certain size thresholds ("regulated
projects") have been required to mitigate impacts on water quality by incorporating "Low Impact
Development" (LID) measures, including site design, pollutant source control, stormwater treatment
and flow control measures as appropriate. LID treatment measures, such as rainwater harvesting and
use, infiltration, and biotreatment, have been required on most regulated projects since December
2011.
Provision C.3.j of the 2016 MRP requires the Town to develop and implement a long-term GSI Plan' for
the inclusion of LID measures into storm drain infrastructure on public and private lands, including
streets, roads, storm drains, parking lots, building roofs, and other elements. The GSI Plan must be
completed and submitted to the Regional Water Board by September 30, 2019.
While Provision C.3.j of the MRP contains the GSI program planning and analysis requirements, other
provisions establish a linkage between public and private GSI features and required reductions of
pollutants in stormwater discharges. Permittees in Santa Clara County (County), collectively, must
implement GSI on public and private property to achieve specified pollutant load reduction goals by the
years 2020, 2030, and 2040. These efforts will be integrated and coordinated countywide for the most
effective and resource -efficient program. As an indication as to whether these load reductions will be
met, Permittees must include in their GSI Plans estimated "targets" for the amounts of impervious
surface to be "retrofitted" as part of public and private projects (i.e., redeveloped or changed such that
runoff from those surfaces will be captured in a stormwater treatment system or GSI measure) over the
same timeframes (2020, 2030, and 2040).
A key part of the GSI definition in the MRP is the inclusion of GSI systems at both private and public
property locations. This has been done in order to plan, analyze, implement and credit GSI systems for
pollutant load reductions on a watershed scale, as well as recognize all GSI accomplishments within a
municipality. The focus of the GSI Plan is the integration of GSI systems into public buildings, parks,
parking lots, and rights-of-way (e.g., road or bike path). However, the GSI Plan may also establish
opportunities to include GSI facilities at private properties or in conjunction with private development,
so they can contribute to meeting the target load reductions on a county -wide level as well as
implement GSI on a larger scale.
1.4 GSI Plan Development Process
1.4.1 GSI Plan Development and Adoption
The GSI Plan development process began with the preparation of the Town's GSI Plan Framework
(Framework), a work plan describing the goals, approach, tasks, and schedule needed to complete the
GSI Plan. Development of the Framework was a regulatory requirement (Provision C.3.j.i(1) of the MRP)
to demonstrate the Town's commitment to completing the GSI Plan by September 30, 2019, The Town
completed the Framework and the Town Council approved it on August 17, 2017.
' Although the MRP uses the term green infrastructure (GI), the agencies within Santa Clara County, including the
City of Santa Clara, prefer to use the term green stormwater infrastructure (GSI). Therefore, the term GSI is used in
this document.
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The Town established a GSI Work Group, consisting of staff from the Town's Public Works and Planning
Departments. The GSI Work Group worked with a consultant team to develop the GSI Plan. The Plan was
adopted by the Town Council on August 21, 2019.
1,4.2 Regional Collaboration
The Town of Los Altos Hills is a member of the Santa Clara Valley Urban Runoff Pollution Prevention
Program (SCVURPPP), an association of thirteen cities and towns in the Santa Clara Valley, the County of
Santa Clara, and Valley Water (formerly called the Santa Clara Valley Water District) that collaborate on
stormwater regulatory activities and compliance. This partnership allows sharing of resources toward
permit compliance and collaboration on projects of mutual benefit. SCVURPPP provided technical
guidance, templates, and completion of certain GSI Plan elements at the countywide level. SCVURPPP
guidance and products are discussed in more detail in relevant sections of the GSI Plan.
The Town, via SCVURPPP, also coordinated with the Bay Area Stormwater Management Agencies
Association (BASMAA) on regional GSI guidance and received feedback through BASMAA from MRP
regulators on GSI expectations and approaches. BASMAA members include other countywide
stormwater programs in Alameda, Contra Costa, and San Mateo Counties, and area -wide programs in
the Vallejo and Fairfield -Suisun portions of Solano County, whose participating municipalities are
permittees under the MRP.
1.4.3 Education and Outreach
One of the first and most important steps in the development of a GSI Plan is educating a municipality's
department staff, managers, and elected officials about the purposes and goals of green infrastructure,
the required elements of the GSI Plan, and steps needed to develop and implement the GSI Plan, and
get their support and commitment to the Plan and this new approach to urban infrastructure. Another
important first step is local community and stakeholder outreach to gain public support. The Town
began this process in FY 15-16; the following list summarizes the education and outreach conducted in
support of developing the GSI Plan:
• Convened interdepartmental meetings with affected department staff and management to
discuss GSI requirements and assigned tasks and to get input on the GSI Plan.
• Discussed with appropriate department staff the MRP requirements to analyze proposed capital
projects for opportunities to incorporate GSI and completed the first list of planned and
potential GSI projects.
• Provided training to department staff on GSI requirements and strategies using the GSI
workshops and other training tools developed by SCVURPPP.
• Established a GSI committee with a set of tasks and schedule.
The Town will continue to conduct the following education and outreach activities as part of the
implementation of the GSI Plan:
• Continue to provide outreach to the general public and development community in
coordination with SCVURPPP.
• Continue to conduct internal training as needed, and send staff to SCVURPPP trainings.
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1.5 GSI Plan Structure and Required Elements
The remainder of the GSI Plan is structured as follows:
Jt U7 714, ?.(JJ =i
Chapter 2 provides the definition, purpose, and benefits of GSI, and describes the different types of GSI
facilities.
Chapter 3 describes the relationship of the GSI Plan to other planning documents and how those
planning documents have been updated or modified, if needed, to support and incorporate GSI
requirements. For documents whose desired updates and modifications have not been accomplished by
the completion of the GSI Plan, a work plan and schedule are laid out to complete them.
Chapter 4 outlines the materials being developed by SCVURPPP and the Town to provide guidelines,
typical details, specifications and standards for municipal staff and others in the design, construction,
and operation and maintenance of GSI measures.
Chapter 5 presents information on the different types of GSI projects and the methodology and results
for identifying and prioritizing areas for potential GSI projects.
Chapter 6 outlines the Town's strategy for implementing potential GSI projects within the next ten years
and through 2040, discusses the variety of mechanisms to be employed by the Town in order to
implement the GSI Plan, and presents the estimated targets for the amounts of impervious surface to be
"retrofitted" as part of public and private projects by 2020, 2030, and 2040.
The GSI Plan elements required by Provision C.3.j.i.(2) of the MRP and the section of the document in
which each component can be found are summarized in Table 1-1.
Table 1-1 Summary of GSI Plan Elements required by Provision C.3.jd of the MRP.
MRP Provision
GSI Plan Elements
GSI Pian Section
C.3.j.i.(2)(a)
Project Identification and Prioritization Mechanism
Chapter 5
C.3.j.i.(2)(b)
Prioritized Project Locations
Section 5.3
C.3.j.i.(2)(c)
Impervious Surface Targets
Section 6.6
C.3.j.i.(2)(d)
Completed Project Tracking System
Section 6.7
C.3.j.i.(2)(e,f)
Guidelines and Specifications
Chapter 4
C.3.j.i.(2)(g)
Alternative Sizing Requirements for Green Street Projects
Section 4.1
C.3.j.i.(2)(h,i)
Integration with Other Municipal Plans
Chapter 3
C.3.j.i.(2)(j)
Workplan to Complete C.3.j. Early Implementation Projects
Section 6.2
C.3.j.1.(2)(k)
Evaluation of Funding Options
Section 6.5
C.3.j.i.(3)
Legal and Implementation Mechanisms
Section 6.4
8
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2. WHAT IS GREEN STORMWATER INFRASTRUCTURE?
In natural landscapes, most of the rainwater soaks into the soil or is taken up by plants and trees.
However, in developed areas, building footprints and paved surfaces such as driveways, sidewalks, and
streets prevent rain from soaking into the ground. As rainwater flows over and runs off these impervious
surfaces, this "urban runoff" or "stormwater runoff' can pick up pollutants such as motor oil, metals,
sediment, pesticides, pet waste, and litter. It then carries these pollutants into the Town's drainage
system, which flows directly to local creeks and San Francisco Bay, without any cleaning or filtering to
remove pollutants. Stormwater runoff is therefore a major contributor to water pollution in developed
areas.
As areas develop, the increase in impervious surface also results in increases in peak flows and volumes
of stormwater runoff from rain events. Traditional "gray" stormwater infrastructure, like portions of the
Town's drainage system, is designed to convey stormwater flows quickly away from developed areas.
However, the increased peak flows and volumes can cause erosion, flooding, and habitat degradation in
downstream creeks to which stormwater is discharged, damaging habitat, property, and infrastructure.
2.1 Green Stormwater Infrastructure
A new approach to managing stormwater is to implement green stormwater infrastructure. GSI uses
vegetation, soils, and other elements and practices to capture, treat, infiltrate and slow urban runoff
and thereby restore some of the natural processes required to manage water and create healthier urban
environments. GSI facilities can also be designed to capture stormwater for uses such as irrigation and
toilet flushing.
GSI integrates building and roadway design, complete streets, drainage infrastructure, urban forestry,
soil conservation and sustainable landscaping practices to achieve multiple benefits. At the town, city or
county scale, GSI is a patchwork of natural areas that provides habitat, flood protection, cleaner air, and
cleaner water. At the neighborhood or site scale, .GSI comprises stormwater management systems that
mimic nature and soak up and store water.'
2.2 Benefits of Green Stormwater Infrastructure
GSI can provide multiple benefits beyond just managing rainfall and runoff. These benefits include
environmental, economic, and social improvements.
GSI measures can mitigate localized flooding and reduce erosive flows and quantities of pollutants being
discharged to local creeks and the San Francisco Bay. Vegetated GSI systems can beautify public places
and help improve air quality by filtering and removing airborne contaminants from vehicle and industrial
sources. They can also reduce urban heat island effects by providing shade and absorbing heat better
than paved surfaces, and provide habitat for birds, butterflies, bees, and other local species. When GSI
facilities are integrated into traffic calming improvements such as curb extensions and bulb -outs at
intersections, they can help increase pedestrian and bicycle safety and promote active transportation,
which in turn can result in improved human health.
GSI facilities designed with extra storage can capture stormwater for later use as irrigation water or non -
potable uses such as toilet flushing and cooling tower supply, thus conserving potable water supplies.
' https://www.epa.gov/green-infrastructure/what-green-infrastructure
Resolution 47-19 Page 19
Widespread implementation of GSI potentially offers significant economic benefits, such as deferring or
eliminating the need for some gray infrastructure projects. By providing more storage within the
watershed, GSI can help reduce the costs of conveyance and pumping of stormwater. When cost -benefit
analyses are performed, GSI Is often the preferred alternative due to the multiple benefits provided by
GSI as compared to conventional infrastructure.
2.3 Types of Green Stormwater Infrastructure Facilities
Integrating GSI into public spaces typically involves construction of stormwater capture and treatment
measures in public streets, parks, and parking lots or as part of public buildings. Types of GSI measures
that can be constructed in public spaces include: (1) bioretention; (2) stormwater tree well filters; (3)
pervious pavement, (4) infiltration facilities, (5) green roofs, and 6) rainwater harvesting and use
facilities. A description of these facility types is provided below.
2.3.1 Biotreatment/Bioretention
Bioretention areas are depressed landscaped areas that consist of a
ponding area, mulch layer, plants, and a special biotreatment soil
media composed of sand and compost, underlain by drain rock and an
underdrain, if required. Bioretention is designed to retain stormwater
runoff, filter stormwater runoff through biotreatment soil media and
plant roots, and either infiltrate stormwater runoff to underlying soils
as allowed by site conditions, or release treated stormwater runoff to
the storm drain system, or both. They can be of any shape and are
adaptable for use on a building or parking lot site or in the street right-
of-way.
Bioretention systems in the streetscape have specific names:
stormwater planters, stormwater curb extensions (or bulb -outs), and
stormwater tree well filters (described in the next section).
Figure 2-1 Stormwater curb extension,
Rosita AvenueLos Altos (Source: City of Los
Altos)
A stormwater curb extension (Figure 2-1) is a bioretention system that extends
into the roadway and involves modification of the curb line and gutter.
Stormwater curb extensions may be installed midblock or at an intersection.
Curb bulb -outs and curb extensions installed for pedestrian safety, traffic
calming, and other transportation benefits can also provide opportunities for
siting bioretention facilities. Parking lots can accommodate
bioretention areas of any shape in medians, corners, and pockets of
space unavailable for parking.
A stormwater planter is a linear bioretention facility in the public right-of-way
along the edge of the street, often in the planter strip between the street and
sidewalk. They are typically designed with vertical (concrete) sides. However, as
shown in Figure 2-2, they can also have sloped sides depending on the amount
of space that is available.
2.3.2 Stormwater Tree Well Filters and Suspended Pavement Systems
A stormwater tree well filter is a type of bioretention system consisting of an
excavated pit or vault that is filled with biotreatment soil media, planted with a
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Figure 2-2 Stormwater planter,
Hacienda Avenue (Source: City of
Campbell)
Resolution 47-19 Page 20
tree and other vegetation, and underlain with drain rock and an underdrain, if needed. Stormwater tree
well filters can be constructed in series and linked via a subsurface trench or underdrain. A stormwater
tree well filter can require less dedicated space than other types of bioretention areas.
Suspended pavement systems may be used to provide increased underground treatment area and soil
volume for tree well filters. These are structural systems designed to provide support for pavement while
preserving large volumes of uncompacted soil for tree roots. Suspended pavement systems may be any
engineered system of structural supports or commercially available proprietary structural systems.
Stormwater tree well filters and suspended pavements systems are especially useful in settings between
existing sidewalk elements where available space is at a premium. They can also be used in curb
extensions or bulb -outs, medians, or parking lots if surrounding grades allow for drainage to those areas.
The systems can be designed to receive runoff through curb cuts or catch basins or allow runoff to enter
through pervious pavers on top of the structural support.
Figure 2-3 Stormwater tree well filter conceptual examples: modular suspended pavement system (left), column
suspended pavement system (right). (Courtesy of City of Philadelphia Water Department)
2.3.3 Pervious Pavement
Pervious pavement is *hardscape that allows water to pass through its surface into a storage area filled
with gravel prior to infiltrating into underlying soils. Types of pervious pavement include permeable
interlocking concrete pavers, pervious concrete, porous asphalt, and grid pavement. Pervious pavement
is often used in parking areas or on streets where bioretention is not feasible due to space constraints or
if there is a need to maintain parking. Pervious pavement— :,raT:-,:'JnTJ
does not require a dedicated surface area for treatment
and allows a site to maintain its existing hardscape.
There are two types of pervious pavers: Permeable
Interlocking Concrete Pavers (PICP) and Permeable Pavers
(PP). PICP allows water to pass through the joint spacing
between solid pavers, and PP allows water to pass through
the paver itself and therefore can have tighter joints.
Porous asphalt and pervious concrete are similar to
traditional asphalt and concrete, but do not include fine
aggregates in the mixture, allowing water to pass through
the surface. All types are supported by several layers of
different sizes of gravel to provide structural support and
water storage.
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Figure 2-4 Permeable interlocking concrete
pavers, Mayfield Playing Fields, Palo Alto
(Source: EOA)
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2.3.4 Infiltration Facilities
Where soil conditions permit, infiltration facilities can be used
to capture stormwater and infiltrate it into native soils. The
two primary types are infiltration trenches and subsurface
infiltration systems.
An infiltration trench is an excavated trench backfilled with a
stone aggregate and lined with a filter fabric. Infiltration
trenches collect and detain runoff, store it in the void spaces
of the aggregate, and allow it to infiltrate into the underlying
soil. Infiltration trenches can be used along roadways,
alleyways, and the edges or medians of parking lots. An
example of an infiltration trench is shown in Figure 2-5.
Subsurface infiltration systems are another type of GSI
measure that may be used beneath parking lots or parks to
infiltrate larger quantities of runoff. These systems, also
known as infiltration galleries, are underground vaults or
pipes that store and infiltrate stormwater while preserving
the uses of the land surface above parking lots, parks and
playingfields. An example is shown in Figure 2-6. Storage can
take the form of large -diameter perforated metal or plastic
pipe, or concrete arches, concrete vaults, plastic chambers
or crates with open bottoms. Prefabricated, modular
infiltration galleries are available in a variety of shapes, sizes,
and material types that are strong enough for heavy vehicle loads.
tIo2 14, i(119
Figure 2-5 Infiltration trench, San Jose
(Source: City of Son Jose)
Figure 2-6 Subsurface infiltration system
(Source: Conteches.com)
2.3.5 Green Roofs
Green roofs are vegetated roof systems that filter, absorb, and
retain or detain the rain that falls upon them (Figure 2-7).
Green roof systems are comprised of a layer of planting media
planted with vegetation, underlain by other structural
components including waterproof memlbranes, synthetic
insulation, geofabrics, and underdrains. A green roof can be
either "extensive", with 3 to 7 inches of lightweight planting
media and low -profile, low -maintenance plants, or "intensive",
with a thicker (8 to 48 inches) of media, more varied plantings,
and a more garden -like appearance. Green roofs can provide
high rates of rainfall retention via plant uptake and
evapotranspiration and can decrease peak flow rates in storm
drain systems because of the storage that occurs in the
planting media during rain events.
12
Figure 2-7 Green Roof of Fourth Street
Apartments, San Jose (Source: EOA)
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2.3.6 Rainwater Harvesting and Use
Rainwater harvesting is the process of collecting rainwater from
impervious surfaces and storing it for later use. Storage facilities that
can be used to capture stormwater include rain barrels, above -ground
or below -ground cisterns (Figure 2-8), open storage reservoirs (e.g.,
ponds), and various underground storage devices (tanks, vaults, pipes,
and proprietary storage systems)(Figure 2-9). The captured water is
then fed into irrigation systems or non -potable water plumbing
systems, either by pumping or by gravity flow. Uses of captured water
may include irrigation, vehicle washing, and indoor non -potable use
such as toilet flushing, heating and cooling, or industrial processing.
The two most common applications of rainwater harvesting are 1)
collection of roof runoff from buildings; and 2) collection of runoff from
at -grade surfaces or diversion of water from storm drains into large
underground storage facilities below parking lots or parks. Rooftop
runoff usually contains lower quantities of pollutants than at -grade
surface runoff and can be collected via gravity flow. Underground
storage systems typically include pre-treatment facilities to remove
pollutants from stormwater prior to storage and use.
2.4 Existing GSI Facilities
Los Altos Hills is a rural residential community, with no commercial or
Figure 2.8 Rainwater Harvesting
cistern, Environmental Innovation
Center, San Jose (Source: City of San
Jose)
Figure 2-9 Subsurface vault under
construction (Source: Conteches.com)
industrial areas. The Town does not have a conventional storm drainage system. A large portion of the
Town has steep slopes, making it unsuitable for installing GSI. Due to these factors, few GSI
opportunities have been identified to date. The Town has used pervious materials on its pathways,
including pervious concrete and decomposed granite, and maintains natural areas and roadside ditches
along most of its roadways to capture runoff.
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3. INTEGRATION WITH OTHER PLANNING DOCUMENTS
To ensure the success of the GSI Plan and its implementation, its goals, policies and implementation
strategies should align with the Town's General Plan and other related planning documents. The MRP
requires that municipal agencies review such documents and include in their GSI Plans a summary of any
planning documents aligned with the GSI Plan or updated or modified to appropriately incorporate GSI
requirements. The GSI Plan must also include a workplan identifying how GSI measures will be included
in future plans.
3.1 Town Planning Document Review
The Town completed a review of its existing planning documents to determine the extent to which GSI -
related language, concepts and policies have been incorporated. The plans that were reviewed are listed
below, with the General Plan as guiding planning document first, followed by remaining plans in order of
most recently prepared/adopted:
• General Plan (Adopted 2007)
• Pavement Management Plan Report (Last release: 2018)
• Storm Drainage Master Plan (Adopted 2004)
The following sections provide a brief description of each plan and the text that supports GSI planning
implementation. A prioritized workplan for the integration of GSI language into existing and future Town
planning documents is provided in Section 3.1.4.
3.1.1 General Plan (2007-2015)
The Los Altos Hills General Plan is an official statement of public policy regarding the future physical
development of the Town. It provides a policy framework within which Los Altos Hills can develop in a
safe, orderly manner while preserving its semi -rural, residential character. The Land Use Element of the
General Plan was last updated in 2007, and the Circulation Element was last updated in 2015. The
General Plan includes some language that broadly supports environmental sustainability and
stormwater best management practices. Examples of this language are provided below:
Introduction, Regional Goals (Page 6)
Government, groups, and individuals should be encouraged to participate in the planning,
management, and use of the limited natural resources of the Bay Area in such a way as to
conserve and restore the environment.
• Land Use Element, Goal 1 (Page LU -4)
Uses of land shall be consistent with the semi -rural atmosphere of the community, minimize
disturbance to natural terrain, minimize removal of the natural vegetation, and create the
maximum compatibility of development with the natural environment through site design and
landscaping.
• Land Use Element, Policy 2.5 (Page LU -9)
Steep slopes, canyons and ravines generally in excess of 30% slope, as well as natural swales and
drainage channels, and geologic hazard areas within areas designated for residential
development shall be left undisturbed and preserved in their natural condition to the maximum
extent feasible.
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Conservation Element; Policy 5.1 (Page CO -11)
Keep or restore major drainage courses in their natural condition insofar as possible because of
their importance in supplying major vegetation, land forms and wildlife habitat, and storm
drainage.
• Pathways Element (Page P-1)
Pathways are frequently constructed of pervious materials to maintain the Town's open and
rural setting, and to further enhance the recreational experience.
• Safety Element; Flood Hazards (Page 5-9)
Traditionally the Town's approach to drainage has been to utilize natural drainage channels
rather than to install pipe drainage systems or to increase capacity by straightening, widening,
or lining creek channels. Given the policy of the Town to preserve the natural quality of creeks
and riparian corridors, it is important to prevent development from increasing runoff to the
point that channels become overloaded, and to avoid new development in natural flood plains.
• Safety Element; Policy 3.1 (Page S-10)
Leave natural channels and flood plains in a natural state, unencumbered by development to
the maximum extent feasible. Exceptions shall be made only in situations where it is essential to
protect established property values or for public safety.
3.1.2 Pavement Management Plan Report (2018)
The Town's Pavement Management Plan Report is updated every two years. It includes a survey of
streets conditions, and prioritization of streets for maintenance and rehabilitation. The 2018 PMP
Report does not include language supporting the inclusion of GSI features during street maintenance
and rehabilitation.
3.1.3 Storm Drainage Master Plan (2004)
The objective of the Storm Drainage Master Plan (SDMP) is to provide the Town with a planning guide
for upgrading, improving, repairing, and maintaining existing drainage systems, both to meet current
stormwater regulations and to plan for future needs. The Town's drainage system consists of a
combination of roadside drainage ditches, cross culverts, and underground pipes. The 2004 SDMP
identified a prioritized list of 28 drainage projects to address specific drainage problems. The SDMP
includes information on Provision C.3 requirements but some of it is outdated. The next update to the
SDMP will include language that refers to current MRP requirements and the GSI Plan.
3.1.4 Workplan for Integration of GSI Language into Existing and Future Town Planning
Documents
The language currently in the reviewed planning documents does not create barriers to implementing
GSI and the Town's General Plan is generally aligned with and supports the GSI Plan. However, GSI
implementation could benefit from the inclusion of additional GSI -related language in the Town's
planning documents. Table 3-1 below summarizes the plans that will be updated and the schedule for
completion.
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Resolution 47-19 Page 25
Table 3-1 Workplan for Integration of GS! Language into Existing Town Planning Documents
Name of Plan To Be Updated
Anticipated Date of
Completion/Update
General Plan
2023-2025
Pavement Management Plan Report
2020
Storm Drainage Master Plan
2021
When preparing new planning documents, the Town will review GSI Plan goals and strategies during the
planning process to ensure that policies supporting GSI are incorporated. Examples of GSI -related
language can be found in references such as SCVURPPP's Model Green Infrastructure Language for
Incorporation into Municipal Plans (2016).
3.2 Regional Plans
The Town is collaborating with SCVURPPP, Valley Water, and other agencies on several large-scale
planning efforts including those described below.
3.2.1 Santa Clara Basin Stormwater Resource Plan
A collaboration between SCVURPPP and Valley Water during 2017 and 2018, the Santa Clara Basin
Storm Water Resources Plan (SWRP) supports municipal GSI Plans by identifying and prioritizing
potential multi -benefit GSI opportunities on public parcels and street rights-of-way throughout the Basin
(i.e., Santa Clara Valley) and allows them to be eligible for State bond -funded implementation grants.
The SWRP includes a list of prioritized GSI opportunity locations for each SCVURPPP agency, including
Los Altos Hills. As described in Section 5.2, the Town's GSI Plan builds on the SWRP output to further
identify, evaluate, and prioritize potential projects.
3.2.2 Santa Clara Valley Water District's One Water Plan
Valley Water's Watershed Division is leading an effort to develop an Integrated Water Resources Master
Plan to identify, prioritize, and implement activities at a watershed scale to maximize established water
supply, flood protection, and environmental stewardship goals and objectives. The "One Water Plan"
establishes a framework for long-term management of Santa Clara County water resources, which
eventually will be used to plan and prioritize projects that maximize multiple benefits. The One Water
Plan incorporates knowledge from past planning efforts, builds on existing and current related planning
efforts; and coordinates with relevant internal and external programs. The One Water Plan has five
goals:
1. "Valued and Respected Rain" —Manage rainwater to improve flood protection, water supply,
and ecosystem health.
2. "Healthful and Reliable Water" — Enhance the quantity and quality of water to support
beneficial uses.
3. "Ecologically Sustainable Streams and Watersheds" — Protect, enhance and sustain healthy and
resilient stream ecosystems.
4. "Resilient Baylands" — Protect, enhance and sustain healthy and resilient baylands ecosystems
and infrastructure.
5. "Community Collaboration" —Work in partnership with an engaged community to champion
wise decisions on water resources.
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Resolution 47-19 Page 26
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Tier 1 of the effort, for which a draft plan was completed in 20164, is a countywide overview of major
resources and key issues along with identified goals and objectives. Tier 2 (2016 to 2020) will include
greater detail on each of the County's major watersheds. The Town's GSI Plan aligns with the goals of
the One Water Plan and may be able to coordinate with specific projects yet to be identified in the
Lower Peninsula watershed area.
3.2.3 Bay Area Integrated Regional Water Management Plan
The Bay Area Integrated Regional Water Management Plan (IRWMP) is a comprehensive water
resources plan for the Bay region that addresses four functional areas: 1) water supply and water
quality; 2) wastewater and recycled water; 3) flood protection and stormwater management; and 4)
watershed management and habitat protection and restoration. It provides a venue for regional
collaboration and serves as a platform to secure state and federal funding. The IRWMP includes a list of
over 300 project proposals, and a methodology for ranking those projects for the purpose of submitting
a compilation of high priority projects for grant funding. The Santa Clara Basin SWRP was submitted to
the Bay Area IRWMP Coordinating Committee and incorporated into the IRWMP as an addendum. As
SWRP projects are proposed for grant funding, they will be added to the IRWMP list using established
procedures.
4 Santa Clara Valley Water District. 2016. One Water Plan for Santa Clara County. An Integrated Approach to Water
Resources Management. Preliminary Draft Report 2016.
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4. GSI DESIGN GUIDELINES, DETAILS, AND SPECIFICATIONS
The MRP requires that the GSI Plan include general design and construction guidelines, standard
specifications and details (or references to those documents) for incorporating GSI components into
projects within the Town. These guidelines and specifications should address the different street and
project types within the Town, as defined by its land use and transportation characteristics, and allow
projects to provide a range of functions and benefits, such as stormwater management, bicycle and
pedestrian mobility and safety, public green space, and urban forestry.
The Town, along with other SCVURPPP agencies, helped fund and provided input to the development of
countywide guidelines by SCVURPPP to address the MRP requirements and guide the implementation of
GSI Plans. The resulting SCVURPPP GSI Handbook (Handbook)' is a comprehensive guide to planning and
implementation of GSI projects in public streetscapes, parking lots and parks. The Handbook consists of
two parts, the contents of which are described in the following sections. The Town intends to use this
Handbook as a reference when creating Town -specific guidelines and specifications to meet the needs
of the various departments.
4.1 Design Guidelines
Part 1 of the Handbook provides guidance on selection, integration, prioritization, sizing, construction,
and maintenance of GSI facilities. It includes sections describing the various types of GSI, their benefits,
and design considerations; how to incorporate GSI with other uses of the public right-of-way, such as
bicycle and pedestrian infrastructure and parking; and guidelines on utility coordination and landscape
design for GSI. In addition, the Handbook also provides guidance on post -construction maintenance
practices and design of GSI to facilitate maintenance.
Part 1 also contains a section on proper sizing of GSI measures. Where possible, GSI measures should be
designed to meet the same sizing requirements as Regulated Projects, which are specified in MRP
Provision C.3.d. In general, the treatment measure design standard is capture and treatment of 80% of
the annual runoff (i.e., capture and treatment of the small, frequent storm events). However, if a GSI
measure cannot be designed to meet this design standard due to constraints in the public right-of-way
or other factors, the Town may still wish to construct the measure to provide some runoff reduction and
water quality benefit and achieve other benefits. For these situations, the Handbook describes (in
Section 4.2) regional guidance on alternative design approaches developed by the Bay Area Stormwater
Management Agencies Association (BASMAA) for use by MRP permittees.
4.2 Details and Specifications
Part 2 of the Handbook contains typical details and specifications that have been compiled from various
sources within California and the U.S. and modified for use in Santa Clara County. The Handbook
includes details for pervious pavement, stormwater planters, stormwater curb extensions, bioretention
in parking lots, infiltration measures, and stormwater tree wells, as well as associated components such
as edge controls, inlets, outlets, and underdrains. It also provides typical design details for GSI facilities
in the public right-of-way that address utility protection measures and consideration of other
infrastructure in that space.
' SCVURPPP (2019) Green Stormwater Infrastructure Handbook. February. Online at
http://scvurppp.org/scvurppp_2018/swrp/resource-I!brary/
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4.3 Incorporation of SCVURPPP Details and Specifications into Town Standards
The Town plans to reference the SCVURPPP GSI Guidelines and Specifications for design of GSI projects.
The Town will evaluate these for consistency with its own local standards, and revise existing guidelines,
standard specifications, design details, and department procedures as needed.
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5. GSI PROJECT PRIORITIZATION AND IMPERVIOUS TARGETS
To meet the requirements of the MRP, the Town's GSI Plan must contain a mechanism to prioritize and
map areas for potential and planned projects, both public and private, for implementation over the .
2020, 2030, and 2040 milestones. The mechanism must include the criteria for prioritization and outputs
that can be incorporated into the Town's long-term planning and capital improvement processes.
This chapter describes different GSI project categories for consideration within the Town, followed by a
description of the process employed by the Town to identify public lands that offer opportunities to
implement GSI and prioritize those opportunities, and the results of the process.
5.1 Project Types
GSI project types that may be implemented in the Town fall into the following categories: Early
Implementation Projects, C3 Regulated Projects, Green Streets, LID Retrofits, and Regional Projects.
Green Streets, LID Retrofits, and Regional Projects are types of GSI capital projects that the Town may
implement to meet the water quality goals in the MRP and multi -benefit objectives defined in the GSI
Plan. These three project types are the focus of the prioritization process described in Section 5.2, but
all five types are considered as part of the overall GSI strategy presented in Chapter 6.
5.1.1 Early Implementation Projects
Early Implementation Projects are GSI projects that have already been implemented or are already
scheduled and funded for implementation during the permit term (i.e., through December 2020). The
Town has not yet identified any GSI projects for implementation during the permit term but will
continue to look for opportunities.
5.1.2 Regulated Projects
C3 Regulated Projects are those implemented as part of new and redevelopment within the Town, both
private and public, that must meet the post -construction stormwater treatment requirements per
Provision C.3 of the MRP. Regulated projects include private development or redevelopment projects,
such as multi -family residential buildings, commercial office buildings, or shopping plazas, as well as
public projects, such as libraries, police stations, and parking lots, exceeding the impervious surface
thresholds. The Town approved its first private Regulated Project, a 16 -acre, 9 -lot single family home
subdivision (with lots to be developed by future owners) in FY 17-18; construction is expected to be
completed in the 2020-2030 timeframe.
5.1.3 LID Projects
LID projects mitigate stormwater impacts by reducing runoff through capture and/or infiltration and
treating stormwater on-site before it enters the storm drain system. LID projects may include
bioretention facilities, infiltration trenches, detention and retention areas in landscaping, pervious
pavement, green roofs, and systems for stormwater capture and use. For the purposes of the GSI Plan,
LID projects are GSI facilities that treat runoff generated from a publicly -owned parcel on that parcel.
5.1.4 Regional Projects
Regional projects capture and treat stormwater runoff from on-site and off-site sources, including
surface runoff and diversions from storm drains. Benefits of regional stormwater capture projects can
include flood risk reduction, stormwater treatment and use, and groundwater recharge. These projects
may take a variety of forms such as detention and retention basins and subsurface vaults and infiltration
20
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galleries. The site characteristics will determine what types of regional projects are feasible, e.g.,
whether a project is on-line or off-line from the storm drain network, whether it is desirable to change
the functionality of the site, whether the project is above ground or underground, and the size of the
project.
5.1.5 Green Street Projects
Green street projects are GSI opportunities in the public right-of-way that capture runoff from the street
and adjacent areas that drain to the street. The technologies used for green streets are similar to those
used in LID projects but are limited to designs that can be used in the right-of-way. Green street projects
may include bioretention (e.g., stormwater planters, stormwater curb extensions or stormwater tree
filters), pervious pavement, and/or infiltration trenches. Green street GSI features can be incorporated
into other improvements in the right-of-way, including complete streets designs and improvements for
pedestrian and cyclist safety.
5.2 Identification and Prioritization Process
The Town of Los Altos Hills GSI opportunity identification and prioritization process involved two steps.
The first step was the screening and prioritization methodology used in the Santa Clara Basin SWRP (see
Section 3.2.1) to identify and prioritize GSI opportunities on public parcels and street segments within
the region. The second step in the process involved overlaying Town -specific priorities onto the regional
prioritization results to align the results of the SWRP prioritization process with the Town's priorities.
These steps are described in detail below. Projects associated with a prioritized parcel or street segment
in the SWRP qualify for State bonded -funded stormwater capture project implementation grants (e.g.,
Proposition 1). Opportunities for projects with GSI measures that arise in areas that are not adjacent to
a prioritized project opportunity area identified in the SWRP may be considered on a case by case basis
for feasibility, cost effectiveness, and availability of funding.
5.2..1 Step 1: Stormwater Resource Plan Prioritization
Building on existing documents that describe the characteristics and water quality and quantity issues
within the Santa Clara Basin (i.e., the portion of Santa Clara County that drains to San Francisco Bay), the
SWRP identified and prioritized multi -benefit GSI opportunities throughout the Basin, using a metrics -
based approach for quantifying project benefits such as volume of stormwater infiltrated and/or
treated, and quantity of pollutants removed. The metrics -based analysis was conducted using
hydrologic/ hydraulic and water quality models coupled with Geographic Information System (GIS)
resources and other tools. The products of these analyses were a map of opportunity areas for GSI
projects throughout the watershed, an initial prioritized list of potential project opportunities, and
strategies for implementation of these and future projects.
The process began by identifying and screening public parcels and public rights-of-way that can support
GSI. Project opportunities were split into the three categories described above — LID, regional, and green
streets projects -- because of fundamental differences in GSI measures used, project scale, and
measures of treatment efficiency. Screening factors are presented in Table 5-1,
After the identification of feasible GSI opportunity locations, screened streets and parcels were
prioritized to aid in the selection of project opportunities that would be the most effective and provide
the greatest number of benefits. In addition to physical characteristics, several special considerations
were included in the prioritization methodology to consider coordination with currently planned
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Resolution 47-19 Page 31
t
projects provided by agencies, as well as consideration of additional benefits that projects could
provide. A discussion of the screening and prioritization process for each project category is presented
in the subsequent sections. Figures 5-1 through 5-3 present the results of the various steps.
LID and Regional Stormwater Capture Project Opportunities
The screening criteria for LID and regional projects were ownership (focusing only on public parcels),
land use, and site slope. As shown in Table 5-1, parcel size was used to determine whether a location
could support a regional or LID project.
Parcels that met the screening criteria were prioritized based on physical characteristics such as soil
group, slope, and percent impervious area, proximity to storm drains, proximity to flood -prone creeks
and areas, proximity to potential pollutant sources, whether they were in a priority development area
(PDA), whether they were within a defined proximity to a planned project, and whether the project was
expected to have other benefits such as augmenting water supply, providing water quality source
control, re-establishing natural hydrology, creating or enhancing habitat, and enhancing the community.
Prioritization metrics for LID project scoring and regional project scoring are shown in separate tables in
Appendix A. The result of the parcel prioritization was a list and map of potential project locations based
on the above criteria.
Green Street Project Opportunities
The screening criteria for green streets projects in the public right-of-way were ownership, surface
material, slope, and speed limit (Table 5-1). The screened public right-of-way street segments were then
prioritized based on physical characteristics, proximity to storm drains, proximity to flood -prone creeks
and areas, proximity to potential pollutant sources, whether they were in a priority development area,
whether they were in proximity to a planned project, and whether the project was expected to have
other benefits (similar to LID and regional projects). Prioritization metrics for green streets projects are
shown in Appendix A.
The initial prioritization process resulted in a large number of potential green streets project
opportunities within the Santa Clara Basin. In order to identify the optimal locations for green street
projects, the street segments in each municipality's jurisdiction with scores in the top 10 percent of
ranked green street opportunities were identified and mapped. This subset of projects from the SWRP
was carried over into Step 2 Town -Specific Prioritization (Section 5.2.2).
22
Resolution 47-19 Page 32
Table 5-1 Screening factors for parcel -based and right-of-way project opportunities
Screening
Opportunity for regional stormwater capture
Characteristic
Criteria
Reason
Factor.:"
Parcel Size
"Parcel -based
Opportunity for on-site LID project
Suitability
County, City, Town,
Steeper grades present additional design
Valley Water, State,
Site Slope
Public
Ownership
Open Space
p p
Identify all public parcels for regional
Parcels
Public
Agencies
stormwater capture projects or onsite LID
retrofits
of-way opportunities
Park, School, Other
Surface
Paved
Only roads with paved surfaces are considered
Land Use
(e.g., Golf Course)
5.2.2 Step 2: Town -Specific Prioritization
The first step in the Town -specific prioritization was to focus on parcels and rights -of -ways owned and
maintained by the Town. The SWRP public parcels and top 10 percent street segments in, and
owned/maintained by, the Town of Los Altos Hills with potential for GSI are shown on the map in Figure
5-1. Note that properties owned by schools/colleges are also shown on the map. Although these are not
under the Town's jurisdiction, they may offer opportunity for collaboration on GSI projects in the future.
As shown on the map, the Town Hall and adjacent parking lot was identified in the SWRP as a parcel
with potential for GSI. The Town's green street project segments are located on the following streets:
• Burke Road
• EI Monte Ave
• Estacada Way
• Fremont Road
23
Resolution 47-19 Page 33
Opportunity for regional stormwater capture
>_ 0.25 acres
project
Parcel Size
< 0.25 acres
Opportunity for on-site LID project
Suitability
Steeper grades present additional design
Site Slope
< 10 %
challenges
" Right,of=Way
Selection
Ownership
Public
Potential projects are focused on public right-
of-way opportunities
Surface
Paved
Only roads with paved surfaces are considered
suitable. Dirt roads were not considered.
Steep grades present additional design
Suitability
Slope
0
< 5/
challenges; reduced capture opportunity due
to increased runoff velocity
Excludes higher speed roads such as major
Speed
_< 45mph
arterials and highways
5.2.2 Step 2: Town -Specific Prioritization
The first step in the Town -specific prioritization was to focus on parcels and rights -of -ways owned and
maintained by the Town. The SWRP public parcels and top 10 percent street segments in, and
owned/maintained by, the Town of Los Altos Hills with potential for GSI are shown on the map in Figure
5-1. Note that properties owned by schools/colleges are also shown on the map. Although these are not
under the Town's jurisdiction, they may offer opportunity for collaboration on GSI projects in the future.
As shown on the map, the Town Hall and adjacent parking lot was identified in the SWRP as a parcel
with potential for GSI. The Town's green street project segments are located on the following streets:
• Burke Road
• EI Monte Ave
• Estacada Way
• Fremont Road
23
Resolution 47-19 Page 33
I o"Nwr Of!,lO A/CO i ilk 6s/ hliq
In addition to the parcels identified in the SWRP, the Town identified the following three areas as
possible opportunity areas for GSI:
Corporation Yard
Juan Prado Mesa Preserve
• Westwind Barn and Byrne Preserve
The Town's second priority for GSI project identification is to focus on upcoming capital projects that
can potentially be combined with GSI project opportunities. As required by the MRP, the Town reviews
its Capital Improvement Program (CIP) project list annually to identify opportunities for GSI. Based on
this review, the Town is required to prepare and maintain a list of any public GSI projects that are
planned for implementation during the permit term and public projects that have potential for GSI
measures. As described in Section 1.2, there are no commercial or industrial uses within the Town limits
and development is constrained by steep slopes, unstable soils, seismic faults and other natural hazards.
Steep slopes also limit opportunity to implement GSI. Due to these factors, no GSI project opportunities
have been identified so far. However, the Town is planning to expand the Town Hall in order to increase
space for recreational activities and uses, improve the staff office area to better accommodate existing
and future staff, and to increase the amount of conference room space for Town Committee meetings
and staff use. The Town will explore opportunities for incorporating GSI features as part of the
expansion project and in the adjacent parking lot.
5.2.3 Prioritization Results
The public parcels and top 10 percent street segments in, and owned by, the Town of Los Altos Hills
identified in the SWRP to have potential for GSI are shown on the map in Figure 5-1. Note that
properties owned by schools/colleges are also shown on the map. Although these are not under the
Town's jurisdiction, they may offer opportunity for collaboration on GSI projects in the future. The SWRP
prioritization scores and additional information such as street name, land use, etc. for the prioritized
parcels and street segments are presented in Appendix B. As discussed in Section 5.2.2, the Town will
explore opportunities for incorporating GSI features as part of the anticipated Town Hall expansion
project. An implementation plan is described in Section 6 to guide the identification, development,
design, and construction of GSI projects.
24
Resolution 47-19 Page 34
Town of Los Altos Hills - Parcels and
Street Segments with Potential for GSI
s Street Segments
with Potential for GSI
Public Parcels with Potential for GSI
Public Building (Town Hall)
Park/Open Space
K-12 School`
Community College'
City -specific Opportunity Areas
A - Corporation Yard
B - Westwind Bam/Byme Preserve
C - Juan Prado Mesa Preserve
=Town Boundary
Roads
Creeks 'AN
'Properties owned by schoolstcodeges are not under the Town's jurisdiction. 0 02 0.4 0.8
However, there may be coordination opportunities in the future.
Miles
Figure 5-1 Town of Los Altos Hill Parcels and Street Segments with Potential for GSI. (Source: EOA, Town of Los
Altos Hills, and Santa Clara Basin Stormwater Resource Plan, 2018)
25
Resolution 47-19
Page 35
6. GSI IMPLEMENTATION PLAN
This chapter provides an overall strategy and steps for implementing GSI within the Town of Los Altos
Hills over the long term. The implementation plan has the following components: (1) the Town GSI
strategy; (2) a workplan to identify and complete Early Implementation projects (3) a workplan for
identifying additional, future GSI opportunities (4) the legal and funding mechanisms that enable .
implementation, (5) estimated targets for the amounts of impervious surface to be "retrofitted" (i.e.,
redeveloped with GSI facilities to treat runoff from impervious surfaces), and (6) the technical tools that
ensure the tracking of implemented projects.
6.1 Town GSI Strategy
The Town's approach to identifying opportunities for GSI will be based on the following priorities:
• The Town will aim to meet the GSI objectives by incorporating GSI, where feasible, into the
Capital Improvements Program. The Town has established a process for CIP review to avoid
missing GSI opportunities (see Section 6.2). Certain Capital Improvement Projects which may
lend themselves to the inclusion of Green Infrastructure are as follows:
o Streets projects that may include traffic calming or Safe Routes to School improvements;
o Drainage improvement projects;
o Reconstruction/improvement of roadways, pathways, and trails;
o Town park projects; and
o Expansion of Town Hall and potential improvements to the adjacent parking lot.
Evaluation of opportunities Identified in the Stormwater Resource Plan —The public parcels and
street segments identified in the SWRP (See Section 5.1 of this report) are opportunity areas for
GSI projects. The Town will use the SWRP list to help identify potential project locations for GSI
implementation, as described in Section 6.2.
Evaluation of non-CIP project opportunities —As awareness of GSI increases, municipal staff or
local community members may also identify and recommend GSI project opportunities. These
projects will be considered using the methodology described in Section 6.2. For example, there
may be opportunities to install GSI in the Town's right-of-way to capture runoff from Interstate
280, before it enters the Town's creeks. The Town may also explore working with Foothill
Community College to install green infrastructure on and around the campus. GSI can
potentially help reduce influx of pollutants from these non -jurisdictional sources.
• Regulated projects — The Town will continue to implement requirements for regulated projects
under Provision C.3 and track completed projects as described in Section 6.7.
• Trail system —The Town has an extensive trail system, and most trails are constructed with
pervious materials. The Town will continue to use pervious materials on trails in the public right-
of-way where feasible and encourage the construction of pervious trails on private property.
In addition, Los Altos Hills intends to preserve its semi -rural atmosphere and will continue to limit
impervious surfaces in private residential projects. Furthermore, to overcome the Town's constraints
(i.e. steep slopes, unstable soils) that prohibit the use of several traditional methods of GSI, the Town
will explore alternatives that allow the reduction of pollutants without the use of infiltration or deep
stormwater systems.
"PZ
Resolution 47-19 Page 36
11lre 1/1, 0 9
6.2 Process for Identifying and Evaluating GSI Project Opportunities
As described in Section 6.1, GSI project opportunities may be identified through various mechanisms,
including 1) review of the Town's CIP projects, 2) recommendations from municipal staff or local
community members, or 3) further evaluation of opportunities identified in the SWRP. The SWRP
results can be used to identify suitable locations for a potential GSI project, or to evaluate the potential
of a planned (CIP) project for GSI.
As mentioned in Section 5.2.2, the Town is required and will continue to review its CIP list annually to
identify projects with potential for GSI, using the SWRP prioritization and the guidance developed by
BASMAA6 (Attachment C) for identifying opportunities to incorporate GSI into CIP projects.
The Town will map potential GSI projects, identified through the CIP review or otherwise, to determine
their proximity to green street or parcel -based project opportunities identified in the SWRP (Section
5.2.1), evaluate each project for GSI and inclusion in the CIP (if not already in the CIP), and update the
SWRP project list when applicable.
The Town of Los Altos Hills updates its CIP plan every year. If not already in the CIP, projects with a GSI
component may be included in the CIP as funded or unfunded projects. An unfunded project's inclusion
in the CIP demonstrates that it is a Town priority pending adequate funding.
Projects with GSI measures may be submitted to the SWRP during the update process. This will allow
those projects to be eligible for state bond funding. The SWRP will likely be updated in the 2022-2023
timeframe. SCVURPPP will reach out to all member agencies to provide their project lists for
prioritization and inclusion in the updated SWRP.
6.3 Workplan for Early Implementation Projects
As discussed in Section 5.2.2 of this GSI Plan, Provision C.3.j. of the MRP requires that the Town identify,
prepare, and maintain a list of GSI projects that are planned for implementation during the permit term,
and infrastructure projects that have potential for GSI measures. The list is submitted with each Annual
Report to the Regional Water Board. Projects with GSI that are scheduled and funded for
implementation during the permit term (i.e., through December 2020) are considered "Early
Implementation Projects".
The Town of Los Altos Hills has not identified any Early Implementation Projects. As discussed in Section
6.2, the Town will continue to review its CIP list annually, using the SWRP prioritization, as well as the
guidance developed by BASMAA9 (Attachment C) for identifying opportunities to incorporate GSI into
CIP projects.
6.4 Legal Mechanisms for GSI Implementation
Provision C.3.j.i.(3) of the MRP requires permittees to "Adopt policies, ordinances, and/or other
appropriate legal mechanisms to ensure implementation of the Green Infrastructure Plan in accordance
with the requirements of this provision."
As described in Section 1.3.2, the Town of Los Altos Hills and other municipalities subject to Provision
C.3 of the MRP must require post -construction stormwater control measures on regulated development
6 BASMAA Development Committee (2016) Guidance for Identifying Green Infrastructure Potential in Municipal Capital
Improvement Program Projects. May.
27
Resolution 47-19 Page 37
iOb! 1) [71' 1 o> r,fto� i;li�i5 �] *l r'iCr l
projects. Post -construction stormwater controls reduce pollutants from flowing to streams, creeks, and
the Bay and help address local flooding by reducing peak flows. Article 14. Stormwater Pollution
Prevention Measures of the Town's Municipal Code provides legal authority for the Town to require
regulated private development projects to comply with MRP requirements. Further, the Town's
Development Area Policy (approved by Town Council on October 11, 2007) requires that all applicants
provide hydrologic calculations prepared by a registered civil engineer to demonstrate that post -
development runoff peak discharge value does not exceed the pre -development peak runoff discharge
for the property. The Policy also mandates that the total development area coverage' on any property
not exceed 34% of the lot size, thereby also limiting the amount of impervious surface.
GSI projects are typically not regulated projects (although they must conform to the sizing and design
requirements contained in Provision C.3, except under certain circumstances) and they are primarily
public projects under control of the Town. As part of the GSI Plan process, the Town reviewed its
existing policies, ordinances, and other legal mechanisms related to the implementation of stormwater
NPDES permit requirements and found that it has sufficient legal authority to implement the GSI Plan.
Adoption of the GSI Plan by the Town's Council will further strenghten this authority.
6.5 Evaluation of Funding Options
The GSI Plan prioritizes specific projects for near-term integration into CIPs and long-term integration
into Town planning efforts. Implementation of these projects is contingent upon the Town identifying
funding sources for GSI planning, design, construction, and maintenance.
The total cost of GSI includes costs for planning, capital (design, engineering, construction) and ongoing
expenditures, including operations and maintenance (O&M), utility relocation, and feature replacement.
It is likely that no single source of revenue will be adequate to fund implementation of -GSI, and a
portfolio of funding sources will be needed. There are a variety of approaches available to help fund up-
front and long-term investments. This section discusses the Town's current stormwater management
funding sources and then describes additional funding strategies available to implement GSI that are
being considered by the Town for future funding.
6.5.1 Current Funding Sources for GSI Program Elements
The Town of Los Altos Hills currently uses a combination of federal and state grants and local revenues
to fund construction of CIP projects and other projects.
6.5.2 Potential Future Funding Options
As required by the MRP, the Town analyzed possible funding options to raise additional revenue for
design, construction, and long-term operation and maintenance (0&M) of GSI projects. The Town used
the guidance on stormwater funding options developed by SCVURPPP (2018) as a reference for
conducting its analysis. Table 6-1 summarizes the funding options that will be considered by the Town as
the GSI Plan is implemented. For each type of funding mechanism, the table provides a brief overview
' Section 10-1.502(b) of the Town's Zoning Code defines "development area" to include floor area as well as other coverage,
including parking areas, patios, decks, walkways, swimming pools, tennis courts, and other surfaces comprised of artificially
emplaced building materials (paving, roofing, masonry, stone or wood).
28
Resolution 47-19 Page 38
jdi)-2
and specifics related to GSI, pros and cons, and applicability to funding planning, capital, and/or long-
term O&M costs.
29
Resolution 47-19 Page 39
Table 6-1 Potential Future Funding Options
Section/Overview
GIS ecitics
Requirements
Pros
Cons
Planning
Capital
O&M .
• Usually a one-time
source of funding only.
• May need to create
new programs and systems for
each grant.
• Usually have strings
attached for matching funds and
3.3 Grants: one time
Application,
Can fund programs or
other requirements.
funds that require an
Could es used to
Plan, design
orcin
reporting, g
systems that would
otherwise take
Little control over timing
Yes
Yes
No
application from a
and/or build GI.
coordination, and
ra
significant general fund
of applications and payment can
funding agency.
grant deliverables.
lead to difficulties in coordination
revenues.
with other programs and grants.
• Can be very
competitive and resource
intensive to apply.
• No guarantee of
success.
• Post -project O&M costs
must be bome by the agency.
• Roadway
projects have more funding
Roadways have been
than stomtwater programs
designed in certain ways with
and are generally more
expectations of costs and
Make the
popular with the public.
purposes for decades.
3.7 Integration with
connections
• Complete and
Transportation
Installation and
between roadways
green streets may be more
Many roadways are in
Projects:
maintenance of
and drainage
popular with the public
poor condition and there is not
transportation
GI facilities as
systems that are
than traditional car -focused
enough funding to fix them all.
funding is leveraged
part of integrated
green and
streets.
Yes
Yes
No
to cost-effectively
roadway
complete, where
• Green streets
GI is perceived as an
Include stormwater
programs.
allowed by
may be less expensive
°added* cost which, could reduce
quality elements.
conditions of the
than traditional streets
the number of roadways that can
funding source.
based on a life cycle cost
be maintained.
analysis.
• Transportation funding
is often restricted to certain
roadway construction elements.
at]
Resolution 47-19 Page 40
3.9 Existing
Permittee
Resources: Utilize
general funds for GI.
Could be used to
plan, design,
build and/or
maintain GI.
Management and
elected officials
agree to use
Glneral funds for
Voter approval or new
revenue sources not
required.
GI must compete with
many other municipal priorities
and essential services.
. Normally not a viable
option for substantial GI
implementation.
Yes
Yes
Yes
• Leverages public
Stormwater fee or other
funds while minimizing
source of stable revenue over
Impacts to a municipality's
the life of the P3 contract is
debt capacity,
required.
Contracts out to the
• Access to
private sector the construction
3.10.2 Public-Privateand
advanced technologies.
maintenance of GI systems,
Partnerships (P3s):
Can provide for
Stormwater fee or
possibly removing some
municipal control.
agreements or
contracts between a
the design,
construction and
other source of
Improved asset
municipality and a
maintenance of
stable revenue
over the life of the
management
Yes
Yes
Yes
private company to
GI systems over
P3 contract
Draws on private
perform specific
a long period.
.
sector expertise and
tasks.
financing.
• Benefits local
economic development
and "green )obs,"
• Relieves
pressure on internal local
government resources.
• A low-cost source
Can be time Intensive
3.10.3 Volunteer
Use volunteer
Administration,
of labor.
for staff to set up and administer.
Programs: provide
programs to help
training, tracking
Educational
May not be dependable
community-based
bind or maintain
and monitoring of
program for community.
in the long run
Yes
Yes
Yes
volunteer labor for
GI facilities.
volunteers.
Can build support
May result In loss of
specific tasks,
for a stormwater fee or
municipal control depending on
other funding source,
I programs ifcs.
31
Resolution 47-19 Page 41
I ml J'!, 20(1
6.6 Impervious Area Targets
MRP provision C.3.j.i.2.(c) requires the Town of Los Altos Hills to develop targets for the amount of
impervious surface in the Town that will be retrofitted via GSI by 2020, 2030 and 2040. To develop
impervious surface retrofit targets, not only the total acres but also the locations and types of land areas
that are anticipated to be addressed by GSI in the future must be identified.
As described in Section 1.2, there are no commercial or industrial uses within the Town limits. The only
non-residential uses within the Town are open space, parks and recreation facilities, a unique pathways
system including miles of well-maintained roadside and off-road paths, and public and private
institutions such as schools, religious facilities and governmental buildings. No parcels developed or
redeveloped to date have triggered the C.3 requirements$. As discussed in Section 5.2.2, there are plans
to expand the Town Hall property, and the project may include GSI measures. Town staff also identified
two new private development projects that could be constructed by 2040 and would require LID
treatment and hydromodification management. The two projects are the planned 16 -acre subdivision at
28030 Natoma Road (APN: 182-10-057) and the potential 6 -acre subdivision off of Elena Road (APN:
182-02-016). However, because these projects represent new development of what is largely open
space now, the amount of existing impervious surface they would replace is limited.
The locations of these planned new and redevelopment projects are shown in Figure 6-1.
8 C.3 site design, treatment, and hydromodification management requirements apply to projects that create and/or replace
10,000 square feet or more of impervious surface, excluding single family homes that are not part of a common plan of
development (such as a subdivision).
32
Resolution 47-19 Page 42
1
r1i115 G)/ l'b7it
Town Hall
(APNa. 175 53 042
175-58-003)
'a
Q� %J
front Rd
51ona Road -i
J Subdivision Project
' (APN:182-10-057)
� m
m
Rd
Natoma Road Project �,od
(APN: 182-10.057) h
82
Town of Los Altos Hills - Parcels Planned for
bevelopmenttRedevelopment
s Parcels Planned for gevelopmenMedevelopment
Town Boundary
Roads
N
creeks
0 0,2 0.4 0.8
Milees
Figure 6-1. Parcels within the Town of los Altos Hill's jurisdiction that are planned for development or
redevelopment with GSI.
The total area of the parcel(s) associated with each location, the estimated amount of impervious
surface that would be addressed by each project, and the milestone by which the project might be
completed are presented in Table 6-1. The existing amount of impervious area in the Town Hall parcels
was estimated using aerial imagery to be approximately 60% of the total area, or 1.71 acres. However, it
33
Resolution 47-19 Page 43
:1I J" GSI ?/tin
was assumed that only half of this existing impervious area (approximately 0.86 acres) would be retrofit
with GSI by 2040. The existing amount of impervious area on the Natoma Road parcel was estimated to
be 0.2 acres based on development plan submittals. The existing amount of impervious area for the
Elena Road Subdivision project was estimated using aerial imagery to be less than 0.1 acres. For both of
these new development projects it was assumed that all existing impervious area would be addressed
by GSI at completion of the project.
The estimated impervious area predicted to be retrofit with GSI by 2020, 2030 and 2040 in the Town of
Los Altos Hills via public and private parcel -based new and redevelopment projects is summarized in
Table 6-1.
Table 6-1. Predicted extent of impervious area to be retrofit via GSI implementation on privately- and publicly -
owned parcels in the Town of Los Altos Hills by 2020, 2030, and 2040.
Project
Total Area (acres)
Existing Impervious Area To Be
Addressed by GSI (acres)9
Milestone for
Construction Completion
Town Hall (APNs: 175-53-
042 and 175-56-003)
2.85
0.86
2040
28030 Natoma Road
(APN:182-10-057)
16
0.2
2030
Elena Road Subdivision
(AP N : 182-02-016)
6
0.1
2040
Total Area by 2018
(existing G51)
0
0
Total Area by 2020
0
0
Total Area by 20302
16
0.2
Total Area by 2040
24.85
1.16
9 Existing impervious area to be addressed by GSI: the existing amount of impervious surface in the Town Hall parcels was
estimated using aerial imagery to be approximately 60% of the total area, or 1.71 acres. However, it was assumed that only half
of this existing impervious surface (approximately 0.86 acres) would be retrofit with GSI by 2040; For Natoma Road the area was
determined using development plan submittals; For Elena Road Subdivision the area was estimated using aerial imagery. For
both of these new development projects it was assumed that all existing impervious area would be addressed by GSI at
completion of the project.
34
Resolution 47-19 Page 44
)Ct i !_� 1:,, ?O I J
6.7 Project Tracking System
A required component of the GSI Plan is to develop a process for tracking and mapping completed
public and private GSI projects and making the information available to the public. The Town will
continue to implement existing internal tracking procedures for processing public and private projects
with GSI, meeting MRP reporting requirements, and managing inspections of stormwater treatment
facilities. In addition, the Town will provide data to SCVURPPP for countywide tracking of completed
public and private GSI projects. This countywide tracking tool will be used to document a project's
pollutant reduction performance as well as overall total progress toward local or county -level
stormwater goals.
6.7.1 Town Project Tracking System (Regulated and GSI)
The Town is following the process described below to collect and track project information:
Information on regulated projects is collected using the SCVURPPP C.3 Data Form. A table
on the project plan sheets is used to collect data on site design or treatment measures
installed for each drainage management area.
Collected information is entered into a spreadsheet. This spreadsheet is updated as the
project moves through the Town's approval process. After the project is constructed, the
spreadsheet is used to manage treatment measure inspections and enforcement actions.
The same spreadsheet will be used to collect and track information on non-regulated GSI
projects.
6.7.2 SCVURPPP Project Tracking System
SCVURPPP has developed a centralized, web -based data management system, with a connection to GIS
platforms, for tracking and mapping all GSI projects in the Santa Clara Valley. The GSI Database provides
a centralized, accessible platform for municipal staff to efficiently and securely collect, upload, and store
GSI project data, and enhances SCVURPPP's ability to efficiently and accurately calculate and report
water quality benefits associated with GSI projects. It also allows portions of the GSI project information
to be made publicly available.
Town staff will collect and manage information on GSI projects locally using the data management
systems described above. Town staff will directly enter project data into the SCVURPPP GSI Database on
an annual basis through a web -based data entry portal for individual projects.
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Resolution 47-19 Page 45