cvEPA
United States
Environmental Protection
Agency
2012 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
Urban Land Conservancy
Denver, Colorado
Conceptual Green Infrastructure Design for the
Blake Street Transit-Oriented Development Site,
City of Denver
Photo: Denver Housing Authority, Park Avenue Development
AUGUST 2013
EPA 830-R-13-002
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, the water is absorbed and filtered by soil and plants. When rain falls on our roofs, streets, and
parking lots, however, the water cannot soak into the ground. In most urban areas, stormwater is
drained through engineered collection systems and discharged into nearby waterbodies. The
stormwater carries trash, bacteria, heavy metals, and other pollutants from the urban landscape,
polluting the receiving waters. Higher flows also can cause erosion and flooding in urban streams,
damaging habitat, property, and infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. At the scale of a city or county, green infrastructure refers to the patchwork of
natural areas that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a
neighborhood or site, green infrastructure refers to stormwater management systems that mimic
nature by soaking up and storing water. These neighborhood or site-scale green infrastructure
approaches are often referred to as low impact development.
EPA encourages the use of green infrastructure to help manage stormwater runoff. In April 2011, EPA
renewed its commitment to green infrastructure with the release of the Strategic Agenda to Protect
Waters and Build More Livable Communities through Green Infrastructure. The agenda identifies
technical assistance as a key activity that EPA will pursue to accelerate the implementation of green
infrastructure.
In February 2012, EPA announced the availability of $950,000 in technical assistance to communities
working to overcome common barriers to green infrastructure. EPA received letters of interest from
over 150 communities across the country, and selected 17 of these communities to receive technical
assistance. Selected communities received assistance with a range of projects aimed at addressing
common barriers to green infrastructure, including code review, green infrastructure design, and cost-
benefit assessments. The Urban Land Conservancy in the City of Denver was selected to receive
assistance identifying green infrastructure opportunities for a 1.44 acre transit-oriented development
site.
For more information, visit http://water.epa.gov/infrastructure/greeninfrastructure/gi support.cfm.
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Acknowledgements
Principal USEPA Staff
Stacey Eriksen, USEPA Region 8
Tamara Mittman, USEPA
Christopher Kloss, USEPA
Community Team
Debra Bustos, Urban Land Conservancy
Cindy Everett, Urban Land Conservancy
Consultant Team
Anne Thomas, Tetra Tech
Jason Wright, Tetra Tech
Erica Hanley, Tetra Tech
October 2012 Housing Colorado's Design by Community Charrette
Harsh Parikh, Parikh Stevens Arch.
Tim Van Meter, Van Meter Williams Pollack, LLC
Fonda Apostolopoulos, CDPHE
James Goodwin, Williams and Co.
Courtland Hyser, City of Denver
Mike Turner, RTD
John Hayden, UC Denver
Patrick Stanley, RTD
Ryan Sagar, UC Denver
Emily Silverman, City and County of Denver
Shannon Haydin, City and County of Denver
Yael Nyholm, Radian
Kevin Larrabee, UC Denver
Chad Holtzinger, OZ Arch
Deirdre Oss, City of Denver
Stacey Eriksen, U.S. EPA
Greg Dorolek, Wenk Associates
Trevor Toms, UC Denver
James Roy II, ULC
Joe Wynn, UC Denver
Kim Allen, UC Denver
Jim Miller, Pinkard Construction
Ken Hoagland, Community Capital
Joshua Radoff, YRNG
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2012 EPA Technical
Assistance Program.
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Contents
1. Introduction 1
2. Report Purpose 3
3. Benefits of Green Infrastructure 4
4. Blake Transit-Oriented Development Site 6
Existing Site Conditions 7
Proposed Site Design 9
5. Goals 10
Project Goals 10
Design Goals 10
1. Peak Flow Control 10
2. Water Quality Control 10
6. Stormwater Management Toolbox 11
Green Infrastructure Practices 11
1. Bioretention Facilities 11
2. Permeable Pavement 14
3. Green Roofs 16
Gray Infrastructure Practices 17
1. Underground Detention/Retention 17
7. Green and Gray Infrastructure Conceptual Design 19
Design Elements 19
Analytical Methods 20
Recommended Sizing and Layout 22
1. Phase 1 23
2. Phase II 26
3. Phase III 29
8. Stormwater Control Measure Technical Specifications 32
9. Operations and Maintenance 32
Bioretention 32
Green Roof 33
Permeable Pavement 34
Underground Detention/Retention 34
10. Stormwater Control Measure Cost Estimates 35
11. Conclusions 39
12. References 40
IV
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Tables
Table 1. Studies Estimating Percent Increase in Property Value from Green Infrastructure 5
Table 2. Comparative Volumetric Unit Costs of Stormwater Control Measures 20
Table 3. Phase I Subcatchment Delineations and Runoff Volumes 21
Table 4. Phase II Subcatchment Delineations and Runoff Volumes 21
Table 5. Phase III Subcatchment Delineations and Runoff Volumes 22
Table 6. Phase I Green Infrastructure Practice Proposed Location and Sizing 24
Table 7. Phase I Green Infrastructure Practice Cross-Sections 24
Table 8. Phase II Green Infrastructure Practice Proposed Location and Sizing 26
Table 9. Phase II Green Infrastructure Practice Cross-Sections 27
Table 10. Phase III Green Infrastructure Practice Proposed Location and Sizing 29
Table 11. Phase III Green Infrastructure Practice Cross-Sections 30
Table 12. Bioretention Operations and Maintenance Considerations 32
Table 13. Green Roof Operations and Maintenance Considerations 33
Table 14. Permeable Pavement Operations and Maintenance Considerations 34
Table 15. Underground Detention/Retention Operations and Maintenance Considerations 34
Table 16. Phase I Cost Estimate 35
Table 17. Phase II Cost Estimate 36
Table 18. Phase III Cost Estimate 37
Figures
Figure 1. Site Location Map 2
Figure 2. Denver Neighborhoods 6
Figures. Blake TOD Site, east side 7
Figure 4. Blake TOD Site, west side 7
Figure 5. Existing Site Conditions 8
Figure 6. Blake TOD Site Phasing 9
Figure 7. Bioretention Incorporated into a Right-of-Way 12
Figure 8. Bioretention Incorporated into Traditional Parking Lot Design 12
Figure 9. Planter Box within Street Right-of-Way 13
Figure 10. Flow-through Planter Box Attached to Building 13
Figure 11. Tree Box Using Grate Inlets in Street 14
Figure 12. Pervious Concrete Parking Stalls 15
Figure 13. Permeable Interlocking Concrete Paver Parking Stalls 15
Figure 14. Extensive Green Roof at EPA Region 8 Headquarters 17
Figure 15. Intensive Green Roof at the Denver Botanic Gardens 17
Figure 16. Green Roof with Fully Contained Trays on a Highly Sloped Roof 17
Figure 17. Examples of Underground Detention Units 18
Figure 18. Phase I Stormwater Control Measure Layout 25
Figure 19. Phase II Stormwater Control Measure Layout 28
Figure 20. Phase III Stormwater Control Measure Layout 31
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1. Introduction
Future Light Rail to Blake TOD Site.
Source: Environmental Evaluation, February 2010.
The Blake Street Transit-Oriented Development
site, commonly referred to as the Blake TOD site,
is located on the northeast fringe of the Five
Points neighborhood at the intersections of 38th
Street, Blake Street, Walnut Street, and Downing
Street (Figure 1). The Five Points neighborhood is
one of Denver's oldest neighborhoods and was
once a thriving district from the 1860's through
the 1950's with local business and renowned jazz
venues.
Since 2008 there has been strong neighborhood
support for a revitalization effort to bring back the
early spirit of the neighborhood, led by the Denver
Office of Economic Development and the Five
Points Business District Office. This effort led to
the development of the Welton Corridor Urban
Redevelopment Plan in 2012 by the Denver
Urban Renewal Authority (DURA). The plan
describes the vision and strategies for rebuilding
and strengthening retail along Welton and
Downing Streets in the heart of the neighborhood. The Blake TOD site presents a unique opportunity for
two of the key strategies in the plan: "Incorporating] sustainable stormwater technologies" and
"Encouraging] Transit-Oriented Development along transit lines and near stations, in order to provide
housing, services and employment opportunities."
The Blake TOD site was acquired by the Urban Land Conservancy (ULC) in 2011. The site is a 1.44-acre
blighted infill site located a few miles north of downtown Denver and directly across the street from the
first station along the future Denver East Corridor commuter rail line on Blake Street (inset map above).
The site is also located several blocks from the South Platte River, and lies within one of five opportunity
areas for redevelopment and reuse identified by the South Platte Corridor Study. The location is ideal for
creating a mixed-use building site to support housing, social services, and employment opportunities.
The development is envisioned as a "cross-road" between the Five Point neighborhood and access to
the future commuter rail line. In addition, ULC is committed to integrating green infrastructure practices
into this urban site to address stormwater quality concerns while simultaneously introducing vegetation
to an otherwise paved landscape.
Urbanization and associated land cover change inhibit many of the processes that drive the natural
hydrologic cycle, including infiltration, percolation to groundwater, and evapotranspiration. Traditional
engineering approaches exacerbate these changes by rapidly conveying stormwater runoff into drainage
systems, discharging higher flows and pollutant loads into receiving waters. As a result, stormwater
runoff from urbanized areas is often a significant source of water quality impairments. In Denver, the
South Platte River quickly becomes degraded as it meanders through the City and County, with large
segments of the river exceeding state pathogen standards.
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0 25 50 100
I Feet
Blake TOD Site
Location Map
TETRATECH
Figure 1. Site Location Map.
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Green infrastructure is an important design strategy for protecting water quality that provides multiple
community benefits. EPA defines green infrastructure as structural or non-structural practices that
mimic or restore natural hydrologic processes within the built environment. Common green
infrastructure practices include permeable pavement, bioretention facilities, and green roofs. These
practices complement conventional stormwater management practices by enhancing infiltration,
storage, and evapotranspiration throughout the built environment and managing runoff at its source.
Implementing green infrastructure concepts on the Blake TOD site will help improve water quality
discharging to the South Platte River, approximately one half mile to the northwest. In addition, it will
enhance the livability of the space by providing a "green" amenity, decreasing urban heat island effects,
and providing an educational opportunity for neighborhood residents and visitors. By identifying
appropriate green infrastructure techniques early in the planning process, this project sought to
seamlessly integrate green infrastructure practices into the revitalization of an urban infill area with
environmental contamination from historical uses. Lessons learned from this project can inform other
revitalization efforts in the Denver area and nationally, demonstrating how transit-oriented infill
projects on potentially contaminated sites can meet water quality and livability objectives as well as
smart growth goals.
2. Report Purpose
The purpose of this report is to provide a conceptual stormwater management design and cost estimate
for the proposed buildings at the Blake TOD site. The proposed buildings and site layout are part of work
done previous to this report and are indicated by the plan-view rendering (Figure 6). The final
stormwater management design should be completed by a stormwater management professional in
conjunction with the final design of the buildings and site.
The conceptual stormwater management design presented herein includes green infrastructure
practices, as much as practicable, to meet the stormwater design criteria. Underground
detention/retention is proposed to supplement the green infrastructure practices in meeting the
criteria.
Stormwater management professionals charged with the stormwater management design for the site
should use the proposed selection, layout, and sizing of the stormwater control measures as an initial
conceptual design. The final design will need to take into account final site/building layout, soil
infiltration rates, and detailed survey information, which will dictate the final layout, sizing, and outlet
control of the proposed stormwater control measures.
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3. Benefits of Green Infrastructure
Green infrastructure can be incorporated into redevelopment sites with relative ease and provides
multiple benefits to the surrounding community. Among the environmental, social, and economic
benefits that green infrastructure can provide are:
Increased enjoyment of surroundings: A large study of inner-city Chicago found that one-third of the
residents surveyed said they would use their courtyard more if trees were planted (Kuo 2003). Residents
living in greener, high-rise apartment buildings reported significantly more use of the area just outside
their building than did residents living in buildings with less vegetation (Hastie 2003; Kuo 2003).
Research has found that people in greener neighborhoods judge distances to be shorter and make more
walking trips (Wolf 2008). Implementing green infrastructure practices that enhance vegetation within
the neighborhood will help to create a more pedestrian-friendly environment that encourages walking
and physical activity.
Increased safety and reduced crime: Researchers examined the relationship between vegetation and
crime for 98 apartment buildings in an inner city neighborhood. The study found the greener a building's
surroundings are, the fewer total crimes (including violent crimes and property crimes), and that levels
of nearby vegetation explained 7 to 8 percent of the variance in crimes reported by building (Kuo
2001a). In investigating the link between green space and its effect on aggression and violence, 145
adult women were randomly assigned to architecturally identical apartment buildings but with differing
degrees of green space. The levels of aggression and violence were significantly lower among the
women who had some natural areas outside their apartments than those who lived with no green space
(Kuo 2001b). The stress-reducing and traffic-calming effects of trees are also likely to reduce road rage
and improve the attention of drivers. Green streets can also increase safety. Generally, if properly
designed, narrower green streets decrease vehicle speeds and make neighborhoods safer for
pedestrians (Wolf 1998; Kuo 2001a).
Increased sense of well-being: There is a large body of literature indicating that green space makes
places more inviting and attractive and enhances people's sense of well-being. People living and working
with a view of natural landscapes appreciate the various textures, colors, and shapes of native plants,
and the progression of hues throughout the seasons (Northeastern Illinois Planning Commission 2004).
Birds, butterflies, and other wildlife attracted to the plants add to the aesthetic beauty and appeal of
green spaces and natural landscaping. "Attention restorative theory" suggests that exposure to nature
reduces mental fatigue, with the rejuvenating effects coming from a variety of natural settings, including
community parks and views of nature through windows. In fact, desk workers who can see nature from
their desks experience 23 percent less time off sick than those who cannot see any nature, and desk
workers who can see nature also report a greater job satisfaction (Wolf 1998).
Increased property values: Many aspects of green infrastructure can potentially increase property
values by improving aesthetics, drainage, and recreation opportunities. These in turn can help restore,
revitalize, and encourage growth in the economically distressed areas. Table 1 summarizes recent
studies that have estimated the effect that green infrastructure or related practices have on property
values. The majority of these studies addressed urban areas, although some suburban studies are also
included. The studies used statistical methods for estimating property value trends from observed data.
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Table 1. Studies Estimating Percent Increase in Property Value from Green Infrastructure
Source
Ward et al. (2008)
Shultz and Schmitz
(2008)
Wachter and Wong
(2006)
Anderson and Cordell
(1988)
Voicu and Been (2008)
Espey and Owasu-Edusei
(2001)
Pincetletal. (2003)
Hobden, Laughton and
Morgan (2004)
New Yorkers for Parks
and Ernst & Young
(2003)
Percent
increase in
Property
Value
3.5 to 5%
0.7 to 2.7%
2%
3.5 to 4.5%
9.4%
11%
1.5%
6.9%
8 to 30%
Notes
Estimated effect of green infrastructure on adjacent
properties relative to those farther away in King County
(Seattle), WA.
Referred to effect of clustered open spaces, greenways and
similar practices in Omaha, NE.
Estimated the effect of tree plantings on property values for
select neighborhoods in Philadelphia.
Estimated value of trees on residential property (differences
between houses with five or more front yard trees and those
that have fewer), Athens-Clarke County (GA).
Refers to property within 1,000 feet of a park or garden and
within 5 years of park opening; effect increases over time
Refers to small, attractive parks with playgrounds within 600
feet of houses
Refers to the effect of an 11% increase in the amount of
greenery (equivalent to a one-third acre garden or park)
within a radius of 200 to 500 feet from the house
Refers to greenway adjacent to property
Refers to homes within a general proximity to parks
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4. Blake Transit-Oriented Development Site
The project site is located on the northeast fringe of the Five Points neighborhood (Figure 2) at the
intersections of 38th Street, Blake Street, Walnut Street, and Downing Street. The neighborhood is about
one mile northeast of downtown Denver. The project site is currently 1.44 acres and is owned by ULC.
There is also interest in coordinating with neighboring property owners for a phased development
within 4 acres of adjacent property. These additional properties extend one block southwest from the
ULC-owned parcels between Downing Street and 36
presented for these properties as well.
th
Street. A conceptual green infrastructure design is
The site is located opposite the future East Corridor rail line at 38th Street and Blake Street. The ULC-
owned property is vacant property with buildings removed (Figure 3 and Figure 4). The current land use
of the adjacent properties include a micro-brewery, liquor store, social club, storage lockers, a small
BMX bike course, and some vacant buildings.
NORTH EAST
Ruby Hill
SOUTH WEST
SOUTH EAST
Figure 2. Denver Neighborhoods.
Source: http://extraextrahomes.com/denver-neighborhoods-property-search/
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Existing Site Conditions
From 1983 until the acquisition of the parcels by the ULC, the Blake TOD site was occupied by a used
truck sales operation that removed and stored truck parts and performed mechanical work on salvaged
trucks. Prior to 1983, the site was used as a trucking operation and as a motor coach terminal operation.
The buildings on the site were recently razed, leaving a concrete slab, asphalt pavement, and compacted
bare soil. With the remaining pavement and compacted soils, the site is effectively 90 percent
impervious. There are currently no stormwater control measures on the site. Runoff flows toward storm
sewer inlets along Blake Street and Walnut Street, which discharge to an 81-inch brick storm sewer
installed under 36th Street and discharging to the South Platte River (Figure 5).
Following acquisition of the site by the ULC, the following assessments were completed:
Updated Phase I Environmental Site Assessment, report dated September 8, 2011
Limited Phase II Environmental Site Assessment (LPIIESA), report dated September 18, 2011
Supplement to the LPIIESA, report dated October 28, 2011
Although surface soil, subsurface soil, and groundwater all contain some degree of contamination
including Perchloroethylene (PCE), benzo(a)pyrene, arsenic, poly-aromatic hydrocarbon (PAH), and lead
(not necessarily due to contaminants from the truck parts operation), it was noted in the LPIIESA that
the surface soils are manageable and could be removed or covered with pavement.
With regard to stormwater management, the main concern, not discussed in the LPIIESA, is whether
infiltration to groundwater will be appropriate given the possibility of transporting contaminates in the
sub-surface soils. Approval for cleanup and reuse would be based on Colorado's Voluntary Cleanup and
Redevelopment program. If infiltration is appropriate, infiltration testing must be performed early in the
design process at each proposed location to account for infiltration in the later design phases.
Figure 3. Blake TOD Site, east side.
Figure 4. Blake TOD Site, west side.
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Legend
Streets
Contours
Water Line
Sanitary
Storm water
Water
0 50 100 200
l Feet
Blake TOD Site
Contours and Utilities
TETRATECH
Figure 5. Existing Site Conditions.
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Proposed Site Design
In October 2012, ULC participated in a Housing Colorado's Design by Community Charrette for the Blake
TOD project. The goal of the design charrette was to develop a site plan for a mixed-use residential
development. The design charrette provided the opportunity for professionals with a wide range of
educational backgrounds including architects, engineers, landscape architects, city planners, and
transportation experts to coordinate and cooperate on the site plan.
The vision for the development was a multi-story mixed-use building situated such that it would draw in
people from the neighborhood as they commuted to the future East Corridor rail line. It was expected
that the upper stories of the building would be reserved for a range of household income levels and the
street-level spaces would be occupied by retail, restaurant, and social services. Green space was to be
incorporated as a visual amenity and also as a place for recreation.
The end result of the charrette was a site development plan meeting the overall vision for the
development. The site plan addressed the parcels owned by ULC as well as 4 acres of additional parcels
that could potentially be developed in the future between Downing Street and 36th Street. The plan was
divided into three phases with the currently-owned parcels making up Phase I and adjacent parcels
making up Phase II and III. ULC would like to reach out to the adjacent parcel owners to share the
conceptual vision of the catalytic development potential shared in this report.
Figure 6 is a plan view of the resulting rendering from the charrette showing buildings, sidewalks, alley,
and street layout for the three phases of the proposed development. The rendering also shows green
space intended to function both as landscaping and stormwater management. Green roofs, roadside
bioretention, and a central green space are included in the drawing. Note the location of the future train
station on Blake Street and street car (i.e. light rail) on 36th Street. More detail on stormwater
management layout is provided in section "Recommended Site Layout."
Legend
Blake TOD Site
Phases
Figure 6. Blake TOD Site Phasing.
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5. Goals
This project is part of a greater urban renewal effort happening around Denver. The ULC works to
preserve real estate to benefit metro Denver communities. The Blake TOD site is one such site that was
strategically acquired to promote a mixed-use community along a transit corridor. This also includes
providing workforce housing and job opportunities within the development. To further the community
benefit of the site and promote environmental stewardship, ULC is also incorporating green
infrastructure.
Project Goals
The overall goal for stormwater management at the site is to restore the hydrologic conditions of the
site prior to development as much as possible while allowing for full site development. The green
infrastructure planned for this project is intended to assist in improving drainage and water quality in
the neighborhood. Secondary goals of the project are to improve the aesthetic appeal of the
neighborhood while maintaining the historic character of the area. These goals will be accomplished
through implementation of permeable pavement, bioretention, and green roofs that enhance
infiltration, evaporation, and detention of stormwater runoff. If infiltration is appropriate at this site
based on Colorado's Voluntary Cleanup and Redevelopment program, infiltration of runoff to
groundwater will be maximized.
Design Goals
Given the dense land use planned for the site, the design will include both traditional
detention/retention practices and green infrastructure practices. Based on outcomes of the design
charrette, the volume of runoff directed to traditional detention/retention practices should be
minimized by first employing green infrastructure to meet the peak flow and water quality design
criteria as much as practicable. Underground detention is strongly discouraged by the City of Denver
due to its tendency to be "out of sight, out of mind" and as a result not regularly maintained.
1. Peak Flow Control
For peak flow control, the goal of this project will be to comply with the City and County of Denver
Storm Drainage Design and Technical Criteria (revised January 2006). To reduce urban drainage
problems and the cost of drainage facilities, the Technical Criteria require on-site detention of the 100-
year storm event for all development and redevelopment projects. For watershed areas less than 10
square miles, a minimum 2-hour storm duration is suggested (UDFCD, Volume 1, RA-3). The maximum
allowable unit release rate for 100-year volumes must be based on the predominant soil type at a site and
ranges from 0.5 to 1.0 cfs/acre (City and County of Denver Storm Drainage Design and Technical Criteria,
Section 13.2)
2. Water Quality Control
For water quality control, the goal of this project will be to provide on-site retention of the 1-year 2-hour
storm event through infiltration and evapotranspiration. The water quality volume requirement is
nested within the peak flow control requirement in that the water quality volume must be retained on-
site while runoff exceeding this amount up to the 100-year 2-hour event must be detained or retained.
10
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The selection of the water quality criterion was an outcome of the charrette process. The criterion is one
of the options to meet the standards for Enterprise Green Communities Criteria, a program which aligns
affordable housing investment strategies with environmentally responsive building practices. The water
quality criterion for Enterprise Green Communities is more stringent than the City's water quality
requirement. Note that the use of infiltration to meet this criterion is dependent on the infiltration
capacity of the soil and the approval of the Colorado Department of Public Health and Environment to
infiltrate stormwater due to the results of the Limited Phase II Environmental Site Assessment.
6. Stormwater Management Toolbox
In order to meet the project and design goals discussed above, the team identified a set of green
infrastructure practices appropriate for the Blake TOD site. These practices manage stormwater at the
source and provide neighborhood amenities by integrating soil and vegetation-based practices into the
planned development.
In addition, the team identified a detention storage practice for project areas in which green
infrastructure could not meet peak flow requirements. While green infrastructure can fulfill both water
quality and peak flow requirements on sites with adequate open space, avoiding the cost of separate
detention facilities, redevelopment projects often pose space constraints that limit the application of
green infrastructure. For infill projects with limited open space, green infrastructure can reduce the size
and cost of required detention facilities, but may not be able to eliminate the need for detention
facilities entirely.
To assist ULC in incorporating green infrastructure practices into the Blake TOD site, the following
discussion addresses constraints and opportunities associated with each stormwater management
practice.
Green Infrastructure Practices
Multiple green infrastructure practices can be incorporated into the development of a site to
complement and enhance the proposed layout while also providing water quality treatment and volume
reduction. The following section describes three common green infrastructure practices that are well-
suited to densely built urban areas.
1. Bioretention Facilities
Bioretention facilities are shallow, depressed areas with a fill soil and vegetation that infiltrate runoff
and remove pollutants through a variety of physical, biological, and chemical treatment processes. The
depressed area is planted with small to medium sized vegetation including trees, shrubs, grasses, and
perennials, and may incorporate a vegetated groundcover or mulch that can withstand urban
environments and tolerate periodic inundation and dry periods. Bioretention may be configured
differently depending on the site context and design goals. This section summarizes general design
considerations for bioretention facilities, and then describes two configurations designed for dense
urban areas: planter boxes and tree boxes. Note that use of these practices within the public right-of-
way will need prior approval from the City of Denver.
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Bioretention is well-suited for removing stormwater pollutants from runoff, particularly for smaller
(water quality) storm events, and can be used to partially or completely meet stormwater management
requirements on smaller sites. Bioretention areas can be incorporated into a development site to
capture roof runoff and parking lot runoff and within rights-of-way to capture sidewalk and street runoff
(Figure 7 and Figure 8).
For unlined systems, maintain a minimum of 5 feet between the facility and a building and at
least 10 feet with a basement.
A surface dewatering time of no greater than 12 hours per UDFCD, Volume 3 either through
infiltration with soils of sufficient percolation capacity or with an underdrain system and outlet
to a drainage system. Use of an underdrain system is very effective in areas with low infiltration
capacity soils.
Planted with native and noninvasive plant species that have tolerance for urban environments,
frequent inundation, and Denver's semi-arid climate.
Inclusion of an overflow structure with a non-erosive overflow channel to safely pass flows that
exceed the capacity of the facility or design the facility as an off-line system.
Inclusion of a pretreatment mechanism such as a grass filter strip, sediment forebay, or grass
swale upstream of the practice to enhance the treatment capacity of the unit.
Figure 7. Bioretention Incorporated into a
Right-of-Way.
Figure 8. Bioretention Incorporated into
Traditional Parking Lot Design.
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Planter Box: Planter boxes are bioretention facilities contained within a concrete box, allowing them to
be incorporated into tighter areas with limited open space. Runoff from a street or parking lot typically
enters a planter box through a curb cut, while runoff from a roof drain typically enters through a
downspout. Planter boxes are often categorized either as flow-through planter boxes or infiltrating
planter boxes. Infiltrating planter boxes have an open bottom to allow infiltration into the underlying
soils. Flow-through planter boxes are completely lined and have an underdrain system to convey flow
that is not taken up by plants to areas that are appropriate for drainage away from building foundations.
Planter boxes are well-suited to narrow areas adjacent to streets and buildings (Figure 9 and Figure 10).
Figure 9. Planter Box within Street
Right-of-Way.
Figure 10. Flow-through Planter Box
Attached to Building.
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Tree Box: Tree boxes are bioretention facilities configured for dense urban areas that use the water-
uptake benefits of trees. They are generally installed along street corridors with curb inlets (Figure 11).
Tree boxes can be incorporated immediately adjacent to streets and sidewalks with the use of a
structural soil, modular suspended pavement, or underground retaining wall to keep uncompacted soil
in its place. Tree boxes typically contain a highly engineered soil media to enhance pollutant removal
while retaining high infiltration rates. The uncompacted media allows urban trees to thrive, providing
shade and an extensive root system for water uptake. For low to moderate flows, stormwater enters
through the tree box inlet and filters through the soil. For high flows, stormwater will bypass the tree
box if it is full and flow directly to the downstream curb inlet.
Figure 11. Tree Box Using Grate
Inlets in Street.
2. Permeable Pavement
Conventional pavement results in increased surface runoff rates and volumes. Permeable pavements, in
contrast, allow streets, parking lots, sidewalks, and other impervious surfaces to retain the underlying
soil's natural infiltration capacity while maintaining the structural and functional features of the
materials they replace. Permeable pavements contain small voids that allow water to drain through the
pavement to an aggregate reservoir and then infiltrate into the soil. If the native soils below the
permeable pavements do not have enough percolation capacity, underdrains can be included to direct
the stormwater to other downstream stormwater control systems. Permeable pavement can be
developed using modular paving systems (e.g., concrete pavers, grass-pave, or gravel-pave) or pour-in-
place solutions (e.g., pervious concrete or permeable asphalt).
Permeable pavement reduces the volume of stormwater runoff by converting an impervious area to a
treatment unit. The aggregate sub-base can provide water quality improvements through filtering and
enhance additional chemical and biological processes. The volume reduction and water treatment
capabilities of permeable pavements are effective at reducing stormwater pollutant loads.
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Permeable pavement can be used to replace traditional impervious pavement for most pedestrian and
vehicular applications. Composite designs that use conventional asphalt or concrete in high-traffic areas
adjacent to permeable pavements along shoulders or in parking areas can be implemented to meet both
transportation and stormwater management needs more cost effectively. Permeable pavements are
most often used in constructing pedestrian walkways, sidewalks, driveways, low-volume roadways, and
parking areas of office buildings, recreational facilities, and shopping centers (Figure 12 and Figure 13).
General guidelines for applying permeable pavement are as follows:
Permeable pavements can be substituted for conventional pavements in parking areas, low-
volume/low-speed roadways, pedestrian areas, and driveways if the grades, native soils,
drainage characteristics, and groundwater conditions of the paved areas are suitable.
Permeable pavement is not appropriate for stormwater hotspots where hazardous materials are
loaded, unloaded, or stored unless the sub-base layers are completely enclosed by an
impermeable liner.
The granular capping and sub-base layers should provide adequate construction platform and
base for the overlying pavement layers.
If permeable pavement is installed over low-permeability soils or temporary surface flooding is a
concern, an underdrain should be installed to ensure water removal from the sub-base reservoir
and pavement.
The infiltration rate of the soils or an installed underdrain should drain the sub-base in 24 to 48
hours.
An impermeable liner can be installed between the sub-base and the native soil to prevent
water infiltration when clay soils have a high shrink-swell potential or if a high water table or
bedrock layer exists.
Measures should be taken to protect permeable pavements from high sediment loads,
particularly fine sediment, to reduce maintenance. Typical maintenance includes removing
sediment with a vacuum truck.
Figure 12. Pervious Concrete Parking Stalls. Figure 13. Permeable Interlocking Concrete
Paver Parking Stalls.
15
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3. Green Roofs
Green roofs introduce vegetation and soil media onto sections of roof tops to reduce imperviousness
and absorb and filter rainfall. At a minimum, a green roof consists of a waterproof membrane and root
barrier system to protect the roof structure, a drainage layer, filter fabric, a lightweight soil media, and
vegetation that filter, absorb, and retain/detain the rainfall. Rainfall that infiltrates into the green roof is
lost to evaporation or transpiration by plants, or, once the soil has become saturated, percolates
through to the drainage layer and is discharged through the roof downspouts. Typically, a green roof is
part of a treatment train with the green roof draining to another stormwater control measure such as a
bioretention cell, bioswale, or cistern. Compared to other green infrastructure practices, they are fairly
expensive, but may be a worthwhile asset if designed to allow human access.
Green roofs may cover large sections of a roof while maintaining access for utilities, maintenance, or
recreation. The green roof design is dictated by the intended use for the space which can range from
serving solely a water quality treatment mechanism, i.e. extensive green roof, to serving as a
recreational space for building tenants, (Figure 14, Figure 15, and Figure 16). The soil media of extensive
green roof systems is typically shallow (i.e. 2 to 6 inches) while the soil media for intensive systems is
deep (i.e. > 6 inches). Green roofs are most often applied to buildings with flat roofs, but can be installed
on roofs with slopes with the use of mesh, stabilization panels, fully contained trays, or battens.
Alternatively, detention on roofs without vegetation (i.e. blue roofs) may be an option as long as the
water drains through a biological filter, such as at ground level.
General guidelines for applying green roofs are as follows:
The building roof must be designed to safely support the saturated weight of the green roof, which
varies depending on the green roof design and manufacturer.
Extensive green roofs, with soil depths of 2 to 6 inches, are most commonly used for stormwater
management.
The soil media for green roofs should be light-weight and largely inorganic.
Plants selected for green roofs should be hardy, self-sustaining, drought-resistant plants able to
withstand daily and seasonal variations in temperature and moisture on rooftops. Typical plants
used for extensive roofs are from the genera Sedum and Delosperma.
At a minimum, a temporary irrigation system should be used to establish plants and ensure success
during drought. This is particularly important in the semi-arid climate of Denver.
A drainage layer installed beneath the green roof routes excess runoff from the roof to the
downspouts.
A root barrier installed below the drainage layer prevents plant roots from damaging structural roof
membranes.
A waterproof membrane is used to prevent transmission of moisture from the green roof to the
structural roof.
An insulation layer between the green roof and structural roof can improve the thermal qualities of
the system.
An optional leak detection membrane can be used to assess the integrity of the waterproof
membranes.
16
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Design Guidelines and Maintenance Manual for Green Roofs in the Semi-Arid and Arid West by Leila
Tolderlund is a local reference for green roofs.
http://www2.epa.gov/sites/production/files/documents/GreenRoofsSemiAridAridWest.pdf
Figure 14. Extensive Green Roof at EPA
Region 8 Headquarters.
(Photo courtesy of Western Solutions.)
Figure 15. Intensive Green Roof at the
Denver Botanic Gardens.
(Photo courtesy of Leila Tolderlund.)
Figure 16. Green Roof with Fully Contained
Trays on a Highly Sloped Roof.
Gray Infrastructure Practices
The Blake TOD site incorporated green infrastructure in all available areas to meet the design criteria
before supplementing with gray infrastructure (in this case underground detention storage) to meet the
peak flow requirements. While underground detention facilities are often more costly on a unit basis
(cost per gallon) than green infrastructure practices, these facilities can save valuable space in space-
limited urban areas. This section discusses design considerations for underground detention/retention
facilities in general and describes the type of detention facility selected for this study.
1. Underground Detention/Retention
Underground detention/retention facilities achieve the capture and temporary storage of stormwater
collected from the tributary drainage area. Curb inlets, surface drains, or overflow from upstream
17
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practices lead stormwater to underground tanks/vaults or systems of large diameter subsurface storage
pipes. The stormwater is then released directly through an outlet pipe back into a stormwater drainage
system or allowed to infiltrate to the groundwater table. The outlet system is designed to meet the
allowable release rates.
Underground detention/retention should not be expected to substantially improve water quality unless
preceded by a pretreatment practice such as a planter box. Underground detention/retention may be
useful for developments where land availability and land costs preclude the development of surface
stormwater control measures and in retrofit and redevelopment settings. Pretreatment is crucial for
minimizing maintenance of the storage unit and should be designed to remove sediment, floatables, and
oils if prevalent in the drainage area. Note that entry into an underground unit typically requires
confined space procedures.
For this conceptual design, large diameter subsurface storage pipes were selected as the detention
storage method. Note that many developments in Denver install more costly underground concrete
tanks/vaults to provide detention storage (Figure 17). The cost savings achieved by implementing green
infrastructure would therefore be greater for a typical design using underground vaults than for the
design described in this study.
Interlocking Plastic Block
Subsurface Pipe Storage
Precast Concrete Vault Cast-in-place Concrete Tank
Figure 17. Examples of Underground Detention Units.
18
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7. Green and Gray Infrastructure Conceptual Design
This section addresses the selection, layout, and design of the stormwater control measures within the
three phases of development of the Blake TOD site. Green infrastructure practices were incorporated
into the proposed site design as much as practicable before supplementing with underground
detention/retention to meet peak flow requirements. While the October charrette provided an initial
proposed layout, the detailed considerations that informed the final design are described in the sections
below.
Design Elements
The selection of green infrastructure practices for the Blake TOD site was guided both by the project
goals and by the physical constraints posed by existing and future conditions. Because this site has
limited available space for stormwater control measures, green infrastructure practices that use vertical
retaining walls rather than gradual side slopes are more applicable in most areas, such as sidewalks and
lanes. Practices with vertical retaining walls include planter boxes, tree boxes, and permeable pavement.
Of the three options, planter boxes and tree boxes were preferred because they include vegetation. In
comparing a planter box and a tree box on the basis of cost per volume of storage, a planter box is more
cost-effective than a tree box, so planter boxes were placed throughout the site to meet the goals of
greening the urban environment while allowing for full site development. Traditional bioretention with
side slopes was used where space allowed.
Where vegetated options were either maximized or not appropriate, permeable pavement was used.
Permeable pavement is easily integrated into paved areas such as parking, sidewalks, or streets without
affecting their use for pedestrian or auto traffic. Visitors would experience no difference between
permeable and conventional pavement, except maybe to see fewer puddles when it rained. On the basis
of cost per volume of storage, permeable pavement is twice the cost of a planter box but still
significantly less than a tree box (Table 2).
Several green roofs were also incorporated in the design during the charrette to aid in improving water
quality and reducing runoff volume and as an amenity to the housing units. In all cases it was assumed
that the green roof would overflow to another stormwater control measure to aid in meeting the design
goals. On the basis of cost per volume of storage, the cost of a green roof is ten times more than that of
permeable pavement (Table 2).
Because of the space constraints of the site, underground detention/retention was also incorporated
into the design to meet peak flow requirements. Although the unit construction cost per volume of
water stored for underground detention/retention is comparable to the unit cost for the planter box,
improving water quality and aesthetic appeal are important project goals that are not achieved by this
stormwater control. Underground detention/retention was therefore placed and sized only after green
infrastructure practices were examined. As there are many types of underground detention/retention
systems, Table 2 provides unit costs of several types for comparison. Large subsurface pipe storage was
the technology envisioned for this conceptual design.
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Table 2. Comparative Volumetric Unit Costs of Stormwater Control Measures.
Stormwater Control Measures
Construction Cost per Volume of Water Stored within
Cross-Section of Practice ($/CF)
Green Infrastructure
Bioretention
Planter Box
Permeable Pavement
Green Roof
Tree Box
$7
$9
$22
$200
$67
Gray Infrastructure
Underground Detention/Retention
Subsurface Pipe Storage (Triton
Stormwater Solutions)
Interlocking Plastic Blocks (Cudo cube)
Cast-in-Place Concrete Tank1
Precast Concrete Vault1
$9
$15
$26
$28
1 The cast-in-place concrete tank cost and the precast concrete vault cost are based on engineering estimates for
construction of a 6,400 cubic foot storage unit. Note that the unit cost of a precast unit is variable depending on how closely
the storage capacity of the manufactured product matches the storage need.
Analytical Methods
A simple volumetric calculation was used to size the green infrastructure practices for each phase of
development. The goal for the sizing of each proposed green infrastructure practice was to contain the
100-year 2-hour storm runoff volume from its tributary drainage area. In some cases, underground
detention/retention was used to supplement the green infrastructure to meet the peak flow
requirement, but the water quality volume from the 1-year 2-hour storm event was, at a minimum, able
to be retained within the green infrastructure practice. During final design, it will be necessary to design
the outlet control such that the 1-year 2-hour storm event, at a minimum, is retained within the
practice.
First, the site was divided into small subcatchments tributary to one or more proposed green
infrastructure practices (Figure 18, Figure 19, and Figure 20). The subcatchment delineation was based
on current architectural renderings (Figure 3-4) and need to be updated as part of the final design.
Rainfall depth was calculated for the 100-year 2-hour storm event (2.98 inches) based on the methods
from the Urban Storm Drainage Criteria Manual, Volume 1, while rainfall depth for the 1-year 2-hour
storm (1.02 inches) was extrapolated from the 2, 5, 10, 25, 50, and 100 year 2-hour rainfall depths.
Runoff coefficients were used to estimate initial abstraction from the subcatchment drainage areas,
most of which consisted of impervious surfaces. Runoff volume from the 100-year 2-hour event for each
subcatchment area was calculated as follows:
Runoff Volume = Subcatchment Area x 100-year Rainfall Depth x Composite Runoff Coefficient
The runoff volume and available physical space were then used to determine surface area and cross-
section of each practice. The storage volume within the bioretention practices took into account surface
20
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storage depth, planting soil depth, aggregate storage depth, and void space ratios of the soil and
aggregate. Permeable pavement storage volume parameters included aggregate storage depth and the
void space ratio.
During final design, stormwater control measure sizes may be reduced by accounting for stormwater
discharging from each practice at the maximum allowable release rate to the City's storm drainage
network along Blake Street and Walnut Street. These storm sewers discharge to the 80-inch brick storm
sewer on 36th Street. The maximum allowable release rate is dependent on the site-specific hydrologic
soil group and is found in Table 13.2 of the City and County of Denver Storm Drainage Design and
Technical Criteria (Revised January 2006). A hydrologic soil analysis will be necessary to determine the
soil characteristics at the proposed stormwater control measure locations.
Table 3, Table 4, and Table 5 include the subcatchment drainage areas, composite runoff coefficients,
and runoff volumes. More detailed information regarding the conceptual sizes of the stormwater
control measures is included in section "Recommended Sizing and Layout".
Table 3. Phase I Subcatchment Delineations and Runoff Volumes.
Subcatchment
01
02
03
04
05
06
Subcatchment
Drainage Area
(sqft)
7,990
13,650
18,900
7,170
8,000
25,000
*- composite
0.90
0.85
0.66
0.85
0.85
0.66
Required Storage
Volume for
1-year, 2-hour Storm
(cuft)
610
990
1,070
520
580
1,400
Required Storage
Volume for
100-year, 2-hour Storm
(cuft)
1,790
2,880
3,120
1,510
1,680
4,080
Table 4. Phase II Subcatchment Delineations and Runoff Volumes.
Subcatchment
01
02
03
04
05
06
07
08
09
10
Subcatchment
Drainage Area
(sqft)
11,950
6,340
6,920
10,240
17,610
4,980
18,830
4,930
8,160
9,110
*- composite
0.89
0.87
0.88
0.89
0.85
0.85
0.85
0.85
0.85
0.85
Required Storage
Volume for
1-year, 2-hour Storm
(cuft)
910
470
520
760
1,280
360
360
360
590
660
Required Storage
Volume for
100-year, 2-hour Storm
(cuft)
2,650
1,370
1,520
2,210
3,720
1,050
3,980
1,040
1,720
1,930
21
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Table 5. Phase III Subcatchment Delineations and Runoff Volumes.
Subcatchment
01
02
03
04
05
06
07
08
09
10
11
Subcatchment
Drainage Area
(sqft)
13,460
6,150
5,000
11,650
5,200
5,250
18,800
6,000
19,350
5,450
9,300
* composite
0.90
0.85
0.85
0.89
0.88
0.87
0.85
0.85
0.85
0.85
0.85
Required Storage
Volume for
1-year, 2-hour Storm
(cuft)
1,030
450
360
880
390
390
1,360
430
1,400
390
670
Required Storage
Volume for
100-year, 2-hour Storm
(cuft)
3,000
1,300
1,050
2,590
1,140
1,140
3,970
1,260
4,080
1,150
1,970
Recommended Sizing and Layout
The conceptual layout and sizing of the green and gray infrastructure practices for each of the project
phases are discussed in this section. Most green infrastructure practices were sized to meet both the
water quality and peak flow criteria described in section "Design Goals" by retaining the 100-year 2-hour
storm event. For some portions of the site, however, retention of the 100-year storm event with green
infrastructure was not feasible given the space constraints, and green infrastructure practices were
designed to retain the water quality storm and overflow to underground detention storage. The cross-
section designs used for the sizing of the green infrastructure practices are in the section on
"Stormwater Control Measure Technical Specifications."
Within the discussion below, note that the water storage volume is the product of the surface area of
the practice and the equivalent storage depth. Equivalent storage depth is the sum of the surface
ponding depth and the product of the void space and applicable underlying layers. The soil layer,
bedding layer, and aggregate storage layer void space are 20 percent, 30 percent, and 40 percent,
respectively. Storage volume indicates the stormwater control measure volume, discounting the
underlying soil infiltration rate, required to meet the design criteria. The cross-section of the final design
can vary from the conceptual design cross-section as long as the water storage volume capacity is
maintained.
The placement of the stormwater control measures across the development is based on the following
routing objectives:
1. Capture adjacent street runoff along the sidewalk, essentially treating right-of-way runoff within
the right-of-way. Outlet to the storm sewer on Walnut Street, Blake Street, and 36th Street.
2. Direct private development runoff including roofs, drives, and walkways to green infrastructure
practices within the development property. For green infrastructure practices able to handle the
100-year storm event volume from the tributary area, discharge the treated runoff to the storm
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sewers on Walnut Street, Blake Street, and 36th Street. For green infrastructure practices not
able to capture the 100-year storm event volume, due to lack of available space, capture the
water quality volume and discharge the overflow to an underground detention system beneath
the building parking lots running under the building terraces.
3. For Phases II and III, construct a storm sewer beneath the lane running parallel to and between
Blake Street and Walnut Street to collect the discharge from the green and gray infrastructure
practices. This storm sewer would discharge to the large 81-inch storm sewer under 36th Street.
It should be recognized that future discussions between stakeholders may result in changes to the
preferred location and sizing of green infrastructure practices based on aesthetics, safety concerns,
constructability, or construction cost.
1. Phase I
Proposed green infrastructure practices for Phase I include a combination of planter boxes, traditional
bioretention, and green roof, providing storage capacity as well as aesthetically-pleasing vegetation. The
runoff from the 100-year 2-hour storm event is able to be stored entirely within these green
infrastructure practices.
Planter boxes are used along Walnut Street and along the entry driveway to the development to capture
road and roof runoff (Subcatchments 01 and 02). They are also used to capture roof runoff between the
building and Blake Street on the northwest side of the building (Subcatchment 04) and terrace runoff
adjacent to the terrace near the driveway (Subcatchment 05).
Traditional bioretention is used around the perimeter of the circular park area and behind the building
along 38th Street where there is more available space. The park area bioretention captures runoff from
the park and surrounding walkway (Subcatchment 03). The bioretention along 38th Street captures
predominately roof runoff and is preceded by a green roof for a portion of the total roof drainage area
(Subcatchment 06).
Refer to Table 6 and Figure 18 for available water storage volume and placement of the green
infrastructure practices, respectively. Table 7 includes the cross-section design for each of the practices.
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Table 6. Phase I Green Infrastructure Practice Proposed Location and Sizing.
Subcatchment
01
02
03
04
05
06
Green
Infrastructure
Practice Type
Planter Box1
Planter Box
Bioretention
Planter Box
Planter Box
Green Roof2,
Bioretention
Location
Sidewalk
Sidewalk
Perimeter
of circular
park
Sidewalk
Adjacent
to
driveway
Open area
behind
building
Width
(ft)
4.5
5
11
4.5
4.5
16
17
Length
(ft)
189
95
261
81
81
50.4
167
Total
Surface
Area
(sqft)
851
452
212
264
475
2,871
729
806
2,839
9,499
Available
Water
Storage
Volume
(cuft)
1,800
2,896
3,184
1,543
1,707
4,081
15,211
Overflow
Volume to
Under-
ground
Detention
(cuft)
0
0
0
0
0
0
0
1 If curbside parking is allowed on this block, pedestrian "bridges" will be needed to cross from the
curbside parking to the sidewalk.
2Subcatchment 06 is partially treated by a green roof draining to the bioretention area.
Table 7. Phase I Green Infrastructure Practice Cross-Sections
Subcatchment
01
02
03
04
05
06
Green
Infrastructure
Practice Type
Planter Box
Planter Box
Bioretention
Planter Box
Planter Box
Bioretention
Location
Sidewalk
Sidewalk
Perimeter of
circular park
Sidewalk
Adjacent to
driveway
Open area
behind
building
Ponding
Depth (inch)
8
8
8
8
8
8
Engineered
Soil Depth
(inch)
18
18
18
18
18
18
Aggregate
Storage Depth
(inch)
30
30
30
30
30
30
24
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Legend
Phases Green Infrastructure Practice
Street Centerline | | Bioretention Area
Subcatchmerits I "1 Green Roof
Planter Box
Blake TOD Site
Stormwater Control Measures
TETRATECH
Figure 18. Phase I Stormwater Control Measure Layout.
25
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2. Phase II
Proposed green infrastructure practices for Phase II include a combination of planter boxes, permeable
pavement, and green roof. A portion of these practices are not able to contain the full 100-year 2-hour
event from each drainage area so underground detention is also provided to supplement these green
infrastructure practices.
Planter boxes are used behind the curb along Walnut Street, a proposed "37th Street", Blake Street, and
the entry driveway to capture primarily road and sidewalk runoff (Subcatchments 01, 02, 03, 04, and
09). The planter boxes along the entry driveway in Subcatchment 09 also capture discharge from a green
roof. These practices are sized to capture the 100-year 2-hour storm event with discharge to the nearest
storm sewers.
Planter boxes are also used to capture just the water quality volume, due to space constraints, from roof
and terrace drainage (Subcatchments 05, 06, 07, and 08). Runoff beyond the 1-year 2-hour volume will
be directed to underground detention located beneath the parking areas, which are beneath the second
floor terraces (Subcatchments 06 and 08). These planter boxes are located adjoined to the building
walls, which means that the building walls will need to be waterproofed. As this water is required to be
retained on-site, the water will need to infiltrate or evapotranspire. Because of its close proximity to the
building, it may be necessary to disperse this water through the aggregate layer beneath the permeable
lane or create an additional subsurface infiltration gallery.
Permeable pavement with subsurface aggregate storage is proposed for the lane (Subcatchment 10).
There is plenty of subsurface storage within the practice to capture the 100-year 2-hour runoff volume
from the lane. The aggregate storage layer depth could be increased to handle discharge from the
planter boxes.
Refer to Table 8 and Figure 19 for available water storage volume and placement of the green
infrastructure practices, respectively. Table 9 includes the cross-section design for each of the practices.
Table 8. Phase II Green Infrastructure Practice Proposed Location and Sizing.
Subcatch-
ment
01
02
03
04
05
06
07
Green
Infrastructure
Practice Type
Planter Box1
Planter Box1
Planter Box1
Planter Box1
Planter Box2
Planter Box2
Planter Box2
Location
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Along
building wall
Along
building wall
Along
building wall
Width
(ft)
5.5
5
5
5
3
3
3
Length
(ft)
225
130
135
215
200
57
215
Surface
Area
(sqft)
1,238
650
675
1,075
600
171
645
Available
Water
Storage
Volume
(cuft)
2,650
1,370
1,435
2,265
1,270
362
1,370
Overflow
Volume to
Under-
ground
Detention
(cuft)
0
0
0
0
2,440
690
2,600
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Subcatch-
ment
08
09
10
Green
Infrastructure
Practice Type
Planter Box2
Green Roof,
Planter Box
Permeable
Pavement
Location
Along
building wall
Green roof
drains to
planter boxes
in sidewalk
Lane
Width
(ft)
3
10
10
10
12
Length
(ft)
57
42
20
20
300
Total
Surface
Area
(sqft)
171
420
200
200
3,600
9,645
Available
Water
Storage
Volume
(cuft)
362
815
2,160
14,060
Overflow
Volume to
Under-
ground
Detention
(cuft)
680
0
0
6,410
1 If curbside parking is allowed on this block, pedestrian "bridges" will be needed to cross from the
curbside parking to the sidewalk.
2The green infrastructure practice treats the 1-yr, 2-hr storm only.
Table 9. Phase II Green Infrastructure Practice Cross-Sections
Subcatch-
ment
01
02
03
04
05
06
07
08
09
10
Green
Infrastructure
Practice Type
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Permeable
Pavement
Location
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Along building
wall
Along building
wall
Along building
wall
Along building
wall
Green roof
drains to planter
boxes in
sidewalk
Lane
Ponding
Depth (inch)
8
8
8
8
8
8
8
8
8
0
Engineered Soil
Depth (inch)
18
18
18
18
18
18
18
18
18
0
Aggregate
Storage Depth
(inch)
30
30
30
30
30
30
30
30
30
18
27
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Legend
Phases Green Infrastructure Practice
Street Centerline | Green Roof
j^^] Subcatchments | | Planter Box
|| 11 11| Planter Box (under Terrace)
| Porous Pavement
Gray Infrastructure Practice
| Underground Detention
WALNUT ST
i nn
0 25 50
100
Ft
Blake TOD Site
Stormwater Control Measures
TETRATECH
Figure 19. Phase II Stormwater Control Measure Layout.
28
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3. Phase III
Proposed green infrastructure practices for Phase III are similar to Phase II and include a combination of
planter boxes, permeable pavement, and green roof. A portion of these practices are not able to contain
the full 100-year 2-hour event from each drainage area so underground detention is also provided to
supplement these green infrastructure practices.
Planter boxes are used behind the curb along Walnut Street, 36th Street, Blake Street, and the proposed
"37th Street" to capture road and sidewalk runoff (Subcatchments 01, 02, 04, 05, and 06). These
practices are sized to capture the 100-year 2-hour storm event with discharge to the nearest storm
sewers.
Planter boxes are also used to capture just the water quality volume, due to space constraints, from roof
and terrace drainage (Subcatchments 07, 08, 09, and 10). Runoff beyond the 1-year 2-hour volume will
be directed to underground detention located beneath the parking areas, which are beneath the second
floor terraces (Subcatchments 10 and 08). These planter boxes are located adjoined to the building
walls, which means that the building walls will need to be waterproofed. As this water is required to be
retained on-site, the water will need to infiltrate or evapotranspire. Because of its close proximity to the
building, it may be necessary to disperse this water through the aggregate layer beneath the permeable
lane or create an additional subsurface infiltration gallery.
Permeable pavement with subsurface aggregate storage is proposed for the lane (Subcatchment 11).
There is plenty of subsurface storage within the practice to capture the 100-year 2-hour runoff volume
from the lane. The aggregate storage layer depth could be increased to handle discharge from the
planter boxes.
Refer to Table 10 and Figure 20 for available water storage volume and placement of the green
infrastructure practices, respectively. Table 11 includes the cross-section design for each of the
practices.
Table 10. Phase III Green Infrastructure Practice Proposed Location and Sizing.
Subcatch-
ment
01
02
03
04
05
06
072
Green
Infrastructure
Practice Type
Planter Box1
Planter Box1
Permeable
Pavement
Planter Box1
Planter Box1
Planter Box1
Green Roof,
Planter Box3
Location
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Along building
wall
Width
(ft)
5
4.5
30
4.5
6
6
3
Length
(ft)
286
136
60
271
90
90
215
Surface
Area
(sqft)
1,430
612
1,800
1,220
540
540
645
Available
Water
Storage
Volume
(cuft)
3,022
1,299
1,080
2,585
1,136
1,143
1,362
Overflow
Volume to
Under-
ground
Detention
(cuft)
0
0
0
0
0
0
2,607
29
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Subcatch-
ment
08
09
10
11
Green
Infrastructure
Practice Type
Planter Box3
Planter Box3
Planter Box3
Permeable
Pavement
Location
Along building
wall
Along building
wall
Along building
wall
Lane
Width
(ft)
3
3
20
3
3
3
12
Length
(ft)
35
35
20
222
60
54
375
Total
Surface
Area
(sqft)
105
105
400
666
180
162
4,500
12,900
Available
Water
Storage
Volume
(cuft)
1,276
1,410
95
95
2,700
17,200
Overflow
Volume to
Under-
ground
Detention
(cuft)
822
2,670
744
0
6,840
1 If curbside parking is allowed on this block, pedestrian "bridges" will be needed to cross from the
curbside parking to the sidewalk.
2The green roof and planter box in Subcatchment 07 treat the water quality volume in parallel prior to
draining to the underground detention.
3 The Green Infrastructure practice treats the 1-yr, 2-hr storm only.
Table 11. Phase III Green Infrastructure Practice Cross-Sections.
Subcatch-
ment
01
02
03
04
05
06
07
08
09
10
11
Green
Infrastructure
Practice Type
Planter Box
Planter Box
Permeable
Pavement
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Planter Box
Permeable
Pavement
Location
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Sidewalk
Along building wall
Along building wall
Along building wall
Along building wall
Lane
Ponding
Depth (inch)
8
8
0
8
8
8
8
8
8
8
0
Engineered
Soil Depth
(inch)
18
18
0
18
18
18
18
18
18
18
0
Aggregate
Storage
Depth
(inch)
30
30
18
30
30
30
30
30
30
30
18
30
-------
Legend
Phases Green Infrastructure Practice
Street Centerline Green Roof
Subcatchments Planter Box
Planter Box (under Terrace)
Porous Pavement
Gray Infrastructure Practice
^^| Underground Detention
Blake TOD Site
Stormwater Control Practices
TETRATECH
Figure 20. Phase III Stormwater Control Measure Layout.
31
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8. Stormwater Control Measure Technical Specifications
As the Denver Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria
Manual, Volume 3 contains extensive design information on bioretention practices, permeable
pavement, green roofs, and underground best management practices, guidance on these practices is
not further addressed in this report.
9. Operations and Maintenance
This section provides recommendations for the maintenance of green and gray infrastructure practices
applicable to the conceptual design at the Blake TOD site. Maintenance tasks and the associated
frequency of the tasks are included for bioretention, green roof, permeable pavement, and
underground detention/retention.
8/oretent/on
Maintenance activities for bioretention are generally similar to maintenance activities for any garden
(Table 12). The focus is to remove trash and monitor the health of the plants, replacing or thinning
plants as needed. Over time, a natural soil horizon should develop which will assist in plant and root
growth. An established plant and soil system will help in improving water quality and keeping the
practice drained. The biological and physical processes over time will lengthen the facility's life span and
reduce the need for extensive maintenance. Irrigation for the landscaped practices may be needed,
especially during plant establishment periods or in periods of extended drought. Irrigation frequency will
depend on the season and type of vegetation. Native plants often require less irrigation than non-native
plants.
Table 12. Bioretention Operations and Maintenance Considerations.
Task
Monitor infiltration
and drainage
Pruning
Mowing
Mulching
Mulch removal
Frequency
1 time/year
1-2 times/year
2-12 times/year
1-2 times/ year
1 time/2-3 years
Maintenance notes
Inspect drainage time (12 hours). Might have to
determine infiltration rate (every 2-3 years).
Turning over or replacing the media (top 2-3
inches) might be necessary to improve infiltration
(at least 0.5 in/hr).
Nutrients in runoff often cause bioretention
vegetation to flourish.
Frequency depends on the location, plant selection
and desired aesthetic appeal.
Recommend maintaining l"-3" uniform mulch
layer.
Mulch accumulation reduces available water
storage volume. Removal of mulch also increases
surface infiltration rate of fill soil.
32
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Task
Watering
Fertilization
Remove and replace
dead plants
Inlet inspection
Outlet inspection
Underdrain inspection
Miscellaneous upkeep
Frequency
1 time/2-3 days for first
1-2 months; sporadically
after establishment
1 time initially
1 time/year
Once after first rain of the
season, then monthly
during the rainy season
Once after first rain of the
season, then monthly
during the rainy season
Once after first rain of the
season, then yearly
during the rainy season
12 times/year
Maintenance notes
If drought conditions exist, watering after the initial
year might be required.
One-time spot fertilization for first year vegetation.
Within the first year, 10% of plants can die. Survival
rates increase with time.
Check for sediment accumulation to ensure that
flow into the retention area is as designed. Remove
any accumulated sediment.
Check for erosion at the outlet and remove any
accumulated mulch or sediment.
Check for accumulated mulch or sediment. Flush if
water is ponded in the bioretention area for more
than 12 hours.
Tasks include trash collection, plant health, spot
weeding, and removing mulch from the overflow
device.
Green Roof
Similar to bioretention maintenance tasks, monitoring the health of the plants is necessary (Table 13). In
areas having a semi-arid climate, such as Denver, it is recommended to install a rooftop irrigation system
to use for plant establishment and in times of drought. Green roofs must also be inspected regularly for
signs of leaks. The proactive removal of roots, leaves, rocks, and debris from features that penetrate the
roof is essential.
Table 13. Green Roof Operations and Maintenance Considerations.
Task
Inspection of features
penetrating roof
Inspection of drains
and rooftop structures
Vegetation upkeep
Irrigation
Frequency
3 times per year
3 times per year and after
major storm events
Twice per year in spring
and fall
As needed
Maintenance notes
Inspect all joints, borders, abutting vertical walls,
roof vent pipes, outlets, air conditioning units and
perimeter areas. Remove roots, leaves, rocks and
debris.
Remove vegetation and debris. Ensure drainage
pathways are clear.
Weed vegetation and remove and replace
unsuccessful or diseased plants. Replant bare spots
in the soil. Fertilization may also be required.
Water vegetation as necessary during
establishment and drought. Flush out irrigation
system before the first winter freeze.
33
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Permeable Pavement
The primary maintenance requirement for permeable pavement consists of regular inspection for
clogging and sweeping with a vacuum-powered street sweeper (Table 14). If interlocking concrete
permeable pavers are installed, the small aggregate used to fill the void between pavers must be
replaced following vacuum sweeping.
Table 14. Permeable Pavement Operations and Maintenance Considerations.
Task
Impervious to Pervious
interface
Vacuum street
sweeper
Replace fill materials
(applies to pervious
pavers only)
Miscellaneous upkeep
Frequency
Once after first rain of the
season, then monthly
during the rainy season
Twice per year as needed
1-2 times per year (and
after any vacuum truck
sweeping)
4 times per year or as
needed for aesthetics
Maintenance notes
Check for sediment accumulation to ensure that
flow onto the permeable pavement is not
restricted. Remove any accumulated sediment.
Stabilize any exposed soil.
Portions of pavement should be swept with a
vacuum street sweeper at least twice per year or as
needed to maintain infiltration rates.
Fill materials will need to be replaced after each
sweeping and as needed to keep voids with the
paver surface.
Tasks include trash collection, sweeping, and spot
weeding.
Underground Detention/Retention
As underground facilities are out of sight, it is critical to establish regularly scheduled maintenance of
these facilities to ensure proper functioning (Table 15). Key maintenance tasks include regular
inspection of the inlet and outlet and removal of sediment and debris. Other maintenance tasks may be
necessary according to the manufacturer's recommendation.
Table 15. Underground Detention/Retention Operations and Maintenance Considerations.
Task
Inlet and outlet
inspection
Manufacturer's
recommended
maintenance.
Frequency
Once after first rain of the
season, then monthly
during the rainy season
Variable
Maintenance notes
Check for debris and sediment accumulation to
ensure that flow into and out of the
detention/retention facility is as designed. Remove
any accumulated debris and sediment using catch
basin cleaning equipment (vacuum pumps).
Other maintenance duties may be necessary
depending on the type and manufacturer of the
underground detention/retention system.
34
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10. Stormwater Control Measure Cost Estimates
Estimated costs for green and gray infrastructure proposed at the Blake TOD site are included in the
tables in this section. Table 16, Table 17, and Table 18 include costs for green and gray infrastructure for
Phase I, Phase II, and Phase II, respectively. The costs are for the construction of stormwater control
measures and do not account for site preparation, mobilization, utility removal/rerouting, soil erosion
control measures during construction, or any costs that would be part of the overall site development. It
is also assumed that all construction is new and not retrofit.
When considering the cost of green infrastructure practices using the totals below, note that the costs
for some of the materials would, to a certain extent, be incurred regardless of whether the practice
were installed or not. For example, in locations where permeable pavement is installed, such as in the
sidewalk and lane, a pavement type would have had to be installed if the permeable pavement were
not. Because of this and because the many indirect monetary benefits often associated with green
infrastructure were not included in the cost estimate, these costs should not be used to directly
compare green and gray infrastructure costs. Indirect monetary benefits may include a decrease in
energy use due to a green roof or shade tree, reduction of air pollution due to trees, and increase in the
value of real estate due to aesthetics. Refer to "The Value of Green Infrastructure" developed by the
Center for Neighborhood Technology and American Rivers for more information regarding the indirect
benefits of green infrastructure (CNT, 2010).
Table 16. Phase I Cost Estimate.
Item
No
Description
Quantity
Unit
Unit Cost
Total
GREEN INFRASTRUCTURE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Traditional Bioretention
Fine Grading
Excavation (includes hauling)
Soil Media
Filter Layer (sand and No. 8 stone)
Drainage Layer (Open graded aggregate)
Underdrains (4" perforated PVC pipe)
Outlet Control Structure (24-inch catch basin)
Cored opening, 4-inch
Native Seed
Mulch
Cleanout, PVC
SCM Sub-Total Cost
Planter Box
Fine Grading
Excavation (includes hauling)
Vertical Concrete Curbl
Soil Media
Filter Layer (sand and No. 8 stone)
5710
540
180
48
242
600
5
2
5710
53
5
3754
649
1253
209
46
SF
CY
CY
CY
CY
LF
EA
EA
SF
CY
EA
SF
CY
LF
CY
CY
$0.72
$10
$40
$45
$50
$5.50
$1,000
$500
$1.11
$45
$70
$0.72
$10
$15
$40
$45
$4,111
$5,405
$7,205
$2,177
$12,111
$3,300
$5,000
$1,000
$6,338
$2,379
$350
$49,377
$2,703
$6,488
$18,792
$8,342
$2,085
35
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Item
No
17
18
19
20
21
22
23
24
Description
Drainage Layer (Open graded aggregate)
Underdrains (4" perforated PVC pipe)
Outlet Control Structure (24-inch catch basin)
Cored opening, 4-inch
Native Seed
Mulch
Cleanout, PVC
SCM Sub-Total Cost
Green Roof
Green Roof (extensive) (includes
waterproofing, modular system, irrigation,
and 2 years of maintenance)
Quantity
348
750
8
4
3754
35
8
2358
Unit
CY
LF
EA
EA
SF
CY
EA
SF
Unit Cost
$50
$5.50
$1,000
$500
$1.11
$45
$70
$20
Sub-total Cost
Construction contingency (20% of subtotal)
Total Cost
Total
$17,379
$4,125
$8,000
$2,000
$4,167
$1,564
$560
$76,206
$47,160
$172,742
$34,548
$208,000
1 When planter boxes are installed adjacent to infrastructure such as roads and buildings, it is necessary to
provide separation between the road or building subsoils and the planter box soils. Use of a 2-foot deep vertical
concrete curb is common, but a geotechnical investigation is necessary in the planter box locations to determine
if expansive soils exist. If expansive soils exist, an impermeable barrier to the bottom of the planter box facility
may be warranted.
Table 17. Phase II Cost Estimate.
Item
No
Description
Quantity
Unit
Unit
Cost
Total
GREEN INFRASTRUCTURE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Planter Box
Fine Grading
Excavation (includes hauling)
Vertical Concrete Curb1
Soil Media
Filter Layer (sand and No. 8 stone)
Drainage Layer (Open graded aggregate)
Underdrains (4" perforated PVC pipe)
Outlet Control Structure (24-inch catch basin)
Cored opening, 4-inch
Native Seed
Mulch
Cleanout, PVC
SCM Sub-Total Cost
Permeable Pavement
Permeable Pavement
Excavation (includes hauling)
4,804
830
2,023
267
59
445
1,300
4
5
4,804
44
9
3,600
200
SF
CY
LF
CY
CY
CY
LF
EA
EA
SF
CY
EA
SF
CY
$0.72
$10
$15
$40
$45
$50
$5.50
$1,000
$500
$1.11
$45
$70
$12
$10
$3,459
$8,304
$30,351
$10,676
$2,669
$22,242
$7,150
$4,000
$2,500
$5,333
$2,002
$630
$99,316
$43,200
$2,000
36
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Item
No
15
16
17
18
19
20
21
Description
Bedding Layer (washed No. 8 stone, 3 inches)
Base Layer (washed No. 56 aggregate)
Concrete Transition
Underdrains (4" perforated PVC pipe)
Cored opening, 4-inch
Cleanout, PVC
SCM Sub-Total Cost
Green Roof
Green Roof (extensive) (includes
waterproofing, modular system, irrigation,
and 2 years of maintenance)
Quantity
33
200
624
314
1
3
3,133
Unit
CY
CY
LF
LF
EA
EA
SF
Unit
Cost
$40
$50
$4
$5
$500
$70
$20
Total
$1,333
$10,000
$2,496
$1,570
$500
$210
$61,309
$62,660
GRAY INFRASTRUCTURE
22
23
24
Underground Detention/Retention
Triton Stormwater Solutions Chambers
(includes labor and material costs)
New Storm Sewer in Lane
12-inch RC Pipe (includes Exc. and backfill)
48-inch Manholes (includes Exc. and backfill)
SCM Sub-Total Cost
Sub-total Cost
Construction contingency (20% of subtotal)
Total Cost
8,400
314
3
CF
LF
EA
$9
$65
$2,600
$75,600
$20,410
$7,800
$28,210
$327,096
$65,419
$393,000
1 When planter boxes are installed adjacent to infrastructure such as roads and buildings, it is necessary to
provide separation between the road or building subsoils and the planter box soils. Use of a 2-foot deep vertical
concrete curb is common, but a geotechnical investigation is necessary in the planter box locations to determine
if expansive soils exist. If expansive soils exist, an impermeable barrier to the bottom of the planter box facility
may be warranted.
Table 18. Phase III Cost Estimate.
Item
No
Description
Quantity
Unit
Unit
Cost
Total
GREEN INFRASTRUCTURE
1
2
3
4
5
6
7
8
9
Planter Box
Fine Grading
Excavation (includes hauling)
Vertical Concrete Curbl
Soil Media
Filter Layer (sand and No. 8 stone)
Drainage Layer (Open graded aggregate)
Underdrains (4" perforated PVC pipe)
Outlet Control Structure (24-inch catch basin)
Cored opening, 4-inch
4,735
818
2,201
263
58
438
1,300
4
5
SF
CY
LF
CY
CY
CY
LF
EA
EA
$0.72
$10
$15
$40
$45
$50
$5.50
$1,000
$500
$3,409
$8,184
$33,020
$10,522
$2,630
$21,921
$7,150
$4,000
$2,500
37
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Item
No
10
11
12
13
14
15
16
17
18
19
20
21
Description
Native Seed
Mulch
Cleanout, PVC
SCM Sub-Total Cost
Permeable Pavement
Permeable Pavement
Excavation (includes hauling)
Bedding Layer (washed No. 8 stone, 3 inches)
Base Layer (washed No. 56 aggregate)
Concrete Transition
Underdrains (4" perforated PVC pipe)
Cored opening, 4-inch
Cleanout, PVC
SCM Sub-Total Cost
Green Roof
Green Roof (extensive) (includes
waterproofing, modular system, irrigation,
and 2 years of maintenance)
Quantity
4,735
44
9
5,510
350
51
306
1,022
504
2
3
14,900
Unit
SF
CY
EA
SF
CY
CY
CY
LF
LF
EA
EA
SF
Unit
Cost
$1.11
$45
$70
$12
$10
$40
$50
$4
$5
$500
$70
$20
Total
$5,256
$1,973
$630
$101,195
$66,120
$3,500
$2,041
$15,306
$4,088
$2,520
$1,000
$210
$94,784
$298,000
GRAY INFRASTRUCTURE
22
23
24
Underground Detention/Retention
Triton Stormwater Solutions Chambers
(includes labor and material costs)
New Storm Sewer in Lane
12-inch RC Pipe (includes Exc. and backfill)
48-inch Manholes (includes Exc. and backfill)
SCM Sub-Total Cost
8,050
384
3
CF
LF
EA
$9
$65
$2,600
Sub-total Cost
Construction contingency (20% of subtotal)
Total Cost
$72,446
$24,960
$7,800
$32,760
$599,185
$119,837
$720,000
When planter boxes are installed adjacent to infrastructure such as roads and buildings, it is necessary to provide
separation between the road or building subsoils and the planter box soils. Use of a 2-foot deep vertical concrete
curb is common, but a geotechnical investigation is necessary in the planter box locations to determine if
expansive soils exist. If expansive soils exist, an impermeable barrier to the bottom of the planter box facility may
be warranted.
38
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11. Conclusions
The conceptual stormwater management design developed for the Blake Transit Oriented Development
site demonstrates how green infrastructure approaches can complement smart growth principles -
providing innovative stormwater management while accommodating infill, transit oriented
development.
The Blake TOD site is an assemblage of six properties in Denver's Five Points neighborhood acquired by
the Urban Land Conservancy with the goal of providing affordable homes close to a major transit line.
The site is several blocks from the South Platte River, and less than one block from the first station along
the planned East Corridor Commuter Rail Line. Recognizing the opportunity to achieve multiple
environmental and livability goals by addressing green infrastructure early in the planning process, the
Urban Land Conservancy sought technical assistance from EPA. Based on the project and design goals,
an EPA team developed a conceptual stormwater management design that would complement and
enhance the planned transit-oriented development.
The final conceptual design achieved the project goals of improving drainage, water quality, and
aesthetic appeal with a combination of bioretention, permeable pavement, green roofs, and detention
storage. In conventional redevelopment projects, peak flow requirements are met by installing single-
purpose gray infrastructure controls (typically underground detention vaults). The conceptual design
developed for this project, in contrast, used multi-functional green infrastructure techniques to provide
some peak flow control, improve water quality, and add amenities to the site. The conceptual design
includes:
Bioretention practices on the private site as well as within the public right-of-way
Permeable pavement in the "lane" between buildings and within the sidewalk
Green roofs to capture and treat stormwater in locations accessible to residents
As cities and towns seek to revitalize historic neighborhoods and redirect growth into existing urban
areas, green infrastructure can complement redevelopment efforts. In addition to meeting stormwater
management goals, this conceptual design illustrates how green infrastructure can help create a more
attractive and livable landscape that weaves functional natural elements into the built environment.
39
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