SUSTAINABLE MAPLEWOOD 2050: Impervious Surfaces

SUSTAINABLE MAPLEWOOD 2050:
Impervious Surfaces & Stormwater Management
Environmental Science, Policy and Management 4041
Report 1/8 Prepared for:
The City of Maplewood
Prepared by:
Marc Thurow (leader)
Catherine Bach
Sam Bevins
Katrina Hill
Erik Joerres
Whitney Olson
December 11, 2008
University of Minnesot
Acknowledgements
We would like to give a special thanks to all who helped us along the way to the
completion of our project in working toward a more sustainable Maplewood.
Steve Kummer – Public Works Engineer, City of Maplewood
Ginny Gaynor – Open Space Naturalist, City of Maplewood
Shann Finwall – Environmental Planner, City of Maplewood
DuWayne Konewko – Deputy Director of Public Works, City of Maplewood
Michael Goodnature – Conservation Specialist, Ramsey Conservation District
Ryan Johnson – Urban BMP Specialist, Ramsey Conservation District
Ron Leaf – Stormwater Consultant, SEH, Inc.
Kristen Nelson – Professor, University of Minnesota
Beth Nixon – Wetlands Scientist, Emmons and Olivier Resources, Inc.
Tom Ritzer – University of Minnesota, Twin Cities Campus, Landscape Architect
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Executive Summary
The City of Maplewood recently began an initiative to become a more sustainable
community by the year 2050. To that end, the City of Maplewood is encouraging
sustainability and stewardship by promoting the efficient use of land through low-impact
development, stormwater best management practices, and the protection of natural
resources. The University of Minnesota’s senior capstone course (Problem Solving for
Environmental Change) worked with the city upon invitation from September 2008 to
December 2008 to help Maplewood achieve this goal. This report summarizes the
following.
Objectives
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Perform a thorough inventory of the impervious surface area in the Maplewood Mall
Commercial Area
Determine existing mitigation practices being used to management stormwater runoff
in the Maplewood Mall Commercial area
Identify local examples of Best Management Practices (BMPs) that illustrate the
recommendations for stormwater management
Develop a primer outlining green design options that utilize the principles of Low
Impact Development of land management for sustainable infrastructure
Methods
Research was conducted on the study area site to take visual inventory of existing
structures and stormwater management practices. Detailed spatial analysis about the
study area was obtained from the use of geographical information system (GIS) software,
which allowed for the accurate assessment of the impervious surfaces.
Findings
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Percent Impervious Surface of Entire Study Area: 62%
Percent Impervious Surface of Maplewood Mall: 91%
Percent Impervious Surface of Strip Mall: 90%
Percent Impervious Surface of Nightclub: 86%
Recommendations
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Stormwater Management and Impervious Surface Primer
- An implementation tool designed to guide urban developers and city planners on
the use of various green building options designed to mitigate the effects of
impervious surfaces and development on surrounding ecosystems.
On-site stormwater management
- Infiltration vs. traditional drainage
- Infiltration practices: rain gardens, filter strips, and swales
- Traditional practices: direct runoff to storm sewer
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•
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Green Building Design
- Buildings and features specifically designed to utilize to use natural resources
more efficiently
- Leadership in Energy and Environmental Design (LEED)® building certification
- Structural Soils
- Manufactured soil that promotes healthy tree growth and stormwater
infiltration
- Vertical structures (parking ramps)
- Above ground and below ground infiltration/storage (cisterns)
- Structural support for green roof
Overall reduction of impervious surface
- Increase green space with more vegetative cover
- Reduce amount of impervious surface by 25 percent
Cost Share Programs
- Ramsey-Washington Metro Watershed District (RWMWD)
- Minnesota Board of Water and Soil Resources (BWSR)
- Soil and Water Conservation Districts (SWCDs)
Stormwater Ordinance
- Implementation would greatly increase compliance with local, state, and federal
stormwater management requirements, as well as contribute to Maplewood’s
vision of sustainability
- Model stormwater ordinances in Metropolitan Council’s Urban Small Sites BMP
Manual
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Table of Contents
List of Figures ...........................................................................................................vi
Introduction................................................................................................................1
Vision Statements .................................................................................................1
Goals and Objectives ...........................................................................................2
Study Area Description..............................................................................................3
Maplewood Mall...................................................................................................3
Strip Mall ..............................................................................................................3
Standalone Business—Nightclub..........................................................................4
Methods......................................................................................................................4
Inventory of Impervious Surfaces.........................................................................4
Findings......................................................................................................................6
Impervious Inventory for Study Area ...................................................................6
Impervious Inventory for Maplewood Mall Case Study ......................................7
Impervious Inventory for Strip Mall Case Study..................................................7
Impervious Inventory for Nightclub Case Study ..................................................8
Storm Sewer Layout .............................................................................................9
Water Quality Concerns in Receiving Waters ......................................................10
Environmental Utility Fees ...................................................................................10
Recommendations......................................................................................................10
On-site Stormwater Management .........................................................................11
Green Building Design .........................................................................................11
Overall Reduction of Impervious Surface ............................................................13
Cost Share Programs.............................................................................................14
Storm Ordinance ...................................................................................................15
Case Study Recommendations—Maplewood Mall ..............................................16
Case Study Recommendations—Strip Mall .........................................................18
Case Study Recommendations—Nightclub..........................................................20
Discussion ..................................................................................................................21
Positive Effects on Consumer Behavior`..............................................................22
Example of Stormwater Management: University of Minnesota
Landscape Arboretum......................................................................................22
Example of Stormwater Management: Oregon Museum of Science and
Industry ............................................................................................................23
Example of Stormwater Management: HB Fuller—Vadnais Heights, MN ........24
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Conclusion .................................................................................................................25
References..................................................................................................................35
Appendices.................................................................................................................29
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List of Figures
Figure 1. Location of Maplewood in the Metro area ................................................2
Figure 2. Study Area .................................................................................................4
Figure 3. Impervious surface (gray) within the study area. The remaining area
is pervious surface (green) ....................................................................................6
Figure 4. Impervious surface (pink) within the Maplewood Mall case study
area. The remaining area is pervious surface (green) ..........................................7
Figure 5. Impervious surface (pink) within the strip mall case study area,
The remaining area is pervious surface (green)....................................................8
Figure 6. Impervious surface (pink) within the nightclub (individual business)
case study area. The remaining area is pervious surface (green).........................9
Figure 7. Structural Soil diagram..............................................................................13
Figure 8. Sources of phosphorus pollution in the RWMWD....................................14
Figure 9. Maplewood Mall Recommendations.........................................................16
Figure 10. Strip Mall Recommendations ..................................................................18
Figure 11. Nightclub Case Study Recommendations ...............................................20
Figure 12. Runoff Model Demonstration Project at the U of M Landscape
Arboretum, Chaska, MN.......................................................................................23
Figure 13. Rain gardens along curbless parking lot at the U of M Landscape
Arboretum in Chaska, MN....................................................................................23
Figure 14. OMSI Parking Lot Bioswale ...................................................................24
Figure 15. Green Parking Lot Design: Rain garden in median................................25
Figure 16. Composition of a green roof....................................................................32
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Introduction
The City of Maplewood is a first ring suburb of St. Paul, Minnesota, located in the
southeast portion of Ramsey County. It is bordered by 11 municipalities (Oakdale, Little
Canada, Vadnais Heights, White Bear Lake, North St. Paul, St. Paul, Woodbury, Gem
Lake, Newport, Roseville, and Landfall). In 2000, the population of Maplewood was
34,947 people US Census Bureau, 2000) and the median annual household income was
$51,596, which was 112.8 percent of the Ramsey County median income (City of
Maplewood, 2008). In the past, the city has shown faster population growth rates than
the county as a whole, and it is estimated that the population of Maplewood will increase
by 2,903 people between 2006 and 2030 (US Census Bureau, 2000). The majority of the
city’s land area is currently developed.
The City of Maplewood recently began an initiative to become a more sustainable
community by the year 2050. It supports the proposals of the US Conference of Mayors
Climate Protection Agreement, which is an initiative started by Seattle Mayor Greg
Nickels to address the issues of climate change in cities across the United States (The
United States Conference of Mayors, 2008). With this agreement, mayors commit to
reduce emissions in their cities to seven percent below 1990 levels by 2012. The city of
Maplewood is encouraging sustainability and stewardship by promoting the efficient use
of land through Low Impact Development (LID), storm water best management
practices, and the protection of natural resources (City of Maplewood, 2008). These
themes prevail in the nearly completed 2008 Comprehensive Plan.
The city of Maplewood invited students from the University of Minnesota College of
Food, Agriculture, and Natural Resource Sciences (CFANS)—specifically from the
Problem Solving for Environmental Change capstone class—to help develop a plan for a
more sustainable community by 2050. The City of Maplewood has a goal of becoming a
model of sustainability for their residents and surrounding communities.
The focus of this report-under the goal of improving the sustainability of the city—is to
improve the quality of the city’s water bodies through the management of stormwater
runoff.
Vision Statements
Maplewood Sustainability Vision Statement:
“The City of Maplewood, in order to ensure stewardship of its environment, will promote
sustainable development and practices for the preservation, design and maintenance of its
natural and built environments. Developments and practices should maintain or enhance
economic opportunity and community well-being while protecting and restoring the
natural environment that people, economies, and ecological systems depend on.”
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Figure 1. Location of Maplewood in the Metro area (Wikimedia Commons, 2008).
Class Vision Statement:
“We are committed to working with the City of Maplewood to assist them in achieving
their vision of a sustainable community. We share their goal of using innovative
solutions to improve and preserve environmental integrity while promoting economic
opportunity and community well-being for current and future generations.”
Group Vision Statement:
“We are committed to assisting the City of Maplewood in the reduction of impervious
surface and the mitigation of stormwater to improve local water quality. To achieve this
vision, sustainable design options will be introduced for new and existing developments
in the Maplewood Mall commercial area.”
Goals and Objectives
The objective of this project is to develop a set of recommendations that best mitigate
stormwater runoff and reduce impervious surface area by creating site designs specific
for sub-sets of the study area. The recommendations will be based on the comparison of
Best Management Practices (BMPs) and current ordinances and policies.
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Perform a thorough inventory of the impervious surface area in the Maplewood Mall
Commercial Area
Determine existing mitigation practices being used to management stormwater runoff
in the Maplewood Mall Commercial area
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List recommendations for impervious surfaces and stormwater management
Simulate the implementation of recommendations on three case study sites (an
individual business, a strip mall, and the Maplewood Mall)
Identify local examples of BMPs that illustrate the recommendations for stormwater
management
Develop a primer outlining green design options that utilize the principles of Low
Impact Development of land management for sustainable infrastructure.
Study Area Description
The study area for this project (Figure 2) focuses on a large swath of land in the
Maplewood Mall commercial area. An impervious surface is one that does not allow the
passing of water through it, particularly rainfall, and therefore generates surface runoff.
Roads, buildings, and sidewalks are all considered impervious because they do not allow
infiltration of rainwater into the soil. Urban areas typically have high percentages of
impervious surface, creating large amounts of stormwater runoff to be managed.
The study site encompasses the area along Highway 61 from Beam Avenue, north to
County Road D, then extends east to White Bear Avenue. The site was chosen because it
is the commercial hub of Maplewood, centered around the Maplewood Mall. A vast
majority of the study area has been developed or is planned for future development,
which makes the site an important piece of the overall “Sustainable Maplewood” project.
The authors of this report divided the Maplewood commercial area into three different
case study sites to help make better recommendations for specific sustainable
modifications. It is a goal that businesses in the immediate area could easily implement
these practices based on the case studies. The sites chosen were the Maplewood Mall
complex itself, the strip mall directly to the west of the mall and The Myth, a small outer
lying business with large percentages of impervious surface.
Maplewood Mall
The first study location is the Maplewood Mall. The mall is located west of White Bear
Avenue and two blocks south of I-694. The mall encompasses 931,000 square feet of
space and has approximately 10 million shoppers annually (Simon Property Group, Inc.,
2008). The Maplewood Mall was first built in 1974 and last renovated in 1998. The mall
is considered a Super-Regional Mall, with five main anchor stores including Macy’s and
Sears. Due to its size, the amount of people that visit the mall, and the vast amount of
impervious surface surrounding the mall it is a significant area to address in order to meet
the “Sustainable Maplewood Vision.”
Strip Mall
The second study area focus is the Birch Run Station strip mall just west of the
Maplewood Mall Complex. It is bordered by Beam Ave to the south, Southlawn Road to
the east, Kennard Street to the west, and an open wooded area with trails that connects to
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the Legacy Village Mixed Use Development to the north. The strip mall itself is an Lshaped building built in 1989, and has an area of 278,000 square feet excluding the
parking lot (RPD Catalyst LLC, 2008).
Standalone Business - Nightclub
The third study area is the Myth nightclub, a single business located along the outer ring
of the mall area. The Myth is a 36,000 square foot nightclub located on the corner of
Southlawn Drive and County Road D (Myth Nightclub, 2008). The Myth nightclub is
used to host an array of events including parties, public or private and also dance events
with live DJ’s from around the world. The area the Myth occupies mainly consists of
parking lot and the building structure itself. By analyzing a single business like the Myth,
the results of this study can be taken and used by any other similar business in the area.
Figure 2. Study Area
Methods
Inventory of Impervious Surfaces
One of the purposes of this study was to assess the amount of impervious surface in the
Maplewood Mall commercial area to address stormwater runoff issues. The report
focused on three main case study areas: the Maplewood Mall, the adjacent strip mall, and
the nightclub. Information was sought as to where the stormwater from these study areas
drained to, what stormwater management features are currently in place, and which
design options are the best for each site to mitigate runoff based on current conditions.
The information acquired about current conditions, flow patterns, and watershed details
was obtained from the City of Maplewood Public Works Department. Various case
studies, primers and best management practice publications about green design were
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consulted (see references) to get ideas for the reduction of impervious surface and the
mitigation of stormwater in the study area.
The team of researchers visited the study area and each case study on at least two
different occasions for at least two hours per visit during the months of September and
October of 2008 to become familiar with the area. It was extremely helpful to see
firsthand the stormwater management features in place, the visual extent of impervious
surface, and other features that seemed applicable to the research. A large collection of
photographs were taken of the entire study area and the case studies during each visit,
which were vital in the assessment of the site.
The inventory of impervious surface for the Maplewood Mall commercial area was
obtained through the use of ArcGIS ® 9 ArcMap TM Version 9.3. This program was
chosen because it provided the geospatial analysis needed to accurately assess the
features of the study area. A 2008 aerial photograph of the area (obtained from Ramsey
County data) was used to assess impervious surface cover. Parcel lines and building
footprint data obtained from the county was superimposed on the aerial photo.
Through visual analysis it was determined that the amount of impervious surface was
greater than the pervious surface, so the pervious surface was digitized first. The term
“digitized” essentially means digital polygons were created to show the surface area of
various features. Features including pervious cover and ponds were digitized at a scale of
1:1500 feet. Once the amount of pervious surface was known, this area was subtracted
from the overall study area, to determine impervious surface area in acres and as a
percentage of the total.
The curb line between the bordering streets and the mall area was used to determine the
Maplewood Mall case study total area. The curb line between the bordering streets and
the strip mall area on the south, east and west sides, and the inner pavement line of the
path that runs along the north edge of the strip mall was used to determine the strip mall
case study total area. On the north and west edges of the nightclub the curb line between
the streets and the sidewalk, the middle line of the sidewalk that runs along the south
edge of the nightclub, and the outer edge of the grass strip along the east side of the
nightclub were used to determine the nightclub case study total area. The methods that
were used to calculate impervious surface in the entire study area were also used to
determine impervious surface cover in each of the case study areas. The building
footprint information was obtained from Ramsey County data.
The volume reduction measurements in the findings section show the amount of runoff
that is required to be managed on-site under the Ramsey-Washington Metro Watershed
District’s (RWMWD) volume reduction requirements. Parcels are required to reduce the
amount of stormwater leaving their site by the amount of runoff that would be generated
during a 1” rainfall over the amount of impervious surface on the site. These calculations
were done using the RWMWD formula volume of runoff formula (Ramsey-Washington
Metro Watershed District, 2006).
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V = A2 * R * 0.90 * 0.0833 ft/in * 7.5 gal/ft3
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V = volume of runoff (gal)
A2 = amount of impervious surface area (square ft.)
R = rainfall (inches)
0.90 = loss (usually though evaporation)
0.0833 = conversion factor (feet per inch)
7.5 = conversion factor (gallons per cubic foot)
The amount of impervious surface area (A2) used the impervious surface values found for
the case study sites.
Findings
Impervious Inventory for Study Area
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Entire Study Area = 654 acres (≈28,485,822 square feet)
Total Impervious Surface Area: 407 acres (≈17,746,687 square feet)
Volume of runoff generated during a 1” rainfall event: 9,978,518 gallons
Impervious surface covers approximately 62% of the entire study area, consisting mostly
of parking lots, roof tops, roads, and ponds (Figure 3). Pond surfaces are also included as
impervious surface, but they must be handled differently than other impervious surfaces
like parking lots and roads since it is difficult to reduce or moderate the effect of
stormwater retention ponds.
Figure 3. Impervious surface (gray) within the study area. The remaining area is pervious surface (green).
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Impervious Inventory for Maplewood Mall Case Study
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Total Area = 126 acres (≈5,499,407 square feet)
Total Impervious Surface Area = 115 acres (≈4,999,548 square feet).
Building Footprint = 14.8 acres (≈644398 ft2)
Required Volume Reduction = 2,811,121 gallons
The Maplewood Mall case study area was found to be approximately 91% impervious.
There were a few islands throughout the parking lot that were not considered pervious
due to excessive compaction and small surface area. The Maplewood Mall case study
area is bounded by County Road D East on the north, Beam Ave on the south, White
Bear Ave. N. on the east, and Southlawn Drive on the west. Under the current volume
reduction requirements of the RWMWD, 2,811,121 gallons of runoff must be managed
on-site. This volume reduction (and the volume reductions for the strip mall and
nightclub case studies) was calculated using the formula provided by RWMWD
described in the methods section (Ramsey-Washington Metro Watershed District, 2006).
Any redevelopment of the Maplewood Mall would require the volume reduction
requirement to be met.
Figure 4. Impervious surface (pink) within the Maplewood Mall case study area. The remaining area is pervious
surface (green).
Impervious Inventory for Strip Mall Case Study
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Total Area = 36 acres (≈1,575,029 square feet)
Total Impervious Surface Area = 32.5 acres (≈1,417,082 square feet)
Building Footprint = 7.0 acres (≈303,365 ft2)
Required Volume Reduction = 796,790 gallons
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The entire strip mall area is primarily impervious with a grass border surrounding the
perimeter, and a few rows of grass between the lots. The strip mall case study area was
found to be approximately 90% impervious. There were additional islands in the parking
lot that were not considered pervious due to excessive compaction and small surface area.
Currently, there is two-way traffic between the rows of parking spaces. There are 11
stores occupying the strip mall, with 6 major department stores as anchors. There are also
four small businesses located within the perimeter of the parking lot, each with its own
required parking stalls. Under the current volume reduction requirements of the
RWMWD, 796,790 gallons of runoff must be managed on-site. Any redevelopment of
the strip mall would require the volume reduction requirement to be met.
Figure 5. Impervious surface (pink) within the strip mall case study area. The remaining area is pervious surface
(green).
Impervious Inventory for Nightclub Case Study
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Total Area: 5.8 acres (≈251,234 square feet)
Impervious Surface Area: 5.0 acres (≈217,183 square feet)
Building Footprint = 0.5 acres (≈23,013 ft2)
Required Volume Reduction = 122,117 gallons
The nightclub was found to be 86% impervious. The nightclub has a contract with the
mall specifying that nightclub patrons can use the mall’s parking spaces in the event that
overflow parking is needed.
The stormwater holding pond adjacent to the nightclub was not included in the
calculation of impervious surface (the middle of the strip of grass between the building
and the pond is the southern border of the impervious inventory area). Open water is
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considered an impervious surface, but there is little that can be done to change the surface
area of the holding pond at the site.
Runoff from the nightclub parking lot flows into several drains which end in the
stormwater retention pond immediately south of the club. Much of the runoff flows over
the surface on a slope towards a curb cut which also flows into the holding pond as
illustrated in Appendix B. This direct flow into the holding pond is responsible for large
amounts of trash, particularly cigarettes, and possibly pollutants into the pond.
Each lane of parking spaces has an end cap on either side. The caps are filled with rocky
material and typically one small tree. Due to soil compaction over time these end caps
most likely do not allow significant infiltration of stormwater.
Under the current volume reduction requirements of the RWMWD, 122,117 gallons of
runoff must be managed on-site. Any redevelopment of the nightclub would require the
volume reduction requirement to be met.
Figure 6. Impervious surface (pink) within the nightclub (individual business) case study area. The remaining area
is pervious surface (green).
Storm Sewer Layout
Most of the runoff from impervious surface within the Maplewood Mall commercial area
is conveyed to a large culvert that runs from east to west along Beam Avenue. The
culvert, immediately south of the Maplewood Mall, is 66” in diameter, and the pipe
enlarges further west to 72” before it drains into Markham Pond (a stormwater retention
pond just south of Beam Ave and west of Kennard Street) (Kummer, 2008). Markham
Pond drains into Kohlman Lake, which is about a mile west of Markham Pond. Kohlman
Lake is on the northern most tip of a chain of lakes that eventually drain into the
Mississippi River. With the existing stormsewer layout, there is little pollutant removal
before the runoff from the Maplewood Mall commercial area enters Markham Pond.
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Water Quality Concerns in Receiving Waters
The following information on impaired waters is from the RWMWD 2006 Watershed
Management Plan (Ramsey-Washington Metro Watershed District, 2007). Under the
federal Clean Water Act (CWA), states must adopt water quality standards to protect the
water resources of the nation. Kohlman Lake was first listed in 2002 as impaired for
excess nutrients on the section 303(d) list under Title III of the Clean Water Act
(Minnesota Pollution Control Agency, 2008). A draft Total Maximum Daily Load
(TMDL) study for Kohlman Lake was recently completed in order to set pollution
reduction goals needed for restoration (Ramsey-Washington Metro Watershed District,
2007).
Environmental Utility Fees
Maplewood Mall is one of the two highest contributors to the City of Maplewood’s
environmental utility fee (EUF) (City of Maplewood Department of Public Works, 2008)
(Appendix A). The 2008 EUF rate for commercial developments is $44.57 per
acre/month (S. Kummer, pers. com., 2008). The EUF can be viewed as a service charge
or fee to finance the administration, planning, implementation, and maintenance of
stormwater BMPs. It is charged against all developed parcels within the city based on
land use type, density, parcel size, and the amount of runoff and/or pollutant loads how
much water runoff and/or pollutant loads are leaving the parcel (City of Maplewood,
2003a).
Recommendations
Based on our findings, an options primer (Appendix A) was developed that can be used
as a tool for urban developers and city planners to use in order to mitigate the effects
impervious surface and development have on an ecosystem. The overarching theme of
the primer is the incorporation of LID technology into new urban development plans, and
more importantly, into existing urban developments, given the large proportion of land
that is already developed. LID is “an approach to land development (or redevelopment)
that works with nature to manage stormwater as close to its source as possible” (US
Environmental Protection Agency, 2008). By incorporating LID technology, the
negative impacts of development on natural ecosystems can be reduced and the natural
movement of water within its watershed will be restored (US Environmental Protection
Agency, 2008). With some preparation and planning ahead, this technology can be
retrofitted onto existing developments relatively easily during renovation or repair. There
are also a wide variety of LID practices that will all work toward the same result, so
depending on the characteristics of a specific site, the developer or planner can choose
which options would work best for that specific site.
The case study sites within the Maplewood Mall commercial area are using traditional
drainage systems that convey water via curb and gutter systems into catch basins. The
stormwater is then conveyed through culverts and eventually is deposited into retention
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ponds. These traditional systems reinforce the “out of sight, out of mind” approach to
stormwater management. The use of LID technology could reduce the need for these
traditional drainage systems by restoring “natural” drainage systems. Implementing LID
technology would provide an opportunity for Maplewood to gain green credibility and
create a more sustainable Maplewood by 2050 by incorporating the following features
into development and redevelopment:
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•
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On-site Stormwater Management
Green Building Design
Overall Reduction of Impervious Surface
On-site Stormwater Management
As opposed to traditional drainage systems that convey water off-site, the LID approach
to stormwater management would utilize systems that allow on-sight stormwater
management. Stormwater should be treated “as a resource rather than a waste product”
US Environmental Protection Agency, 2008). On-site stormwater management options
include biologically enhanced systems (rain gardens, filter strips, swales), and infiltration
practices (infiltration trenches/basins, porous pavement, pervious asphalt, turf pavers).
By adding more vegetation to an urban development, more water will be allowed to
infiltrate, and evapotranspiration will transfer water into the atmosphere. On-site
stormwater management reduces the overall volume of water that needs to be managed as
surface water. Infiltration practices can also effectively retain pollutants commonly
found in stormwater runoff (Water Resources Center, 2007). Stormwater can also be reused on a site for irrigation of vegetation by collecting it in an above ground or
underground cistern, or by directly connecting roof gutters to an irrigation line.
Credits to Reduce Environmental Utility Fees
The EUF provides the opportunity to receive credits for using stormwater BMPs through
the use of stormwater ponds, green space, and undeveloped land, among others (City of
Maplewood, 2008). For more information on the credit program, see Appendix A.
Green Building Design
Green building design can be implemented on both existing and new developments. In
either case, the objective is to incorporate design options that use natural resources more
efficiently while reducing its impact on the surrounding environment. Green building
design can be achieved in many ways and perform many functions. In the case of
stormwater mitigation, existing buildings can be retrofitted with green rooftops
(specifically designed for its infrastructure) and rainwater cisterns (Appendix A). Any
design options will need to be taken on a case-by-case basis, as the infrastructure in some
older building may not be able to withstand certain these designs. New developments can
be designed with these features in mind, and may be easier to implement than retrofitting
existing developments.
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LEED Certification
The Leadership in Energy and Environmental Design (LEED)® building certification
system is a valuable green design option that works to create a standard of green building
design in the global market. The LEED building certification system is voluntary and
works to promote sustainability into the whole building construction process. There are
nine LEED Rating Systems that provide guidelines to engineers, architects and other
professionals on constructing buildings that are sustainable and environmentally friendly.
Important features recognized from LEED certification are energy efficiency, water
quality, and indoor air quality (US Green Building Council, 2008). Rating systems used
in the LEED building certification are New Construction, Existing Buildings: Operations
& Maintenance, Commercial Interiors, Core & Shell, Schools, Retail, Healthcare,
Homes, and Neighborhood Development.
The LEED for retail building certification recognizes the different type of building
environment required for the retail business sector. These buildings are designed in a
specific way that characterizes the product being sold, and requires a unique certification
system. There is currently an upgrade being made (the LEED for Retail Certification) that
will cover New Construction and Commercial Interiors. These new rating systems will
not be available until the beginning of 2009 (US Green Building Council, 2008). It
would contribute to Maplewood’s image of sustainability to achieve LEED certification
on new developments and through redevelopment.
Structural Soils
The problem of impervious surface area is that it not only has an impact on the amount
and quality of stormwater runoff over a surface area, it also has an adverse affect on the
growth of trees. In urban settings, the expected lifespan of some urban trees is well below
that of trees in their natural setting (Canadian Broadcasting Corporation News, 2005).
These trees are often planted in proximity to concrete or pavement, which can restrict
growth. The types of soils that support concrete are typically not supportive of tree
growth due the dense structure of the soil (American Public Works Association, 2006).
Soil conditions are a major factor in the survivability of a tree, which means that there
must be suitable soil conditions to facilitate the growth and development of the tree. Past
research has shown that the soil conditions in many urban areas have reached a level of
severity that does not facilitate the growth of any tree species (Urban, 1992).
In order to address the problem of unsuitable soil conditions, a new type of soil has been
manufactured that provides a medium for tree roots to grow under the concrete pavement.
Structural soils mimic natural soil and are also designed to withstand the soil compaction
that occurs in urban areas. These soils are porous and can provide the necessary space
and volume required for root penetration and tree growth. There are several types of
structural soils being manufactured. One type of structural soil, the CU-Structural Soil®,
development at Cornell University’s Urban Horticultural Institute is currently being used
in many landscapes (Urban Horticulture Institute, 2008). An example community using
the CU-Structural Soil® is the City of Palo Alto, California (American Public Works
Association, 2006). Palo Alto has been using the structured soil since 1998 and currently
has the soil installed on 28 sites.
12
Structural soil is composed of crushed gravel, soil, and a gel material to bind the gravel
and soil together (Bassuk, 2008). The structural soil is designed to be placed under
pavement surfaces and can also withstand heavy loads such as vehicle traffic in parking
lots. The soil characteristics and composition allow tree roots to grow in between the
gravel in an outward and downward direction instead of upwards causing pavement
upheaval.
Figure 7. Structural Soil diagram (Bussak, 2008).
Overall Reduction of Impervious Surface
In the Maplewood Mall commercial area, the parking lots of the Maplewood Mall, strip
mall, and Myth nightclub comprised a significant percentage of the total impervious
surface area. The RWMWD discovered that 71% of total annual phosphorus pollution
comes from roads, driveways, and parking lots (Ramsey-Washington Metro Watershed
District and Capitol Region Watershed District, 2008).
13
Figure 8. Sources of phosphorus pollution in the RWMWD (Ramsey-Washington Metro Watershed District and
Capitol Region Watershed District, 2008)
Impervious surface can be reduced by using alternative materials like porous pavement,
pervious asphalt, and turf pavers, and incorporating features like filter strips, swales, and
rain gardens. Increasing the amount of vegetative cover such as tree/shrubs and grasses
are also important factors to incorporate when reducing impervious surface. The national
tree nonprofit organization American Forests suggests a goal of 15% tree canopy cover in
business districts (University of Washington, 1998). This could be an attainable goal for
the City of Maplewood by 2050. Most retail environments in the US have 5% or less.
In order to reduce impervious surfaces, an accurate inventory must be completed in order
to identify areas for improvement. For example, the city of Burnsville has an impervious
surface worksheet as part of their Shoreland Ordinance (City of Burnsville, 2006). In
order to properly reduce the impact of impervious surfaces on stormwater runoff, it is
recommended that impervious surfaces on a development be reduced to 25% or less of
the total site area (City of Burnsville, 2006). If impervious surface on a development will
be greater than 25% of the total site area, the runoff volume must be mitigated to the 25%
impervious level. Mitigation practices required for developments with over 25%
impervious surface include LID infiltration and storage practices.
Cost Share Programs
There are usually opportunities to receive funding for implementing storm water BMPs
from state agencies and/or watershed districts. The RWMWDistrict has a BMP Cost
Share program that offers financial support to public and private land owners for efforts
14
that will improve water quality and enhance natural resources within its watershed. For
commercial developments, the maximum grant amount is $30,000. The funds are
distributed as a reimbursement of 50% of the total cost for materials and labor (RamseyWashington Metro Watershed District, 2008a). Some examples of projects eligible to
receive funding through the RWMWD Cost Share Program include:
•
•
•
•
Rain gardens
Rain barrels
Pervious asphalt and pavers
Volume reduction and runoff treatment practices (infiltration basins & trenches,
cisterns, green roofs, filtration)
For more information on the RWMWD BMP Cost Share Program, contact Julie VignessPint (RWMWD) at 651-792-7959 or [email protected]. Information can
also be found at www.rwmwd.org by clicking the “BMP Cost Share Program” link on the
left side of the page.
There is also a state cost share program funded by the Minnesota Board of Water and Soil
Resources (BWSR) that provides grants to Soil and Water Conservation Districts
(SWCDs) so they can help local land owners/occupiers pay for the installation
conservation projects that will improve water quality (Board of Water and Soil
Resources, 2008). For more information on state cost share programs, contact your local Soil
and Water Conservation District. For developments within Ramsey County, contact Ryan
Johnson (Ramsey Conservation District) at 651-266-7275 or [email protected]. Stormwater Ordinance
In order to restore and preserve the water quality in local lakes and streams, a stormwater
ordinance could be implemented. The Metropolitan Council’s Urban Small Sites BMP
Manual (Metropolitan Council, 2007) documents model stormwater ordinances available
to help municipalities incorporate sustainable stormwater management into policy:
•
•
•
Metropolitan Council Model Ordinance
o www.metrocouncil.org/environment/Watershed/model_sw_ord.pdf
MPCA Model Ordinance
o http://www.pca.state.mn.us/publications/wq-strm2-16a.pdf
Minnesota Planning-From Policy to Reality: Model Ordinances for Sustainable
Development
o http://www.gda.state.mn.us/pdf/2000/eqb/ModelOrdWhole.pdf
The creation of a Maplewood stormwater ordinance would not only regulate and mitigate the
negative effects of stormwater on local water quality, but it would contribute to the image of
Maplewood as a sustainable community the city is striving for.
15
Case Study Recommendations - Maplewood Mall
A
G
B
C
E
F
D
Figure 9. Maplewood Mall Recommendations.
A. Install a multilevel parking ramp to decrease horizontal parking and lessen total
impervious surface area. The gutters on the mall could be connected to an irrigation line
leading to onsite vegetation. Excess stormwater could be drained to areas with pervious
pavement.
B. Install green roof strips on outer portions of roof to reduce runoff volume.
C. All impervious pavement could be replaced with with pervious asphalt.
D. Place end caps with a pervious medium and vegetation to reduce runoff from the parking
lot and to increase aesthetic value. Structural soil should be installed beneath pavement
for tree plantings to prolong the life of the trees.
E. Add a park next to the mall in order to increase pervious area.
16
F. Add a walking trail composed of porous asphalt between the transit station and the mall
that runs through the park. This could bring more foot traffic to the mall.
G. Add a trail composed of porous asphalt that connects the Bruce Vento trail to the County
Road D trail to make the mall more accessible to walkers and bikers.
There are several options that should be considered in order to decrease the amount of
impervious surface around the Maplewood Mall. One option is to install a parking ramp on
the east side of the mall. The ramp would create spaces closer to the mall and create space to
implement green design options without losing total parking area. During the cold winter
months, shoppers would have a sheltered place to park and walk. It would be ideal to
construct a ramp consisting of one level at street level and one to two levels below grade
when or where possible in order to preserve the mall’s visibility. Connecting the mall’s
gutters to an irrigation line leading to onsite vegetation could help mitigate stormwater
coming off the top level of the ramp. Excess stormwater could be drained to areas with
pervious pavement. The addition of a green roof to the mall would provide insulation that
could potentially reduce energy costs and allows for slow release of runoff (Appendix A).
Another option is to replace the current parking surface with pervious pavement. The
pervious pavement would only be needed on the west side because the parking ramp will be
on the east side. Installation of end caps with a pervious medium and vegetation would create
shade for customers to park under as well as intercept and infiltrate stormwater. The use of
structural soil beneath tree plantings can prolong the life of the trees (Urban Horticulture
Institute, 2008). The space saved by the parking ramp can be used to create green space in
the form of a park. A park next to the mall could add to the visual appeal of the mall. A trail
composed of pervious asphalt connecting the transit station to the mall would run through the
park. The trail should be lined with vegetation to add to its visual appeal. This would make
it easier for people to walk between the transit station to the mall.
Finally, a trail composed of pervious asphalt could be installed on the north side of the mall
parking lot in order to connect the Bruce Vento Trail to the County Road D Trail. The trail
would increase foot and bike traffic.
These recommendations for the Maplewood Mall are a good way for the mall to gain green
credibility and visibility in the surrounding commercial area (City of Maplewood Department
of Public Works, 2008).
17
Case Study Recommendations - Strip Mall
A
B
E
F
G
D
C
Figure 10. Strip Mall Recommendations.
A. Use angled parking around infiltration basin. Trees and grassed areas should be planted at
28
the ends of the infiltration basin (Metropolitan Council, 2007) .
B. Use angled parking with trees/shrubs and grassed areas at end caps around parking lot (see
schematic diagram of “Green Design Parking Lot” in Appendix A).
• Install a grass swale strip approximately 3-4 feet wide in between parking rows.
C. Install compact vehicle parking spaces with turf pavers in overflow parking (designed to
increase more room for green space design).
• Parking spaces will be sized in accordance with the Mixed Use Zoning District
Parking Requirements (City of Maplewood, 2003b).
D. Reduce two-way traffic between lanes to one way in between angled aisles.
• This will create more space for green design options.
18
E. Replace all rock beds with grass, mulch, or some other pervious material to encourage
filtration of pollutants from stormwater.
F. Plant more trees/shrubs in the grassy areas surrounding the entire strip mall to reach the
recommended tree canopy cover of 15%. The use of structural soils beneath tree plantings
can prolong the life of the trees.
G. Above ground cisterns attached to the corners of the building will be used to capture rainfall
and irrigate vegetation in parking lot.
Several recommendations have been made to reduce the amount of impervious surface at
the strip mall. The main goal is to install an infiltration basin that would capture pooling
rainfall runoff in the parking lot in front of the Joann Etc. store. This infiltration basin
would serve to filter runoff and allow it to slowly percolate into the ground instead of
running off of the surface into a stormwater drain. Planting trees and other vegetation
surrounding the infiltration basin would also help to infiltrate rainfall, as well as help to
reduce the ‘heat island effect’ of the parking lot.
Implementing an angled parking scheme with one-way traffic between rows will increase
the amount surface available for expanding the current vegetation surrounding the
perimeter of the strip mall, as well as install more tree/shrub canopy cover. Further, to
increase the vegetative cover in the parking lot and reduce imperviousness a vegetated
strip will be placed in between the facing angled parking spaces. In order to maintain
visibility, shrubs less than 30” in height and trees that get tall enough to remove lower
limbs to a height of 8’ could be used.
The current parking lot has “rock gardens” planted throughout, mostly on end caps.
These impervious end caps will be replaced with trees/shrub and other vegetation such as
grass or mulch. The overflow parking spaces could be maintained in place but installed
with turf pavers to help facilitate the infiltration of water flowing over the parking lot.
The turf pavers could also be instrumental in allowing the meltwater from snow buildup
to percolate through the soil instead of pooling on the surface. Finally, to help address the
problem of rainfall runoff from the roof of the strip mall, there could be aboveground
cisterns attached at the corners of the building to capture rainfall. The rainwater can then
be used to irrigate the new vegetation in the parking lot.
19
Case Study Recommendations - Nightclub
B
A
C
F
D
E
G
Figure 11. Nightclub Case Study Recommendations.
A. An angled parking system could be used to conserve space and clear room for central
rain garden.
B. Eliminate the cement curbed end caps on parking rows. Replace the coarse aggregate
rock in end caps with grasses and a porous medium that will increase the infiltration
rate. Replace the curb with a guardrail to ensure driver and tree trunk safety.
C. Add a central rain garden and smoking area surrounded by benches for patrons and a
grass filter strip to reduce sedimentation.
D. Add an area of pervious pavement to reduce runoff into the holding pond.
E. Install an underground cistern to catch runoff. This water can be used for watering
trees and grasses during times of drought.
F. Add a pervious pavement corridor leading from the building to the central garden and
smoking area.
G. Install green roof strips to reduce volume of runoff going into the holding pond.
H. Use structural soil beneath pavement for tree plantings.
20
The nightclub has tremendous potential for impervious surface reduction. First the
parking lot can be changed from traditional parking stalls to angled parking with one-way
lanes, which will add more spaces without increasing the area of the lot. The increase in
parking spaces would allow room to implement other green design options for a no net
loss in parking spaces. Next, pervious pavement could be installed in the lot. A portion of
pervious pavement near the drainage pond is recommended, however conversion of the
entire lot is ideal.
Due to the amount of trash found on site, especially near the holding pond south of the
building, a multipurpose central rain garden could be constructed in the parking lot. The
rain garden will serve as green space for infiltration and an area for smoking facilitated
with trash bins and ash trays to reduce cigarette litter on site.
The existing end caps in the parking lot filled with aggregate rock do not allow
infiltration. The aggregate rock could be replaced by porous medium and vegetation to
allow infiltration of stormwater. Larger shade trees could be planted in the end caps with
structural soil to reduce the heat island effect.
The roof on the building is also considered impervious, which can be decreased by the
installation of a green roof. Green roofs can be expensive, so portions of the roof can be
covered rather than the entire roof. If funding is available, coverage of the entire roof is
recommended. Excess runoff from the rooftop can be collected in either above ground or
below ground cisterns. Cisterns will reduce the amount of stormwater flow and can be
reused for irrigation of surrounding vegetations. These practices combined will
drastically reduce impervious surface on the property and subsequently improve water
management and quality issues.
Discussion
As green technology improves, new BMPs for stormwater management are constantly
being developed. When considering implementation of certain green technology and
techniques, the scale and scope of the project must be thoroughly assessed. Three case
study areas were chosen based on criteria that differentiated one structure from the next.
The study sites (Mall, strip mall, and nightclub) were selected because of the differences
in usage, building and parking lot structure, and total amount of impervious surface. The
case studies tried to identify businesses with differing characteristics to show that
successful BMP implementation depends on the scale of the project.
The largest of the three study areas is the Maplewood Mall. The mall has approximately
130 total businesses and was selected due to its high amount of impervious surface
(4,999,548 square feet) and its unique potential for large scale redesign (i.e., double level
parking system). The strip mall study site is on a smaller scale (1,417,082 square feet
impervious) and was selected because the building structure and parking lot layout of the
site differs significantly from that of the Maplewood Mall. Therefore, some of the design
21
options that were applicable to the Maplewood Mall would not be as effective on a site
such as the strip mall and other techniques must be used to manage runoff (large water
cisterns).
The smallest of the three study sites was the nightclub. The nightclub varies from the
description of the other sites because it is a standalone business and covers a much
smaller area (217,183 square feet impervious). There is a wide range of design options
for this type of business because of the relatively small amount of runoff generated by the
lot size. Therefore many techniques can be considered (rain gardens, cisterns, pervious
pavers, etc.).
Positive Effects on Consumer Behavior
Research has shown that consumers respond positively to landscaping and tree cover in
retail shopping environments. In 1998, the University of Washington sent survey
questionnaires to business owners, managers, and residents in cities of the Pacific
Northwest: Austin, Los Angeles, Chicago, Pittsburgh, and Washington D.C., to gauge
their perceptions about the role of trees in revitalizing business districts University of
Washington, 1998). The results indicated that consumer ratings regarding amenity and
comfort, interaction with merchants, quality of products and maintenance and upkeep
were significantly higher for districts that had invested in street trees and other
landscaping. When asked about travel time, travel distance, duration of a visit, frequency
of visits and willingness to pay for parking, higher ratings for all of these measures were
received for districts having trees. Strikingly, when consumers were asked to specify a
price per item for a basket of 15 items containing convenience, shopping and specialty
goods, prices were on average 11% higher for products in the landscaped compared to
districts with no trees. This suggests that consumers may be willing to pay more for
goods in a well-landscaped shopping district. In summary, investments in tree cover and
landscaping in commercial areas can have a positive effect on business.
Example of Stormwater Management: University of Minnesota Landscape
Arboretum
In 2001, the University of Minnesota Landscape Arboretum, located in Chaska, MN,
created a runoff water disposal model in a new parking lot that demonstrates the
difference between approximately 100% runoff to approximately 0% runoff (Minnesota
Pollution Control Agency, 2005) (Figure 12). The intention of the project was to provide
an example of alternative stormwater management techniques to commercial developers
and public officials, who are facing stricter regulations and costs related to stormwater
(Minnesota Pollution Control Agency, 2005). The stormwater management techniques
integrated in the Arboretum example include: curbless paving, bioretention techniques
such as rain gardens, infiltration strips, planted filter swales, sedimentation basins, and
rain gardens (Figure 13). Although this site has heavy clay/silt soils which typically do
not drain easily, the infiltration techniques implemented on the site have been successful.
The Arboretum has been successful in achieving a goal of improving the appearance of a
parking lot while reducing the adverse impacts stormwater runoff can have on water
quality.
22
Figure 12. Runoff Model Demonstration Project at the U of M Landscape Arboretum. Chaska, MN (Minnesota
Pollution Control Agency, 2005).
Figure 13. Rain gardens along curbless parking lot at the U of M Landscape Arboretum in Chaska, MN (Minnesota
Pollution Control Agency, 2005).
Example of Stormwater Management: Oregon Museum of Science and
Industry
In 1990, plans were in the works for the redevelopment of an old industrial site in
downtown Portland, Oregon. The Oregon Museum of Science and Industry (OMSI) was
to be built there, and the plans caught the attention of Portland’s Bureau of
Environmental Services (BES). The site was of particular interest for stormwater
management because it is located directly on the Willamette River. OMSI and BES
worked together to create a design plan for the parking lot. The end result was a lot with
four acres draining to vegetated bioswales containing native wetland vegetation. These
structures have the capacity to eliminate 50% of sediment from stormwater runoff and
have a capacity to infiltrate .83 inches of rainfall in 24 hours (US EPA, 2008).
23
Figure 14. OMSI Parking Lot Bioswale (Oregon Museum of Science and Industry (2005).
Example of Stormwater Management: HB Fuller – Vadnais Heights, MN
The HB Fuller Company is a firm that manufactures and markets adhesives, paints,
sealants, and other specialty chemical products. The company does business in 32
countries and its headquarters is in St. Paul, MN (H.B. Fuller, 2008). The company
decided to incorporate a green parking lot design on their property at their Vadnais
Heights location. A large rain garden was installed in the middle of the parking lot and
planted it with deep rooted wetland vegetation known to hold and filter large volumes of
water. The parking lot is designed so that water flows to the rain garden, is filtered, and
then flows to nearby Willow Lake. The primary purpose of the parking lot was to treat
stormwater runoff ending in Willow Lake, store snow during winter months, as well as be
aesthetically pleasing to customers and employees.
The HB Fuller site is an award winning property, having received the RamseyWashington Metro Watershed District LEAP (Landscape Ecology Awards Program)
award in 2002 for commitment to conservation (Ramsey-Washington Metro Watershed
District, 2008b). Since installation, RWMWD has been monitoring the amount and
quality of stormwater runoff in the green parking lot and in another parking lot on the
property. The results of their study showed that rainfall runoff in the rain garden parking
lot was 70% less than in the other parking lot, as well as 73% less phosphorus discharge
(Bassett Creek Water Management Commission, 2002).
24
Figure 15. Green Parking Lot Design: Rain garden in median (Ramsey-Washington Metro Watershed District.
2008c).
Conclusion
The myriad of options for reducing stormwater runoff provide innovative ways for
rethinking the way that stormwater is managed. The current system for managing runoff
brings pollutants that accumulate on impervious surfaces (oil, gasoline, fertilizers) and
transports them directly into area lakes and rivers. Eutrophication of the lakes in
Maplewood and bodies of water across the nation is a major concern for everyone. Clean
water is in the best interest of society as a whole, and bodies of water will be further
impaired by runoff pollutants if measures are not taken. For this reason it is imperative to
the future of Maplewood that the city recognize and address this problem before local
ecosystem health are irreversibly damaged. Through LID, protection of natural resources,
and stormwater management communities like Maplewood can do their part to address
climate change. In taking the measures to reduce runoff, improve water quality, and
create a sustainable community, Maplewood can set an example for other municipalities
to follow in hopes of someday being a cleaner and more ecoconscious country.
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28
Appendices
Appendix A:
Appendix B:
Appendix C:
29
Appendix A. Stormwater Management and Impervious Surface Primer
City of Maplewood, 2008
The purpose of this primer is to provide options to current and prospective business owners and
developers within the city of Maplewood, MN in regards to their storm water management
practices. The city of Maplewood has included a goal of sustainability by the year 2050 in their
most current comprehensive plan. Major concerns of the city included future development and its
effect on the environment, surface water quality and runoff, as well as water quantity as
population increases. Although all of these issues are connected, this primer focuses on practices
that reduce impervious surfaces such as roads and parking lots in order to improve water quality
and reduce surface runoff.
What is the Concern about Impervious Surfaces?
Impervious surfaces such as sidewalks, parking lots, and even compacted soil common to urban
areas present a problem for water quality. When precipitation falls on these surfaces it does not
infiltrate into the soil. Instead the water runs off on the surface into nearby drainage systems, and
eventually into local waterways. Increased volume of water going into lakes and streams can have
a detrimental effect on those ecosystems. Along with surface runoff, chemicals and excess
sediments are carried to waterways which also cause environmental issues. Through innovative
30
design options, impervious surfaces can be reduced in urban areas, lessening pressure on
stormwater infrastructure, decreasing management costs, and improving environmental quality.
Benefits from Reduction of Impervious Surface
In 2003 the city of Maplewood instituted an environmental utility (Ordinance No. 839) in order to
fund its Storm Water Management Program. The fee categories are based on parcel size, land use,
and density1. The property owner is then charged based on the amount of runoff contributed to
local waterways. Property owners pay monthly through their water and sanitary sewer utility
bills. The city has provided a credit program for industrial, institutional, or commercial entities
that reduce their storm water runoff by at least 20%. Storm water runoff can be reduced by
implementing any of the approved best management practices discussed herein. Credits for best
management practices can be combined for a total reduction in utility cost of up to 75%. The
benefit is quite clear: businesses can save money on their monthly utility charges.
Trees and other vegetation have many potential positive effects in urban areas2. Healthy trees in a
commercial setting send positive messages to the consumer about what can be expected during
their shopping experience and tend to attract customers. American Forests, a national tree nonprofit organization, suggests 15% tree canopy cover as a goal in retail areas where a large amount
of impervious surface cover exists. Research suggests that trees are good for business 3. It is
estimated that every urban tree with at least a 50-year life span will provide cost savings of $273
annually through energy savings, stormwater mitigation, air pollution, wildlife shelter, and
erosion control4.
Design Options for Existing Businesses
Each business will face challenges in implementing practices to reduce impervious surface.
Discussed here are the pros and cons of common design options that will be beneficial and cost
effective. Many of these green design options can be used for various types of businesses and
property sites, but careful site planning is recommended. Based on soils, hydrology, and existing
infrastructure certain design options may be more appropriate than others.
Green Rooftops
Rooftop area is considered impervious surface because it does not allow the infiltration of
rainwater. Green roofs are very effective in reducing runoff from the tops buildings. Rooftop
gardens slow the rate of runoff and retain it, which reduces storm surges in the sewage system
during precipitation events. Green roofs can also decrease energy requirements for a building
through temperature regulation.
• Traditional Green Roofs
Traditional green roofs are the most effective way to reduce building runoff but they require a
certain load-bearing capacity because of their structure (soil, drainage, plant material) and it can
be quite expensive to retrofit a building to support these structures. However, true green roofs are
recommended for use on buildings with larger potential runoff volume because of their retention
capability.
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Figure 16. Composition of a green roof (Courtesy of Metropolitan Council).5
• Modular Green Roof Tray System
A more cost effective option is modular green roof tray system, which comes with soil and
vegetation intact. These trays can be easily moved and maintained. This option retains less water
than a true green roof but may be more desirable for businesses with less potential runoff volume.
It is also a good option for businesses that do not wish to invest a large sum of money and need a
more affordable way to mitigate storm runoff.
Figure 17. Courtesy of Weston Solutions, Inc.6
•
Figure 18. Courtesy of Weston Solutions, Inc.6
More information about green roofs:
http://www.mngreenroofs.org/node/238
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Permeable Pavement
Permeable pavement contains pores, which allow for the infiltration of rainwater. There are
various types, including interlocking concrete pavers, permeable asphalt, and cellular paving
systems.
• Concrete cellular paving systems
Matrices of pavers and grass recommended for use in low traffic areas. This type of system is
recommended for overflow parking.
Figure 19. Courtesy of Bonestroo7
•
Interlocking concrete pavers
Allow water to seep between the cracks. The edges are separated by small rubber dividers that
ensure that water is able to percolate through. This type of system is recommended for walkways
and small business parking lots.
Figure 20. Courtesy of Bonestroo7
• Permeable asphalt
Permeable asphalt is granular asphalt with pore spaces that allow water to infiltrate. This is the
most cost effective option for permeable pavement and is recommended for large or small
parking lots.
33
Figure 21. Courtesy of Bonestroo7
•
More information about permeable pavements:
http://www.paversearch.com/permeable-pavers-menu.htm
Infiltration Systems: Bio-swales and Rain Gardens
These features will filter pollutants out of stormwater runoff and contribute to improving the local
water quality. Rain gardens can be very aesthetically pleasing to the public and reduce the
amount of stormwater runoff and reduce the risk of flooding during storm events. There are
many different types of structures that can be deemed a rain garden or bio-swale and different
types may be more appropriate for each individual situation.
• Bio-swales
Bio-swales are an effective way to deal with a large volume of runoff. A bio-swale is essentially
a vegetated infiltration ditch that allows runoff to percolate back into the ground and be filtered
by the soil. These are recommended on large sites but can be supplemented by rain gardens for
aesthetic purposes.
Figure 22. Courtesy of Tualatin Riverkeepers8
• Rain gardens
Different from bio-swales in the respect that they are much more aesthetically pleasing and they
work on a much smaller scale than bio-swales. Rain gardens are planted with plugs that have
high water uptake and clear pollutants such as nitrogen from the system.
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Figure 23. Photo by Marc Thurow
• More information about infiltration systems:
http://www.tualatinriverkeepers.org/lid_website/swales.html
On-Site Storage: Rainwater Cisterns
Above ground or underground storage systems hold stormwater that can be used for on-site
irrigation.
• Below ground storage cisterns
These structures are more applicable to new developments since it requires a relatively invasive
installation process. However when these cisterns can be installed they are one of the most
effective ways to reduce runoff from both buildings and paved surfaces.
Figure 24. Courtesy of Darco Inc.9
• More information about below ground rainwater cisterns:
http://www.infolink.com.au/t/Below-Ground-Rainwater-Tanks
• Above ground storage cisterns
These are a very effective and inexpensive way to capture runoff from buildings because gravity
is the mode of transport. These structures require some special adaptations to be able to collect
runoff from paved surfaces but can also be installed at a relatively low cost when compared to
underground cisterns.
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Figure 25. Courtesy of Plumb Tank10
• More information about above ground rainwater cisterns:
http://www.lid-stormwater.net/raincist_home.htm
Parking Lot Design
Parking lots comprise the majority of impervious surfaces in most commercial areas. The
reduction of impervious surface in parking lots may be the most important and also the most
challenging in terms of green design. Most businesses do not want to reduce parking lot sizes,
especially in high-density urban areas where space is limited. There are a number of options that
address this issue for businesses.
• Angled Parking
Converting parking lots from traditional design to angled parking can increase the amount of
parking stalls. This is accomplished by simply re-painting a lot with the rows designed for oneway traffic with 45 degree parking stalls. The increase in parking stalls may free up space to
implement other practices on-site in order to reduce impervious surface and mitigate storm water.
Angled parking is effective for us on any size parking lot.
Figure 26. Courtesy of the City of Edinburg.11
Figure 27.
• Parking Ramps
Parking ramps are an excellent green design option. Parking ramps allow for vertical expansion
instead of more common single level parking lots with a large impervious surface area (build up,
not out). A parking ramp is particularly valuable to residents that live in regions that experience
harsh winters as ramps provide an enclosed place to park and a shorter distance to walk. Parking
36
ramps can be expensive to construct and are usually implemented on large business lots.
However, this should not to discourage innovative use of multilevel parking systems.
Figure 28. Rosedale Mall parking ramp
Photo by Katrina Hill
• Green Islands
Not only do consumers gravitate towards stores with a green image but they will also gravitate
towards random areas of green in parking lots because they provide shade and possess aesthetic
appeal. These areas can be rain gardens, patches of trees or even native grass plantings. It is also
recommended that structural soil (CU-Soil) be used when planting trees. Structural soil allows
root penetration on compacted, developed soils which improves their function and longevity12.
This option is recommended for large lots with parking space to spare but innovative
implementation is not discouraged.
Figure 29. Courtesy of University of Wisconsin Green Bay13
• Shared Parking
Shared Parking between businesses is a noble approach to reducing impervious surface. Since
large building structures such as the Maplewood Mall rarely have full parking lots it is
37
recommended that these large businesses lease out parking space to smaller surrounding
businesses in an attempt to share resources and conserve space.
Example of a Green Design Parking Lot
Figure 30. Courtesy of Metropolitan Council5
• More information about parking lot design:
http://www.designcenter.umn.edu/projects/direct_design_asst/2004/proto_lot.html
Other Considerations
Scale and Scope of Development
The design options for stormwater management discussed above can be most easily applied to
new developments. The implementation of this type of infrastructure will be less costly when
applied during the development process, as opposed to redesigning and investing in them later.
Looking ahead, municipalities or even state governments may require the use of one or more of
these options in development. The incorporation of these practices into development could get
businesses ahead of the curve if a policy in the future were to require them.
Some of the more invasive options such as underground cisterns are most easily implemented
from the ground up. On existing developments, stormwater management infrastructure should be
put into place during reconstruction in order to avoid excess costs. For example, when a parking
lot needs to be repaved, use pervious pavement instead of traditional pavement.
When evaluating a site for possible design options, the differences in business type, building and
parking lot structure, and total amount of impervious surface must be considered. Not every
practice will make sense or be economical for every site. Soils, hydrology, and vegetation of a
38
site also need to be evaluated, to ensure the effectiveness of these practices once they are
implemented.
Cost Share Programs
The Ramsey-Washington Metro Watershed District (RWMWD) offers a BMP Cost Share
program that offers financial support to public and private land owners for efforts that will
improve water quality and enhance natural resources within its watershed. For commercial
developments, the maximum grant amount is $30,000. The funds are distributed as a
reimbursement of 50% of the total cost for materials and labor14. Some examples of stormwater
management practices eligible to receive funding through the RWMWD Cost Share Program
include:
• Rain gardens
•
Pervious asphalt and pavers
•
Volume reduction and runoff treatment practices (infiltration basins &
trenches, cisterns, green roofs, filtration)
There is also a state cost share program funded by the Minnesota Board of Water and Soil
Resources (BWSR) that provides grants to Soil and Water Conservation Districts (SWCDs) so
they can help local land owners/occupiers pay for the installation conservation projects that will
improve water quality15. These cost share program should be utilized when applicable and are
incentive for the incorporation stormwater management practices in new developments or during
redevelopment.
Primer References
1. City of Maplewood. Environmental Utility Best Management Practices Credit, 2003. Path:
http://www.ci.maplewood.mn.us/index.asp?nid=454; Environmental Utility Best
Management Practices Credit (12 November 2008).
2. University of Washington, College of Forest Resources, Center for Urban Horticulture. Trees
in Business Districts: Comparing Values of Consumers and Business. Human Dimensions of
the Urban Forest, Fact Sheet #4, 1998. (18 November 2008).
3. University of Washington, College of Forest Resources, Center for Urban Horticulture. Trees
in Business Districts: Positive Effects on Consumer Behavior. Human Dimensions of the
Urban Forest, Fact Sheet #5, 1998. (18 November 2008).
4. The Registry of Nature Habitats. Tree Facts, 2008.
http://www.registryofnaturehabitats.org/treefacts.html (11 November 2008).
5. Metropolitan Council. Urban Small Sites Best Management Practice Manual. (Metropolitan
Council 2007). http://www.metrocouncil.org/environment/Watershed/bmp/manual.htm (9
September 2008).
6. Weston Solutions, Inc. GreenGrid: The Premier Green Roof System, 2006.
http://www.greengridroofs.com/pdf_docs/B-D066-greengrid.pdf (12 November 2008).
7. John Uban, American Society of Landscape Architects, Bonestroo. Low Impact Development
Techniques: Permeable Pavement, Draft. 6 October 2008, personal email. (6 October 2008).
39
8. Tualatin Riverkeepers. Low Impact Development: Examples from the Tualatin Basin.
http://www.tualatinriverkeepers.org/lid_website/swales.html (24 November 2008).
9. Darco Incorporated. Underground Tankage, 2008. http://www.darcoinc.com/index.html (24
November 2008).
10. Plumb Tank. Water Storage and Plumbing Solutions, 2007.
http://www.plumbtank.com/residential.html (24 November 2008).
11. City of Edinburg Unified Development Code. Parking Space Standards.
http://www.bufferbuilder.com/CZO/Edinburg/maintain/ViewCode.asp?Index=4559 (24
November 2008).
12. Urban Horticulture Institute, Department of Horticulture, Cornell University. Cornell
Structural Soil. http://www.hort.cornell.edu/uhi/outreach/csc/ (11 November 2008).
13. University of Wisconsin Green Bay, 2006 Master Plan. Parking.
http://www.uwgb.edu/masterplan/physicalElements/parking.html (24 November 2008).
14. Ramsey-Washington Metro Watershed District. Best Management Practices (BMP) Cost
Share Program. http://www.rwmwd.org/index.asp?Type=B_BASIC&SEC={E574596678DF-4558-8C39-431D6D450673} (20 November 2008).
15. Board of Water and Soil Resources (BWSR). State Cost Share Program Fact Sheet.
http://www.bwsr.state.mn.us/grantscostshare/costshare/factsheet2.html (20 November 2008).
*Cover Photo by Catherine Bach
40
Appendix B: Nightclub Parking Lot
Figure 31. The holding pond south of the nightclub parking lot. Photo by Marc Thurow
Figure 32. Runoff from the nightclub parking lot running directly into holding pond
Photo by Marc Thurow
41
Appendix C: Cost Estimate for Stormwater BMPs
Treatment
Cisterns
Type
Above Ground
Below Ground
Size
300 gal
4000 gal
10,000 gal
4,000 gal
20,000 gal
Cost
$230
$1800
$4,670
$7,794
$27,756
Per sq/ft
$2.70
Per sq/ft
Per sq/ft
Per sq/ft
$0.50
$3.33
$1,500 each
Per sq/ft
$2,500 each
Per sq/ft
Per sq/ft
Per sq/ft
$1.50 linear
ft.
$1.70
$10.00
$0.70
Comments
Source: Plastic-mart1
Photo: Plumb Tank2
Source: Darco Incorporated3
Estimates include : tanks,
accessories, and shipping
Figure 33.
Rain Garden
(Infiltration basin)
Site prep
Excavation
Grading
Soil hauling
Structural
Inlet
components
structure
(if necessary)
Outlet
structure
(overflow)
Site
Sod
restoration
(filter strip)
Soil Prep
Planting
Mulch
Source: Minnesota Storm Water
Manual4
Photo: Marc Thurow
Figure 34.
Green Roof
Planting trays (flat roof)
2ft x 2ft
Planting packs (pitched
roof)
20in x32in
Source: Green Roof Blocks5,
$ 22 sq/ft Green Roof Pricing Worksheet
$ 34 sq/ft Price includes:
Barrier and Pack
Source: Green Roof Blocks5,
Green Roof
Pricing Worksheet
Photo: Weston Solutions, Inc6
Figure 35.
42
Continued.
Treatment
Pervious
Type
Porous concrete
Size
Per Sq/ft
Porous asphalt
Pavers (interlocking or
turf)
Cost
$8 material
$11-16 subbase
$10 material
$8 sub- base
$5-12
material
$12-21 subbase
Comments
Source: Bonestroo7
Photo: Land and Water8
Initial costs of permeable paving
may be more than traditional
methods, but these costs are
often offset when the need for
other storm water management
systems is eliminated.
Figure 36.
Traditional Pavement
Concrete
Per sq/ft
Asphalt
$28
$15
Figure 37.
43
Source: Twin City Concrete9
Photo: Pervious Concrete10
References for Appendix C.
1
Plastic-Mart. Storage Tanks and Containment: Plastic Water Tanks http://www.plasticmart.com/class.php?cat=9 (25 November 2008).
2
Plumb Tank. http://www.plumbtank.com/products.html (20 November 2008).
3
Darco Incorporated. 2008. Underground Tank Project Estimate.
http://www.darcoinc.com/TankQuote.php (15 November 2008).
4
Minnesota Pollution Control Agency. 2005. Stormwater Manual, 2005.
http://www.pca.state.mn.us/water/stormwater/stormwater-manual.html (10 September
2008).
5
Green Roof Blocks. www.greenroofblocks.com. Path: Downloads and Price Calculators;
Price Calculator. (15 November 2008).
6
Weston Solutions, Inc. 2006. GreenGrid: The Premier Green Roof System.
http://www.greengridroofs.com/projects/retail/projects_applestore.htm (25 November
2008).
7
Bonestroo, Personal Communication; Pavement cost estimation. 2 November 2008
8
Land and Water: The Magazine of Natural Resource Management and Restoration.
http://www.landandwater.com/features/vol51no1/vol51no1_2C.jpg (25 November
2008).
9
Twin City Concrete, Personal Communication; Pavement cost estimation. 2 November
2008.
10
Pervious Concrete: When it Rains it Drains. 2008.
http://www.perviouspavement.org/asphalt%20vs.concrete.htm (25 November 2008).
44