METROPOLITAN DESIGN CENTER
City of Afton
RENOVATING TOWN SQUARE PARK: Landscape Design and Stormwater Management Strategies
A ‘space’ is something that has been made room for…with a boundary. A boundary is not that at which something stops but, as the Greeks recognized, the boundary is that from which something begins its presencing. [Therefore] the space ‘gathers’ its essence from locations (boundaries) and not from the space itself. Martin Heidegger Poetry, Language Thought
The expression ‘CITY’ and ‘urban agglomeration’ are commonly used as if they were interchangeable. But there are differences of a more qualitative nature between the two expressions. The spirit of a real city has subtle qualities more difficult to understand— let alone to create at will—than the quantitative aspects of an urban agglomeration. Planners are primarily concerned with the technological efficiency of the urban system…They pay less attention to the psychological and emotional needs of city dwellers or to the relation between city life and civilization. René Dubos Life in the City, From Beast or Angel
A Special Thanks Funding for this Direct Design Assistance project is provided through generous support from the McKnight Foundation and the Dayton Hudson Endowment.
TABLE OF CONTENTS Site Reconnaissance
06
Geomorphology
06
Fluvial System
08
Exploring the “Ancient Garden�
09
Ecological Habitats
10
Site Analysis: Solar Path & Slope Attitude
12
Town Square Park Design Concept
14
Issue 1: Resolving Drainage
14
Issue 2: Resolving the Edges
16
Proposed Site Plan
18
Reconfiguring the Edge at the Base of the Slope
20
Transition Zone: From Turf Grass to Prairie Vegetation
21
St. Croix Trail Streetscape
22
Rethinking Street Configuration
22
Rethinking Stormwater Management
24
Stormwater Management: The Benefits of Using Permeable Pavement
26
Planting Suggestions
28
Public Meeting
30
Project Participants
31
References
31
Site Reconnaissance: Geomorphology Afton, MN
Town Square Park in the Old Village Area of Afton
TWIN CITIES METRO Afton, MN
In the summer of 2013, the Park Committee of the City of Afton approached the Metropolitan Design Center (MDC) to ask for assistance in rethinking the aesthetics and infrastructural functionality of their public park, Town Square Park. The City of Afton is located approximately fifteen miles east of downtown St. Paul, MN. It lies on the western shore of Lake St. Croix, a wide section of the St. Croix River, which makes up the eastern border of Minnesota.
Town Square Park, the first public square park platted in the Minnesota Territory in 1855, is located in the heart of the Old Village Area in Afton. The 2-acre park, featuring recreational and community facilities and a beautiful grove of oak trees, is well-used for several annual events, such as the Afton Strawberry Festival. County Highway 21, also known as St. Croix Trail, runs north-south through the Old Village Area and makes up the eastern boundary of Town Square Park.
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Overlooking the St. Croix River just north of Afton, MN (photo by Christopher Williams, www.flickr.com/photos/cdwilliams1)
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Town Square Park
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drainage channels drain the bluff toward the lower terrace of the floodplain of the St. Croix River. Kelle’s Creek, one of the remaining creeks, is two blocks south of the park. The western edge of Town Square Park is a steep wooded slope (30% slope). The Old Village Area of Afton experiences frequent problems with flooding. Town t3 Square Park lies within the 100-year floodplain.
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Lower Terraces - Generally course sand and gravel. Surface of terrace level t1 is about 55 to 80 feet about floodplain level; terrace t1’, about 10 to 30 feet above floodplain level.
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Middle Terraces - Sand, gravelly sand, and gravel; surface of terrace t2 is about 115 to 140 feet about floodplain level; t1 terrace fs level t2’, about 85 to 110 feet about floodplain level.t1`
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t2` Upper Terrace - Sand, gravelly sand, and gravel; surface about 160 to 220 feet above floodplain level.
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Outwash (Superior Lobe Deposit) - Sand, fs loamy sand, and gravel. Outwash plains are highly collapsed in places, particularly over buried bedrock valleys, owing to ice-block melt out.
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Glacial Till (Pre-late Wisconsinan Superior Lobe Deposit) - Chiefly sandy-loam-textured, unsorted sediment; pebbles, cobbles, and t1` boulders are common, as are sand and gravel lenses and beds.
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Dolomite, Limestone, Sandstone, and Shale (Ordovician and Cambriant2 Bedrock) - Discontinuously exposed bedrock generally mantled by less than 5 feet of sandy to rocky colluvium andt1` loess.
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Source: Geologic Atlas of Washington County, MN from Minnesota Geological Survey
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Site Reconnaissance: Fluvial System Subwatersheds
Depth to Groundwater
Pediment
Kelle’s Creek
Kelle’s Creek Outflow
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Exploring the “Ancient Garden”: Cambrian & Ordovician Sediments Integrating Town Square Park to the Kelle’s Creek Ecology and the St. Croix Fluvial Wetlands Ecosystem
The St. Laurence and Franconia Formations at the site are from the Cambrian and Ordovician periods which mark the beginning of recorded life on the planet. The “Cambrian Explosion” provides a rich fossil record imbedded on the marine sediments. Sediments of this age are present along the erosional slopes of Kelle’s Creek which could provide an excellent opportunity for school field trips in addition to studying the fluvial and riparian ecology of Kelle’s Creek and the floodplain lagoon ecosystems.
Stratigraphic Column of Southeastern Minnesota Bedrock Geology
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Site Reconnaissance: Ecological Habitats
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Site Analysis: Solar Path & Slope Attitude Topography
Existing Site Plan
Section A: Slope Through Town Square Park
Drainage Along Slope
12
Solar Orientation
Wind Direction
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Town Square Park Design Concept Issue 1: Resolving Drainage To assist in resolving the drainage and flooding issues in the Old Village Area of Afton, the park redesign calls for stormwater to be managed on site. Two catchment areas capture surface flow, clean the water through infiltration, and redirect the water to Kelle’s Creek, a natural outflow to the St. Croix River. The first catchment area is at the base of the slope on the west end of Town Square Park, located within the public right-of-way known as Perrot Ave S. This feature would capture water flowing downhill from the slope in a constructed creek bed, providing the added benefit of offering habitat for animals, as well as educational and recreational opportunities for park visitors, especially children. The second catchment area would be constructed within the right-of-way of St. Croix Trail on the eastern border of the park. Stormwater flowing from both the park and the street would be captured, cleaned, and transported to Kelle’s Creek for outflow to the St. Croix River.
Area Drainage Plan
Base of Slope Existing Conditions
1st Catchment Area Concept
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Slope Section
Schematic Drainage Proposal
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Town Square Park Design Concept Issue 2: Resolving the Edges
Existing Conditions A. SLOPE AND WOODLAND
• Surface water erodes soil on steep slope. • Invasive plants choke out native species, leaving low-quality habitat for animals and birds. • Potential for play in woodland hindered by overgrown vegetation and a lack of open areas or paths. • Wall of thick vegetation creates inaccessible edge between woodland and park.
B. PARK EDGES
• Narrow sidewalk limits pedestrian use. • Park space undefined from street and parking space. • No defined park entrance. • Baseball diamond sits directly along street edge, limiting spectator access and visitor movement.
A: Inaccessible woodland edge
A: Invasives crowding woodland
B: Undefined street edge
C: Erosion in parking area
C PARKING AREA
• Unpaved parking area causes erosion. • No spatial differentiation between parking area and park. • Form/material lacks character & definition.
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Proposed Condition A. NEW CATCHMENT AREA • Creek-like water feature captures surface water at toe of slope and directs flow to Kelle’s Creek. • Creates aquatic habitat for plants and animals. • Provides educational and play area for children.
B. EXPANDED OPEN SPACE - BASE OF SLOPE
• Invasive trees along existing woodland edge thinned to provide openings. New native tree species introduced around openings. • Openings in woodland edge offer gathering areas for quiet reflection, picnicking, play, etc. • Solar access in openings allow for restoration of greater variety of woodland and prairie plant species, providing quality habitat for animals and birds.
C. DEFINED STREET EDGE
• Sidewalk widened to accommodate pedestrians. • New row of trees along street defines park space from street space. • New welcoming park entrance. • Stormwater system along St. Croix Trail protects area from flooding.
D. DEFINED PARK EDGE
• New row of trees defines park space from parking area. • Park edge allows room for tents during park events. • Baseball diamond is moved away from street edges providing more room for spectators and movement along park edge.
E. PLANTING BEDS
• New plantings bring color, texture, and winter interest to the current monoculture landscape of the park. • Plantings provide natural transition between woodland and park. • Paths weave in and out of beds, allowing for exploration.
F. IMPROVED PARKING AREA
• Pervious pavement manages stormwater through infiltration and prevents erosion. • Pavement pattern spatially differentiates parking area from park.
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Town Square Park: Proposed Site Plan
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Reconfiguring the Edge at the Base of the Slope
Before
After
• Remove invasive vegetation to provide openings for natural light reaching the ground. • Plant new native grasses, shrubs, and trees to provide for picnic areas and habitat exploration. • Solar access in openings will allow for greater variety of woodland and prairie vegetation.
Prairie Grasses, Sedges, and Shrubs 20
Transition Zone: From Turf Grass to Prairie Vegetation
Retaining wall
Rock (No depth)
Curb
Path
Rock (depth)
Metal piece Metal edge
Natural edge
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St. Croix Trail Streetscape: Rethinking Street Configuration Existing Condition:
Section Looking North Through Edge of Town Square Park and St. Croix Trail (Co. Rd. 21)
The current streetscape of St. Croix Trail consists of two 25’ lanes, which serve both parking and driving. There are no curbs on either side of the road along the Town Square block stormwater appears to collect along the road edges and move south until it empties into ditches and drains directly into the St. Croix River. An opportunity exists to re-think both the street configuration and the stormwater management within the road right-of-way. The current fifty-foot width between curbs provides plenty of space with which to experiment with different lane widths and configurations, with options to allow bike lanes or introduce planted boulevards. The right-of-way along the length of St. Croix Trail provides plenty of space to manage the stormwater from the roadway as well as from the bluffs to the west. The system design depends heavily on the amount of water that needs to be managed. Either a single integrated system or a dual system would collect, clean, store, and, transport stormwater, helping to address the flooding issues with which historic Afton currently struggles. Some systems allow for infiltration into the native soils, which would reduce the amount of water being drained to the river. Underground systems can be sized to hold large amounts of water associated with large rain events.
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Streetscape Option 1:
Separated Bike Path and Colored Paving in Parking Lanes
Bike lanes separated from traffic, NYC
By narrowing the existing driving and parking lanes and shifting them to one side, we gain enough road space to add designated bike lanes. This option shows a two-way bike path separated from the driving lanes by one of the parking lanes. Colored paving in the parking lanes helps to visually narrow the roadway, cueing drivers to slow down.
Streetscape Option 2:
Planted Median and Colored Paving in Parking Lanes
Planted boulevard with pedestrian crossing
Another option is to narrow the lanes and move them to either side of the roadway, gaining enough to space to introduce a planted median in the center. Colored paving in the parking lanes helps to visually narrow the roadway, cueing drivers to slow down.
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St. Croix Trail Streetscape: Rethinking Stormwater Management Stormwater Option 1: Dual System Along Park Edge
Along sections of St. Croix Trail where it might be possible to utilize additional space beyond the right-of-way, such as along the park edge, a dual system can collect, clean, infiltrate, store, and transport stormwater. A linear tree trench between the sidewalk and the edge of the park captures water that flows down through the park. A linear infiltration basin between the sidewalk and the street treats stormwater from the street.
Tree Trench
Installing a Silva Cell system
Silva Cell system in place, Minneapolis
Infiltration Basin
Infiltration basin with curb cuts & parking buffer
Infiltration basin with curb cuts
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Stormwater Option 2: Single System within Right-of-Way
Along sections of St. Croix Trail where it is necessary to work within the right-of-way (such as along private property), a single system can collect, clean, infiltrate, store, and transport stormwater. A stormwater planter between the edge of private property and the sidewalk treats stormwater that flows in from the street.
Stormwater Planter
Stormwater planter with sidewalk buffer
Stormwater planter inlet detail
Stormwater planter with curb cuts
Pervious paving
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Stormwater Management: The Benefits of Using Permeable Pavement Parking areas are currently situated along three edges of the park, with street parking along St. Croix Trail, and gravel parking lots on the streets to the north and south. The gravel parking lots have experienced large amounts of erosion, as water flows down the slope of the park to the street. Introducing permeanable paving in these areas should solve the issue of erosion, as well as allow for stormwater to infiltrate into the ground below the parking areas, helping to reduce the amount of surface flow and alleviate flooding. Spaces between permeable pavers allow storm water to percolate into a layer of gravel below. The gravel layer provides support for vehicles as well as a short-term storage area for water before it infiltrates into the soil and groundwater below. A drainage pipe may be needed to store and transport large amounts of water to a storm sewer. This ensures that, even in extreme weather, all water leaves the parking surface. Currently there are no definable edges between the park and the parking areas, creating the perception of space “leaking� from the park. Permeable paving, with its clearly distinguishable patterns, helps to establish a visual boundary. With the addition of a line of trees and sidewalk on the edge of the park, a clearer and more comfortable differentiation of space is established.
Existing Parking Areas
Pavement Section Detail
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Parking Areas with Permeable Paving
Permeable Pavement Choices
TREES SEPARATE PARKING AREA FROM PARK INTERIOR
SIDEWALK
PERMEABLE PAVEMENT
WOODLAND EDGE
Parking Area Along 34th Street South and Upper 34th Street South
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Planting Suggestions Wildflowers/Forbs
Stream Bank Plants
Butterfly Milkweed/ Asclepias tuberosa
New England Aster/ Symphyotrichum novae-angliae
H 12-18” B May-Sep Habitat: prairies, open woods, hillsides Soil: prefers well-drained sandy soils, tolerates drought Light: sun, part shade Attracts butterflies and hummingbirds.
H 24-48” B Aug-Oct Habitat: moist, open, wooded areas, meadows, mesic prairies, disturbed sites, stream banks Soil: moist soils Flowers attract bees and butterflies. Can be aggressive.
Meadow-rue/Thalictrum
Honewort/ Cryptotaenia canadensis
H 12-36” B Apr-May Habitat: rich woods, slopes, alluvial terraces Soil: rich, moist soils Light: part shade
H 12-36” B Jun-Sep Habitat: at edges of streams and low, wet ground Soil: moist Light: part shade
Sky-blue Aster/ Aster oolentangiensis
Wood Nettle/ Laportea canadensis
H 18-36” B Aug-Oct Habitat: prairie, rocky upland woods, savannas, woodland borders, sandy meadows, roadsides Soil: loamy sandy, rocky, or contains clay Flowers attract bees, flies, butterflies, skippers, small mammals.
H 12-36” Habitat: low woods, stream banks Soil: moist, loamy soils Light: part sun, medium shade Provides valuable cover for wildlife.
Yellow Coneflower/ Ratibida pinnata
Marsh marigold/ Caltha palustris
H 24-48” B Jun-Aug Habitat: prairies, thickets, woodland edges Soil: tolerant of a wide range of soils Flowers attract birds and butterflies.
H 12-24” Habitat: Wet woods, stream banks, marshes Light: part shade to full shade Upland game birds eat the seeds. Used by frogs and insects as well.
Zigzag Goldenrod/ Solidago flexicaulis
Jewelweed/ Impatiens capensis
H 24-48” B Jul-Oct Habitat: rich woods and slopes Not require mulching Flowers attract butterflies. Seeds attract birds.
H 3-5’ Habitat: Wetland habitats, stream banks, flood plain forests, marshes, swamps Light: sun to shade Provides important nectar source for hummingbirds, orioles, and bees. Provides cover for frogs and other reptiles.
Black Eyed Susan/ Rudbeckia hirta
Lake sedge/ Carex lacustris
H 12-24” B May-Sep Habitat: prairie, meadows, pastures, savannahs, woodlands edge,opening Soil: moist to dry, well-drained soils Nectar attracts bees, butterflies, insects. Can be aggressive.
H 24-36” Habitat: wooded swamps, stream borders, wetlands Light: sun to part shade An essential food source for a variety of wildlife, including many birds and mammals.
Giant Hyssop/ Agastache foeniculum
Sensitive Fern/ Onoclea sensibilis
H 24-48” B Jun-Sep Habitat: dry, open, semi-shaded areas, roadsides Soil: sandy, well-drained soils Light: sun, part shade, shade Attracts butterflies and hummingbirds.
H 12-24” Habitat: Swampy woods, low areas in moist forests, wet meadows, and shaded ponds Light: part sun to shade Provides habitat cover for small mammals and songbirds.
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Grasses/Sedges
Trees
Pennsylvania sedge/ Carex pensylvanica
Crabapple/ Malus ‘Adams’
H 6-10’ Soil: medium moist soils Light: full sun to part shade Attracts birds, showy flowers, foliage and seed heads. Can be aggressive.
H 15-20’ Best grown in medium moisture, well-drained, acidic loams Soil: a wide range of soils Light: full sun Attracts birds and butterflies.
Big Bluestem/ Andropogon gerardii
Sugar maple/ Acer saccharum
H 48-72” Habitat: usually in low meadows and prairies, warm season grass, moderate salt tolerance, attractive color Light: sun to part shade Provides cover and nesting sites for songbirds.
H 60-75’ Habitat: moist bottomlands, rich, wooded slopes Soil: rich, moist, well-drained soils Light: sun, part shade, shade Susceptible to salt, excessive heat, and leaf scorch in drought. Attracts birds and honey bees.
Small Bluestem/ Schizachyrium scoparium
Crabapple/ Malus ‘Donald Wyman’
H 12-36” Habitat: woodlands edge, opening, hillsides, slopes, prairie, plains, meadows, pastures, savannahs Light: sun to part shade Soil: tolerant of a wide range of soils
H 15-20’ Best grown in medium moisture, welldrained, acidic loams Soil: tolerant of a wide range of soils Light: sun Attracts butterflies and birds.
Blue Grama/ Bouteloua gracilis
Amur Maackii/ Maackia amurensis
H 12-14” Habitat: a dominant grass in dry shortgrass prairies, warm season grass Soil: the most drought-tolerant native turf grass Seeds attract birds.
H 20-30’ Best grown in average, medium moisture, well-drained soil Light: sun, part shade Showy and fragrant flowers.
Karl Foerster Grass/ Calamagrostis x acutiflora
Common Choke Cherry/ Prunus virginiana
H 36-60” Soil: medium to wet soil; does well in heavy clay soils Light: full sun Seeds and showy flowers attract birds. Attractive color, typical ornamental grass.
H 12-36’ Habitat: moist woods, stream banks, prairie hillsides, fence rows, rocky bluffs, roadsides Soil: tolerant of a wide range of soils Light: sun, part shade, shade Fruit attracts wildlife.
Porcupine Grass/ Panicum virgatum
Northern Red Oak/ Quercus rubra
H 24-48” Habitat: dry prairie and open woodlands Light: sun Soil: Dry, rocky or sandy soils Provides nesting materials for native bees.
H 75-100’ Habitat: mesic upland, forests, ravines, north and east slopes Soil: well-drained, loamy sands Light: sun, part shade Attracts songbirds, ground birds and mammals.
Indian Grass/ Sorghastrum nutans
Acer saccharinum/ Silver Maple
H 60-84” Habitat: prairie, open woods, seasonal poor drainage okay Soil: tolerant of a wide range of soils Seeds attract small mammals, birds Flowers attract butterflies. Can be nesting material.
H 75-100’ Habitat: rich bottomlands, moist hillsides, river banks Soil: rich, wet to moist, slightly acid soils Attracts birds A larval host and nectar source ofr butterflies
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City of Afton Public Meeting
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PROJECT PARTICIPANTS City of Afton Afton Park Committee Steve Dorgan, Chair Darcy Cernohous Nathan Shaw Karen Weiss Julianne Berg Ken Johnson, Afton Public Works Supervisor Randy Nelson, Council Member Ward 4 Bill Palmquist, Council Member Ward 1 Diane Hankee, City of Afton Engineer, WSB & Associates, Inc.
Washington County Conservation District Bryan Pynn, Sr. Watershed Restoration Technician
REFERENCES • Audubon Minnesota: mn.audubon.org • Dines, N. & Brown, K. (2001). Landscape Architect’s Portable Handbook. McGraw-Hill Education. • Krauel, J. (2006). The Art of Landscape. Barcelona, Spain: Carles Broto. • Minnesota Department of Natural Resources. (2005). Field Guide to the Native Plant Communities of Minnesota: The Eastern Broadleaf Forest Province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. St. Paul, MN: MNDNR. • Minnesota Department of Natural Resources: www.dnr.state.mn.us. • Shaw, R. & Schmidt, R. (2003). Plants for Stormwater Design: Species Selection for the Upper Midwest. St. Paul, MN: Minnesota Pollution Control Agency. • U.S. Department of Commerce | National Oceanic & Atmospheric Administration | NOAA Research Resources: www.esrl.noaa.gov • Wovcha, D., Delaney, B., & Nordquist, G. (1995). Minnesota’s St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats. St. Paul, MN: State of Minnesota, Department of Natural Resources. • WSB & Associates, Inc. (June 27, 2011). Stormwater Management Plan for County Road 21 and the Old Village Area of Afton. Prepared for Washington County and the City of Afton.
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METROPOLITAN DESIGN CENTER Ignacio San Martin, Dayton Hudson Professor, Chair of Urban Design and Director of the Metropolitan Design Center Adrienne Bockheim, MLA, Research Fellow, DDA Program Coordinator Danfeng Zhang, MLA candidate, Research Assistant 2013 The University of Minnesota is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation. This publication/material is available in alternative formats upon request. Please contact Ignacio San Martin, 612-625-9000. Š 2013 University of Minnesota, Metropolitan Design Center, College of Design Printed on 100 percent post-consumer fiber, processed chlorine free, FSC recycled certified, and manufactured using biogas energy.
For additional information contact METROPOLITAN DESIGN CENTER COLLEGE OF DESIGN University of Minnesota
1 Ralph Rapson Hall, 89 Church Street SE, Minneapolis, MN 55455
smartin@umn.edu