Renaissance Park

Challenge

Monitoring wells installed as part of environmental assessment efforts indicated that capped waste cells located within the site’s 100-year flood plain were leaching semi-volatile organic compounds (SVOCs) and heavy metal contaminants into the groundwater. These cells contained postindustrial waste from the site’s previous use as an appliance manufacturing and enameling facility. Until environmental regulation outlawed such practices, post-process wastes – including enamel frit – were disposed of on-site in receiving cells that were capped once full.

Solution

Following extensive analysis of historic site topographic maps to determine the probable volume of soils commingled with post-industrial waste, more than 18,000 cubic yards of contaminated soil were excavated. Rather than dispose of this material offsite, the design incorporated iconic landforms that would safely seal the contaminated material inside above the 100-year flood elevation, while offering opportunities for recreation, creative play, and views to the Chattanooga skyline. The excavated void was creatively redesigned as a constructed wetland that treats stormwater, increases the Market Street Branch’s floodplain storage capacity, and serves as a backdrop for a 490-seat amphitheater.

• Test wells indicated a bloom of contaminated groundwater down-gradient from the known location of previously capped industrial waste settling ponds within the 100-year flood plain. 34,000 cu yd of contaminated soils were excavated and placed in upland containment cells, safely sealed within the park’s iconic landforms. A drainage system beneath the cells diverts any lingering leachate to the sanitary sewer.
• The portion of the site from which contaminated soils were excavated was creatively redesigned as a one-acre constructed wetland. This feature receives, holds and treats runoff from the site while increasing floodplain storage capacity by 9.32 acre feet. The wetland is lined with a bentonite geosynthetic clay liner to prevent further groundwater contamination. Two feet of freeboard is provided between the wetland’s normal pool level and outfall orifices which discharge into the stream. Gabions, buffered with wetland plantings, artfully establish the water’s meandering path through the wetland.
• A terraced, 490-seat amphitheater arises from the wetland bank, which provides a backdrop to this gathering space.
• Passive controls for wetland inlets and outlets save on energy and maintenance costs.
• 18,000 cu yd of concrete factory floor was salvaged, crushed, and reused on site as fill.
• 300 linear ft of eroded riverbank was stabilized with a bioengineered system consisting of rip-rap, gabions, seeded coir erosion control blanket, logs, root wads and live stakes.
• 708 linear ft of the North Market Branch stream bank was stabilized using planted coir logs, seeded erosion control mat and live stakes. Native riparian species planted along the stream bank improve stream ecology.
• 76% of the landscaped area is planted with non-irrigated, adapted and native plants (23%) and preserved riparian landscape (53%). The planting palette consists of 39 native riparian and wetland plant species, including 4 aquatic plants, 7 forbs and grasses, and 28 trees and shrubs.
• The impervious area of the site was reduced by 21%, from 382,207 sf to 301,849 sf. Most of the existing forest was retained, and the former factory rooftop, asphalt parking areas, and concrete are now meadows, grassy open space, and wetlands.
• 9,025 linear ft of walkways provide multiple opportunities for exercise, relaxation and wildlife viewing. Walkway surfaces include asphalt with loose aggregate finish, pavers and concrete.
• Elevated piers over wetlands and riparian banks provide environmental education and wildlife viewing opportunities. 5 interpretive signs illustrate the cultural history and stormwater treatment process. The signs highlight the site’s heritage as a location of strategic river crossing during the Civil War, “Camp Contraband” encampment for refugee slaves and colored Civil War regiments, and a point of disembarkation for the Trail of Tears. Prompted by signage at strategic locations, park users may take a cell phone audio tour to learn about the environmental and cultural features.
• A new boat ramp, which is accessible from the parking lot under Market Street Bridge, provides river access for kayaks and canoes.
• A 34,400 sf parcel on the northern end of the park was cleared, and contaminated soil was removed so that it meets Tennessee Department of Environment and Conservation standards that allow for future mixed-use development. The property is presently owned by a developer that, at the time of this writing, has expressed interest in building a boutique hotel on the site given proper economic circumstances.

• The client explored alternative “hard engineering solutions” to manage contaminated soils and prevent further groundwater contamination, such as subterranean groundwater diversion walls and an asphalt cap. The implemented “soft” approach was 25% less expensive than these alternatives.
• Remediating 12,000 cubic yards of leaching soil containing commingled frit on site cost $180,000, 75% less than the $720,000 estimated cost to haul the same volume of soil to a proper landfill.

• Accurately calculating the volume of contaminated soil that would be excavated and remediated was critical to managing project budgets. The cost of excavation and remediation activities would limit budget available for other site development agendas and features, and the volume of soil to be treated would dictate the amount of area to be committed to the encapsulation of contaminated soil. The design team was not comfortable basing estimates on conventional methods of extrapolating data from a grid of soil borings alone. Therefore, they conducted a “forensic” topographic analysis using historical maps of the site’s undeveloped and post-industrial conditions, in addition to analysis of 60 soil borings and groundwater monitoring data to generate three-dimensional models of the likely extent of contaminated soil. This in-depth analysis gave the design team the information necessary to allocate budget for remediation activities and design the site accounting for proper soil storage capacity.
   
• During the process of excavating contaminated soils from the site, seasonal rains saturated the soil, prohibiting the contractor from placing it directly into the containment cells as planned. A conventional approach to resolving this challenge suggested that the saturated soils should be spread and air-dried before being placed in their permanent location within the park’s iconic landforms. Air drying the soil on-site would come at a significant expense of time and capital to the project and would risk further saturation by imminent storms. Knowing that the contaminated soil was to be sealed beneath the park’s landforms, the contractor suggested that gravity and the weight of the landforms be leveraged to displace contaminated water from the saturated soil. A wellpoint system was installed to drain the contaminated water as the landforms were built. Contaminated water extracted from the soil was pumped into frac tanks where the frit and commingled soils equalized and settled. The treated water was then released into North Market Branch stream and the remaining solids were added to the containment cells. The system was removed after construction was complete. The cost of the wellpoint system was less than the cost of time that would have been lost spreading the saturated soil on site and allowing them to air-dry.
   
• Commitment from the City to create this park leveraged private development in the neighborhood. During the park’s planning and construction phases, an adjacent property was sold and developed into a residential condominium complex. All the units sold before the park was complete despite the unsightly nature of the construction process. A webcam was even installed by the condominium developers during the predevelopment sales phase, enabling owners and prospective buyers to track the park construction progress. (Note that a number of committed buyers did not follow through with their purchases due to the real estate crisis and recession in 2008.)
   
• A change in City administration and subsequent shift in the project’s priorities resulted in changes to the proposed program. An adventure playground and on-site nursery to cultivate plant materials for adaptive landscape management were originally included in the project concept proposal. The playground was never implemented, and the portion of the site that was to become the nursery was leased to an adjacent bridge reconstruction project for use as a staging and lay-down area. It was never developed for its intended purpose. However, the park’s landforms still inspire creative play; sliding down the hills, on sleds in winter and on cardboard through summer, is a popular Chattanooga pastime featured in Chattanooga Visitor Bureau commercials.
   
• The densely vegetated nature of the preserved riparian floodplain forest raised public safety concerns with City administration. To mitigate these concerns and maintain the project’s design intent in these areas, wider corridors of landscape were cleared around paths and gathering spaces to allow for longer site lines, and security cameras mounted on light fixtures were added throughout the site.

Wetland Liner: CETCO Bentomat geosynthetic clay liner
Wetland Inlets & Outlets: Agri Drain
Light Poles: Hess
Prefabricated Bridges: Moosman Bridge
Site Furniture: Maglin

Project Team

Landscape Architect & Lead Designer: Hargreaves Associates
Structural & Electrical Engineer: Moffatt & Nichol Engineers
Environmental Engineer: S&ME
Lighting Designer: LAM Partners, Inc.
Pavilion Architects: Eskew+Dumez+Ripple, Hefferlin+Kronenberg Architects
Pavilion Engineer: March Adams & Associates, Inc.
Pavilion Lighting Designer: Fisher Marantz Stone
General Contractor: Stein Construction Corporation
Landscape Contractor: Earthscapes
Client: River City Company for Chattanooga Downtown Redevelopment Corporation
Agencies & Organizations: Tennessee Department of Environment and Conservation, U.S. Army Corps of Engineers, Tennessee Valley Authority, City of Chattanooga, The Audubon Society

Role of the Landscape Architect

The landscape Architect led the master planning, resource assessments and permitting of the larger waterfront as well as the design of Renaissance Park. The landscape architect collaborated with the client, consulted with the community and coordinated a multidisciplinary team including marine engineering, environmental engineering, electrical engineering and lighting design.