Dune Peninsula at Point Defiance Park

Challenge

• Contain contaminated soil and remediate a toxic Superfund site by transforming it into a public destination park.
• Make publicly accessible for the first time a waterfront vantage point with uniquely beautiful vistas and the opportunity to observe marine habitat with and watch whales, orcas, and seal in an adjacent habitat basin.
• Create healthy, biodiverse nearshore and terrestrial habitat for local plants and wildlife by reducing pollutants entering the water and reintroducing Puget Sound prairie, an endangered landscape with only 3% of its original range remaining.
• Showcase a prairie landscape typology and encourage replication of planting approaches throughout district parks and interstitial sites to provide habitat connectivity within Tacoma’s Metro Parks, and serve as an example for future projects aiming to reclaim industrial sites as recreational destinations that promote rich, productive habitat and varied ecologies.
• Positively impact mental and physical well-being, social engagement, and access for visitors by connecting the park and waterfront to the rest of the city via a universally accessible multi-modal trail, filling a critical missing link in the long-planned Downtown-to-Defiance multi-modal trail, and offering new intergenerational recreational opportunities and meaningful engagement with nature.
• Offer inclusive opportunities for all ages and abilities to engage in discovery and play through wide accessible paths, ample seating, interactive art, and additional design elements with flexible uses.
• Provide educational opportunities for visitors that support environmental awareness, conservation, and approaches to low-maintenance landscapes while demonstrating to the Tacoma Parks Department that people respond positively to parks with native habitat.
• Connect visitors with the site’s “spirit of place” by expressing through landscape, art, and word a narrative that reflects the complex identity of Tacoma, its aspirations for the future, and the tension between the site’s productive industrial past and its rich natural history.
• Catalyze the local economy and encourage new development by providing a desirable public amenity through the remediation of an industrial-era environmental hazard that has been unjustly burdening the nearby, largely working-class and minority, community for years, through contamination of air, soil, and water.
• Show sensitivity to the maintenance limitations of small parks departments while providing a greater ecological benefit than typical monoculture landscaping.

• 11 acres of soil and slag contaminated with lead, arsenic, and copper (comprising over 400,000 cu yds of soil and a 5,000-ft perimeter of slag slopes) were recycled, capped, and stabilized to protect the adjacent waterway, which supports endangered king salmon and orca whales, from toxic erosion and pollution. The capped fill was sculpted to provide an ADA-accessible slope for parking areas and trails, and raised landforms were carefully amended in planting areas. Sculpted landforms called “sail mounds” are built up with contaminated fill and capped with clean soil.
• Dune Peninsula’s 16-ft-wide main pathway provides a universally accessible multi-use trail connection from the Ruston Way waterfront into Point Defiance Park, previously a “missing link” without connectivity for pedestrians. 4-ft-wide and 8-ft-wide loop paths offer prospects of the Puget Sound atop elevated mounds that complement the main path. Paths are used for walking, jogging, dog walking, skating, and cycling, and the site also hosts a pathside bike repair station.
• 5 acres of native prairie habitat were created on site to support the recovery of an endangered ecosystem and reflect the site’s pre-industrial condition. Native species include slender cinquefoil (Potentilla gracilis) and common woolly sunflower (Eriophyllum lanatum). 
• 3 works of site-responsive public art, one referencing the park’s namesake (Frank Herbert’s classic science fiction book Dune), along with landscape features and narrative signage, communicate a “spirit of place” conveying the tension between a productive but polluting industrial past and the reintroduction of an endangered native habitat. Along with the native flora and fauna on display, these storytelling elements offer enhanced ecoliteracy.
• An accessible picnic pavilion; a lawn with a theater switchboard and power source for concerts, performances, and other social events; and ample and varied seating provide opportunities for building positive social and community connections.
• Features that encourage play and exploration include precast concrete “kettles,” seat steps, a zig-zag mow strip, and sand-lens walls.
• At the north end of the park, a sail mound slope and an open lawn form an amphitheater and concrete stage supporting multi-use, outdoor events capable of hosting up to 2,000 people.
• The site provides equitable access and connections with nature in an area that was previously inaccessible for residents and visitors, offering unparalleled 270-degree vistas of the Puget Sound, ferries, Vashon Island, the Olympic and Cascade ranges, and the iconic Mount Rainier.

Dune Peninsula is a site of remediation; it is the result of a decades-long project to transform a Superfund site on Tacoma’s waterfront into an intergenerational recreational space that celebrates the region’s natural history and acknowledges its industrial past.

Once pristine waters fished by indigenous populations, this man-made peninsula was formed through the accretion of arsenic and lead-laden slag that was dumped into the Puget Sound by the American Smelting & Refining Company (ASARCO) for nearly 100 years until the plant’s closure in 1985. The smelter’s 571-ft smokestack was a symbol for jobs and community-building but also stood as an ominous reminder of environmental damage and health costs that resulted from its toxic pollutants. This environmental destruction was so epic, it is reputed to have inspired the plot of the novel Dune written by Tacoma’s own Frank Herbert. The implosion of the smokestack in 1993 was witnessed and celebrated by the community as a sign of progress and renewal.

To make the peninsula safe, a cap was added to contain the slag and its dangerous heavy metal pollutants. There are three kinds of caps on the peninsula: low permeability asphalt, low permeability concrete, and a multilayer cap composed of a geocomposite clay layer, 40-mil high-density polyethylene geomembrane, and a geonet. Each cap type prevents water from infiltrating the contaminants and entering Commencement Bay. The cap system is required to have a very low permeability rate. It covers the entire peninsula and ties into the adjacent Point Ruston site, which is also a Superfund site with a cap underneath. Mounds of clean soil were layered over the cap to keep contaminants sealed off from plants, animals, and humans. The shoreline was armored with clean rock to prevent slag from eroding into the bay.

As part of the shoreline armoring, the slag was excavated to a 2:1 slope and materials were relocated on the peninsula in the Yacht Club parking lot and under the park. This stabilizes the cap, raises the site’s overall elevation by 10 to 20 ft, and offers a path of travel easy enough for those with limited physical abilities. The installation of Dune Peninsula at Point Defiance Park, named in honor of Herbert’s famous novel, allowed people to safely access the peninsula for the first time in history.

The site’s history is told through public art, signage, industrial relics, and most notably through the reintroduction of native Puget Sound prairie. Dune quotes embedded in the sidewalk offer moments of discovery, and art by Adam Kuby and Nicole Rathburn further reference the site’s industrial and literary ties. Descriptive illustrations of several native plants and animals that can be found in the park or just offshore contextualize these stories within present-day Dune Peninsula at Point Defiance Park to demonstrate the value of habitat restoration and creation.

The multi-use play features throughout the site eliminated an estimated cost of $380,000 for the sole-use play equipment that is typically used in traditional park design while maintaining the developmental benefits of supporting play. This alternative approach expanded opportunities for play to a wider set of users, including adults.

• The Puget Sound prairie plantings initially suffered from over-irrigation. The prairie, as a native habitat, is able to succeed with minimal external inputs of water or fertilizer. However, entrenched maintenance regimes combined with COVID-19 pandemic-related staff turnover caused disruptions in communication, which led to misunderstandings about the appropriate ongoing care for prairie plantings and too much irrigation. Ensuring continuity of plant care information for park staff is needed, particularly when introducing landscape typologies that are different from what is currently typical.
• The planting plans were designed in large part in response to uncontaminated sandy soils found beneath the contaminated layer of soil that were identified during a deep excavation related to an adjacent project. The landscape architects created soil test plots to determine the most appropriate amendments for the desired plant palette and available soils. The adjacent project site was then used to supply the clean soil used on the Dune Peninsula Park site. However, construction sequencing did not expose the required soils at the right time, so a compromise was made to use available soils that had higher silt content. The use of siltier soils caused delays in wet season construction and increased the compaction of planting soils, leading to some areas holding much more water than intended. This problem was compounded by the over-irrigation described above. The impact on the prairie is a reduced species diversity in some pockets where the more the drought-tolerant local sedges, grasses, and wildflowers have been replaced by water-loving volunteer species like juncus, cattails, and clover.
• The strategy to use amended site soils depended on utilizing sterile subsurface soils from deeper excavations, which were free of weed seed bank. However, several landscaping areas within the project and adjacent areas saw significant weed eruption. The design team discovered that the contractor had exhausted stockpiles of subsurface soils and resorted to using soil from more recent surface excavations. As a result, the weed burden in those areas is dramatically higher than in the other areas of the park, leading to increased maintenance costs and decreased biodiversity in those areas.
• The addition of native prairie instead of lawn has prompted interest in, and revealed a pattern of respect for the native plantings by park visitors. The low cable fence and the occasional “Keep off of the Prairie” sign has been successful at preventing visitors from walking on the prairie, and plant enthusiasts have been posting on social media about the unusual species discovered on the site.
• When planning seed mixes for native restoration projects it is important to consider that seed availability is highly variable at large scales. In the case of Dune Peninsula, the weather negatively impacted the harvest of some seeds with the required genetics, requiring additional effort and resulting in a seed mix missing the full complement of species needed to replicate the desired native prairie ecosystem.
• Early designs were criticized for not including a formal playground. However, several special landscape features have proven to encourage a variety of exploration and play activities and engage both children and adults. These features include vertical elements like precast concrete “kettles,” unusual seat steps, a zig-zag mow strip, and sand-lens walls. Each sail mound includes a unique discovery at the summit to complement their respective dramatic views.

Irrigation Heads and Controller: Rain Bird
Segmental Retaining Wall: Ultrablock
Rock and Boulders: Washington Rock and Quarry
Stormwater Filtration: Contech Filterra
Turfgrass Seed: Barenburg
Prairie Seed: Center for Natural Lands Management
 

Project Team

Client: Metro Parks Tacoma
Landscape Architect and Prime Consultant: Site Workshop
Artists: Adam Kuby and Nicole Rathburn
Remedial Action Engineering: Jacobs Engineering Group
Civil Engineering and Shoreline Permitting: Parametrix
Bridge Engineering: COWI
Architecture: BOEarchitects
Geotechnical Engineering and Environmental: GeoEngineers
Electrical Engineering: Cross Engineers
Cost Estimating: Project Delivery Analysts
Prairie Consultation and Primary Seed Source, Consulting Resource ISWP, Irrigation Design: Center for Natural Lands Management
Soil Science: Rozewood Environmental Services
Environmental Graphics: Michael Courtney Design

Role of the Landscape Architect

As prime consultants, the landscape architects managed the project including coordination with the Superfund stakeholders and cleanup. They performed all site planning and design from concept development through construction administration including grading and earthwork, planting design, construction detailing, and incorporation of artworks and environmental graphics.