Remediation of Contaminated Sites |
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A more and more common site planning problem is presented to the designer as
former industrial sites are converted to other uses. This is commonly
called brown field development. In association with a host of
consultants, the designer must devise a way of cleaning (or at least
sequestering) toxins to protect public health and environmental systems. The
case study below was developed by Douglas Wright.
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Project DataClick thumbnails for a detailed view
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Project Elements
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Gas Works Park is located
directly north of downtown Seattle on the north shore of Lake Union.
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History
Lake Union Plant during production. (Archive photo)
Richard Haag proposed retaining some of the industrial artifacts of the site. Why?
Site plan of Gas Works Park with significant spaces identified. ( from Johnson and Frankel, 1991)
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The site of Gas Works Park is the former home of the Seattle Gas Company's manufactured gas plant. From 1906 to 1956, the plant manufactured gas from coal and oil. As natural gas imported from Canada became commonplace, the market for manufactured gas dried up and the plant was closed (Richard 1983).
In 1970, the Seattle design firm of Richard Haag Associates was selected to develop the master plan for the park site. In April 1971, Haag submitted his master plan proposal to the city which proposed retaining many of the existing structures, even incorporating them into the new park, stating that the preservation of such objects demonstrated their "historic, esthetic, and utilitarian value" (Richard 1983, p. 9). In addition, the plan called for a minimum number of traditional park plantings. Haag realized that most people in Seattle did not share his sentiment regarding the ugly gas plant structures. With this in mind, he embarked on an extensive campaign to "save the gas works" . The park is basically a number of uniquely defined spaces loosely linked by an asphalt pathway. These spaces include:
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Site Images
Childrens' play area located south of the Playbarn. Pieces of the gas plant machinery have been used in the development of this space and the boundary of the area is formed by a former building foundation.
Panoramic of the North Lawn. Concrete structure in background is a former building foundation which now accommodates a lone picnic table. Both evergreens and deciduous species contain the space, giving way at the lakefront and pulling users toward the water.
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 View of Picnic shelter (l) and Playbarn (r) as one enters the park. (Wright, 2003)
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Design Development
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Master Plan for Gas Works Park, submitted to the Seattle City Council in April 1971. Notice the numerous boat accommodations as well as the plantings near the cracking towers and north of the mound. Boat moorings and plantings in these locations, as well as improvements west of the Prow and throughout the Concourse area were not constructed. Compare with the site plan displayed previously. (from Haag 1971)
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Environmental Issues
How would you characterize the degree of contamination of this site?
True/False One way that contaminated soil was managed at Gas Works Park was to simply bury it in an enormous mound.
Which two additives were ploughed into the contaminated soil to foster micro-biotic soil treatment?
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The operation of the Seattle Gas Light Company manufactured gas plant had a devastating effect on its site. The park proposal required the publication of an Environmental Impact Statement which analyzed existing conditions and considered possible impacts of the proposed park on the site itself as well as on the surrounding area. In addition, the statement proposed mitigation measures which addressed the identified adverse impacts. This document not only considers impacts on natural systems such as plant and wildlife habitat, but also impacts on traffic, neighboring properties, and area economy. But as Elizabeth K. Meyer writes, not all of the existing conditions were examined with equal weight.
Haag understood that the soil in its contaminated condition could not support plant life. To this end, Haag embraced a method of soil remediation which involved the excavation of the contaminated topsoil (approximately 20,000-30,000 cubic yards) and subsequent "burial" in the mound (along with the concrete foundations, slabs, pits, supports, and miscellaneous structures). Soil from the grading of the site and parking lot were spread over the site, and subsequently mixed with bio-degradeable elements such as sawdust and leaves to allow air to circulate in the soil. On top of this material, treated sewage sludge, complete with oil-degrading enzymes, was placed and plowed into the soil. The increased air circulation and the sewage sludge enhanced the bacterial action within the soil, bacteria which would break down the harmful chemicals in the soil. In the end, the bacteria "would literally eat up whatever contaminants had saturated the ground" (Van Dyne 2000). This alternative was weighed against that of removing entirely the contaminated soil but this was cost-prohibitive. Following the soil treatment, the ground was hydro-seeded, grass grew and the park was opened in 1975.
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Post Development Environmental Issues
Study the plan above. The areas outlined in yellow define areas where additional remediation was necessary. Was the majority of the site remediated through Richard Haags method?
True/False Air sparging is a remediation technique that oxygenates the ground water to stimulate micro-oragnisms to convert toxins into harmless forms.
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Testing and scientific studies continued throughout the 1980s and first half of the 1990s, a result of the heightening of environmental awareness. In 1997, funding became available to address the remaining contamination issues at Gas Works Park. Field studies determined that carcinogenic polynuclear aromatic hydrocarbons (PAHs), arsenic benzene and tuolene as well as non-carcinogenic PAHs in the groundwater exceeded the acceptable levels. In addition, the field studies identified two areas within the park which had tar residue near the surface, and this tar and adjacent contaminated soil was removed and remediated using high temperature heating system. The cleanup plan consisted of: • The soils in the southeast area of the park were found to contain levels of benzene which exceeded the mandated cleanup levels. To address this situation, an air sparging and soil vapor extraction system was installed. This system consists of pumping compressed air into the saturated soil through approximately 50 vertical well points. As the air moves to the surface it both oxygenates the groundwater and strips volatile organic compounds (VOC), such as benzene, from the soil. This oxygenation of the groundwater stimulates the biodegradation of dissolved hydrocarbons by native organisms present in the soil (ThermoRetec 20000 As this VOC-laden air reaches the surface it is treated by thermal/catalytic oxydization prior to being discharged into the atmosphere (ThermoRetec 2000). With this system, both the volatile organic compounds such as benzene as well as polynuclear aromatic hydrocarbons are remediated. It is anticipated that the operation of the air sparging and soil vapor extraction treatment system will operate for another eighteen years.
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Project Review
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For his design of Gas Works Park, Richard Haag was awarded the President's Award for Design Excellence from the American Society of Landscape Architects.
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Application of Remediation Principles Define phytoremeiation
Provide an example of plants being used to remove soil or groundwater toxins. Which five of these materials have been effectively removed through phytoremediation according to this web page? arsenic, mustard gas, lead, zinc, cadmium, coal, uranium, nitrates,
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Richard Haag's intuitive belief that soil organism and plants could remediate much of the toxins on the site has proven to be true. Other techniques were required to address some deep contaminants and ground water pollution, but the use of plants to rehabilitate toxic conditions (called phytoremediation) is often very effective and economic. For example the Army Corps of Engineers conducted a study using wetlands plants to extract TNT and other explosive contaminants from the soil and ground water at the Volunteer Army Ammunition Plant, Chattanooga, TN. Cattails, in full sunlight, were able to extract all TNT, and other explosive contaminates steadily from the soil.[5] The cattails in their native habitat extracted more explosive material from the groundwater than in controlled laboratory experiments. The conclusion was that the increase in extraction was due to natural interaction between microbes, plants, and photolytic mechanisms. Other plants for phytoremediation and their application[2]:
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Remediation proposal by Douglas Wright
Which five plants were specified for the removal of contaminants in Wright's remediation proposal for a site in Moscow? By reviewing the three plan phases explain how public use of the site would be possible before the contamination is completely removed. |
These three plans are phases in a toxic soil remediation proposal for a site in
Moscow near the intersection of Highways 8 and 95, where there was a fuel depot.
Research identified a group of plants effective in the removal of contaminants
associated with petroleum spills. The long term contamination resulted in
both shallow and deep penetration of the contaminants. The proposal
devises a way to restore the site while it receives progressively more intense
public use. The large green square in the first plan indicates the
contaminated area to be planted with Poplar trees (cottonwood), apple trees, and
three grasses - rye, fescue and bermuda. The grasses address the
contaminants in the first 18" of the soil while the tree address the deep
contamination.
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