In the United States, the Army Corps of Engineers is responsible for maintaining over 30,578 km (19,000 miles) of navigable waterways in over 1000 harbors and ports. These navigation activities in the ports are currently managed by dredging the bottom sediments (annually, which accounts for 300 million cubic yards or 230 million cubic meters) and transporting it elsewhere for disposal. The water bodies accumulate upstream sediments in the bottom of the lakes or river channel beds as a natural process of aggradation that is intensified in urbanized watersheds [1
]. The disposal of the dredged material is executed either through open water disposal (OWD) or placed in confined disposal facilities (CDF) [1
The dumping of dredged material in a CDF or OWD in the prolonged duration is recognized to have environmental impacts on the areas of disposal and its immediate surroundings [3
]. As illustrated in Figure 1
, the dredged material disposal leads to three main concerns. First, the migration of contaminants is caused by the transportation of heavy metals like arsenic, cadmium, chromium, copper, lead, manganese, mercury, etc. For example, in the case of OWD, the exchange of nutrients in sediments and organometallic interaction results in the release of toxic substances into the water column [4
]. In case of CDF, the leachate leaches through the underlying soil into the groundwater [3
]. Second, the environmental concerns on OWD question the quality of water and its effect on aquatic life [4
]. The disposition of dredged material in the CDF raises a red flag due to the deterioration of a groundwater table and contamination of underlying soil, which causes health hazards to the surrounding neighbourhood [3
]. Third, the dredged material management poses difficulties in the disposal of a huge quantity of material annually in the existing CDFs; resulting in a requirement for new CDFs. However, due to urbanization surrounding the ports and harbors, the new CDFs are forced to be located at a greater distance from the dredging site, increasing the disposal cost due to transportation [1
An alternative to disposal is to reuse the dredged material in the built environment like construction and landscaping [7
]. Moreover, 90 percent of the dredged material is considered acceptable for alternative reuses [1
] as the dredged material primarily consists of natural sediments such as gravel, sand, silt, clay, and organic particles [1
]. However, these sediments could be contaminated by municipal or industrial wastes or by runoff from terrestrial sources such as agriculture land [4
]. Therefore, the examination of contaminants like heavy metals, fertilizers, sewer waste, pesticides, and petroleum products is recommended to evaluate and treat the material before re-use [11
], along with testing on physical characteristics (grain size distribution and plasticity); engineering characteristics (compaction, consolidationm and shear strength), and chemical characteristics (cation exchange capacity, nitrogen content, and sulfur content), depending on the structural or non-structural application of dredged material [1
]. See Table 1
The use of dredged material is a widely used methodology resulting in nearly 2000 man-made islands and 1100 habitat development projects [1
]. As illustrated in Figure 2
, the environmental enhancement using dredged material generally refers to formation and management of relatively perpetual and biologically productive manmade plant and animal habitats, such as enhancements of harbor and port facilities, strip mine reclamation and solid waste landfill, parks and recreation enhancement, and beach nourishment, where the dredged material feasibility is employed. The utilization of dredged material in agriculture, horticulture, and forestry is primarily used to enhance marginal soil to elevate the productivity of the vegetables, fruits, ornamental plants, orchards, sod farms, and trees with its rich mineral contents for commercial uses. Lastly, one of the unique beneficial uses of the dredged material, identified by U.S. Army Corps of Engineers, is to produce lightweight aggregate (LWA) that can be used in subsequent constructions [1
], which are formed by sintering the dredged material with or without mineral admixtures (e.g., calcium and magnesium carbonates and/or silicates) [1
]. The applications of dredged material in the habitat development, agriculture, and engineering use, such as a land creation, land improvement, berm creation, shore protection, capping, construction material, topsoil, fisheries improvement, and wetland restoration demonstrates the feasible alternatives that are more economical, social, and environmentally beneficial to the surrounding environment, in comparison to the traditional OWD and CDF disposals [1
As recognized by the United States Environmental Protection Agency (US EPA), green infrastructure (GI), which includes bioretention, rain gardens, rain barrels, swales, permeable pavement, and constructed wetlands [14
], is an approach using vegetation and growth media (natural process in the built environment) that urban dwellers can choose to maintain healthy water, provide multiple social, economic and environmental benefits, and support sustainable community development [16
]. GI restores dwindling green spaces available in urban and suburban areas, with major functions of reducing the volume of stormwater runoff and peak flow [17
] and providing a broad range of ecosystem services, e.g., reduction of concentrations of nutrients and metals in nearby water bodies [20
], mitigation of urban heat island effect [17
], carbon sequestration [29
], improvement of aesthetics, noise reduction [32
], and community livability [20
Living architecture (LA), in the form of vegetated roofs and walls, provides an array of ecological services in hydrology [14
], air temperature [17
], biological diversity [15
], human wellness and it separates itself as a field of study focusing on structural and mechanical building adaptions using soil and vegetation [20
]. Conceived mainly as rainfall interceptors to reduce storm water runoff [18
], roofs are now being designed as novel ecosystems possessing suites of ecosystem services ranging from providing habitat for rare wildlife species [15
] to nature access for human restoration and wellness [43
The high-water absorption rate (10.96–23.40%) and low specific gravity (SG) of the LWA made by dredge material samples (SG 1.46–1.74) [6
] demonstrates a potential beneficial use in green infrastructure and living architecture to enhance its hydraulic soil performance, by increasing infiltration and permeability preventing site stormwater runoff.
The LA/GI rely on soil-plant interactions where the soil provides an environment to anchor plants to the site while containing essential plant nutrients, and in turn, the plant roots prevent soil erosion and utilize soil nutrients and organic matter for growth and defense. However, most forms of LA/GI use engineered soil in the place of natural soil to retain greater volumes of water and nutrients that improve storm water runoff quantity and quality [44
]. The plants use physical, chemical, and biological processes to filter and clean the storm water, improving the water quality [14
]. The benefits of GI, especially in stormwater management and the urban heat island effect, is successfully obtained by cautiously choosing the engineered growth media as it influences the plant growth by providing nutrients and enhances the GI performance due to peak flow reduction, improvement in water quality, thermal insulation, and sound insulation in case of green roofs [44
The engineered growth media is heterogeneous in nature, consisting of coarse aggregate (lightweight and porous), fine aggregate (sand), and organic matter [52
]. Currently, there are numerous commercial engineered growth media available in the market, manufactured using naturally available LWA like lava, pumice, expanded slate, clay, and shale. However, they are costly due to the utilization of finite natural resources, which are mostly available in few locations resulting in increased substrate cost. Hence, there is a need for additional investigation for alternative lightweight material to use in growth media, which is locally available to lower the construction cost of GI [45
]. One such attempt is made in this study and discusses the strategy of how dredge material could be used in the construction of GI. The study discusses the beneficial uses of dredged material in GI by investigating the quality of dredged material and the performances of GI built using dredged material through laboratory and field-testing. The paper also discusses the initial performance criteria that can be achieved and acknowledges the sustainability achieved using the dredged material.
2. Site Description
Lake Erie is the most productive lake among the five Great Lakes. It promotes tourism, recreational opportunities, and serves as a source of drinking water for millions of people living along its shoreline. The Lake is divided into three basins: The Western basin, the Central basin, and the Eastern basin (Figure 3
). It is 388 km (241 miles) long and about 92 km (57 miles) wide, where the Eastern basin has a maximum depth of 64 m (210 feet). It has 502 km (312 miles) of shoreline in the State of Ohio where there are eight major federal navigation harbors built along the coast. These harbors serve the purposes of either commercial (i.e., to transport mineral sources like salt and limestone within the basin), recreational, or both [5
To maintain economic viability and the sustainable development of harbors and ports built along the coast of Lake Erie, 1.15 million cubic meters (1.5 million cubic yards, CY) of dredged material needs to be removed annually. Landfill of the dredged material is costly and occupies valuable land space, while OWD has the potential to deteriorate water quality through siltation, increased turbidity, and mobilization of potential contaminants, therefore increasing the risk of algal bloom [4
]. The OWD of dredged material in Lake Erie will be banned in the State of Ohio after 1 July 2020 [53
]. In Cleveland, dredged material is disposed off in a 42.1-hectare (104-acre) CDF, maintained by the Cleveland-Cuyahoga County Port Authority.
Nevertheless, additional capacity is needed to accommodate the 172,000 m3
(225,000 CY) of sediment that needs to be disposed off in this facility annually to keep the site operational and maintain its economic viability for the Port of Cleveland; therefore, raising a major challenge of how to treat the huge amount of material removed from the ports in Ohio. Moreover, the disposal of dredged material in a CDF is costly and has a major influence on the surroundings and the water table below. An alternative to disposal is to reuse the dredged material in the built environment like construction and landscaping material [6
During the study, it was observed that there were two types of dredged material products, that could be used in the GI construction, raw dredged material [1
], and sintered products [6
]. The raw dredged material is the sediment in its original unaltered form, and the sintered material is the manufacturing and processing of the sediment into an industrial “baked” commercial product [1
]. The application of raw dredge is most common and occurs within the categories of beneficial uses discussed above [1
]. The beneficial use of raw dredge material stems from the growing demand for construction materials and dwindling inland sources. LWA has been successfully made from sintered dredged material taken from the Harbor of Cleveland [6
], which could potentially create an ecologically beneficial product, as well as an economical alternative compared to the currently produced LWA.
The suitability of using the dredged material from the Harbor of Cleveland in the built environment was evaluated by Liu and Coffman [6
]. The paper in Reference [8
] demonstrated the contents of the major heavy metals (Arsenic, Cadmium, Chromium, Copper, Iron, Lead, Manganese and Mercury) to be lower than the Risk Screen Levels specified by U.S. EPA (EPA SW846 6010B, EPA SW846 7471A, EPA 335.2 and EPA SW846 7196A) for residential and industrial uses. In addition, the research group completed the leaching test to examine leaching potentials of heavy metals from the sintered lightweight aggregate made from dredged material taken from the CDF in Cleveland. Heavy metals were not detected from the leachate. Hence, the toxicity risk of the aggregates, sintered from the dredged material, has been proved to be low in this study.
Many cities in the Lake Erie region are transitioning away from industry and manufacturing economies in the hope of reclaiming urban cores lost later in the 20th century, as a part of global trade and suburbanization [54
]. This has resulted in new core architecture growth and dispersed remnant vacant post-industry lands. In some cases, the combination of concentrating development in urban centers, while planning for distributed urban green infrastructure could be mutually beneficial. For example, the City of Cleveland, being the manufacturing and industrial center for Cuyahoga County, hosted many industries back in the day, which resulted in dense residential neighborhoods. After the 1980’s, the City observed a period of high unemployment due to the shutdown of industries. Most of these industrial sites, which were heavily polluted, turned out to be brownfields (5666 hectares/14,000 acres) with almost 90 percent of impervious surfaces [10
]. These impervious surfaces adversely contribute to the water quality impairment of urban waterways due to the reduction in volume of soil infiltration, resulting in the increase of the rate and volume of storm water runoff in nearby water bodies [55
]. In addition, these un-remediated brownfields devalue and destabilize neighborhoods around this area, and the impervious surface increases flooding concerns in combined sewer overflow areas where many brownfields are located [54
The growth media in GI could help emphasize infiltration and hydrological retention, whereas, plants using biological processes could potentially provide a flexible and affordable solution to reduce stormwater runoff in the urban brownfields in Cleveland and many other cities. Living architecture, e.g., vegetated roofs and walls, can provide rainfall capture and recycle for environmental co-benefits on building structure and infiltration limited locations. Therefore, utilizing the dredged material in GI and living architecture would help improve the resilience of Lake Erie, on the one hand, and mitigating the issue of infiltration on the other, a seemingly inevitably circular economy [56
] solution. The dredged material may supply nutrients to plant growth in GI, and raw mineral materials to produce LWA, which has a high hydrological retention capacity for GI construction. This study discusses the potential applications of dredged material in the construction of GI by investigating the water quality and hydraulic performances of two types of substrate mix using dredged material through laboratory and field testing to reduce storm water runoff, which affects people residing on the coast of Lake Erie.
This study examined the current challenges facing Lake Erie and surrounding communities: Algal blooms due to the eutrophication especially increasing phosphorus content in the lake, and dredged material management. To manage stormwater runoff is the necessary step to address the issue of non-point phosphorus pollution in Lake Erie. This article strategically proposed how to use raw dredged material and LWA sintered from dredged material in GI constructions. Here, the quality of the raw dredged material was examined in the lab through chemical and physical testing, its suitability for lightweight aggregate production and GI construction for industrial and residential use. Then, the dredged material was used to develop the engineered filter media for bioretention systems and growth media for green roofs.
The two types of growth media (type 1 and type 2) made from dredged material were successfully developed in the lab, with excellent water retention capabilities to manage the storm water. However, the two engineered growth media had high wet unit weights, due to the heterogeneous nature of the substrate and different densities of LWA, sand, silt, and clay. Hence, there is a need to develop a lightweight growth media composition with a high water retention capacity that would help retain high volume of storm water. Further, the leachate test results demonstrated the water quality of Type 1 and Type 2 substrates, comparable with the drained water from commercial product Rooflite®
The study only investigated Viola pedatifida because of its difficulty to establish and persist in disturbed and engineered soils. Field testing plots for additional green roof microcosms have be constructed at the Cleveland Industrial Innovation Center (CIIC) through an existing memorandum of understanding between CIIC and Kent State University. Native, exotic, and rare plants including Sedum album, Sedum kamchaticum, and Solidago ptarmicoides are under investigation for their potential applications in the newly developed growing media made from the dredged material.
To beneficially use the dredged material in GI construction, several challenges must be addressed: (1) Determine the contamination of the dredged material and its suitability to be used in the built environment; (2) evaluate the performance of the dredged material as a GI construction material; (3) investigate the cost and sustainability issues; and (4) evaluate regulatory issues and public acceptance. This study proposed solutions to the first two challenges. The research team is developing a business model that determines market relevance of the technology through partnerships with industry and manufacturing involving direct, indirect, and life cycle cost analysis. In addition, the research team is collaborating with Ohio EPA to evaluate regulatory issues and to promote its beneficial uses in the built environment. The research team will also investigate other ecosystems benefits of green infrastructures made from dredged material and strategies to install these infrastructures in the urban area to improve the resilience of Lake Erie and its local communities in the future.