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Because of the inherent complexity of sediment remediation projects, site characteristics (such as source areas, transport mechanisms, background and upstream areas, and key site features) should be clearly identified in a conceptual site model (CSM) before evaluating and selecting remedial alternatives.<\/p>\n
The remedy evaluation framework presented here assists in selecting remedial technologies and evaluating remedial alternatives that are applicable to contaminated sediment sites based on site-specific conditions.<\/p>\n
Background Condition<\/p>\n\t\t\t\t\t<\/div>\n
The term “background” typically refers to substances, conditions, or locations that are not influenced by the chemical releases from the site being evaluated. Background is usually described as either naturally occurring (consistently present in the environment and not influenced by human activity) or anthropogenic (influenced by human activity but not related to specific activities at the site).<\/p>\n
Background conditions and concentrations of chemicals for sediment sites are typically determined from reference samples (obtained from upstream or areas unaffected by site-related sources) and may include the following:<\/p>\n\t \n\t\t
A background data set or threshold value, once calculated, can be used in many stages of a site cleanup including:<\/p>\n\t \n\t\t
Source Control<\/p>\n\t\t\t\t\t<\/div>\n
Identifying and controlling the sources of contaminants to an aquatic system is an integral component to remediating contaminated sediments and effective source control is a prerequisite for applying any of the remedial technologies.<\/p>\n
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Multiple source is possible in large complex site<\/p>\n
Sources that should be controlled can include the following:<\/p>\n\t \n\t\t
When multiple sources exist, they must be prioritized according to risk in order to determine where to best focus resources. Generally, any significant continuing site-related upland sources (including contaminated groundwater, stormwater, NAPL migration, or other releases) should be controlled in a manner and time frame compatible with the sediment remedy.<\/p>\n
Site Characterization Data<\/p>\n\t\t\t\t\t<\/div>\n![\"\"](\"https:\/\/www.envguide.com\/wp-content\/uploads\/2018\/02\/image2-300x213.jpg\")
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Collecting site data for remedial evaluation<\/p>\n
Evaluating remedial technologies requires site-specific data that may affect a technology\u2019s performance. These data needs go beyond the data necessary to delineate the nature and extent of contamination and include information necessary to evaluate sediment stability and transport, contaminant mobility, waterway characteristics, hydrology and adjacent land and waterway use.<\/p>\n
The table 1 in the presents a summary of the types of data that may be required at contaminated sediment sites, potential approaches to obtain the data, and the implications of the data types for remedy selection.<\/p>\n
Remedial Zone Identification and Mapping<\/p>\n\t\t\t\t\t<\/div>\n
Defining remedial zones delineates the overall area and volume of contaminated sediments into workable units that are subsequently considered for remediation. Identifying these units based on site-specific conditions simplifies the evaluation of remedial technologies. Zone identification may not be applicable at every site, but the concept should at least be examined at each site.<\/p>\n
Zones should first be identified based on the distribution of contamination and preliminary remedial goals (PRGs). These zones should be further refined based on site-specific information relevant to the evaluation of remedial technologies. At large complicated sediment sites, however, dividing the site into specific remedial zones will facilitate the focused evaluation of remedial technologies and the development, screening, and evaluation of remedial action alternatives.<\/p>\n
Screening of Remedial Technologies<\/p>\n\t\t\t\t\t<\/div>\n
To simplify this screening step, questions are included as part of the remedy selection framework to help conduct an initial screening assessment of MNR, EMNR, in situ treatment, conventional capping, amended capping, and excavation and dredging. The screening questions may be used to evaluate and screen remedial technologies from further consideration on a zone by zone basis. Further information about screening remedial technologies can be found in other sediment remedy articles.<\/p>\n
Evaluation of remedial technologies<\/p>\n\t\t\t\t\t<\/div>\n
Detailed evaluations of remedial technologies retained after the initial screening step are conducted using site-specific information to identify the most favorable technologies. Based on these evaluations, additional remedial technologies may be eliminated.<\/p>\n
Table 2 lists the physical, sediment, contaminant, and land and waterway use characteristics used to establish the applicability of each of the technologies (MNR, EMNR, in situ treatment, conventional capping, amended capping, dredging and excavation). Each cell corresponds to a characteristic and technology. Each cell also contains a ranking of importance of each characteristic for specific technologies.<\/p>\n