1, repair technology screening steps Screening of restoration techniques generally takes into account a number of factors such as the characteristics of pollutants, the hydrogeological conditions of the contaminated site, and the characteristics of the remediation technology. Due to the complexity of actual groundwater contaminated sites, the more preferred repair techniques or combinations of technologies can only be determined through analysis and assessment. There is subjectivity in the screening of repair techniques, and there may be multiple solutions. There is no fixed pattern for the screening of repair techniques, and the screening assessment methods vary. The author refers to the United States "based on risk assessment and non-risk considerations of repair technology selection criteria guide", put forward a simple, easy screening method, the specific screening steps are as follows: 1) Elimination of improper repair technologies Firstly, a list of the technologies currently available for groundwater contaminated site restoration is listed, and the "removal" investigation of various repair technologies is conducted for specific groundwater contaminated sites. This phase requires the discovery of those that do not meet the target site Fix the required technologies and exclude them from further evaluation to narrow the range of technologies available for screening. Such as: contaminated groundwater depth, PRB technology can be ruled out; the existence of free-phase NAPL, can be ruled out the first use of AS technology; belong to heavy metal pollution, can rule out microbial degradation of organic pollutants and other technologies. Elimination of pollution remediation technologies requires familiarity with different remediation technologies used in groundwater contaminated sites at home and abroad to master the characteristics and application conditions of various technologies. In the removal of repair techniques, the main consideration of two factors. â‘ pollutant characteristics: pollutant types (organic pollutants, heavy metals, etc.), pollution levels and pollution range. Some repair techniques target only specific types of contaminants. â‘¡ groundwater contaminated sites hydrogeological conditions: aquifer permeability, thickness, depth, aquifer and gas zone with heterogeneity, groundwater flow rate and so on. 2) Evaluation and selection of alternative repair technologies The list of alternative repair technologies for specific groundwater contaminated sites needs to be further screened through the removal of inappropriate repair technologies. Through the establishment of evaluation index system, the groundwater pollution remediation technology can be evaluated and analyzed. There are different evaluation methods and models, such as AHP, ranking comparison analysis model. Different models may consider different factors and different levels of complexity. However, if too many factors are considered in the screening model, the acquisition of model parameters and weights has a greater impact on the evaluation results, but not conducive to practical application and poor operability. In terms of the choice of remediation technologies, there is a need to have a rich background in hydrogeology and practical experience in the repair of groundwater contaminants, and simple methods are often most suitable. The characteristics of different remediation technologies, the characteristics of contaminants and aquifers, and the conditions of contaminated sites can be fully analyzed. Various screened remediation techniques and high scoring remediation techniques can be used to repair groundwater contaminated sites. The choice of groundwater pollution repair technology is closely related to the conditions of the contaminated site and the characteristics of the target pollutants. Therefore, the applicable remediation technologies (or technology combinations) are different for different contaminated sites. 2, repair technology screening scoring method Screening assessment of groundwater contaminated site rehabilitation techniques can include five main areas: technical acceptability, site availability, effectiveness, repair time and repair costs. The technical acceptability score is mainly based on the compatibility of current functional and repair technologies, public concerns and other acceptable standards at the contaminated site; it is fully acceptable (4 points), acceptable (3 points), generally acceptable (2 points), partially acceptable (1 point). The applicability of the site scoring mainly considers the feasibility and reliability of the restoration technology under the stratigraphic conditions of the site and whether the restoration technology has been implemented on the same type of site. It is divided into fully applicable (4 points), applicable (3 points), Generally applicable (2 points), locally applicable (1 point). The validity score was evaluated based on the repair effect of the repair technique on similar sites; it was classified as: very effective (4 points), effective (3 points), generally effective (2 points), and locally effective (1 point). The repair time score is assigned based on the expected repair time; it is divided into short (4 points), medium (3 points), long (2 points) and very long (1 point). The reimbursement rates are based on expected remediation costs; they are divided into low (4 points), medium (3 points), high (2 points), high (1 point). Each repair technique is divided into five indicators were scored, each index can be assigned the value of 1, 2, 3, or 4 points; score higher, indicating that the technology is more conducive to the application of site repair. The total score of 5 to 20. In addition to the five indicators listed in the table, the screening of groundwater contaminated sites remediation techniques sometimes need to take into account factors such as the sustainability of remediation technologies and environmental impacts. Especially in developed countries, at present, the application of remediation technologies for contaminated groundwater places more emphasis on green and low-carbon requirements.
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