Technical method for monitoring natural attenuation of hexavalent chromium polluted underground water

Abstract

The invention relates to the technical field of natural attenuation monitoring, and discloses a technical method for monitoring natural attenuation of hexavalent chromium polluted groundwater, and the method comprises the following steps: judging whether a hexavalent chromium groundwater polluted land parcel is suitable for adopting a natural attenuation monitoring technology or not; if yes, updating the plot conceptual model and carrying out simulation analysis, and integrating various feasibility evaluation factors to judge whether the natural attenuation monitoring technology is feasible or not; if yes, an application scene is determined, a monitoring scheme for monitoring the natural attenuation project is designed, and a periodic target of project operation is formulated; and finally, evaluating the monitoring natural attenuation implementation effect from two aspects of process evaluation and end evaluation. The method has the advantages of being scientific, efficient and high in practicability, and reference and technical support can be provided for underground water risk management and control of the chromium pollution site in China.

Description

Technical Field

[0001] The invention relates to the technical field of natural attenuation monitoring, and in particular to a technical method for monitoring natural attenuation of hexavalent chromium-contaminated groundwater. Background Art

[0002] Groundwater is an important component of water resources. It is of great strategic significance in ensuring the lives of urban and rural residents, supporting economic and social development, and maintaining ecological balance. The safety of groundwater drinking water sources is related to the health of the people. The prevention and control of groundwater pollution is an important part of promoting ecological civilization and ensuring national security. Chromium is involved in industries such as alloy manufacturing, electroplating, tanning, glass, dyes, pigments, oil and gas. The improper storage of waste residues and waste liquids accumulated over many years of production has made chromium one of the most common heavy metal pollutants in my country's soil and groundwater. Chromium pollution is mostly caused by disorderly accumulation of chromium residues on the surface and contaminated soil in the aeration zone that continuously enters groundwater. Due to the strong mobility of hexavalent chromium in groundwater, chromium-contaminated sites often form pollution plumes with long vertical travel. In order to strengthen the risk control of groundwater in chromium-contaminated sites, it is urgent to conduct in-depth research and application of green and low-energy technologies such as monitoring natural attenuation, microbial remediation, and institutional control.

[0003] Monitored natural attenuation (MNA) is a remediation method that reduces the concentration, total amount, toxicity and mobility of pollutants in soil and groundwater to an acceptable risk level within a reasonable time frame by implementing a planned monitoring strategy based on the natural attenuation effects of physical, chemical and biological processes that occur naturally at contaminated sites. Compared with other "active" remediation technologies (physical, chemical or biological remediation), MNA has been widely used, especially for groundwater pollution remediation, because it has the advantages of less interference with the underground environment and relatively low remediation costs.

[0004] At present, the technical documents on monitoring natural attenuation issued by some developed countries such as the United States, the United Kingdom, and the Netherlands are mainly aimed at the overall work of monitoring natural attenuation. For example, some technical documents are specifically aimed at organic pollutants such as gasoline and organic chlorides. The above guidelines all provide evaluation processes and methods suitable for their respective national conditions and pollution site supervision models, but the guidance on chromium-contaminated groundwater sites is not targeted enough. As an active heavy metal, chromium can be converted between trivalent and hexavalent valence states. At the same time, the complex anion of hexavalent chromium has stronger water solubility and mobility than other heavy metal ions. Its natural attenuation mechanism is significantly different from that of organic and other inorganic substances. Existing technical achievements focus more on the universal concept and technical process of monitoring natural attenuation. No technical requirements for monitoring natural attenuation are proposed for the migration and transformation mechanism of hexavalent chromium. There are obvious deficiencies in guiding the work of monitoring natural attenuation in hexavalent chromium groundwater contaminated sites.

[0005] The current management of groundwater contaminated sites in my country is mainly based on a series of guidelines such as the "Technical Guidelines for Groundwater Remediation and Risk Control in Contaminated Sites (HJ 25.6-2019)". There is still a blank in the guidelines specifically for the natural attenuation technology of hexavalent chromium monitoring in my country, and the existing technical achievements in foreign countries and other developed regions cannot be effectively connected with the management requirements of contaminated sites in my country, and cannot provide guidance and reference for industry practitioners in this field. Therefore, combining my country's contaminated site supervision system and technical requirements, inventing a natural attenuation technology system for monitoring chromium groundwater pollution is an important technical means to solve the problem of the blank of the technical system for monitoring the natural attenuation of hexavalent chromium groundwater contaminated sites in my country. Summary of the invention

[0006] The purpose of the present invention is to provide a technical method for monitoring the natural attenuation of hexavalent chromium contaminated groundwater. On the premise of judging whether the natural attenuation monitoring technology is suitable for chromium contaminated groundwater, a comprehensive technical feasibility assessment is carried out to further guide engineering design and construction, and ensure the safe operation of the natural attenuation monitoring project. The method has the characteristics of scientific efficiency and strong practicality, and can provide reference and technical support for the risk control of groundwater in chromium contaminated sites in my country.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for monitoring natural attenuation of hexavalent chromium contaminated groundwater, the method comprising the following steps:

[0009] S1, Applicability analysis: Based on the basic conditions for site screening, hydrogeological conditions, and site pollution survey data, determine whether the hexavalent chromium groundwater contaminated site is suitable for the monitoring natural attenuation technology;

[0010] S2, feasibility analysis: If the hexavalent chromium groundwater contaminated land is suitable for the monitoring of natural attenuation technology, a supplementary survey of the land will be conducted based on the risk control objectives, and the conceptual model of the land will be updated; a simulation analysis will be conducted based on the updated conceptual model of the land, and a variety of feasibility assessment factors will be combined to determine whether the monitoring of natural attenuation technology is feasible;

[0011] S3, Project design and implementation: If the technology for monitoring natural attenuation is feasible, the application scenario will be determined in combination with the hydrogeological conditions of the site and the temporal and spatial evolution trend of groundwater pollutants, a monitoring plan for monitoring natural attenuation projects will be designed, and phased goals for project operation will be formulated;

[0012] S4, Effect evaluation: Evaluate the effect of natural attenuation monitoring implementation from two aspects: process evaluation and final evaluation.

[0013] Furthermore, in S1, whether the hexavalent chromium groundwater contaminated land is suitable for the monitoring natural attenuation technology is determined based on the basic conditions for land screening, specifically including:

[0014] Determine whether the hexavalent chromium groundwater contaminated land is not suitable for monitoring natural attenuation technology, including:

[0015] The targeted pollution plume control and remediation work is urgent;

[0016] Located in groundwater sensitive areas such as groundwater drinking water source protection areas;

[0017] Failure to meet the requirements of land use planning or environmental assessment;

[0018] The risk to human health in the area where the groundwater contamination plume is distributed is unacceptable;

[0019] Pollution sources or high-concentration pollution centers have not been eliminated or risk control plans have not been implemented.

[0020] Furthermore, in S1, judging whether the hexavalent chromium groundwater contaminated land is suitable for the monitoring natural attenuation technology based on the hydrogeological conditions includes:

[0021] Based on four hydrogeological conditions, namely, rock and soil pore type, aquifer medium type, stratum structure, and topography, the suitability of the hexavalent chromium groundwater contaminated land for the use of monitoring natural attenuation technology is divided into three categories: high, medium, and low. Among them, the hexavalent chromium groundwater contaminated land is judged to be suitable for the use of monitoring natural attenuation technology when the suitability is high.

[0022] Furthermore, in S1, judging whether the hexavalent chromium groundwater contaminated land is suitable for the monitoring natural attenuation technology based on the land pollution survey data specifically includes:

[0023] Obtain site pollution survey data including groundwater pollution plume morphology and change characteristics and chromium contaminated soil and aquatic media monitoring data;

[0024] Based on the hydrogeological conditions and the analysis of the land pollution survey data, if the following two conditions are met, the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology:

[0025] (1) The existence of natural attenuation is judged based on the spatial variation of the ratio of conservative ions and pollutant concentrations in a single-period pollution plume;

[0026] (2) Based on the changes in the morphology of the pollution plume over time, it is judged that the pollution plume is showing a stable or shrinking trend;

[0027] (3) Based on soil and water-containing media chromium pollution monitoring, it is determined that the hexavalent chromium or trivalent chromium content exceeds the background value.

[0028] Furthermore, in S2, supplementary land survey is conducted based on the risk control objectives to update the land conceptual model, specifically including:

[0029] Conduct supplementary investigations on hydrogeological conditions, characteristic pollutants, biogeochemical conditions, and biogeochemical reaction parameter characterization to obtain supplementary survey data for the plots;

[0030] Identify natural attenuation based on the characteristics of pollution plume changes, geochemical indicators, indigenous microbial species and capabilities;

[0031] Update the conceptual model of the plot based on the supplementary survey data of the plot and the natural attenuation effect.

[0032] Furthermore, in S2, simulation analysis is performed based on the updated conceptual model of the plot, and a variety of feasibility assessment factors are comprehensively considered to determine whether the natural attenuation monitoring technology is feasible, including:

[0033] Based on the updated conceptual model of the land parcel, simulation analysis is carried out by setting assessment objectives, selecting assessment models, calibrating model parameters, identifying and verifying models, and conducting model prediction, sensitivity analysis and uncertainty analysis;

[0034] Comprehensively consider technical feasibility assessment factors, economic feasibility assessment factors and regulatory feasibility assessment factors to determine whether the natural attenuation monitoring technology is feasible.

[0035] Furthermore, in S3, the application scenario is determined in combination with the hydrogeological conditions of the plot and the temporal and spatial evolution trend of groundwater pollutants, a monitoring plan for monitoring the natural attenuation project is designed, and phased goals for the project operation are formulated, including:

[0036] S3.1, determine the application scenario: Under the determined risk control or remediation model, based on the technical feasibility assessment results, select a single monitoring natural attenuation technology or a combination of other technologies to carry out groundwater pollution risk control and remediation; other technologies include hydraulic control, in-situ reaction zone, PRB, barrier wall, contaminated soil remediation, extraction treatment, and in-situ injection technology;

[0037] S3.2, Design a monitoring plan for natural attenuation engineering: Update the conceptual model of the plot through supplementary investigations during the engineering phase and identification of natural attenuation effects; determine the monitoring scope; design the monitoring well network, monitoring items and monitoring frequency;

[0038] S3.3, formulate phased goals for the project operation, including: proving that the pollution plume remains stationary or shrinks; no changes are found in key conditions of hydrogeology, geochemistry, and microbial communities; setting compliance points at different stages based on expectations, and whether the compliance points meet the standards; and whether the overall project can meet the established control and remediation goals under the scenario of multiple technologies being used in conjunction.

[0039] Furthermore, in S3, the engineering design and implementation also includes formulating an emergency plan; the formulating an emergency plan specifically includes:

[0040] Determine the conditions for activating the emergency plan;

[0041] The emergency plan is designed based on the basis for implementing the emergency plan, the spatial scope and time nodes of emergency response, the technical route of the emergency plan, the specific measures to be taken, and the evaluation of the effectiveness of the emergency plan.

[0042] Furthermore, in S4, the implementation effect of monitoring natural attenuation is evaluated from two aspects: process evaluation and final evaluation, specifically including:

[0043] Use graphic and mathematical statistical methods to conduct process evaluation;

[0044] A final assessment was conducted based on the Technical Guidelines for Groundwater Remediation and Risk Control in Contaminated Sites HJ 25.6.

[0045] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the technical method for monitoring natural attenuation of hexavalent chromium contaminated groundwater provided by the present invention includes the steps of technical applicability analysis, technical feasibility analysis, design and implementation of monitoring natural attenuation engineering, and evaluation of monitoring natural attenuation effects, wherein the applicability analysis is used to determine whether the hexavalent chromium groundwater contaminated land is suitable for the use of monitoring natural attenuation technology, which is a prerequisite for conducting feasibility analysis. The feasibility analysis is an extension and deepening of the applicability analysis, and is used to obtain the necessary parameter basis for engineering design and construction; engineering design and construction are based on the parameters obtained from the feasibility analysis, combined with the relevant requirements of HJ 25.6, to carry out engineering design and implementation of monitoring natural attenuation; the effect evaluation includes process evaluation and final evaluation. The main purpose of the process evaluation is to guide the operation of the project and the monitoring during the process. The final evaluation corresponds to the regulatory requirements of HJ 25.6, and evaluates whether the monitoring natural attenuation project meets the project expectations. This invention fully considers the regulatory needs and technical requirements for groundwater contaminated plots in my country, and carries out the guiding principles, work flow, work content and technical requirements for monitoring natural attenuation of chromium-contaminated groundwater. It is suitable for using a single monitoring natural attenuation technology and combining it with other technologies to carry out groundwater pollution prevention, control and remediation. The monitoring of natural attenuation of groundwater for other pollutants can be implemented as a reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 The present invention is a flow chart of the natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The regulatory requirements and technical requirements for groundwater contaminated land in my country referred to in this invention include:

[0050] HJ 25.1 Technical Guidelines for Investigation of Soil Pollution Status of Construction Land;

[0051] HJ 25.2 Technical Guidelines for Risk Control and Remediation Monitoring of Soil Pollution in Construction Land;

[0052] HJ 25.3 Technical Guidelines for Soil Pollution Risk Assessment for Construction Land;

[0053] HJ 25.4 Technical Guidelines for Soil Remediation of Construction Land;

[0054] HJ 25.5 Technical Guidelines for Risk Control of Contaminated Land and Evaluation of Soil Remediation Effects;

[0055] HJ 25.6 Technical Guidelines for Groundwater Remediation and Risk Control in Contaminated Sites;

[0056] HJ / T 166 Technical Specifications for Soil Environmental Monitoring;

[0057] HJ 164 Technical Specifications for Groundwater Environmental Monitoring;

[0058] HJ 610 Technical Guidelines for Environmental Impact Assessment Groundwater Environment;

[0059] DZ / T 0282 Specification for hydrogeological survey (1:50000);

[0060] GB 14848-2017 Groundwater Quality Standard;

[0061] HJ 493 Technical regulations for the storage and management of water quality sampling samples;

[0062] HJ 494 Water Quality Sampling Technical Guidance;

[0063] "Guidelines for Simulation, Prediction and Assessment of Groundwater Pollution" (Environmental Protection Office Soil Letter

[2019] No. 770);

[0064] Handbook of Hydrogeology.

[0065] The present invention provides guiding principles for monitoring natural attenuation of chromium-contaminated groundwater:

[0066] (1) Scientific principle

[0067] Taking into account constraints such as time cost, economic cost and work objectives, scientifically determine the monitoring plan to maximize benefits. Taking into account the hydrogeological conditions of the polluted land, the uncertainty of the spatial distribution of pollutants, the changes in the degree and scope of pollution, the evolution of the biogeochemical environment of pollutants, etc., on the basis of data obtained through technical execution, dynamically optimize the plan based on the data.

[0068] (2) Normative principle

[0069] A procedural and systematic approach is used to standardize the work content and process of natural attenuation technology for monitoring chromium-contaminated groundwater, ensuring the standardized implementation of natural attenuation monitoring work.

[0070] (3) Feasibility principle

[0071] Based on the hydrogeological conditions of the polluted site, the degree and scope of pollution, the properties and historical characteristics of the pollutants, the geochemical environment in which the pollutants are stored, the structural characteristics of the microbial community, the receptors and the surrounding environment, etc., the natural attenuation capacity is analyzed and determined, and the feasibility of monitoring natural attenuation technology is determined.

[0072] The present invention is applicable to the prevention, control and restoration of groundwater pollution using a single natural attenuation monitoring technology and in combination with other technologies. The natural attenuation monitoring of groundwater with other pollutants can be implemented as a reference.

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0074] like Figure 1 As shown, the natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater provided by the present invention comprises the following steps:

[0075] S1, Applicability analysis: Based on the basic conditions for site screening, hydrogeological conditions, and site pollution survey data, determine whether the hexavalent chromium groundwater contaminated site is suitable for the monitoring natural attenuation technology;

[0076] S2, feasibility analysis: If the hexavalent chromium groundwater contaminated land is suitable for the monitoring of natural attenuation technology, a supplementary survey of the land will be conducted based on the risk control objectives, and the conceptual model of the land will be updated; a simulation analysis will be conducted based on the updated conceptual model of the land, and a variety of feasibility assessment factors will be combined to determine whether the monitoring of natural attenuation technology is feasible;

[0077] S3, Project design and implementation: If the technology for monitoring natural attenuation is feasible, the application scenario will be determined in combination with the hydrogeological conditions of the site and the temporal and spatial evolution trend of groundwater pollutants, a monitoring plan for monitoring natural attenuation projects will be designed, and phased goals for project operation will be formulated;

[0078] S4, Effect evaluation: Evaluate the effect of natural attenuation monitoring implementation from two aspects: process evaluation and final evaluation.

[0079] Specifically, in S1, the applicability analysis specifically includes:

[0080] S1.1, determine whether the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology based on the basic conditions for land screening, including:

[0081] Determine whether the hexavalent chromium groundwater contaminated land is not suitable for monitoring natural attenuation technology. If not, the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology;

[0082] Among them, the situations where natural attenuation monitoring technology is not suitable include:

[0083] The targeted pollution plume control and remediation work is urgent;

[0084] Located in groundwater sensitive areas such as groundwater drinking water source protection areas;

[0085] Failure to meet the requirements of land use planning or environmental assessment;

[0086] The risk to human health in the area where the groundwater contamination plume is distributed is unacceptable;

[0087] Pollution sources or high-concentration pollution centers have not been eliminated or risk control plans have not been implemented.

[0088] S1.2, determine whether the hexavalent chromium groundwater contaminated area is suitable for monitoring natural attenuation technology based on hydrogeological conditions, including:

[0089] Based on the environmental investigation and risk assessment completed in accordance with HJ 25.1, HJ 25.2 and HJ 25.3, the suitability of the hydrogeological conditions of the plot is determined according to Table 1. For plots with high suitability, the feasibility analysis can be further combined with the results of the pollution investigation data analysis of the plot to decide whether to conduct a feasibility analysis; for plots with medium and low suitability, other technologies should be considered for the control and remediation of groundwater pollution.

[0090] Table 1 Evaluation table of suitability of hydrogeological conditions of plots

[0091]

[0092] S1.3, based on the land pollution survey data, determine whether the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology, including:

[0093] S1.3.1, obtain site pollution survey data including groundwater pollution plume morphology and change characteristics and chromium contaminated soil and water-containing media monitoring data;

[0094] 1.3.1.1. Morphology and changing characteristics of groundwater pollution plumes

[0095] Single-period pollution plume: If only the pollution plume information of a plot at a certain time is available, a preliminary assessment of the migration process of chromium pollutants should be conducted based on the pollution history of the plot and the distance to the current pollution plume front. The spatial variation of the ratio of conservative ions and pollutant concentrations along the groundwater flow direction can be combined to determine whether the pollutants have natural attenuation behavior;

[0096] Multi-period pollution plume: If the pollution plume information of a plot of land is available at multiple times, it is possible to comprehensively judge whether the pollution plume has a stable or shrinking trend by analyzing the changes in the overall morphology of the multi-period pollution plume over time (vertical migration diffusion distance, lateral migration diffusion distance, etc.) and the concentration change trends at specific points.

[0097] 1.3.1.2 Monitoring data of chromium-contaminated soil and water-containing media

[0098] The contents of adsorbed hexavalent chromium and trivalent chromium in the soil and groundwater at key locations were analyzed, and the background values ​​of hexavalent chromium and trivalent chromium in the region were compared to preliminarily analyze whether hexavalent chromium was fixed on the aqueous medium through adsorption or reduction.

[0099] S1.3.2, based on the hydrogeological conditions and the land pollution survey data, if the following two conditions are met, further feasibility analysis can be carried out. Otherwise, other technologies should be considered for the control and remediation of groundwater pollution:

[0100] (1) The existence of natural attenuation is judged based on the spatial variation of the ratio of conservative ions and pollutant concentrations in a single-period pollution plume;

[0101] (2) Based on the changes in the morphology of the pollution plume over time, it is judged that the pollution plume is showing a stable or shrinking trend;

[0102] (3) Based on soil and water-containing media chromium pollution monitoring, it is determined that the hexavalent chromium or trivalent chromium content exceeds the background value.

[0103] Specifically, in S2, the feasibility analysis specifically includes:

[0104] S2.1, conduct additional land surveys based on risk management objectives and update the land conceptual model, including:

[0105] 2.1.1 Supplementary investigation

[0106] 2.1.1.1. Supplementary investigation of hydrogeological conditions

[0107] (1) Detailed characterization of aquifers: Based on the detailed investigation results of the previous plots, hydrogeological boreholes were arranged along the migration path of chromium pollutants in the source-path-sink to further characterize the three-dimensional structure and distribution of aquifers. Representative points were selected to collect samples of media in different layers, and particle analysis was carried out to further determine the lithology of the formation.

[0108] (2) Obtaining heterogeneous hydrogeological parameters: Based on field pumping tests, infiltration tests, tracer tests and indoor tests, the hydrogeological parameters of aquifers at different locations, such as permeability coefficient, water supply degree, water storage rate, dispersion, porosity, and rainfall infiltration coefficient, are obtained.

[0109] For details on how to obtain the above parameters, please refer to the "Hydrogeology Manual" and the "Guidelines for Groundwater Pollution Simulation, Prediction and Assessment".

[0110] 2.1.1.2. Supplementary investigation of characteristic pollutants

[0111] Based on the monitoring wells of the detailed site survey and risk assessment, appropriate hydrogeological drilling is supplemented to collect soil and groundwater samples, and determine the total chromium, hexavalent chromium and other water quality indicators that need to be determined. Select typical sections to carry out chromium form analysis of soil and water-containing medium samples, with no less than 3 typical section control points.

[0112] 2.1.1.3. Supplementary investigation of biogeochemical conditions

[0113] Supplementary investigation of biogeochemical conditions should include geochemical characteristics of aquifers and groundwater. Select key points and measure the following indicators: pH, temperature and conductivity, redox potential, electron acceptors (O2, Fe(Ⅲ), NO3 - and SO4 2- ), reduction products (CH4, Fe(Ⅱ)), concentration of dissolved inorganic carbon and alkalinity.

[0114] Microbial indicators can consider plate spreading method, metagenomics, microbial DNA sequencing and other methods to determine the types and functional genes of microorganisms.

[0115] 2.1.1.4 Characterization of biogeochemical reaction parameters

[0116] The parameters related to the natural attenuation of chromium in soil and groundwater mainly include adsorption equilibrium constant, adsorption rate constant and maximum adsorption capacity, reduction rate and maximum reduction capacity, microbial community composition and functional gene abundance analysis, etc. The experimental method for obtaining relevant parameters is carried out through field experiments.

[0117] 2.1.2 Identification of natural attenuation

[0118] Identify natural attenuation based on the characteristics of pollution plume changes, geochemical index changes, indigenous microbial species and capabilities, including:

[0119] The role of natural attenuation of chromium in groundwater is evaluated through monitoring. There are three main aspects of evidence to indicate the actual occurrence of natural attenuation. These three aspects can provide direct or favorable evidence for the natural attenuation of hexavalent chromium alone or in combination, as shown in Table 2.

[0120] Table 2 Evidence for three aspects of monitoring natural attenuation

[0121]

[0122] 2.1.2.1. Characterization of the contamination plume: Site contaminant characterization demonstrates that the contamination plume is static or shrinking, has not reached sensitive boundaries, and will not affect existing water supplies. Once this is established through groundwater characterization, evidence can be collected to demonstrate the partitioning of chromium in the contamination plume to aquifer solids, including:

[0123] (1) Use historical pollutant data to determine whether pollutant concentrations show a gradient downward trend along the groundwater flow path;

[0124] (2) Conduct long-term concentration monitoring at specific points and make statistical analyses, and analyze the status of the pollution plume (shrinking, stable, or expanding) based on the trend of pollutant concentration changes;

[0125] (3) Use mass conservation analysis to determine the mass of the remaining pollutant after degradation and the mass of the degradation products;

[0126] (4) Calculate the mass flux of pollutants through a specific cross section to evaluate the state of the pollution plume (shrinking, stable or expanding);

[0127] (5) Use solute transport analytical models to simulate and predict the migration distance of the pollution plume and the time required for the pollution to reach a stable state, so as to evaluate the ability of natural attenuation;

[0128] (6) The temporal and spatial variations of pollutant concentrations are characterized by a numerical solute transport model, thereby identifying the natural attenuation capacity and analyzing the natural attenuation mechanism.

[0129] Pollutants often diffuse in plume-like form as they flow along groundwater. In the conceptual model of the site, it is necessary to determine the pollution source area and the outline of the pollution plume. When monitoring and analyzing the changing characteristics of the pollution plume, it should be noted that the attenuation trends of pollutants in each single well may not be the same. Therefore, it is necessary to measure whether the pollutants show a gradient downward trend at the level of the entire pollution plume.

[0130] 2.1.2.2. Characteristics of geochemical index changes: The geochemical data of aquifers can be used as an indicator of pollutant degradation, which is very important for determining the natural attenuation capacity of aquifer pollutants. The geochemical indicators that can indicate the occurrence of natural attenuation are as follows:

[0131] (1) Electron acceptors in the polluted plume (mainly O2, Fe(III), NO3 - and SO4 2- ) concentration decreased compared with the local geochemical background concentration, and the concentration of reduction products (such as CH4 and Fe(Ⅱ)) increased;

[0132] (2) Changes in dissolved inorganic carbon concentration and alkalinity: Microbial metabolism produces carbon dioxide. The increase in carbon dioxide concentration will cause changes in groundwater alkalinity. The change curve of groundwater alkalinity can be used to determine the progress of microbial degradation in the pollution plume.

[0133] (3) pH, temperature and conductivity: The pH of groundwater affects the existence and activity of microbial populations, the temperature directly affects the metabolic activity of microorganisms in groundwater, and the conductivity is proportional to the amount of ions in groundwater. All of these can be used as indicators of the conditions for biodegradation of pollutants.

[0134] (4) Redox potential: Certain microbial degradation processes can only occur within a specific range of redox potential conditions. Generally, low redox potential values ​​are conducive to microbial degradation.

[0135] 2.1.2.3. Indigenous microbial species and capabilities: Microbial flora analysis can indicate the natural attenuation process in contaminated sites and the ability of microorganisms to degrade target pollutants. Microbial detection and analysis can be used to assess whether the site microorganisms are capable of degrading target pollutants, serving as direct evidence to support the determination of the site's natural attenuation capacity and process. Specifically, (1) in situ microbial flora detection is conducted on site; (2) microbial flora in collected groundwater or soil samples are cultured in the laboratory to quantitatively measure their degradation rate of pollutants.

[0136] 2.1.2.4 Comprehensive determination of natural attenuation capacity: Based on the results of the assessment and monitoring plan, identify and determine whether monitoring natural attenuation is an acceptable restoration strategy. When one of the following conditions is met, monitoring natural attenuation is considered to be a feasible strategy, and the more conditions are met, the higher the credibility:

[0137] (1) The natural decay process is identified, such as one line of evidence showing the decay phenomenon of the pollutant mass and another line of evidence showing its decay mechanism;

[0138] (2) The plume dispersion state is identified (i.e., stable, decreasing, or expanding), such as a single parameter of a pollutant, metabolite, electron donor, or electron acceptor showing a downward trend (medium confidence) or two or more parameters showing correlated downward trends (high confidence);

[0139] (3) As some indicators of the chain of evidence, the monitoring trends show consistency;

[0140] (4) The observed conditions and decay characteristics were reproduced and simulated using a migration fate model;

[0141] (6) The geochemical environment is consistent with the attenuation mechanism, for example, redox conditions reflect the degradation process;

[0142] (7) There is no inconsistency between the observed conditions and the conceptual model;

[0143] (5) Microbiological studies provide supporting evidence for biodegradation;

[0144] (8) Sensitivity parameters are fully confirmed, such as the range of permeability coefficients confirmed by field tests;

[0145] (9) The uncertainty regarding pollution sources, pollution plumes, and pollution pathways has been significantly reduced.

[0146] The following factors should also be considered in the assessment of natural attenuation processes:

[0147] (1) Changes in land use or site conditions that could affect natural attenuation, such as introducing oxygen into the system and changing the aquifer environment from anaerobic to aerobic;

[0148] (2) Assimilation capacity of the aquifer. The assessment needs to demonstrate that the assimilation capacity of the aquifer is sufficient to protect sensitive targets identified in the future;

[0149] (3) Desorption of contaminants. For contaminants whose natural attenuation processes are non-destructive, such as adsorption or precipitation, the assessment needs to demonstrate that these contaminants will not reactivate, or that the reactivation rate is insufficient to affect identified sensitive targets. For example, hexavalent chromium is relatively mobile and toxic. Under certain conditions, hexavalent chromium can be reduced to less toxic trivalent chromium, which is less soluble and is likely to precipitate from solution. Subsequent changes in the chemical environment may cause the trivalent chromium to be oxidized to hexavalent chromium, which will reactivate and enter the groundwater.

[0150] Update the conceptual model of the plot based on the supplementary survey data of the plot and the natural attenuation effect.

[0151] S2.2, based on the updated conceptual model of the plot, conducts simulation analysis and combines various feasibility assessment factors to determine whether the natural attenuation monitoring technology is feasible, including:

[0152] Based on the updated conceptual model of the land parcel, simulation analysis is carried out by setting assessment objectives, selecting assessment models, calibrating model parameters, identifying and verifying models, and conducting model prediction, sensitivity analysis and uncertainty analysis;

[0153] Comprehensively consider technical feasibility assessment factors, economic feasibility assessment factors and regulatory feasibility assessment factors to determine whether the natural attenuation monitoring technology is feasible.

[0154] Among them, 2.2.1, simulation analysis is specifically introduced as follows:

[0155] (1) Determine the assessment objectives: The main objectives of the simulation analysis are to ensure that the health risks and environmental risks to sensitive receptors are acceptable, the target pollution plume continues to shrink, and the attenuation rate can meet the control and remediation objectives at different stages.

[0156] (2) Selection and construction of assessment model: Depending on the site hydrogeological conditions and the complexity of the morphological characteristics of the groundwater contamination plume, a simple analytical model or a complex numerical model can be selected to evaluate the long-term effectiveness of natural attenuation. If it is found that the model cannot fully reflect the attenuation process or there is insufficient monitoring data to verify the simulation results, further supplementary investigation is required. The selection of analytical models can refer to Appendix B.2 of the "Guidelines for Groundwater Contamination Simulation Prediction and Assessment".

[0157] (3) Calibration of model parameters: For key parameters such as permeability coefficient and attenuation rate, field measured data should be used as much as possible. The calibration process of parameter values ​​should be fully explained, including data sources, analysis methods, parameter value ranges and uncertainties. If off-site measured parameters such as water supply degree and water release (storage) coefficient are used, it should be proved that: 1. The off-site measured data is adjacent to or similar to the actual plot environment; 2. The model prediction is not sensitive to the parameter; 3. The empirical value range of the parameter value is determined through literature research, and conservative values ​​are used in the assessment. For example, the porosity of sand recorded in the literature is usually between 10% and 40%. Since lower values ​​of porosity will lead to an increase in the calculated pollutant migration rate, in this case, a value of 10% is used to represent a conservative assessment. The values ​​of off-site parameters can be referred to Appendix C of the "Hydrogeology Manual" and the "Guidelines for Groundwater Pollution Simulation Prediction and Assessment".

[0158] (4) Identification and verification of the model: The model should be verified based on multiple periods of field measured data, at least one period of water level data in the normal water period of the hydrological year or the effective average of multiple periods of water level data in a complete hydrological year. The model output variables can be indicators such as head, flow, concentration, pollutant migration time, and pollutant removal rate; the calibration basis is to achieve that the main characteristics of the simulated groundwater flow field or pollution plume shape, range, direction, etc. are basically consistent with the actual situation; the calibrated hydrogeological parameters must meet the actual hydrogeological conditions; the migration model parameters must meet the solute migration characteristics and the hexavalent chromium migration law. Unless the degree of agreement between the model simulation value and the measured value of the hexavalent chromium concentration on site is acceptable, the model cannot be reliably used to evaluate the long-term effectiveness of natural attenuation.

[0159] (5) Model prediction: Model predictions should include the following: 1. Changes in pollutant concentrations over time; 2. The volume of the affected aquifer (especially if the plume may migrate); 3. The rate of pollutant migration and the time required to reach sensitive receptors; 4. The time scale for achieving remediation goals; and 5. Determination of the location of compliance points.

[0160] (6) Sensitivity analysis: The indicators for analyzing the response of the model mainly include water head, flow velocity, pollutant concentration, etc. Sensitivity analysis is also used to identify uncertainties in groundwater simulation prediction.

[0161] (7) Uncertainty analysis: The impact of uncertainty in the conceptual model and uncertainty in parameter calibration on the model results should be fully considered. If the assessment shows that the certainty is insufficient, further information and data should be obtained. Commonly used methods for evaluating uncertainty include: sensitivity analysis, Monte Carlo method, first-order error analysis, etc. Through the analysis of parameter uncertainty, the simulation results can be expressed as an interval of possible results, thereby reflecting the uncertainty of the simulation parameters.

[0162] 2.2.1 Comprehensive evaluation of technical feasibility

[0163] A comprehensive assessment is then conducted based on the results of the technical, economic and regulatory feasibility analysis, and the feasibility of the natural attenuation monitoring technology is judged based on the consideration of the weights of each factor. The feasibility summary of each factor is shown in Table 3.

[0164] Table 3 Summary of comprehensive feasibility assessment factors

[0165]

[0166]

[0167] Based on the preliminary assessment results of the feasibility of monitoring natural attenuation, a comprehensive judgment is made as to whether the following conditions are met, thus ultimately deciding whether monitoring natural attenuation is a feasible option:

[0168] (1) The evaluation process showed that there were basically no restrictions on the use of natural attenuation technology;

[0169] (2) After evaluation, monitoring of natural attenuation has the potential to achieve control and restoration objectives;

[0170] (3) Compared with other repair methods, it has greater cost-effectiveness.

[0171] Specifically, in S3, engineering design and implementation, combined with the hydrogeological conditions of the plot and the temporal and spatial evolution trend of groundwater pollutants, determine the application scenario, design a monitoring plan for monitoring the natural attenuation project, and formulate phased goals and emergency plans for the project operation, specifically including:

[0172] S3.1, Application scenario analysis: Under a determined risk control or remediation model, based on technical feasibility assessment, a single monitoring natural attenuation technology or a combination of other technologies can be selected to carry out groundwater pollution risk control and remediation. See Table 4 for details.

[0173] Table 4 Scenario analysis of available technologies for monitoring natural attenuation

[0174]

[0175]

[0176] S3.2, Monitoring Natural Attenuation Engineering Design:

[0177] S3.2.1. Update the conceptual model of the site during the engineering phase: Carry out additional investigations and identification of natural attenuation effects during the engineering phase, and update the conceptual model of the site to support engineering design.

[0178] S3.2.2. Determination of monitoring scope: For plots where only natural attenuation monitoring technology is used, the monitoring scope should cover the upstream uncontaminated area, the entire pollution plume, and the range from the downstream of the pollution plume to the sensitive receptors; for plots where natural attenuation monitoring technology is combined with other combined technologies, the monitoring scope should cover the upstream uncontaminated area, the pollution plume outside the treatment range of other combined technologies, and the range from the downstream of the pollution plume to the sensitive receptors.

[0179] S3.2.3. Monitoring well network design, including:

[0180] (1) Monitoring type

[0181] Monitoring sites can be divided into three categories: monitoring conditions outside the boundaries of the contamination plume (environmental monitoring), monitoring natural attenuation processes (process monitoring), and monitoring the spread of the contamination plume and verifying the impact on receptors (migration monitoring).

[0182] Environmental monitoring should be conducted beyond the contaminant plume boundaries with the goal of identifying control conditions and providing a probability of plume migration where redox and the ability of the aquifer medium to fix the contaminant are the major controls on migration. The extent and duration of environmental monitoring will be affected by the sensitivity of the aquifer chemistry to changes in the quality of the recharge water and to processes that may alter its composition.

[0183] Process monitoring is used to verify that degradation is occurring according to predictions. If process monitoring indicates that degradation is not occurring as expected, changes to the remediation approach may be necessary. Process monitoring is contaminant specific.

[0184] Monitoring the spread of the contamination plume (migration monitoring) and any impact on receptors is another important aspect of the monitoring program. This monitoring objective can be achieved by performing multi-level monitoring below the contamination plume, or near the lateral gradient boundaries, and near any other boundaries specified in the backup emergency plan, and monitoring possible sensitive target locations (e.g., drinking water or other ecologically sensitive targets) to directly verify whether the contamination has an impact. The location of monitoring wells between the contamination plume and the boundary or possible receptors should be close enough to the contamination plume to allow the implementation of the emergency plan before the contaminant migrates through the warning point or affects the sensitive target. The determination of the location of monitoring wells for migration monitoring ultimately depends on the on-site assessment of the migration and transformation of the contaminants.

[0185] (2) Point density design

[0186] The density design of monitoring points should follow the following principles: the density of monitoring wells (including location and number) should be determined comprehensively according to the hydrogeological conditions of the plot and the characteristics of groundwater pollution; when designing the initial monitoring well network, the density should reach 40m×40m at the boundary of the target pollution plume range of the natural attenuation technology; during the monitoring process, if the scope of the pollution plume expands or shrinks significantly, monitoring wells should be appropriately added at the boundary; existing monitoring wells (civilian wells, production wells or springs) can be selected, and on the basis of meeting the project monitoring needs, they can be screened with reference to the "Technical Specifications for Groundwater Environmental Monitoring" (HJ 164-2020); vertical monitoring should also consider the changes in hexavalent chromium concentration with depth. For aquifers with thicker thickness or stronger aquifer heterogeneity, it is recommended to build wells or take samples in layers.

[0187] (3) Design and construction of monitoring wells

[0188] (3.1) Design of monitoring wells

[0189] Screen design requirements: The monitoring well is set in the target aquifer where the pollution plume is located, and should meet the monitoring requirements of groundwater level, water temperature, water quality and other indicators. The top of the screen is at least 1.0m above the water surface in the flood season, and the bottom of the screen is at least 1.0m below the water surface in the dry season. The specific length of the screen and the opening position can be optimized and adjusted according to the monitoring purpose.

[0190] Design requirements for aperture and well diameter: The inner diameter of the monitoring well pipe is required to be no less than 68mm to meet the requirements of water level measurement, well washing and sampling, and can be increased according to actual needs. The final hole diameter should be determined according to the type of well, the specifications of the well pipe and screen pipe, the thickness of the gravel filling, etc. For aperture-related standards, please refer to DZ / T 0148. The inner diameter of the monitoring well pipe is required to be no less than 50mm, with a caliber that can meet the requirements of well washing and sampling. Other monitoring well construction requirements shall refer to HJ 164.

[0191] Well pipe material design requirements: The selection of well pipe material should take into account factors such as well depth, well diameter, material strength, material chemical properties, groundwater corrosiveness, microbial action and cost. It should be made of strong, corrosion-resistant materials that have no effect on groundwater quality. Generally, PVC-U materials, steel pipes or stainless steel pipes can be used as well pipe materials, and the compatibility of well pipe materials with pollutants should be considered to avoid the well pipe materials affecting water quality monitoring results. Well pipes should use threaded interfaces and no adhesives should be used.

[0192] (3.2) Construction of monitoring wells

[0193] The construction shall be carried out in accordance with the technical specifications such as HJ 164, DZ / T 0270, DZ / T 0148, etc.

[0194] S3.2.4 Monitoring items and monitoring frequency

[0195] Groundwater: pollutant indicators, including hexavalent chromium, total chromium, manganese and other plot characteristic indicators; hydrogeochemical indicators, including pH, Eh, DO, conductivity, temperature, TOC value, etc.; chemical indicators, such as the content of major anions and cations (potassium, sodium, calcium, magnesium, bicarbonate, carbonate, chloride, sulfate), the content of minor ions (Fe 2+ , S 2- 、NO 3- 、NO 2- wait).

[0196] Soil and aquifer media: pollutant indicators, plot characteristic indicators such as hexavalent chromium and total chromium; geochemical indicators, dry matter, moisture, pH, bulk density, redox potential, cation exchange capacity, organic matter content, electrical conductivity, sulfate, sulfide, and the occurrence form of chromium pollutants in the solid phase.

[0197] Monitoring frequency: For groundwater monitoring, the monitoring frequency is once per quarter in the first two years of the project implementation phase; after two years, the monitoring frequency will be determined based on the trend of pollution plume changes and groundwater chemical conditions. If the groundwater chemical conditions are stable and the pollution plume morphology is stable or shrinking, it can be adjusted to once per half year or once per year. For soil and aquifer medium testing frequency, the testing will be conducted once at the beginning of the project, and the subsequent monitoring frequency will be determined by the trend of pollution plume changes and groundwater chemical conditions.

[0198] S3.3, the establishment of phased objectives, specifically including: the monitoring plan should include phased objectives to continuously optimize the monitoring plan during the monitoring process. The phased objectives of the monitoring plan should include: proving that the pollution plume remains stationary or shrinks; no changes in key conditions such as hydrogeology, geochemistry, and microbial communities are found; setting compliance points at different stages according to expectations, and whether the compliance points meet the standards; whether the overall project can meet the established control and remediation goals in the context of multiple technologies.

[0199] S3.4, emergency plan formulation, including:

[0200] 3.4.1. The conditions for determining when to activate the emergency plan are as follows:

[0201] (1) The concentration of pollutants in groundwater increases significantly, or new pollutants appear in groundwater;

[0202] (2) A significant increase in pollutant concentrations near pollution sources indicates the possible release of new unknown pollution sources;

[0203] (3) Pollutants were detected in monitoring wells outside the known contamination plume boundary;

[0204] (4) The concentration of pollutants in groundwater at compliance points or downstream sensitive targets set up for land restoration and risk control projects exceeds the limit;

[0205] (5) The decay rate of pollutant concentration in groundwater slows down, and it is assessed that the treatment target cannot be achieved within the expected time frame;

[0206] (6) Changes in hydrogeological conditions or geochemical parameters may indirectly affect the chemical or biological attenuation process of pollutants;

[0207] (7) Changes in the use of land or groundwater have changed the human health risks and environmental risks of groundwater;

[0208] (8) Other pollution incidents occurred within the site.

[0209] 3.4.2. Emergency plan design:

[0210] The emergency plan can be a single technology or a combination of several technologies. The available measures mainly include extraction treatment, in-situ injection, enhanced monitoring of natural attenuation, etc. The management model of the selected plot, restoration and risk control objectives, and the maturity of the technology should be comprehensively considered. For details, please refer to HJ 25.6 for technology selection. The emergency plan includes:

[0211] (1) The basis for implementing the emergency plan;

[0212] (2) The spatial scope and time points of emergency response;

[0213] (3) Technical route of emergency plan;

[0214] (4) Specific measures to be taken;

[0215] (5) Evaluation of the effectiveness of emergency plans.

[0216] Specifically, in S4, the implementation effect of monitoring natural attenuation is evaluated from two aspects: process evaluation and final evaluation, including:

[0217] 4.1. Process evaluation (project operation and monitoring analysis)

[0218] Carry out monitoring and analysis according to the established monitoring indicators and monitoring frequency, update the conceptual model and numerical model in a timely manner, evaluate the changes in the natural attenuation conditions of the plot, and evaluate the effectiveness of natural attenuation on the site to determine whether natural attenuation can achieve the expected goals. The evaluation can be carried out in the following aspects:

[0219] (1) It can be demonstrated that natural attenuation is occurring as expected;

[0220] (2) Be able to detect any changes in environmental conditions that could reduce the effectiveness of natural attenuation, including changes in hydrogeology, geochemistry, microbial communities, or other conditions;

[0221] (3) Products that can reduce the toxicity or mobility of pollutants;

[0222] (4) It can be demonstrated that the pollution plume is continuing to shrink;

[0223] (5) Be able to demonstrate that the health and environmental risks to sensitive receptors are acceptable;

[0224] (6) Ability to monitor new pollutant releases into the environment that may affect the effectiveness of natural attenuation;

[0225] (7) Ability to demonstrate that control and restoration objectives can be achieved.

[0226] 4.1.1 Principles of process evaluation

[0227] The basis of process evaluation is the detection data obtained during the monitoring process, so it is necessary to analyze the monitoring data to determine whether the natural attenuation process has achieved the expected goals. The objects of effect evaluation can be mainly divided into two aspects: changes in pollutants and changes in environmental factors. Among them, changes in pollutants mainly include: the natural attenuation process of pollutants is in line with expectations, the scope of the pollution plume continues to shrink, and the downstream sensitive targets are not affected by the contaminated groundwater, and the restoration goals can be achieved; changes in environmental factors mainly include: the hydrogeological, geochemical and microbiological information that may affect the long-term effectiveness of natural attenuation has not changed significantly, and the natural attenuation products of hexavalent chromium (adsorbed Cr(VI) and reduced product Cr(III)) have not migrated and released. In summary, the key to the evaluation of the effect of monitoring natural attenuation is to use the results of on-site monitoring to explain the temporal and spatial changes of pollutants in groundwater, so as to evaluate the implementation effect of monitoring natural attenuation. Effect evaluation should be carried out continuously along with the implementation process of monitoring natural attenuation, at least once a year, so as to help determine whether the monitoring of natural attenuation meets the expected goals and whether it is necessary to initiate an emergency plan to control groundwater pollution.

[0228] 4.1.2 Process evaluation method

[0229] The graphical method can use pollutant concentration contour maps and pollutant concentration trend maps in monitoring wells over time or distance to present the changes in the pollution plume.

[0230] (1) Pollutant concentration contour map

[0231] Based on the monitoring results of groundwater pollutant concentrations in the plot, a groundwater pollutant concentration contour map can be drawn to understand the pollution degree of different areas in the plot, including heavily polluted areas, unpolluted areas and pollution plume ranges. Further, the monitoring results of different periods are drawn into concentration contour maps to understand the temporal and spatial variation of the groundwater pollutant plume.

[0232] Data from the same quarter of different years should be selected for analysis as much as possible to exclude the influence of seasonal flood and dry seasons. For thick aquifers or when multiple aquifers are contaminated at the same time, it is necessary to draw contour maps of groundwater pollutant concentrations at different depths or layers.

[0233] (2) Monitoring well pollutant concentration over time or distance trend chart

[0234] The existence of a natural attenuation process can be identified by looking at the trend of hexavalent chromium concentration over time in the same monitoring well, or the change of hexavalent chromium concentration over distance in monitoring wells at different periods.

[0235] Mathematical statistical methods: When the change pattern of hexavalent chromium concentration is not obvious or when there is a lot of monitoring data, statistical analysis methods can be used to evaluate the changing trend of pollution.

[0236] 4.2. Summative Evaluation

[0237] During the implementation of natural attenuation monitoring, if the monitoring data of the target pollution plume are lower than the restoration target value or the risk control target has been achieved, and the assessed pollution still has a trend of further attenuation, an effect evaluation can be carried out according to the governance model implemented on the site, referring to HJ 25.6.

[0238] Example:

[0239] For hexavalent chromium groundwater contaminated sites, the present invention will form a long vertical feather pollution zone (hereinafter referred to as "pollution feather") in the groundwater due to the strong mobility of hexavalent chromium;

[0240] For the pollution plume beyond the pollution source boundary (or factory boundary), after meeting the conditions of the applicability analysis, the technical method and monitoring system recommended by this patent can be used to carry out the monitoring and natural attenuation of hexavalent chromium. Based on the natural attenuation effect identified in the feasibility study, geochemical parameter characterization tests are carried out, and the natural attenuation rate constant is calculated. A numerical model is constructed based on the updated conceptual model and related data (stratum, groundwater flow simulation, hexavalent chromium distribution and dynamic change trend, etc.), which can predict the distribution of the target pollution plume in time and space without taking any artificial measures or certain enhanced monitoring and natural attenuation measures for the target pollution plume;

[0241] According to the given principles and methods, carry out engineering design and construction, select the control and restoration model, formulate phased goals, formulate emergency measures, and evaluate whether the phased goals have been achieved based on the project implementation and monitoring;

[0242] If the interim goals cannot be achieved, emergency measures should be initiated to achieve the interim goals. At the same time, the parameters of the existing prediction model should be optimized based on the latest monitoring data to better meet the actual situation. The setting of the interim goals and the engineering technology plan should be further optimized based on the revised and iterative prediction model.

[0243] Ultimately, the pollution plume can be kept stable or continuously reduced in accordance with the established goals and meet the established objectives of the project.

[0244] In summary, the present invention proposes a technical process for natural attenuation of hexavalent chromium groundwater pollution monitoring. Compared with the relevant technical achievements published in developed countries and regions, its structure fully considers my country's regulatory needs and technical requirements for groundwater contaminated plots; each technical link has a rigorous structure and a clear logical relationship, forming a closed structure from technology selection to project cessation. The evaluation method, monitoring index requirements, monitoring network construction requirements, and data analysis methods provided in each technical process of the present invention conform to scientific laws and are highly scientific; specific algorithms are given, which are highly operational; they are in line with my country's groundwater pollution prevention and control management ideas and are highly practical.

[0245] The present invention also provides an electronic device, comprising one or more processors; a memory; and one or more applications, wherein the one or more applications are stored in the memory and configured to be executed by the one or more processors, and the one or more programs are configured to execute the natural attenuation technology method for monitoring hexavalent chromium-contaminated groundwater as described above.

[0246] Of course, those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing related hardware (such as a processor, a controller, etc.) through a computer program, and the program can be stored in a computer-readable storage medium, and the program can include the processes of the above-mentioned method embodiments when executed. The storage medium can be a memory, a disk, an optical disk, etc.

[0247] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for monitoring the natural attenuation of hexavalent chromium contaminated groundwater, characterized in that: The following steps are involved: S1, Applicability analysis: Based on the basic conditions for site screening, hydrogeological conditions, and site pollution survey data, determine whether the hexavalent chromium groundwater contaminated site is suitable for the monitoring natural attenuation technology; S2, feasibility analysis: If the hexavalent chromium groundwater contaminated land is suitable for the monitoring of natural attenuation technology, a supplementary survey of the land will be conducted based on the risk control objectives, and the conceptual model of the land will be updated; a simulation analysis will be conducted based on the updated conceptual model of the land, and a variety of feasibility assessment factors will be combined to determine whether the monitoring of natural attenuation technology is feasible; S3, Project design and implementation: If the technology for monitoring natural attenuation is feasible, the application scenario will be determined in combination with the hydrogeological conditions of the site and the temporal and spatial evolution trend of groundwater pollutants, a monitoring plan for monitoring natural attenuation projects will be designed, and phased goals for project operation will be formulated; S4, Effect evaluation: Evaluate the effect of natural attenuation monitoring implementation from two aspects: process evaluation and final evaluation.

2. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1 is characterized in that: In S1, whether the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology is determined based on the basic conditions for land screening, specifically including: Determine whether the hexavalent chromium groundwater contaminated land is not suitable for monitoring natural attenuation technology, including: The targeted pollution plume control and remediation work is urgent; Located in groundwater sensitive areas such as groundwater drinking water source protection areas; Failure to meet the requirements of land use planning or environmental assessment; The risk to human health in the area where the groundwater contamination plume is distributed is unacceptable; Pollution sources or high-concentration pollution centers have not been cleared or risk control plans have not been implemented.

3. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1 is characterized in that: In S1, judging whether the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology based on hydrogeological conditions includes: Based on four hydrogeological conditions, namely, rock and soil pore type, aquifer medium type, stratum structure, and topography, the suitability of the hexavalent chromium groundwater contaminated land for the use of monitoring natural attenuation technology is divided into three categories: high, medium, and low. Among them, the hexavalent chromium groundwater contaminated land is judged to be suitable for the use of monitoring natural attenuation technology when the suitability is high.

4. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1 is characterized in that: In S1, judging whether the hexavalent chromium groundwater contaminated land is suitable for the monitoring natural attenuation technology based on the land pollution survey data includes: Obtain site pollution survey data including groundwater pollution plume morphology and change characteristics and chromium contaminated soil and water-containing media monitoring data; Based on the hydrogeological conditions and the analysis of the land pollution survey data, if the following two conditions are met, the hexavalent chromium groundwater contaminated land is suitable for monitoring natural attenuation technology: (1) The existence of natural attenuation is judged based on the spatial variation of the ratio of conservative ions and pollutant concentrations in a single-period pollution plume; (2) Based on the changes in the morphology of the pollution plume over time, it is judged that the pollution plume is showing a stable or shrinking trend; (3) Based on soil and water-containing media chromium pollution monitoring, it is determined that the hexavalent chromium or trivalent chromium content exceeds the background value.

5. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1, characterized in that: In S2, a supplementary land survey is conducted based on the risk control objectives to update the land conceptual model, including: Conduct supplementary investigations on hydrogeological conditions, characteristic pollutants, biogeochemical conditions, and biogeochemical reaction parameter characterization to obtain supplementary survey data for the plots; Identify natural attenuation based on the characteristics of pollution plume changes, geochemical indicators, indigenous microbial species and capabilities; Update the conceptual model of the plot based on the supplementary survey data of the plot and the natural attenuation effect.

6. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1 is characterized in that: In S2, simulation analysis is performed based on the updated conceptual model of the plot, and a variety of feasibility assessment factors are combined to determine whether the natural attenuation monitoring technology is feasible, including: Based on the updated conceptual model of the land parcel, simulation analysis is carried out by setting assessment objectives, selecting assessment models, calibrating model parameters, identifying and verifying models, and conducting model prediction, sensitivity analysis and uncertainty analysis; Comprehensively consider technical feasibility assessment factors, economic feasibility assessment factors and regulatory feasibility assessment factors to determine whether the natural attenuation monitoring technology is feasible.

7. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1, characterized in that: In S3, the application scenario is determined based on the hydrogeological conditions of the plot and the temporal and spatial evolution trend of groundwater pollutants, a monitoring plan for the natural attenuation project is designed, and phased goals for the project operation are formulated, including: S3.1, determine the application scenario: Under the determined risk control or remediation model, based on the technical feasibility assessment results, select a single monitoring natural attenuation technology or a combination of other technologies to carry out groundwater pollution risk control and remediation; other technologies include hydraulic control, in-situ reaction zone, PRB, barrier wall, contaminated soil remediation, extraction treatment, and in-situ injection technology; S3.2, Design a monitoring plan for natural attenuation engineering: Update the conceptual model of the plot through supplementary investigations during the engineering phase and identification of natural attenuation effects; determine the monitoring scope; design the monitoring well network, monitoring items and monitoring frequency; S3.3, formulate phased goals for the project operation, including: proving that the pollution plume remains stationary or shrinks; no changes are found in key conditions of hydrogeology, geochemistry, and microbial communities; setting compliance points at different stages based on expectations, and whether the compliance points meet the standards; and whether the overall project can meet the established control and remediation goals under the scenario of multiple technologies being used in conjunction.

8. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 7, characterized in that: In S3, the engineering design and implementation also includes formulating an emergency plan; the formulating an emergency plan specifically includes: Determine when to activate the emergency plan; Design an emergency plan based on the basis for implementing the emergency plan, the spatial scope and time nodes of emergency response, the technical route of the emergency plan, the specific measures to be taken, and the evaluation of the effectiveness of the emergency plan.

9. The natural attenuation technology method for monitoring hexavalent chromium contaminated groundwater according to claim 1, characterized in that: In S4, the implementation effect of monitoring natural attenuation is evaluated from two aspects: process evaluation and final evaluation, including: Use graphic and mathematical statistical methods to conduct process evaluation; A final assessment was conducted based on the Technical Guidelines for Groundwater Remediation and Risk Control in Contaminated Sites HJ 25.6.

Images