A monitoring method for in-situ site remediation technology

Abstract

The present invention discloses a monitoring method for an in-situ site remediation process, which uses the ratio of the heavy isotope and light isotope of the C element and the ratio of the heavy isotope and light isotope of the H element of the target pollutant as the coordinate axis, draws a C-H double isotope ratio difference analysis diagram by using the characteristic interval intercepted by a specific linear formula, and then draws the variation of the value obtained by sampling during the remediation process compared with the benchmark data in the C-H double isotope ratio difference analysis diagram, and monitors the in-situ site remediation effect according to its positional relationship with the characteristic interval. The present invention tracks the change of the carbon and hydrogen isotope abundance ratio of the target organic compound over time during the physical / chemical / biological process, thereby determining the main mechanism of action of the organic compound removal and degradation, and monitoring the remediation effect of the in-situ site remediation process.

Description

Technical Field

[0001] The present invention relates to the technical field of in-situ remediation, and in particular to a monitoring method for an in-situ site remediation process. Background Art

[0002] At present, the remediation of soil and groundwater in organically contaminated sites is mainly based on physical, chemical, and biological processes to remove underground pollutants. Among them, physical processes mainly use thermal energy, multiphase extraction treatment, elution and other means; chemical processes mainly use chemical reduction and oxidation; and biological processes mainly use metabolic degradation of microorganisms. However, in various major remediation processes, the various processes actually interact with each other. For example, in the in-situ aeration-extraction process for treating petroleum hydrocarbon pollution, the physical process of volatile gas extraction of volatile pollutants may occur, the physical process of water extraction of soluble pollutants may occur, and the aerobic degradation process of biological aeration may also occur; in the in-situ chemical oxidation / reduction process for treating chlorinated hydrocarbon pollution, chemical degradation processes and microbial stimulation of pollutant degradation processes will occur at different stages.

[0003] The mechanisms and principles governing remediation processes vary significantly for different remediation processes. Accurately identifying the key process mechanisms influencing remediation efficiency and adjusting operating parameters through process conditions directly determines the success of site remediation. Identifying the key factors influencing the remediation process can significantly improve remediation efficiency, resulting in shorter project times and lower operating costs. However, in complex remediation systems, existing technologies struggle to assess and quantify key factors, making it impossible to distinguish the relative contributions of multiple, simultaneous pollutant removal processes.

[0004] Currently, the quality of pollutant removal or degradation is typically assessed by conventional spatial and temporal variations in pollutant concentrations. However, simply monitoring pollutant data only reflects trends in the total amount and concentration of underground pollutants. It cannot determine the relative contribution of removal and degradation processes to specific pollutants, nor can it clearly indicate whether a particular process (such as vapor stripping, biodegradation, or chemical reaction) has occurred, as these processes occur simultaneously. Remediation projects also monitor operational parameters, such as the redox point (ORP) and pH in chemical oxidation / reduction remediation, pipeline pressure in soil vapor extraction, and groundwater dissolved oxygen (DO) in biological aeration. However, these parameters only demonstrate the occurrence of a particular process and cannot determine its contribution to the removal of the target pollutant. These parameters are also affected by soil and groundwater heterogeneity, resulting in significant data errors and unclear or even misleading feedback on project operating parameters. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem that the existing technical solutions are difficult to accurately monitor whether the key factors affecting the remediation efficiency play a role in the degradation of pollutants during the remediation process, such as whether microorganisms undergo metabolism, metabolic intensity, metabolic degradation mechanism (aerobic / anaerobic), groundwater aeration volume / extraction pressure / chemical oxidant concentration and other process parameters, and thus cannot effectively and dynamically control the key process parameters, thereby providing a monitoring method for in-situ site remediation process.

[0006] To this end, the present invention adopts the following technical solutions:

[0007] The present invention provides a monitoring method for an in-situ site remediation process, comprising the following steps:

[0008] S1: Identify the target pollutants of the site to be remediated;

[0009] S2: Sampling the groundwater and soil gas at the site to be remediated, and obtaining the ratio of the heavy and light isotopes of the C element of the target pollutant, δ0 13 The ratio of heavy and light isotopes of C and H elements δ0 2 H, as the benchmark data;

[0010] S3: The change Δδ compared with the reference data obtained in step S2 13 C. Δδ 2 H is the coordinate axis, through Δδ 13 C / Δδ 2 The characteristic interval intercepted by the linear formula defined by H is used to draw the CH double isotope ratio difference analysis diagram;

[0011] S3: In-situ site remediation process for the site to be remediated;

[0012] S4: During the remediation process, sampling is performed on day n to detect the ratio of heavy and light isotopes of C element of the target pollutant δ n 13 The ratio of heavy and light isotopes of C and H elements, δ n 2 H;

[0013] S6: Get δ from each sampling n 13 C and δ n 2 The change Δδ of H compared with the baseline data n 13 C. Δδ n 2 H is plotted on the CH biisotope ratio difference analysis diagram obtained in step S3, according to Δδ n 13 C and Δδn 2 The positional relationship between H and the characteristic interval monitors the in-situ site remediation effect in step S3.

[0014] Furthermore, in step S3, the characteristic interval includes:

[0015] Anaerobic microbial reaction area:

[0016] By Δδ 2 H=0.054*Δδ 13 C and Δδ 2 H=0.089*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure;

[0017] Aerobic microbial reaction area:

[0018] By Δδ 2 H=0.224*Δδ 13 C and Δδ 2 H=0.429*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure;

[0019] Chemical oxidation zone:

[0020] From the Δδ in the first quadrant of the figure 2 H=1.684*Δδ 13 C and Δδ in the fourth quadrant 2 H=-1.684*Δδ 13 The region where C crossover is formed is determined;

[0021] Air-water exchange area:

[0022] By Δδ 2 H=-0.024*Δδ 13 C and Δδ 2 H=-0.011*Δδ 13 C is determined by the area formed by the intersection of the second quadrant of the figure;

[0023] Gas-NAPL exchange zone:

[0024] By Δδ 2 H=0.042*Δδ 13 C and Δδ 2 H=0.024*Δδ 13 C is determined by the area formed by the intersection of the third quadrant in the figure.

[0025] The monitoring result in step S6 is:

[0026] When Δδ n 13 C / Δδn 2 When H falls within the characteristic interval represented by the expected repair degradation mechanism, it is determined that the repair process effect meets the requirements and the original repair process operation status is maintained;

[0027] When Δδ n 13 C / Δδ n 2 When H does not fall within the characteristic interval represented by the expected repair and degradation mechanism, if Δδ n 13 C / Δδ n 2 The length difference between the intersection of H and the vertical line of the nearest characteristic interval is no more than Δδ n 13 C / Δδ n 2 If the length difference between H and the endpoint value is 10%, the repair process is considered feasible, but the efficiency is insufficient and the process parameters need to be improved;

[0028] When Δδ n 13 C / Δδ n 2 When H does not fall within the characteristic interval represented by the expected repair and degradation mechanism, if Δδ n 13 C / Δδ n 2 The length difference between the intersection of H and the vertical line of the nearest characteristic interval is greater than Δδ n 13 C / Δδ n 2 If the length difference between H and the endpoint value is 10%, the repair process is judged to be infeasible, or the actual repair mechanism is not the designed effect of the repair process. 13 C / Δδ 2 If H falls in the second quadrant, it means that the technology is invalid. 13 C / Δδ 2 If H falls on the microbial reaction zone, the actual degradation mechanism is microbial degradation rather than extraction, etc. In such cases, it is necessary to adjust the process route or optimize the technical design (such as adjusting aeration, injection points, changing the reagent ratio, etc.) according to the actual process conditions.

[0029] The improved process parameters include but are not limited to increasing the aeration volume by aeration technology, increasing the input of reagents by microbial stimulation technology, and increasing the extraction pressure by extraction process.

[0030] In steps S2 and S4, the ratio of heavy isotopes to light isotopes, δ, is calculated as follows:

[0031]

[0032] Among them, R and R std are the heavy and light isotope ratios of the test sample and the heavy and light isotope ratios of the international reference standard, respectively;

[0033] When calculating δ 13 C, R std is the Vienna Pee Dee Belemnite (VPDB) value;

[0034] When calculating δ 2 When H, R std is the Vienna Standard Mean Ocean Water (VSMOW) value.

[0035] In step S2, it also includes confirming δ0 13 C and δ0 2 The specific steps for whether H can be used as the benchmark data are as follows: 13 C and δ0 2 H is placed at the endpoint 0, Δδ 13 C and Δδ 2 In the graph where H is the coordinate axis, when it is located at Δδ 2 H=4, Δδ 2 H=-4, Δδ 13 C=0.2, Δδ 13 When C=-0.2 and the four straight lines are in the rectangular frame around the endpoints, δ0 13 C and δ0 2 H is used as the benchmark data.

[0036] Preferably, in step S4, the sampling on the nth day is to sample the groundwater and soil gas every 4 to 7 days 30 days before the repair, and to sample the groundwater and soil gas every 15 to 30 days after the repair 30 days.

[0037] The in situ remediation process described in step S3 includes but is not limited to one or more of soil vapor extraction (SVE), multiphase extraction (MPE), groundwater extraction and treatment, groundwater aeration, groundwater circulation wells, bioventilation, microbial stimulation, microbial enhancement, natural monitoring attenuation, and chemical oxidation technology.

[0038] The target pollutants in step S1 include but are not limited to one or more of polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, petroleum hydrocarbons or benzene series.

[0039] The technical solution of the present invention has the following advantages:

[0040] (1) The present invention tracks the carbon (δ13 C) and hydrogen (δ 2 H) Changes in isotope abundance ratios over time can be used to determine the primary removal and degradation mechanisms of organic compounds, monitor the effectiveness of in situ site remediation processes, and ultimately optimize pollutant removal efficiency during environmental remediation, thereby reducing remediation time and costs.

[0041] (2) The present invention uses sampling and monitoring at different stages of the restoration process to analyze carbon (δ 13 C) and hydrogen (δ 2 H) Analyze the time-dependent changes in isotope abundance ratios, track the main mechanisms of target pollutant removal, and evaluate the effectiveness of the remediation system and its key influencing factors, thereby supporting engineering design and process implementation, optimizing system operation, maximizing the efficiency of the remediation system, and achieving the goal of reducing the time and economic costs of remediation projects.

[0042] (3) The present invention is based on the compound-specific isotope analysis (CSIA) method, which determines at the molecular level whether the in-situ remediation system of the contaminated site has initiated the removal and degradation process of the target pollutants. By tracking the relative changes in the in-situ pollutant attenuation process caused by physical, chemical, biological and other processes in the site remediation, the dominant factors and relative contributions of the pollutant removal and degradation process can be clearly determined, solving the problem that current monitoring technology is difficult to accurately determine the key factors affecting the remediation efficiency through single indicator analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is the CH double isotope ratio difference analysis diagram;

[0045] Figure 2 is the groundwater Δδ of benzene in Example 1 13 C / Δδ 2 H result;

[0046] Figure 3 is the soil gas Δδ of isooctane in Example 1 13 C / Δδ 2 H result;

[0047] Figure 4 is the groundwater Δδ in Example 2 13 C / Δδ 2 H result;

[0048] Figure 5 is the soil gas Δδ in Example 2 13 C / Δδ 2 H results.

[0049] Reference numerals:

[0050] 21- Δδ of benzene D0~D28 in Example 1 13 C / Δδ 2 H migration trend;

[0051] 22- Δδ of D28~D60 benzene in Example 1 13 C / Δδ 2 H migration trend;

[0052] 23- Δδ of D60~D120 benzene in Example 1 13 C / Δδ 2 H migration trend;

[0053] 31- Δδ of D0~D28 isooctane in Example 1 13 C / Δδ 2 H migration trend;

[0054] 32- Δδ of D28~D150 isooctane in Example 1 13 C / Δδ 2 H migration trend;

[0055] 41-Example 2 Chemical Oxidation Experiment D0~D7 Trichloroethylene Δδ 13 C / Δδ 2 H migration trend;

[0056] 42-Example 2 Chemical Oxidation Experiment D7~D14 Trichloroethylene Δδ 13 C / Δδ 2 H migration trend;

[0057] 51-Example 2 Δδ of trichloroethylene D0~D28 in gas phase extraction experiment 13 C / Δδ 2 H migration trend. DETAILED DESCRIPTION

[0058] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0059] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0060] First, the background value of H and C isotope abundance in the environment is taken as the origin (time t=0), and the change Δδ of the C and H isotope abundance ratio at a certain time and state compared with the baseline value at t=0 is used. 13 C. Δδ 2 H is the coordinate to draw the CH double isotope ratio difference analysis diagram, through Δδ 13 C / Δδ 2 The characteristic interval cut by the linear formula defined by H includes:

[0061] Anaerobic microbial reaction area:

[0062] By Δδ 2 H=0.054*Δδ 13 C and Δδ 2 H=0.089*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure;

[0063] Aerobic microbial reaction area:

[0064] By Δδ 2 H=0.224*Δδ 13 C and Δδ 2 H=0.429*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure;

[0065] Chemical oxidation zone:

[0066] From the Δδ in the first quadrant of the figure 2 H=1.684*Δδ 13 C and Δδ in the fourth quadrant 2 H=-1.684*Δδ 13 The region where C crossover is formed is determined;

[0067] Air-water exchange area:

[0068] By Δδ 2 H=-0.024*Δδ 13 C and Δδ 2 H=-0.011*Δδ 13 C is determined by the area formed by the intersection of the second quadrant of the figure;

[0069] Gas-NAPL exchange zone:

[0070] By Δδ 2H=0.042*Δδ 13 C and Δδ 2 H=0.024*Δδ 13 C is determined by the area formed by the intersection of the third quadrant in the figure.

[0071] The final CH double isotope ratio difference analysis diagram is as follows Figure 1 As shown. When the target organic pollutant undergoes a physical / chemical / biological process, Δδ at t=n n 13 C. Δδ n 2 The area where H falls on the coordinate can characterize the main process mechanism affected by the change of the organic pollutant. For example, when Δδ n 13 C. Δδ n 2 When H falls in the first quadrant, it indicates that the degradation of organic pollutants mainly undergoes microbial metabolism. Furthermore, since hydrocarbons are degraded through different mechanisms under aerobic and anaerobic conditions, different δ 13 C, δ 2 In the H isotope fractionation pattern, the first quadrant can be further divided into “aerobic microbial reaction zone” and “anaerobic microbial reaction zone”; when Δδ n 13 C. Δδ n 2 When H falls near the x-axis, it indicates that the degradation of the organic pollutant mainly undergoes chemical oxidation; when Δδ n 13 C. Δδ n 2 When H falls near the y-axis in the fourth quadrant, it indicates that the organic pollutant is mainly dissolved in the water phase and volatilized into the atmosphere through the contact between water and air; when Δδ n 13 C. Δδ n 2 When H falls near the y-axis in the third quadrant, it indicates that the organic pollutant NAPL is volatilized in direct contact with the atmosphere.

[0072] Since this analytical method targets target pollutants in the environmental remediation process, it includes initial environmental base sampling, and the target pollutants in the process sampling samples must be greater than the detection limit.

[0073] Example 1:

[0074] This example provides a monitoring method for an in-situ site remediation process, using an in-situ bioventilation process to remediate groundwater contaminated by petroleum hydrocarbons and benzene derivatives (benzene, toluene, ethylbenzene, xylene, BTEX). This process, based on indigenous microorganisms, first stimulates the underground microbial response by injecting electron acceptors (such as sulfate, nitrate, and small organic molecules) and nutrients (organic carbon sources, organic nitrogen sources, and phosphates). Air is then injected into the groundwater through wells, increasing the dissolved oxygen concentration through aeration and enhancing aerobic microbial activity. Simultaneously, HDPE film is applied as a barrier layer to the surface of the remediation area. Soil vapor extraction is performed using negative pressure fans and extraction wells, creating a microbial ventilation effect and effectively extracting volatile organic compounds.

[0075] Before the process is implemented, a detailed site investigation is carried out, and the groundwater and extracted gas in the pollution source area are used as the benchmark data of the heavy isotope / light isotope ratio δ of the C and H elements in the site (t=D0, day 0). The benchmark data are shown in Table 1:

[0076] Table 1 Benchmark data

[0077]

[0078] like Figure 2 As shown in D0, D0 is located at Δδ 2 H=4, Δδ 2 H=-4, Δδ 13 C=0.2, Δδ 13 C=-0.2 The four straight lines are enclosed in a rectangular box around the endpoints and can be used as a benchmark reference value.

[0079] The repair implementation is mainly divided into three stages according to the process characteristics:

[0080] Phase 1, 1-30 days: Electron acceptors and nutrients are injected starting on day 1 (D1) to stimulate underground microbial reaction conditions. This phase lasts until day 30 (D30).

[0081] Phase 2, 30-60 days: Starting on the 30th day, air is injected into the groundwater for biological aeration to stimulate microbial aerobic reactions.

[0082] Phase 3, 60-150 days: On the 60th day, the soil vapor extraction system is turned on to create a biological ventilation effect and extract volatile organic compounds.

[0083] During the process implementation, groundwater samples were collected at the same sampling point in the area with high initial pollution concentration at 7, 14, 21, 28, 60, 90, and 150 hours respectively, and a sampling port was set up in the soil gas extraction pipeline to sample the gas. 13 C / 12 C and 2 H / 1 The CSIA analysis of H was used to calculate the heavy and light isotope ratios of the test samples and obtain the R values. The results are shown in Table 1.

[0084] Table 2 R values ​​obtained by sampling

[0085]

[0086] According to the formula Calculate, where:

[0087] When calculating δ 13 C, R std The Vienna Pee Dee Belemnite (VPDB) value is 0.011;

[0088] When calculating δ 2 H std is the Vienna Standard Mean Ocean Water (VSMOW) value, which is 0.00014.

[0089] Then subtract δ0 and calculate Δδ. The results are shown in Table 3:

[0090] Table 3 Calculated Δδ values

[0091]

[0092] Before the process is implemented, a detailed site investigation is carried out, and the groundwater and extracted gas in the pollution source area are used as the benchmark data for the heavy isotope / light isotope ratio δ of the C and H elements in the site (t=D0, day 0). The results show that the site environmental isotope ratio benchmark falls within the standard value range and can be used as a benchmark reference value (coordinate origin).

[0093] Calculate Δδ 13 C. Δδ 2 H and analyze the key removal mechanisms of pollutants at each stage. Benzene has a high solubility and is easy to migrate into groundwater to participate in biochemical reactions. The groundwater Δδ 13 C / Δδ 2 The results of H Figure 2As shown. The results show that during the injection of biostimulants and nutrients in the first 30 days of stage one, the values ​​of D7, D14, D21, and D28 fell in the "anaerobic microbial reaction" area along the dotted arrow 21, indicating that in the early stage of the establishment of the reaction environment, due to the low oxygen content in the groundwater, the degradation of benzene by microorganisms mainly relied on anaerobic reactions, and as the biological metabolism consumed oxygen, the anaerobic reaction further increased with time. The result of D60 obviously migrated to the "aerobic microbial reaction" area (arrow 22), proving that the biological aeration in the second stage effectively promoted the aerobic biological reaction. The results of D60, D90, and D120 formed an arrow 23 pointing to the baseline area, indicating that aerobic biodegradation is weakening (or the dilution effect of large amounts of precipitation or groundwater inflow causes Δδ 13 C / Δδ 2 H returns to background value). This assessment requires consideration based on groundwater pollutant concentration monitoring results. The results of this example indicate that the site pollutant concentration has significantly decreased compared to the initial level, indicating a decrease in biodegradation intensity due to the reduced pollutant supply. In this example, the D150 pollutant was not detected, so the CSIA results for D150 cannot be plotted. However, this result indirectly demonstrates that the remediation system's microbial response is effective in removing benzene. Further monitoring of groundwater pollutant concentrations can be used to determine the next steps in remediation implementation (e.g., completing remediation to meet standards, entering the natural monitoring attenuation phase of the contaminant plume, or continuing to stimulate enhanced microbial degradation).

[0094] In this embodiment, it should be noted that the results of D21, D60, and D90 fall outside the edge of the discrimination area. Such results are acceptable, and the acceptable range is Δδ n 13 C / Δδ n 2 The difference between the intersection value of H and the vertical line of the judgment area boundary is ≤ Δδ n 13 C / Δδ n 2 The reasons for this result are: first, the existence of sampling and analysis errors; second, soil vapor extraction was started after D60, which strengthened the water-air exchange process and thus affected Δδ 13 C / Δδ 2 H result (shifted towards the positive direction of the y axis). It can also be seen from this that δ 13 C / Δδ 2 H analysis is affected by the comprehensive influence of each process, and the analysis results reflect the most important influencing factors. If the contribution of multiple influencing factors is large, Δδ 13 C / Δδ 2 If the H result falls outside the judgment area, further analysis and judgment are required based on site conditions and other parameters.

[0095] For isooctane, which is relatively volatile, poorly soluble in water, and not easily absorbed and degraded by organisms, the extraction gas Δδ 13 C / Δδ 2 The results of H Figure 3 The results show that the δ 13 C / δ 2 The H data are all located near the origin, indicating that the degradation of isooctane by microorganisms is not obvious and is between anaerobic and aerobic reactions. 13 C / Δδ 2 H obviously migrates toward the y-axis; the results from D90 to D150 clearly fall within the “gas-water exchange” region, proving that the removal of isooctane is mainly affected by the water-gas exchange enhancement mechanism brought about by gas phase extraction. 13 C / Δδ 2 The H value has not yet returned to the baseline value, so it can be judged that the intensity of the isooctane removal process is still relatively high, and the extraction state needs to be maintained. The subsequent CSIA results combined with the pollutant concentration data will further determine the remediation implementation strategy.

[0096] Based on the above Δδ for benzene and isooctane 13 C / Δδ 2 Analysis of the H results indicates that microbial action plays a key role in the degradation of benzene, and that the anaerobic reaction is converted to an aerobic reaction after groundwater aeration. The microbial reaction has little effect on the removal of isooctane, and the main removal mechanism is affected by the enhanced water-air exchange caused by extraction. The analysis results can accurately determine whether the degradation and removal process of the target pollutant has begun, at what stage, and at what intensity, and thus feedback can be adjusted to optimize the in-situ remediation process. For example, in this example, if no significant microbial degradation of benzene is observed between D7 and D28, the dosage of stimulants and nutrients can be increased. If no significant aerobic reaction occurs after aeration between D30 and D120, consideration can be given to increasing the aeration volume or adjusting the aeration area as needed.

[0097] Although Δδ 13 C / Δδ 2 The H analysis index cannot quantify the removal of pollutants, and the process effect still needs to be judged in combination with the pollutant concentration sampling data. However, the method of the present invention helps to determine whether the removal process has been initiated, track the relative changes of the remediation process to the in-situ pollutant attenuation process, and timely adjust the process parameters and remediation implementation strategy.

[0098] Example 2:

[0099] The technical feasibility of in-situ remediation technology is often determined by conducting sandbox pilot experiments. In this example, trichloroethylene (TCE) was injected into the sandbox soil to test the remediation efficiency of chemical oxidation and gas phase extraction technology through pilot experiments, and the Δδ 13C / Δδ 2 The results of the H test show the feasibility of implementing these two technologies on a pilot scale or above. The following will introduce the two pilot tests in detail.

[0100] (1) Chemical oxidation test

[0101] An excess of 10% hydrogen peroxide (H2O2) was added to the sandbox on D0 and D15 to oxidize and remove TCE. The Δδ in soil water was measured on D7, D14, D21, and D28. 13 C / Δδ 2 H, the result is Figure 4 As shown. At D7, Δδ 13 C / Δδ 2 H significantly migrated to the "chemical oxidation" area (arrow 41), proving that the oxidant was effective in removing TCE. However, it returned to the baseline value at D14 (arrow 42). This was because the effective oxidation time of the Fenton agent was limited (about 7 days), and the agent added at D0 was unable to degrade TCE NAPL. After the oxidant failed, the NAPL-state pollutants migrated back into the soil, and the resulting "dilution" caused the Δδ 13 C / Δδ 2 H returned to the baseline value. Results from Days 21 to 28 were similar, indicating that the chemical injection at Day 15 was unable to completely remove NAPL-bound TCE within its effective period. This result indicates that while in-situ chemical injection can effectively remove TCE that migrates into aqueous solution, it is not possible to completely remove NAPLs with a second injection, as NAPLs continue to enter the soil through mass transfer. This experiment demonstrates that chemical oxidation processes have limitations for TCE and NAPL removal, and that increasing the number of oxidant injections is necessary if this technology is chosen.

[0102] (2) Gas phase extraction test

[0103] A small-scale test of negative pressure gas extraction treatment was carried out in a sand box with the same settings as the previous example. Negative pressure extraction lasted for 30 days from D0 to D30. The Δδ in the extracted gas was measured on D7, D14, D21, and D28. 13 C / Δδ 2 H, the result is Figure 5 The results show that Δδ 13 C / Δδ 2 The H value gradually deviated significantly from the baseline value, falling within the air-NAPL region. This indicates that negative pressure extraction, through direct contact and exchange between TCE NAPL and air, removed significant amounts of TCE, with increasing intensity. This test was limited in duration, and further monitoring is recommended to determine when extraction should conclude to achieve complete contaminant removal.

[0104] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for monitoring an in-situ site remediation process, characterized in that: The steps include: S1: Identify the target pollutants of the site to be remediated; S2: Sampling the groundwater and soil gas at the site to be remediated, and obtaining the ratio of the heavy and light isotopes of the C element of the target pollutant, δ0 13 The ratio of heavy and light isotopes of C and H elements δ0 2 H, as the benchmark data; S3: The change Δδ compared with the reference data obtained in step S2 13 C. Δδ 2 H is the coordinate axis, through Δδ 13 C / Δδ 2 The characteristic interval intercepted by the linear formula defined by H is used to draw the CH double isotope ratio difference analysis diagram; S4: In-situ site remediation process for the site to be remediated; S5: During the remediation process, sampling is performed on day n to detect the ratio of heavy and light isotopes of C element of the target pollutant δ n 13 The ratio of heavy and light isotopes of C and H elements, δ n 2 H; S6: Get δ from each sampling n 13 C and δ n 2 The change Δδ of H compared with the baseline data n 13 C. Δδ n 2 H is plotted on the CH biisotope ratio difference analysis diagram obtained in step S3, according to Δδ n 13 C and Δδ n 2 The positional relationship between H and the characteristic interval monitors the in-situ site remediation effect in step S3.

2. The monitoring method according to claim 1, characterized in that: In step S3, the characteristic interval includes: Anaerobic microbial reaction area: By Δδ 2 H=0.054*Δδ 13 C and Δδ 2 H=0.089*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure; Aerobic microbial reaction area: By Δδ 2 H=0.224*Δδ 13 C and Δδ 2 H=0.429*Δδ 13 C is determined by the area formed by the intersection of the first quadrant of the figure; Chemical oxidation zone: From the Δδ in the first quadrant of the figure 2 H=1.684*Δδ 13 C and Δδ in the fourth quadrant 2 H=-1.684*Δδ 13 The region where C crossover is formed is determined; Air-water exchange area: By Δδ 2 H=-0.024*Δδ 13 C and Δδ 2 H=-0.011*Δδ 13 C is determined by the area formed by the intersection of the second quadrant of the figure; Gas-NAPL exchange zone: By Δδ 2 H=0.042*Δδ 13 C and Δδ 2 H=0.024*Δδ 13 C is determined by the area formed by the intersection of the third quadrant in the figure.

3. The monitoring method according to claim 1 or 2, characterized in that: The monitoring result in step S6 is: When Δδ n 13 C / Δδ n 2 When H falls within the characteristic interval represented by the expected repair degradation mechanism, it is determined that the repair process effect meets the requirements and the original repair process operation status is maintained; When Δδ n 13 C / Δδ n 2 When H does not fall within the characteristic interval represented by the expected repair and degradation mechanism, if Δδ n 13 C / Δδ n 2 The length difference between the intersection of H and the vertical line of the nearest characteristic interval is no more than Δδ n 13 C / Δδ n 2 If the length difference between H and the endpoint value is 10%, the repair process is considered feasible, but the efficiency is insufficient and the process parameters need to be improved; When Δδ n 13 C / Δδ n 2 When H does not fall within the characteristic interval represented by the expected repair and degradation mechanism, if Δδ n 13 C / Δδ n 2 The length difference between the intersection of H and the vertical line of the nearest characteristic interval is greater than Δδ n 13 C / Δδ n 2 If the length difference between H and the endpoint value is 10%, the repair process is judged to be infeasible, or the actual repair mechanism is not the designed effect of the repair process.

4. The monitoring method according to claim 3, characterized in that: The improved process parameters include but are not limited to increasing the aeration volume by aeration technology, increasing the input of reagents by microbial stimulation technology, and increasing the extraction pressure by extraction process.

5. The monitoring method according to claim 1, characterized in that: In steps S2 and S5, the ratio of heavy isotopes to light isotopes δ is calculated by the following formula: Among them, R and R std are the heavy and light isotope ratios of the test sample and the heavy and light isotope ratios of the international reference standard, respectively; When calculating δ 13 C, R std For Vienna Pee Dee Belemnite value; When calculating δ 2 When H, R std This is the Vienna standard mean seawater value.

6. The monitoring method according to claim 1, characterized in that: In step S2, it also includes confirming δ0 13 C and δ0 2 The specific steps for whether H can be used as the benchmark data are as follows: 13 C and δ0 2 H is placed at the endpoint 0, Δδ 13 C and Δδ 2 In the graph where H is the coordinate axis, when it is located at Δδ 2 H=4, Δδ 2 H=-4, Δδ 13 C=0.2, Δδ 13 When C=-0.2 and the four straight lines are in the rectangular frame formed by the endpoints, δ0 13 C and δ0 2 H can be used as a benchmark data.

7. The monitoring method according to claim 1, characterized in that: In step S5, the sampling on the nth day is to sample the groundwater and soil gas every 4 to 7 days 30 days before the repair, and to sample the groundwater and soil gas every 15 to 35 days after 30 days of repair.

8. The monitoring method according to claim 1, characterized in that: The in situ site remediation process described in step S4 includes but is not limited to one or more of soil vapor extraction, multiphase extraction, groundwater extraction and treatment, groundwater aeration, groundwater circulation wells, bioventilation, microbial stimulation, microbial enhancement, natural monitoring attenuation, and chemical oxidation technology.

9. The monitoring method according to claim 1, characterized in that: The target pollutants in step S1 include but are not limited to one or more of polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, petroleum hydrocarbons or benzene series.

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