Underground water pollution diffusion management and control effect monitoring and evaluating method based on isotope labeling

Abstract

The invention belongs to the field of groundwater pollution diffusion management and control evaluation, and discloses a groundwater pollution diffusion management and control effect monitoring and evaluation method based on isotope labeling, which can accurately evaluate the actual effect of site groundwater pollution diffusion control measures. The method comprises the following steps: determining a tracer marked by 14C according to site groundwater environment investigation and pollution risk assessment results; determining a tracer agent putting well, and determining a monitoring well outside the site boundary; initial background values of the radioactive specific activity of 14C in the tracer agent putting well and the monitoring well are obtained; after the underground water pollution diffusion management and control project is started, a tracer agent is put into the tracer agent putting well; collecting underground water samples from all the monitoring wells according to a preset sampling frequency; performing a 14C radioactivity specific activity test on the underground water sample to obtain the 14C radioactivity specific activity of the underground water sample; and according to the 14C radioactivity specific activity of the underground water sample, obtaining an underground water pollution diffusion management and control evaluation result.

Description

Technical Field

[0001] The present invention belongs to the field of monitoring and evaluation of the effect of groundwater pollution diffusion control on sites, and specifically relates to a method for monitoring and evaluation of the effect of groundwater pollution diffusion control based on isotope labeling. Background Art

[0002] With the rapid development of industrialization and urbanization, the problem of groundwater pollution is becoming increasingly serious, threatening the balance of the ecosystem and human health. Groundwater pollution diffusion control is one of the commonly used measures for groundwater pollution control and remediation on-site, especially for sites of existing enterprises or sites with limited construction conditions for remediation projects. Common control measures include vertical barriers (building vertical barrier walls at the site boundary) and hydraulic control (controlling the groundwater flow field by extracting groundwater in heavily polluted areas of the site to prevent pollutants from migrating outward). Control measures are used to prevent groundwater pollution within the site from spreading outside the site boundary. The effectiveness of control measures requires scientific evaluation. Monitoring the effectiveness of groundwater pollution diffusion control is of vital importance for evaluating the effectiveness of control measures and timely adjusting pollution control strategies.

[0003] Traditional monitoring of control effectiveness for commonly used control measures relies primarily on regular water quality sampling in monitoring wells outside the site boundary to measure target pollutant concentrations. Control effectiveness is assessed by analyzing the changing trends in these wells. This method suffers from significant sensitivity limitations. Before the control project is implemented, groundwater outside the site boundary may already contain high background concentrations of the target pollutant, or the target pollutant may have diffused beyond the site boundary, resulting in a significant concentration of the target pollutant in the groundwater outside the boundary. In this case, if the concentration of the pollutant diffused from the site is not too high, it will not cause significant fluctuations in the pollutant concentration in the monitoring wells, which can easily lead to misjudgment of control effectiveness. Furthermore, groundwater concentrations exhibit natural fluctuations. Even if the pollutant has not diffused beyond the site, the pollutant concentration in the monitoring wells may show an increasing trend. Alternatively, even if the pollutant has diffused beyond the site, the pollutant concentration in the monitoring wells may not show an increasing trend, potentially leading to misjudgment of control effectiveness. In summary, traditional assessment methods that rely on changing trends in pollutant concentrations are subject to significant inaccuracies. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a monitoring and evaluation method for groundwater pollution diffusion control effect based on isotope labeling, accurately monitor the groundwater pollution diffusion dynamics, and accurately evaluate the actual effect of the groundwater pollution diffusion control measures on the site.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling, the method comprising: Step 10: Determine the site's groundwater environmental survey and pollution risk assessment results. 14 C-labeled tracer; Step 20: Based on the results of the groundwater environmental survey and pollution risk assessment, determine the tracer placement wells within the groundwater pollution control area of ​​the site and the monitoring wells outside the site boundary; Step 30: Obtain the tracer placement well and monitoring well 14 Initial background value of C radioactivity specific activity; Step 40: After the groundwater pollution diffusion control project is initiated, the tracer determined in step 10 is placed in the tracer placement well; Step 50: Collect groundwater samples from all monitoring wells according to the preset sampling frequency; 14 C radioactivity specific activity test to obtain the groundwater samples 14 C radioactivity specific activity; Step 60: The groundwater sample obtained in step 50 14 C radioactive specific activity to obtain the groundwater pollution diffusion control assessment results.

[0006] As a preferred example, in step 10, according to the results of the groundwater environmental investigation and pollution risk assessment, if the target pollutants in the groundwater environment are inorganic substances, then select 14 C-labeled non-toxic and harmless inorganic substances are used as tracers; if the target pollutants in the groundwater environment are organic substances, then 14 C-labeled non-toxic and harmless organic matter is used as a tracer; if the target pollutant in the groundwater environment is a mixture of inorganic and organic matter, then 14 C-labeled non-toxic and harmless inorganic substances and 14 C-labeled non-toxic and harmless organic matter was used as a tracer.

[0007] As a preferred example, the 14 C-labeled non-toxic and harmless inorganic substances are 14 C-labeled sodium bicarbonate; 14 C-labeled non-toxic and harmless organic matter is 14 C-labeled acetic acid.

[0008] As a preferred example, in step 20, there are at least two deployment wells, which are dispersed within the groundwater pollution control area of ​​the site.

[0009] As a preferred example, in step 20, all monitoring wells are set outside the site boundary and in the area close to the site boundary, and when the groundwater flows downstream, a monitoring well is set every N meters along the site boundary; when the groundwater flows in both sides, two monitoring wells are set on each side of the site boundary; when the groundwater flows upstream, one monitoring well is set outside the site boundary; N is less than or equal to 300.

[0010] As a preferred example, the step 30 specifically includes: Groundwater samples were obtained by sampling the tracer placement well and the monitoring well; Groundwater samples from various locations 14 C radioactivity specific activity detection to obtain the groundwater in the tracer placement well and monitoring well 14 C radioactivity specific activity initial background value A0.

[0011] As a preferred example, the step 40 specifically includes: Configure the content determined in step 10 14 The solution of C-labeled substance is used as tracer. 14 The specific activity of C in groundwater from all injection wells and monitoring wells is at least 14 The maximum value of the initial background value of C radioactivity was 1 order of magnitude higher than that of the tracer. 14 The mass concentration of the C-labeled substance is not less than the highest concentration of the target pollutant in the site; the volume V of the tracer added to each tracer placement well is determined according to formula (1): V=100+(L / 100)×60 Formula (1) Where L is the farthest distance from the site boundary among all tracer placement wells, unit: meter; Pour the prepared tracer into the tracer delivery well at a uniform speed, and the tracer does not overflow from the wellhead of the tracer delivery well.

[0012] As a preferred example, in step 40, the first monitoring sampling time is the second day after the tracer is injected into the well.

[0013] As a preferred example, step 60 specifically includes: The control effect index is used to evaluate the control effect, and the control effect index is shown in formula (2): E=(A Si -A 0i ) / A 0i Formula (2) Where, E represents the control effect index, unit is %; A Si It indicates that after the implementation of the groundwater pollution diffusion control project and the placement of tracers, the groundwater sample obtained from the monitoring well No. i 14C radioactivity specific activity, unit: Bq / kg carbon; A 0i is the groundwater sample of monitoring well No. i 14 Initial background value of C radioactivity specific activity, unit: Bq / kg carbon; If the control effect index E of any batch is greater than the preset risk threshold, there is a risk of groundwater pollution spreading; if the control effect index E of all batches is less than or equal to the preset risk threshold, there is no risk of groundwater pollution spreading.

[0014] As a preferred example, the preset risk threshold is 3%.

[0015] Compared with the existing technology, the groundwater pollution diffusion control effect monitoring and evaluation method based on isotope labeling of the present invention can accurately monitor the groundwater pollution diffusion dynamics and accurately evaluate the actual effect of the groundwater pollution diffusion control measures on the site. The method includes: step 10, based on the results of the site groundwater environmental investigation and pollution risk assessment, determine 14 C-labeled tracer; Step 20, based on the results of the groundwater environmental investigation and pollution risk assessment of the site, determine the tracer placement well within the groundwater pollution control area of ​​the site and determine the monitoring well outside the site boundary; Step 30, obtain the tracer placement well and the monitoring well 14 C radioactivity specific activity initial background value; Step 40, after the groundwater pollution diffusion control project is started, the tracer determined in Step 10 is put into the tracer placement well; Step 50, according to the preset sampling frequency, groundwater samples are collected from all monitoring wells; the groundwater samples are subjected to 14 C radioactivity specific activity test to obtain the groundwater samples 14 C radioactivity specific activity; Step 60, the groundwater sample obtained according to step 50 14 The method is based on the co-migration characteristics of specific tracers and target pollutants, 14 The high sensitivity and low background value of C radioactive specific activity detection have established quantitative evaluation indicators to accurately monitor and evaluate the effectiveness of groundwater pollution diffusion control. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of groundwater pollution site management and control in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0018] The technical solution of the present invention is applicable to sites that are not contaminated by nuclear power.

[0019] A method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling in an embodiment of the present invention includes: Step 10: Determine the site's groundwater environmental survey and pollution risk assessment results. 14 C-labeled tracer.

[0020] because 14 C is a pure β decay isotope, its β ray energy is 156keV, and its half-life is 5730a. Compared with other radioactive isotopes, 14 C has the advantages of low energy, easy protection, high detection sensitivity and no need to consider decay correction when applied, making it suitable for use as a tracer. 14 C background level is low. Therefore, the present invention selects 14 The marker of C is used as a tracer.

[0021] In step 10, based on the results of the groundwater environmental investigation and pollution risk assessment, if the target pollutants in the groundwater environment are inorganic substances, select 14 C-labeled non-toxic and harmless inorganic substances are used as tracers. Preferably, 14 C-labeled non-toxic and harmless inorganic substances are 14 C-labeled sodium bicarbonate (NaH 14 CO3). If the target pollutant in the groundwater environment is organic matter, select 14 C-labeled non-toxic and harmless organic matter is used as a tracer. Preferably, 14 C-labeled non-toxic and harmless organic matter is 14 C-labeled acetic acid ( 14 CH3COOH). If the target pollutant in the groundwater environment is a mixture of inorganic and organic substances, select 14 C-labeled non-toxic and harmless inorganic substances and 14 C-labeled non-toxic and harmless organic matter is used as a tracer. Preferably, 14 C-labeled non-toxic and harmless inorganic substances are 14 C-labeled sodium bicarbonate, 14 C-labeled non-toxic and harmless organic matter is 14 C-labeled acetic acid. 14 C-labeled non-toxic and harmless inorganic or organic matter is added as a tracer to existing contaminated groundwater. On the one hand, it will not add new pollutants to the groundwater environment. On the other hand, it will utilize the co-migration characteristics of the tracer and the target pollutants. 14 The high detection sensitivity of C can well represent the migration of target pollutants with groundwater and easily identify whether pollutants have migrated outside the site.

[0022] Step 20: Based on the results of the groundwater environmental survey and pollution risk assessment on the site, determine the tracer placement wells within the groundwater pollution control area of ​​the site and determine the monitoring wells outside the site boundary.

[0023] Preferably, in step 20, there are at least two delivery wells, which are dispersed in the groundwater pollution control area of ​​the site. The groundwater pollution control area is located inside the site. The delivery well is located in the groundwater pollution control area. In this way, the tracer is put into the delivery well, and the tracer enters the groundwater in the groundwater pollution control area and flows with the groundwater. Multiple delivery wells are dispersed in the groundwater pollution control area of ​​the site, which can disperse the tracer as much as possible throughout the groundwater pollution control area. This is closer to the initial distribution state of pollutants in the groundwater in the groundwater pollution control area. For example, Figure 1 In the middle, three injection wells are arranged. The three injection wells are approximately the three vertices of an equilateral triangle and are arranged in the groundwater pollution control area.

[0024] Preferably, in step 20, all monitoring wells are set up outside the site boundary and in an area close to the site boundary. The monitoring wells are located outside the site boundary and close to the site boundary. In the downstream direction of groundwater flow, that is, downstream of the groundwater pollution control area, a monitoring well is set up every N meters along the site boundary. N is less than or equal to 300. A monitoring well is set up every N meters. It is easier to capture the diffusion of pollutants in the downstream direction. Setting a reasonable well spacing can, on the one hand, avoid laying out a large number of monitoring wells, and on the other hand, avoid failing to capture possible pollutant diffusion due to excessive well spacing. For example, Figure 1 In the downstream direction of groundwater flow, monitoring wells MW1, MW2 and MW3 are set at the site boundary. Two monitoring wells are set on each side of the site boundary on both sides of the groundwater flow. That is, at the site boundary opposite to the groundwater pollution control zone, two monitoring wells are set on each side of the site boundary on both sides of the groundwater flow. Groundwater pollutants diffuse in the downstream direction first, followed by diffusion in the directions on both sides of the groundwater flow. Generally, two monitoring wells are set on each side of the site boundary on both sides of the groundwater pollution control zone to meet the monitoring of pollutant diffusion. For example, Figure 1 In the process, monitoring wells MW7 and MW4, MW6 and MW5 are set up in pairs on both sides of the groundwater flow at the site boundary. In the upstream direction of the groundwater flow, that is, upstream of the groundwater pollution control area, a monitoring well is set up outside the site boundary. The possibility of groundwater pollutants diffusing and leaking upstream to outside the site is small or the rate is very slow. The upstream direction is not the key area for monitoring. From a conservative point of view, one monitoring well is set up upstream to monitor the small probability of pollutant diffusion and leakage. For example, Figure 1 In the upstream direction of groundwater flow, monitoring well MW8 is set outside the site boundary. All monitoring wells are selected from wells found to be contaminated with target pollutants during the preliminary site investigation or newly built monitoring wells.

[0025] Step 30: Obtain the tracer placement well and monitoring well 14 C initial background value of radioactivity specific activity.

[0026] The step 30 specifically includes: Step 301: sampling groundwater in the tracer placement well and the monitoring well to obtain groundwater samples; Step 302: Conduct 14 C radioactivity specific activity detection to obtain the groundwater in the tracer placement well and monitoring well 14 C radioactivity specific activity initial background value A0.

[0027] Step 30 is to sample groundwater from the tracer placement well and the monitoring well before placing the tracer into the tracer placement well to obtain groundwater samples; 14 C radioactivity specific activity detection to obtain the groundwater in the tracer placement well and monitoring well 14 C radioactivity specific activity initial background value A0.

[0028] based on 14 The initial background value A0 of C radioactivity specific activity may fluctuate. Preferably, at least two batches of groundwater samples should be collected. 14 C radioactivity specific activity detection to obtain the specific activity of different batches of groundwater samples 14 The initial background value of C radioactivity specific activity A0. The interval between two consecutive batches of sampling is at least 7 days, and the average value of multiple test results is taken as the value of each tracer placement well and monitoring well. 14 The initial background value of C radioactivity specific activity A0 is in Bq / kg carbon.

[0029] Step 40: After the groundwater contamination diffusion control project is initiated, the tracer determined in step 10 is placed into the tracer placement well. The groundwater contamination diffusion control project is initiated when the vertical barrier wall is completed or when the hydraulic control project begins pumping.

[0030] Preferably, the step 40 specifically includes: Step 401: Configure the data determined in step 10. 14 The solution of C-labeled substance is used as tracer. 14 The specific activity of C in groundwater from all injection wells and monitoring wells is at least 14 The maximum value of the initial background value of C radioactivity is one order of magnitude higher to reflect the 14The radioactivity of C is significantly different from the initial background value. The radioactivity of the tracer is significantly higher than the initial background value. In this way, once it spreads to the monitoring well outside the site, the radioactivity in the monitoring well will change significantly, making it easier to identify the spread of pollutants and improving the evaluation sensitivity of the method. 14 The mass concentration of the C-labeled substance is no less than the highest concentration of the target pollutant in the site. This ensures that the tracer mass concentration is closer to the pollutant concentration, making the tracer more representative of the pollutant; it also ensures that a sufficient amount of tracer is available to migrate and diffuse with the groundwater. The volume V of tracer added to each tracer placement well is determined according to formula (1): V=100+(L / 100)×60 Formula (1) Where L is the maximum distance from all tracer wells to the site boundary, measured in meters. Each tracer well corresponds to a distance from each site boundary. Among all the distances from each tracer well to the site boundary, the maximum distance is selected as L.

[0031] Step 402: Pour the prepared tracer into the tracer delivery well at a uniform rate, preventing the tracer from overflowing from the wellhead. Pour the tracer at a uniform rate to prevent the tracer from overflowing from the wellhead due to insufficient penetration into the aquifer.

[0032] In order to avoid missing the capture of the tracer, preferably, in step 40, the first monitoring sampling time is the second day after the tracer is put into the well.

[0033] Step 50: Collect groundwater samples from all monitoring wells according to the preset sampling frequency; 14 C radioactivity specific activity test to obtain the groundwater samples 14 C radioactivity specific activity.

[0034] Preferably, at least eight batches of samples should be collected, with a sampling duration of at least one year and a sampling frequency of once per quarter, with an interval of at least one month between batches. For sites with large variations in groundwater flow patterns, the sampling frequency may be appropriately increased.

[0035] investment 14 After the tracer is labeled with C, according to the permeability of the site, if the permeability is good, collect groundwater samples from all monitoring wells once a month to conduct 14 C radioactivity specific activity test, a total of 12 batches of samples were collected for 1 year; if the permeability is poor, groundwater samples were collected from all monitoring wells every 2 months for 14 For the C radioactivity specific activity test, a total of 8 batches of samples were collected over a period of 16 months.

[0036] Step 60: The groundwater sample obtained in step 50 14 C radioactive specific activity to obtain the groundwater pollution diffusion control assessment results.

[0037] The step 60 specifically includes: evaluating the control effect using a control effect index, where the control effect index is shown in formula (2): E=(A Si -A 0i ) / A 0i Formula (2) Where, E represents the control effect index, unit is %; A Si It indicates that after the implementation of the groundwater pollution diffusion control project and the placement of tracers, the groundwater sample obtained from the monitoring well No. i 14 C radioactivity specific activity, unit: Bq / kg carbon; A 0i is the groundwater sample of monitoring well No. i 14 The initial background value of C radioactivity specific activity, unit: Bq / kg carbon.

[0038] If the control effect index E of any batch is greater than the preset risk threshold, there is a risk of groundwater pollution spreading, that is, there is a hidden danger in the control effect; if the control effect index E of all batches is less than or equal to the preset risk threshold, there is no risk of groundwater pollution spreading, that is, the control is successful.

[0039] Considering the possible errors in the detection of radioactivity specific activity and 14 C detection sensitivity is high, and the principle of strict evaluation of control effect is followed. Preferably, the preset risk threshold is 3%. 14 If the radioactive specific activity of C is significantly greater than its initial background value, it means that the tracer (i.e., the pollutant) has migrated and diffused beyond the site boundary, that is, there are hidden dangers in the control effect of the management and control project on the groundwater pollution diffusion in the direction of the monitoring well, and further investigation and optimization of control measures are needed; if E does not exceed 3% during the entire effect evaluation period (control effect monitoring period), it means that the tracer (i.e., the pollutant) has not migrated and diffused beyond the site boundary, that is, the control effect of the management and control project on the groundwater pollution diffusion in the direction of the monitoring well is successful and effective.

[0040] The method of the above embodiment determines the 14 C-labeled tracer. Select a tracer with similar properties to the target pollutant. 14 The C-labeled substance is used as a tracer. On the one hand, it can be as close to the migration characteristics of the target pollutant as possible (co-migration characteristics with the target pollutant). On the other hand, it can be used to 14The high sensitivity of C radioactivity detection (capable of detecting 0.01 Bq / kg of carbon radioactivity) and low environmental background values ​​(at sites without nuclear contamination) overcome the shortcomings of existing methods, such as low sensitivity and poor ability to distinguish interference from natural environmental factors. This method accurately monitors the spread of groundwater contamination and accurately assesses the effectiveness of site-specific groundwater contamination control measures, with broad applicability to diverse sites.

[0041] The method of the above embodiment is based on the co-migration characteristics of a specific tracer and a target pollutant, 14 The high sensitivity and low background value of C radioactivity specific activity detection establish a quantitative evaluation index to assess the effectiveness of groundwater contamination diffusion control measures. Compared with traditional methods, the method of this embodiment has higher sensitivity and lower uncertainty, and can simply, intuitively, and accurately evaluate the effectiveness of groundwater contamination diffusion control measures.

[0042] An embodiment is provided below.

[0043] like Figure 1 As shown, this embodiment selects a contaminated site where a chemical company is located. After preliminary groundwater environmental investigation and pollution risk assessment of the site, it was determined that the groundwater pollutants of concern in the site are benzene series (organic matter), and the overall flow direction of the groundwater in the site is from northwest to southeast. The target aquifer of the site is mainly silt sand layer. According to the groundwater pollution control technical plan determined by the site, vertical barrier walls are built around the site boundary as a groundwater pollution diffusion control measure. Based on this site, a groundwater pollution diffusion control effect monitoring and evaluation method based on isotope labeling includes the following steps: Step 10: Determine the site's groundwater environmental survey and pollution risk assessment results. 14 C-labeled tracer. Since the target pollutants are organic matter, 14 C-labeled acetic acid ( 14 CH3COOH) as a tracer, its properties are similar to the migration characteristics of benzene-based organic compounds in groundwater, and it is non-toxic and harmless.

[0044] Step 20: Based on the results of the groundwater environmental survey and pollution risk assessment on the site, determine the tracer placement wells within the groundwater pollution control area of ​​the site and determine the monitoring wells outside the site boundary.

[0045] Tracer delivery wells: Based on the site's groundwater pollution control zone, three relatively dispersed wells within the groundwater pollution control zone were selected as tracer delivery wells, numbered TW1, TW2, and TW3. TW3 was the furthest from the site boundary, at 200 meters (L = 200 meters).

[0046] Monitoring Wells: Select monitoring wells identified as contaminated by target pollutants during the preliminary site survey and locate them immediately outside the site boundary. Three monitoring wells, numbered MW1, MW2, and MW3, will be located along the site boundary, no more than 300 meters downstream of the groundwater flow. Two monitoring wells, numbered MW4, MW5, MW6, and MW7, will be located on each side of the site boundary. One monitoring well, numbered MW8, will be located upstream of the groundwater flow.

[0047] Step 30: Obtain the tracer placement well and monitoring well 14 C initial background value of radioactivity specific activity.

[0048] Conduct 2 initial background value sampling and monitoring. The first sampling: Before the tracer is placed, collect groundwater samples from all 11 tracer placement wells and monitoring wells. 14 C radioactivity specific activity was measured. Seven days later, a second sample was collected for initial background value testing. The average of these two test results was taken as the initial background value for each well. The test results are shown in Table 1.

[0049] Table 1 Background value observation results (unit: Bq / kg carbon)

[0050] The maximum initial background value A0 of all injection wells and monitoring wells is 3.613 Bq / kg carbon.

[0051] Step 40: After the groundwater pollution diffusion control project is initiated, the tracer determined in step 10 is placed into the tracer placement well.

[0052] Tracer preparation: Prepare the 14 C-labeled acetic acid solution was used as a tracer to ensure that the tracer 14 The radioactivity of C is at least one order of magnitude greater than 3.613 Bq / kg carbon. 14 The radioactivity of C is 70Bq / kg carbon. 14 The mass concentration of C-labeled acetic acid is not lower than the maximum concentration of the target pollutant benzene series (the maximum concentration of benzene series in the previous investigation is 17 mg / L). 14 The mass concentration of C-labeled acetic acid was 30 mg / L.

[0053] Calculate the injection volume: The volume V (liters) of tracer solution added to each tracer injection well is calculated according to the formula V = 100 + (L / 100) × 60. Assuming L = 200 meters, then V = 100 + (200 / 100) × 60 = 100 + 120 = 220 liters.

[0054] Tracer Placement: After the vertical barrier wall is constructed, pour the prepared tracer into three tracer placement wells at a slow and uniform rate. Add 220 liters of the prepared tracer solution to each well.

[0055] Step 50: Collect groundwater samples from all monitoring wells according to the preset sampling frequency; 14 C radioactivity specific activity test to obtain the groundwater samples 14 C radioactivity specific activity.

[0056] According to the results of the previous site hydrogeological survey, the target aquifer on the site is mainly silt sand layer with relatively good permeability. Groundwater samples are collected from all 8 monitoring wells once a month. 14 The radioactivity of C was tested. A total of 12 batches of samples were collected over a period of 1 year. The first sampling time was the second day after the tracer was put into use. Table 2 shows the results of 12 batches of groundwater samples from 8 monitoring wells. 14 C radioactivity specific activity test results, unit: Bq / kg carbon.

[0057] Table 2

[0058] Step 60: The groundwater sample obtained in step 50 14 C radioactivity specific activity to obtain groundwater contamination spread control assessment results. The preset risk threshold is 3%.

[0059] According to the formula E=(A Si -A 0i ) / A 0i Calculate the pollution diffusion control effect index E. Take the 1st, 2nd, 10th, 11th, and 12th sampling data of MW1 monitoring well as an example: 1st time: A S1 =3.462Bq / kg carbon, A 01 =3.485Bq / kg carbon, E1=(3.462-3.485) / 3.485≈-0.0066, i.e. -0.66%, which is less than 3%.

[0060] 2nd time: A S1 =3.498Bq / kg carbon, A 01 =3.485Bq / kg carbon, E1=(3.498-3.485) / 3.485≈0.0037, i.e. 0.37%, which is less than 3%.

[0061] 10th: A S1 =3.509Bq / kg carbon, A 01=3.485Bq / kg carbon, E1=(3.509-3.485) / 3.485≈0.0069, i.e. 0.69%, which is less than 3%.

[0062] 11th: A S1 =3.495Bq / kg carbon, A 01 =3.485Bq / kg carbon, E1=(3.495-3.485) / 3.485≈0.0029, i.e. 0.29%, which is less than 3%.

[0063] 12th: A S1 =3.473Bq / kg carbon, A 01 =3.485Bq / kg carbon, E1=(3.473-3.485) / 3.485≈-0.0034, i.e. -0.34%, less than 3%.

[0064] During the one-year evaluation period, the E value for each of the eight monitoring wells was calculated based on the sampling data from each sampling period. The calculation results showed that the E value for all sampling batches did not exceed 3%.

[0065] According to the assessment criteria, the E values ​​for all eight monitoring wells did not exceed 3% in any sampling batch, indicating that the tracer (and therefore the contaminant) did not migrate or diffuse beyond the site boundaries. This demonstrates that the control measures for groundwater contamination in the direction of these monitoring wells were successful, and that the vertical barrier wall control measures effectively controlled the spread of groundwater contamination within the site.

[0066] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the specific embodiments described above. The specific embodiments and descriptions in the specification are only intended to further illustrate the principles of the present invention. Various changes and improvements are possible without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the invention as claimed.

Claims

1. A method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling, characterized in that: The method comprises: Step 10: Determine the site's groundwater environmental survey and pollution risk assessment results. 14 C-labeled tracer; Step 20: Based on the results of the groundwater environmental survey and pollution risk assessment, determine the tracer placement wells within the groundwater pollution control area of ​​the site and the monitoring wells outside the site boundary; Step 30: Obtain the tracer placement well and monitoring well 14 Initial background value of C radioactivity specific activity; Step 40: After the groundwater pollution diffusion control project is initiated, the tracer determined in step 10 is placed in the tracer placement well; Step 50: Collect groundwater samples from all monitoring wells according to the preset sampling frequency; 14 C radioactivity specific activity test to obtain the groundwater samples 14 C radioactivity specific activity; Step 60: The groundwater sample obtained in step 50 14 C radioactive specific activity to obtain the groundwater pollution diffusion control assessment results.

2. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: In step 10, according to the results of the groundwater environmental investigation and pollution risk assessment, if the target pollutants in the groundwater environment are inorganic substances, then select 14 C-labeled non-toxic and harmless inorganic substances are used as tracers; if the target pollutants in the groundwater environment are organic substances, then 14 C-labeled non-toxic and harmless organic matter is used as a tracer; if the target pollutant in the groundwater environment is a mixture of inorganic and organic matter, then 14 C-labeled non-toxic and harmless inorganic substances and 14 C-labeled non-toxic and harmless organic matter was used as a tracer.

3. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 2 is characterized in that: described 14 C-labeled non-toxic and harmless inorganic substances are 14 C-labeled sodium bicarbonate; 14 C-labeled non-toxic and harmless organic matter is 14 C-labeled acetic acid.

4. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: In step 20, there are at least two placement wells, which are dispersed within the groundwater pollution control area of ​​the site.

5. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: In step 20, all monitoring wells are set outside the site boundary and in the area close to the site boundary, and a monitoring well is set every N meters along the site boundary when the groundwater flows downstream; two monitoring wells are set on each side of the site boundary when the groundwater flows on both sides; and one monitoring well is set outside the site boundary when the groundwater flows upstream; N is less than or equal to 300.

6. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: The step 30 specifically includes: Groundwater samples were obtained by sampling the tracer placement well and the monitoring well; Groundwater samples from various locations 14 C radioactivity specific activity detection to obtain the groundwater in the tracer placement well and monitoring well 14 C radioactivity specific activity initial background value A0.

7. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: The step 40 specifically includes: Configure the content determined in step 10 14 The solution of C-labeled substance is used as tracer. 14 The specific activity of C in groundwater from all injection wells and monitoring wells is at least 14 The maximum value of the initial background value of C radioactivity was 1 order of magnitude higher than that of the tracer. 14 The mass concentration of the C-labeled substance is not less than the highest concentration of the target pollutant in the site; the volume V of the tracer added to each tracer placement well is determined according to formula (1): V=100+(L / 100)×60 Formula (1) Where L is the farthest distance from the site boundary among all tracer placement wells, unit: meter; Pour the prepared tracer into the tracer delivery well at a uniform speed, and the tracer does not overflow from the wellhead of the tracer delivery well.

8. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: In step 40, the first monitoring sampling time is the second day after the tracer is put into the well.

9. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 1 is characterized in that: The step 60 specifically includes: The control effect index is used to evaluate the control effect, and the control effect index is shown in formula (2): E = (A Si -A 0i ) / A 0i Formula (2) Where, E represents the control effect index, unit is %; A Si It indicates that after the implementation of the groundwater pollution diffusion control project and the placement of tracers, the groundwater sample obtained from the monitoring well No. i 14 C radioactivity specific activity, unit: Bq / kg carbon; A 0i is the groundwater sample of monitoring well No. i 14 Initial background value of C radioactivity specific activity, unit: Bq / kg carbon; If the control effect index E of any batch is greater than the preset risk threshold, there is a risk of groundwater pollution spreading; if the control effect index E of all batches is less than or equal to the preset risk threshold, there is no risk of groundwater pollution spreading.

10. The method for monitoring and evaluating the effect of groundwater pollution diffusion control based on isotope labeling according to claim 9, characterized in that: The preset risk threshold is 3%.

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