A groundwater remediation system and method for low-permeability formations based on groundwater circulation wells

Abstract

The present invention belongs to the technical field of groundwater remediation, and includes a groundwater remediation system and method for low-permeability formations based on groundwater circulation wells. The remediation system device includes a groundwater circulation well, which continuously separates the volatile pollutants dissolved in the groundwater into gas and liquid and pumps them to the ground for treatment; a pumping unit, which is used to pump the contaminated groundwater to the ground, increase the internal and external pressure difference of the surrounding groundwater circulation wells to promote the return of groundwater, and expand the influence radius; a ground treatment unit, which consists of two boxes with replaceable packing modules; a recharging unit, which connects the ground treatment unit and the water circulation well to realize the large-scale groundwater circulation of the entire disposal system. The present invention extracts the groundwater from the central pumping well, increases the water head difference inside and outside the well pipe of the surrounding groundwater circulation wells, accelerates the release of groundwater in the low-permeability formation, promotes groundwater circulation, and can be flexibly applied to the remediation of groundwater pollution of various pollution types, and adjusts the remediation mode according to the change of the pollutant removal rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of groundwater remediation, and particularly relates to a groundwater remediation system and method for low-permeability formations based on groundwater circulation wells. Background Art

[0002] In China, heavily polluted sites are mainly concentrated in the eastern coastal areas, and low-permeability formations such as silty clay are generally developed. The low-permeability characteristics hinder the mass transfer effect of the remediation agent and reduce the remediation efficiency.

[0003] Traditional in-situ remediation processes often show short-term "false compliance". Pollutants that are not easily removed in the low-permeability area slowly and continuously diffuse to the high-permeability area, thus serving as new pollution sources and causing pollution rebound.

[0004] Water circulation wells have the characteristics of low remediation cost, small environmental disturbance, low energy consumption, etc., and can be coupled with a variety of remediation technologies, with great application potential. However, due to the influence of device technology and method levels, the problems of screen clogging and insufficient lower circulation have not been well solved. Especially in low-permeability formations, the influence radius of groundwater circulation is small, the remediation efficiency is not strong, and at the same time, the repeated scouring of the circulating water flow is likely to cause the precipitation of aquifer mud, and large particles clog the screen, resulting in a gradual reduction in the influence radius of groundwater circulation and even interruption of the water cycle, leading to a deterioration in the remediation effect of the water circulation well and even the scrapping of the water circulation well facilities. Not only is it difficult to achieve the remediation goal, but it will also cause incalculable economic losses.

[0005] At the same time, groundwater pollution often shows the characteristics of multi-pollutant types and compound pollution of multiple pollutants. Technologies such as heating, electrolysis, and in-situ high-pressure injection often can only remove trace organic pollutants, or the pollutants that can be treated are relatively single, or can only remove organic pollutants in groundwater, or have almost no remediation effect on heavy metal pollutants, or need to add a variety of agents to promote the reaction and use a large amount of leaching agents to cause secondary pollution problems. Water circulation wells are mainly used for the pollution remediation of VOCs and SVOCs. The combined remediation of multiple technologies in compound pollution sites will involve the problem of repeated construction, which does not conform to the policy orientation of pollution reduction and carbon emission reduction, and a systematic solution needs to be provided.

[0006] The present invention aims to provide a groundwater remediation system device suitable for various pollution types, and realizes a flexible and effective remediation method for multiple scenarios through the adjustment of the ground device. Summary of the Invention

[0007] The purpose of the present invention is to provide a groundwater remediation system and method for low-permeability formations based on groundwater circulation wells, so as to solve the problems of poor remediation effect, common pollution tailing and rebound in the existing in-situ remediation of low-permeability formation pollution sites as mentioned in the above background art.

[0008] A groundwater remediation system for low-permeability formations based on a groundwater circulation well, comprising a central pumping well and a number of water circulation wells arranged around the central pumping well, and further comprising a central pumping unit, a plurality of recharge units and a ground treatment unit; wherein the pumping object of the central pumping unit is the central pumping well, the recharge object of the recharge unit is each water circulation well, and the end of the central pumping unit is connected to the water inlet end of the ground treatment unit, and the recharge unit is connected to the water outlet end of the ground treatment unit; the remediation system further comprises a gas treatment unit, and the treatment object of the gas treatment unit is each water circulation well, including an air injection unit and an air extraction unit, wherein the air injection unit comprises an air injection pump and an air diffuser pipe connected to the air injection pump, the lower end of the air diffuser pipe is inserted into the bottom of the water body of the water circulation well, the air extraction unit comprises an air extraction pump and an air extraction pipe connected to the air extraction pump, the lower end of the air extraction pipe is located at the wellhead of the water circulation well, and an activated carbon tank for purifying the internal air flow is installed on the air extraction pipe.

[0009] Preferably, the central pumping unit comprises a water extraction pipe and a water pump, and the lower end of the water extraction pipe extends to the bottom of the central pumping well.

[0010] Preferably, the recharge unit comprises a number of recharge water pipes with the upper ends connected to the ground treatment unit and the lower ends extending into the water circulation wells, and a stop valve is arranged on the recharge water pipes.

[0011] Preferably, the water circulation well has an upper water circulation well upper packing section and a lower water circulation well lower packing section, and there is an isolation packing section between the water circulation well upper packing section and the water circulation well lower packing section, and the upper part of the water circulation well upper packing section is not lower than the local original groundwater level line.

[0012] Preferably, the central pumping well has a filter packing section, the upper part of the filter packing section is not lower than the local original groundwater level line, and the lower part extends to the bottom of the central pumping well, and groundwater enters the central pumping well through the filter packing section.

[0013] Preferably, a positioning structure is arranged at the wellhead of the water circulation well, and the positioning structure fixes the recharge water pipe, the air diffuser pipe and the air extraction pipe.

[0014] Preferably, the ground treatment unit comprises a packing box I and a packing box II, and the packing inside the packing box I and the packing box II can be replaced, including activated carbon filtration and adsorption materials or chemical oxidation-reduction slow-release agents or microbial agents or surfactants.

[0015] Preferably, the water circulation wells are evenly arranged around the central pumping well, and the number S thereof is calculated according to the formula S = πr / R 循 wherein r represents the distance between the water circulation well and the central pumping well, and R 循 represents the influence radius of the water circulation well, and the distance r between the water circulation well and the central pumping well is less than the influence radius R of the central pumping well 抽 .

[0016] The object of the present invention is to provide a method for repairing groundwater in low-permeability formations based on a water circulation well. The repair method comprises the following steps:

[0017] Step 1: Set a central pumping well with a well diameter of r at the center of the polluted area, measure the original groundwater level Ho of the polluted area, the water level h of the central pumping well, and the local permeability coefficient K, and calculate the influence radius R of the preset central pumping well according to the formula w wherein, Q is the pumping flow rate; w 抽

[0018] Step 2: Designate a point where one of the water circulation wells is located within the influence radius R of the central pumping well, measure the distance r between this point and the central pumping well, and calculate its influence radius R according to the specifications of the preset water circulation well 抽 ; Calculate the number S of water circulation wells to be set according to the formula S = πr / R 循 ; 循

[0019] Step 3: Set a plurality of water circulation wells with the above characteristics around the central pumping well according to the data r and S

[0020] Step 4: Lay the central pumping unit. Connect the upper end of the pumping pipe to the water pump and extend the lower end to the bottom of the central pumping well; connect the end drain pipe of the central pumping unit to the packing box I, and then connect the packing box I to the packing box II so that the water pumped out by the central pumping unit passes through the packing box I and the packing box II in sequence; select the packing for the two packing boxes according to the type of pollutants

[0021] Step 5: Lay the recharge unit, equip each water circulation well with a recharge water pipeline with a stop valve, and connect the recharge water pipeline to the packing box II

[0022] Step 6: Equip each water circulation well with an air injection unit and an air extraction unit with the above characteristics, and extend the aeration pipe of the air injection unit to the lower packing section of the water circulation well of the water circulation well

[0023] Step 7: Start the air extraction unit, then start the air injection unit, open the stop valve, and then start the central pumping unit to pump the sewage in the central pumping well to the ground, increase the internal and external pressure difference of the surrounding water circulation wells to promote the groundwater reflux, and expand the groundwater influence radius; make the pumped sewage pass through the packing box I and the packing box II in sequence, and then recharge it into the surrounding water circulation wells; at the same time, as the air injection unit aerates the water body of the water circulation well, promote the gas-liquid separation of the volatile pollutants dissolved in the water body, and use the air extraction unit to extract it, and finally discharge it to the atmosphere after being treated by the activated carbon tank ​​​​

[0024] During the above operation process, it is necessary to regularly monitor the water body:

[0025] When the VOCs pollution concentration in groundwater is high and there is a NAPL phase, the packing box adsorbs high-concentration organic pollutants in the groundwater to improve the remediation efficiency; when it comes to the latter stage of remediation, as the NAPL decreases and disappears, the pollutants are mainly in the dissolved phase, and targeted materials are added to the packing box according to the properties of the pollution components;

[0026] When the groundwater contains heavy metal pollutants, alkaline materials are added to the packing box I to adjust the pH of the groundwater, and targeted adsorption materials are added to the packing box II to adsorb the heavy metal pollutants precipitated in the groundwater;

[0027] When the organic pollutants in the groundwater are stubborn and difficult to be quickly extracted by cyclic aeration, the central pumping unit is closed, surfactants, chemical agents or microbial materials are added to the packing box, and the additives are transported into the target aquifer through the recharge unit. The circulation system is run for a period of time first, and then the central pumping unit is restarted after an interval of time to promote the pollutants to enter the ground treatment system through the extraction device.

[0028] The influence radius of the general silty sand formation is 25 - 50m, that of medium and coarse sand can reach 200 - 300m, while the influence radius of the low-permeability formation mainly composed of silty clay is only 5 - 10m. Therefore, the influence radius of in-situ remediation of water circulation wells in low-permeability formations is extremely limited. By constructing a central pumping well and water circulation wells, the present invention can effectively promote groundwater circulation and enhance the system remediation efficiency. Its beneficial effects are specifically manifested as follows:

[0029] (1) For several water circulation wells around the central pumping well, the upper packing section and the lower packing section of each water circulation well respectively form an upper water filtration device and a lower water filtration device capable of filtering water. Under the action of the internal and external pressure difference, water flows from the upper water filtration device into the ground and from the lower water filtration device into the water circulation well. Therefore, each water circulation well is equivalent to a local small circulation system around the central pumping well;

[0030] (2) Under the combined action of the pumping unit and the recharge unit, the polluted water enters the water circulation well from the central pumping well, and after gas-liquid separation treatment, it enters the central pumping well from the water circulation well under the action of osmosis. This circulation process is carried out multiple times, thus forming a large groundwater circulation system from the central pumping well → pumping unit → recharge unit → water circulation well → central pumping well. Through the extraction of groundwater from the central pumping well, the head difference inside and outside the well pipe of the surrounding water circulation wells is increased, and the release of groundwater in the low-permeability formation is accelerated. For the low-permeability formation, this method can greatly enhance the remediation efficiency of groundwater pollution in the low-permeability formation.

[0031] (3) The system can be flexibly applied to the remediation of groundwater pollution of various pollution types and adjust the remediation mode according to the change of the pollutant removal rate; in addition, the ground stuffing box can adsorb NAPL phase and particulate matter in groundwater, and fundamentally alleviate the problems of resistance to the backflow of groundwater from the upper screen pipe to the formation and the blockage of the screen pipe to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The illustrative embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0033] Figure 1 is a longitudinal plane structure schematic diagram of the groundwater remediation system according to the middle embodiment provided by the present invention;

[0034] Figure 2 is a schematic diagram of the position distribution of the central pumping well and the water circulation well in the groundwater remediation system according to the middle embodiment provided by the present invention;

[0035] Figure 3 is a schematic diagram of the connection structure of stuffing box I and stuffing box II.

[0036] In the figure, central pumping well 7, water extraction pipe 8, stuffing box I 9, stuffing box II 10, reclaimed water pipeline 11, air injection pump 12, air diffuser pipe 13, water circulation well 14, upper packing section of water circulation well 15, lower packing section of water circulation well 16, air extraction pipe 17, activated carbon tank 18, air extraction pump 19, water stop valve 20, water filtering packing section 21, shunt pipe 101. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will describe in detail the embodiments of the present application in conjunction with the drawings and embodiments, so as to fully understand how the present application uses technical means to solve technical problems and achieve the realization process of technical effects and implement accordingly.

[0038] Figure 1 and Figure 2 is an embodiment of the present invention, a low-permeability formation groundwater remediation system based on a groundwater circulation well. Comprising:

[0039] A central pumping well 7, located at the center of the pollution area, set and having a water filtering packing section 21, the upper part of the water filtering packing section 21 is not lower than the local original groundwater level line, and the lower part extends to the bottom of the central pumping well 7, and groundwater enters the central pumping well 7 through the water filtering packing section 21;

[0040] A water circulation well 2, and is arranged around the central pumping well 1 in the pollution area, according to the formula S = πr / R 循, calculate the number S of water circulation wells, where r represents the distance between the water circulation well 14 and the central pumping well 7, and R 循 represents the influence radius of the water circulation well 14 (measured), and the distance r between the water circulation well 14 and the central pumping well 7 is less than the influence radius R of the central pumping well 7 抽 (measured). In this embodiment, eight water circulation wells 2 are provided. Each water circulation well 2 has an upper water circulation well upper packing section 15 and a lower water circulation well lower packing section 16. Between the water circulation well upper packing section 15 and the water circulation well lower packing section 16 is an isolation packing section, and the upper part of the water circulation well upper packing section 15 exceeds the local original groundwater level line. Based on the above structural characteristics, each water circulation well forms an independent circulation system around the central pumping well 7;

[0041] The central pumping unit is used to pump out the groundwater in the central pumping well 7 to expand the internal and external water head difference of the surrounding water circulation wells through the groundwater depression funnel.

[0042] The ground treatment unit 6 pumps the groundwater out and sends it to the ground treatment unit; activated carbon filtration and adsorption materials, chemical oxidation-reduction slow-release agents, microbial agents, surfactants, etc. can be installed in the ground treatment unit as needed to construct a coupling repair technology and equipment system with the water circulation well as the core to achieve the coupling repair of multiple technologies and the water circulation well.

[0043] The recharge unit recharges the groundwater from the ground treatment unit to the water circulation well, connecting the ground treatment unit and the water circulation well, and transporting substances such as surfactants and microbial agents added in the packing box to the water circulation well through groundwater recharge to achieve the flexible application of in-situ repair technologies such as coupled bioremediation and chemical oxidation-reduction.

[0044] The gas treatment unit aerates the water circulation well 14, and at the same time extracts the floating gas carrying pollutants, and discharges it to the atmosphere after gas-liquid separation treatment.

[0045] Among them, the pumping unit and the recharge unit form a large groundwater circulation system, and the water circulation well is a small circulation system.

[0046] Specifically, the pumping object of the central pumping unit is the central pumping well 7, including a pumping pipe 8 and a water pump. The lower end of the pumping pipe 8 extends to the bottom of the central pumping well 7, and the upper end is connected to the stuffing box I9 in the ground treatment unit. The stuffing box I9 is ​​connected to the stuffing box II10, so that the sewage passes through the stuffing box I9 and the stuffing box II10 in turn. The internal stuffing of the stuffing box I9 and the stuffing box II10 used in this embodiment can be replaced, and a diversion pipe 101 with eight connecting ports is arranged at the rear of the stuffing box II10; the above-mentioned recharge unit includes eight recharge water pipes 11 whose upper ends are connected to the diversion pipe 101, and the lower end of each recharge water pipe 11 extends into the bottom of the water circulation well 14 respectively, and a water stop valve 20 is arranged on the recharge water pipe 11. Each water circulation well 14 is provided with a gas processing unit, including an injection unit and an air extraction unit, wherein the injection unit includes an injection pump 12 and an aeration pipe 13 connected to the injection pump 12, the lower end of the aeration pipe 13 is inserted into the bottom of the water body of the water circulation well 14, and the air extraction unit includes an air extraction pump 19 and an air extraction pipe 17 connected to the air extraction pump 19, the lower end of the air extraction pipe 17 is located at the wellhead of the water circulation well 14, and an activated carbon tank 18 for purifying the internal air flow is installed on the air extraction pipe 17. For the water circulation well 14, a positioning frame is provided at the wellhead, and the reinjection water pipeline 11, the aeration pipe 13 and the air extraction pipe 17 extending into the water circulation well 14 are fixed to the positioning frame.

[0047] According to the above-mentioned groundwater remediation system, this embodiment provides a groundwater remediation method, which includes the following steps:

[0048] Step 1: Measure the original groundwater level in the contaminated area and use the formula Calculate the influence radius R of the preset central pumping well 7 抽 , where K is the permeability coefficient of the contaminated site, r w is the diameter of the preset central pumping well, Ho is the original water level, h w is the water level of the central pumping well, Q is the pumping flow rate; then a central pumping well 7 with the above characteristics is selected and set;

[0049] Step 2: Influence radius R of the central pumping well 7 抽 The point where one of the water circulation wells 14 is located is demarcated within the range, and the distance r between this point and the central pumping well 7 is measured. The influence radius R is calculated according to the specifications of the preset water circulation well. 循 ; According to the formula S = πr / R 循 , calculate the number S of water circulation wells 14 to be set, and eight water circulation wells are selected in this embodiment;

[0050] Step 3, according to the data r and S, eight water circulation wells 14 with the above characteristics are set around the central pumping well 7;

[0051] Step 4: Lay the central pumping unit. Connect the upper end of the water suction pipe 8 to the water pump and extend the lower end to the bottom of the central pumping well 7. Connect the end drain pipe of the central pumping unit to the packing box I9, and then connect the packing box I9 to the packing box II10 so that the water pumped out by the central pumping unit passes through the packing box I9 and the packing box II10 in sequence. Select the packing materials for the two packing boxes according to the type of pollutants.

[0052] Step 5: Lay the recharge unit. Provide each water circulation well 14 with a recharge water pipeline 11 equipped with a water stop valve 20, and connect the recharge water pipeline 11 to the packing box II10.

[0053] Step 6: Provide each water circulation well 14 with an air injection unit and an air extraction unit with the above characteristics, and extend the aeration pipe 13 of the air injection unit to the lower packing section 16 of the water circulation well 14 of the water circulation well.

[0054] Step 7: First, start the air extraction unit, then start the air injection unit, and then start the central pumping unit. Open the water stop valve 20. Pump the sewage in the central pumping well 7 to the ground, increase the internal and external pressure difference of the surrounding water circulation wells to promote the groundwater reflux, expand the groundwater influence radius, so that the pumped sewage passes through the packing box I9 and the packing box II10 in sequence, and then recharge it into the surrounding water circulation wells 14. At the same time, use the air injection unit to aerate the water body in the water circulation well 14 to promote the gas-liquid separation of the volatile pollutants dissolved in the water body, and use the air extraction unit to extract it. Finally, it is discharged to the atmosphere after being treated by the activated carbon tank 18.

[0055] During the above operation process, it is necessary to regularly monitor the water body and adjust the operation process according to the monitoring results:

[0056] When the VOCs pollution concentration in the groundwater is relatively high and there is a NAPL phase, the packing box 1 adsorbs the high-concentration organic pollutants in the groundwater to improve the remediation efficiency. When it comes to the later stage of remediation, as the NAPL decreases and disappears, the pollutants are mainly in the dissolved phase, and targeted materials are added according to the properties of the pollution components.

[0057] When the groundwater contains heavy metal pollutants, add alkaline materials to the packing box 1 to adjust the pH of the groundwater, and add targeted adsorption materials to the packing box 2 to adsorb the heavy metal pollutants in the groundwater and precipitate them.

[0058] When the organic pollutants in the groundwater are stubborn and difficult to be quickly cycled and aerated and extracted, close the central pumping unit, add surfactants, chemical agents or microbial materials to the packing box, and transport the additives to the target aquifer through the recharge unit. First, run the circulation system for a period of time, and then start the central pumping unit again after an interval of time to promote the pollutants to enter the ground treatment system through the extraction device.

[0059] Based on the technology disclosed in the present invention, first, the upper packing section 15 and the lower packing section 16 of each water circulation well 14 respectively form an upper water filtering device and a lower water filtering device capable of filtering water bodies. Under the action of the internal and external pressure difference, the water body flows into the ground from the upper water filtering device and into the water circulation well 14 from the lower water filtering device. Therefore, each water circulation well 14 is equivalent to a local small circulation system around the central pumping well 7.

[0060] Secondly, the coordinated operation of the pumping unit and the recharge unit accelerates the water circulation. The polluted water enters the water circulation well 14 from the central pumping well 7. After gas-liquid separation treatment, it enters the central pumping well 7 from the water circulation well 14 under the action of osmosis. This circulation process is carried out multiple times, thus forming a large groundwater circulation system from the central pumping well 7 → pumping unit → recharge unit → water circulation well 14 → central pumping well 7. By pumping groundwater from the central pumping well, the water head difference inside and outside the well pipe of the surrounding water circulation wells is increased, and the release of groundwater in the low-permeability formation is accelerated. For the low-permeability formation, this method can greatly enhance the groundwater pollution remediation efficiency of the low-permeability formation.

[0061] In addition, the system can be flexibly applied to the remediation of groundwater pollution of various pollution types and adjust the remediation mode according to the change of the pollutant removal rate. In addition, the ground packing box can adsorb NAPL phase and particulate matter in groundwater, and fundamentally alleviate the problem of resistance when groundwater flows back from the upper screen pipe to the formation and the problem of screen pipe blockage to the greatest extent.

[0062] For example, certain terms are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. The specification and claims do not use the difference in names as a way to distinguish components, but use the difference in functions of components as the criterion for distinction. As mentioned throughout the specification and claims, "comprising" is an open-ended term and should be interpreted as "including but not limited to". "Substantially" means within an acceptable error range. Those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect.

[0063] It should be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a commodity or system including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent in such a commodity or system. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the commodity or system including the said element.

[0064] The foregoing description has shown and described several preferred embodiments of the present invention. However, as previously mentioned, it should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the above teachings or the skills or knowledge in related fields. Any alterations and changes made by those skilled in the art that do not depart from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A groundwater remediation system for low-permeability formations based on groundwater circulation wells, characterized in that: It includes a central pumping well and several groundwater circulation wells arranged around the central pumping well, and also includes a central pumping unit, multiple recharge units and a ground treatment unit; among them, the pumping object of the central pumping unit is the central pumping well, the recharge object of the recharge unit is each water circulation well, and the end of the central pumping unit is connected to the water inlet end of the ground treatment unit, and the recharge unit is connected to the water outlet end of the ground treatment unit; the remediation system also includes a gas treatment unit, and the treatment object of the gas treatment unit is each water circulation well, including an air injection unit and an air extraction unit. Among them, the air injection unit includes an air injection pump and an air diffuser pipe connected to the air injection pump. The lower end of the air diffuser pipe is inserted into the bottom of the water body of the water circulation well. The air extraction unit includes an air extraction pump and an air extraction pipe connected to the air extraction pump. The lower end of the air extraction pipe is located at the wellhead of the water circulation well, and an activated carbon tank for purifying the internal air flow is installed on the air extraction pipe; the ground treatment unit includes a packing box I and a packing box II, and the packing inside the packing box I and the packing box II can be replaced, including activated carbon filtration and adsorption materials or chemical oxidation-reduction slow-release agents or microbial agents or surfactants, and the packing of the two packing boxes is selected according to the type of pollutants; The water circulation wells are evenly arranged around the central pumping well, and the number S is calculated according to the formula S = πr / R 循 where r represents the distance between the water circulation well and the central pumping well, and R 循 represents the influence radius of the water circulation well, and the distance r between the water circulation well and the central pumping well is less than the influence radius R of the central pumping well 抽 .

2. A groundwater remediation system for low-permeability formations based on groundwater circulation wells according to claim 1, characterized in that: The central pumping unit includes a pumping pipe and a water pump, and the lower end of the pumping pipe extends to the bottom of the central pumping well.

3. A groundwater remediation system for low-permeability formations based on groundwater circulation wells according to claim 1, characterized in that: The recharge unit includes several recharge water pipes with the upper ends connected to the ground treatment unit and the lower ends extending into the water circulation wells, and a stop valve is arranged on the recharge water pipes.

4. A groundwater remediation system for low-permeability formations based on groundwater circulation wells according to claim 3, characterized in that: The water circulation well has an upper water circulation well upper packing section and a lower water circulation well lower packing section. Between the water circulation well upper packing section and the water circulation well lower packing section is an isolation packing section, and the upper part of the water circulation well upper packing section is not lower than the local original groundwater level line.

5. A groundwater remediation system for low-permeability formations based on groundwater circulation wells according to claim 4, characterized in that: The central pumping well has a filter packing section, the upper part of which is not lower than the local original groundwater level line, and the lower part extends to the bottom of the central pumping well, and groundwater enters the central pumping well through the filter packing section.

6. A groundwater remediation system for low-permeability formations based on groundwater circulation wells according to claim 5, characterized in that: A positioning structure is arranged at the wellhead of the water circulation well, and the positioning structure fixes the recharge water pipe, the air diffuser pipe and the air extraction pipe.

7. A remediation method applicable to the groundwater remediation system for low-permeability formations based on groundwater circulation wells according to any one of claims 1-6, which includes the following steps: Step 1, set a central pumping well with a well diameter of r in the center of the polluted area, measure the original groundwater level Ho in the polluted area, the water level h of the central pumping well w and the local permeability coefficient K, according to the formula w , , Among them, Calculate the influence radius R of the preset central pumping well 抽 , where Q is the pumping flow rate; Step 2, within the influence radius R of the central pumping well 抽 locate one of the points where the water circulation well is to be located, measure the distance r between this point and the central pumping well, and calculate its influence radius R according to the specifications of the preset water circulation well 循 ; According to the formula S = πr / R 循 , calculate the number S of the water circulation wells to be set Step 3, according to the data r and S, uniformly arrange a plurality of the above-mentioned water circulation wells around the central pumping well; Step 4: Lay the central pumping unit. Connect the upper end of the water suction pipe to the water pump and extend the lower end to the bottom of the central pumping well. Connect the end drain pipe of the central pumping unit to the packing box I, and then connect the packing box I to the packing box II, so that the water pumped out by the central pumping unit passes through the packing box I and the packing box II in sequence. Select the packing materials for the two packing boxes according to the type of pollutants. Step 5: Lay the recharge unit. Equip each water circulation well with a recharge water pipeline with a stop valve and connect the recharge water pipeline to the packing box II. Step 6: Equip each water circulation well with an air injection unit and an air extraction unit with the above characteristics, and extend the aeration pipe of the air injection unit to the lower packing section of the water circulation well of the water circulation well. Step 7: Start the air extraction unit, then start the air injection unit, open the stop valve, and then start the central pumping unit. Pump the sewage in the central pumping well to the ground to increase the internal and external pressure difference of the surrounding water circulation wells and promote the groundwater reflux, expanding the groundwater influence radius. Make the pumped sewage pass through the packing box I and the packing box II in sequence, and then recharge it into the surrounding water circulation wells. At the same time, as the air injection unit aerates the water body in the water circulation well, promote the gas-liquid separation of the volatile pollutants dissolved in the water body, and use the air extraction unit to extract them. Finally, after being treated by the activated carbon tank, it is discharged into the atmosphere. During the above operation process, it is necessary to monitor the water body regularly: When the VOCs pollution concentration in the groundwater is relatively high and there is a NAPL phase, the packing box adsorbs the high-concentration organic pollutants in the groundwater to improve the remediation efficiency. When it comes to the later stage of remediation, as the NAPL decreases and disappears, the pollutants are mainly in the dissolved phase. Add targeted materials to the packing box according to the properties of the pollution components. When the groundwater contains heavy metal pollutants, add alkaline materials to the packing box I to adjust the pH of the groundwater, and add targeted adsorption materials to the packing box II to adsorb the heavy metal pollutants in the groundwater and precipitate them. When the organic pollutants in the groundwater are stubborn and difficult to be quickly cycled and aerated and extracted, turn off the central pumping unit, add surfactants, chemical agents or microbial materials to the packing box, and transport the additives to the target aquifer through the recharge unit. First, operate the central pumping unit and the recharge unit for a period of time, and then start the central pumping unit again after an interval of time to promote the pollutants to enter the ground treatment system through the extraction device.

Images