Methods for blocking the migration of pollutants from shallow contaminated sites due to groundwater dynamics

Abstract

The present invention discloses a method for blocking the migration of pollutants in a shallow contaminated site under the action of groundwater dynamics. The contaminated soil layer of the contaminated site is higher than the groundwater layer. A trench is dug around the contaminated site, and the depth is dug to below the contaminated soil layer. A tubular water guide device is placed in the trench, and then the trench is backfilled. The groundwater flows to the corresponding tubular water guide device on the front and is drained independently. The remaining tubular water guide devices are interconnected and discharged externally. The present invention arranges tubular water guide devices around the shallow contaminated site. The clean water on the front of the contaminated site is drained separately and can be recycled for secondary use. The water carrying pollutants flowing through the contaminated site is discharged externally under the action of the remaining tubular water guide devices, thereby blocking the contaminated site from infiltrating and migrating pollutants outwards under the action of groundwater dynamics, and avoiding the spread of pollution. The method is suitable for shallow contaminated sites such as temporary stacking and shallow pollution, and the contaminated soil layer is higher than the groundwater layer.

Description

Technical Field

[0001] The invention belongs to the technical field of pollution control, and in particular relates to a method for blocking pollutants from migrating from shallow contaminated sites under the action of groundwater dynamics. Background Art

[0002] For sites where hazardous wastes have been stored for a long time and no risk control measures have been taken, after the hazardous wastes are cleaned up, the shallow surface soil occupied by them will often be contaminated, especially when the groundwater is shallow, the site will experience "salt return" phenomenon. The main reason is that the groundwater seeps upward and diffuses outward, bringing out pollutants from the contaminated soil, causing pollutants to migrate and diffuse upward and outward. In the process of conducting field surveys of the site soil environment, due to the long time required, there is currently no effective method for temporary and rapid risk control of pollutant diffusion on site. For this reason, it is very necessary to develop a method that meets the risk control requirements and is easy to quickly construct to block the migration of pollutants from shallow contaminated sites due to the dynamic effects of groundwater. Summary of the invention

[0003] The purpose of the present invention is to provide a method for blocking the migration of pollutants in shallow contaminated sites due to the dynamic effect of groundwater.

[0004] The object of the present invention is achieved in this way: the contaminated soil layer of the contaminated site is higher than the groundwater layer, trenches are dug around the contaminated site, and the depth is dug below the contaminated soil layer. A tubular water guide device is placed in the trench, and then the trench is backfilled. The groundwater flows to the corresponding tubular water guide device on the opposite side and is discharged independently, and the remaining tubular water guide devices are connected to each other and discharged externally.

[0005] A shallow contaminated site refers to a contaminated site where the depth of the contaminated soil layer is less than 5 meters.

[0006] Preferably, the tubular water guide device comprises a tube body, a first filter layer, and a second filter layer. The tube wall from one third of the diameter of the tube body to the edge of the tube body is a solid tube wall, and the remaining tube wall positions are uniformly provided with water guide holes with a pore size of 3-5 mm. The first filter layer is wrapped outside the tube body, and the second filter layer is wrapped outside the first filter layer; the first filter layer is a filter screen, using 400g / cm 3 Non-woven fabric or nylon mesh, the second filter layer is a 20~30cm thick gravel layer with a gravel diameter of 2~5cm; after the groundwater is dispersed by the gravel in the second filter layer, it evenly passes through the first filter layer and enters the pipe body through the water conducting holes. Since the lower part of the pipe body is a solid pipe wall, the water in the pipe body flows out by gravity; the first filter layer prevents gravel from entering the pipe body.

[0007] Preferably, the pipe body is a PVC pipe or a PPR pipe with a diameter not less than DN80.

[0008] Preferably, the inclination angle between the tubular water-conducting device and the horizontal plane is 4-6°. When the site is flat, the inclination angle can be set when burying the tubular water-conducting device to facilitate the gravity discharge of water in the pipe body.

[0009] Preferably, the tubular water guiding device corresponding to the direction in which the groundwater flows is located outside the contaminated site, and the distance between the tubular water guiding device and the edge of the contaminated site is 0.4~0.6m. The tubular water guiding device first discharges the groundwater independently. Since the tubular water guiding device is located outside the contaminated site, the water discharged at this time is clean water; after the residual groundwater enters the contaminated site, the sewage carrying the site pollutants is discharged by the remaining connected tubular water guiding devices.

[0010] Preferably, if the groundwater flows in a direction facing a corresponding groove, and the length of the longer tubular water guiding device in the adjacent groove of the groove is greater than the following influence range, a number of parallel grooves with equal spacing are dug in the contaminated site, and the spacing is equal to the value of the influence range. The grooves are all perpendicular to the groundwater flow direction, and tubular water guiding devices are set. The grooves in the contaminated site are connected with the grooves at the edge of the corresponding contaminated site, so that the corresponding tubular water guiding devices are connected; when the length of the site is greater than the influence range of the tubular water guiding device, the tubular water guiding device cannot block all the groundwater. At this time, the tubular water guiding device should be installed according to the length of the site and the influence range of the tubular water guiding device to ensure that most of the groundwater can be blocked from migrating to the contaminated soil.

[0011] If the groundwater flows in the direction of two corresponding trenches, and the distance from the intersection of the two trenches to the intersection of the diagonal is greater than the following impact range, then a number of parallel trenches with equal spacing are dug in the contaminated site, and the spacing is equal to the value of the impact range. The trenches are perpendicular to the groundwater flow direction, and tubular water guides are installed. The trenches in the contaminated site are connected to the trenches at the edge of the corresponding contaminated site, so that the corresponding tubular water guides are connected; when the length of the site diagonal is greater than the impact range of the tubular water guide, the tubular water guide cannot block all groundwater. At this time, tubular water guides should be installed according to the length of the site diagonal and the impact range of the tubular water guide to ensure that most of the groundwater can be blocked from migrating to the contaminated soil;

[0012] .

[0013] Preferably, before trench excavation, if pollutants have accumulated on the surface of the contaminated site, the pollutants accumulated on the surface of the contaminated site are cleaned first.

[0014] Preferably, an impermeable concrete enclosure is buried outside the contaminated site, and an impermeable membrane is laid on the surface of the impermeable concrete enclosure; the impermeable concrete enclosure and the impermeable membrane play an auxiliary role in preventing pollutants from migrating outward.

[0015] Preferably, residual pollutants on the inner and outer surfaces of the enclosure should be cleaned regularly to avoid accumulation of pollutants.

[0016] Preferably, the groundwater flows toward the corresponding tubular water-conducting device to independently discharge clean water, and the other interconnected tubular water-conducting devices are connected to the wastewater collection tank through an external delivery pipe, and sewage treatment agents are added to the wastewater in the wastewater collection tank. After treatment, the wastewater is discharged after meeting the standards; the sewage treatment agents can be flexibly selected according to the type of pollutants, such as flocculants.

[0017] Compared with the prior art, the present invention has the following technical effects:

[0018] 1. The present invention arranges tubular water guides around the shallow contaminated site. The clean water facing the contaminated site is drained separately and can be recycled for secondary use. The water carrying pollutants flowing through the contaminated site is discharged under the action of the remaining tubular water guides, thereby preventing the contaminated site from infiltrating and migrating pollutants outward due to the action of groundwater dynamics, thereby preventing the spread of pollution. The present invention is suitable for shallow contaminated sites such as temporary stacking and shallow pollution, and the contaminated soil layer is higher than the groundwater layer. It can effectively block more than 90% of groundwater migration pollutants. The present invention can be used as a temporary measure to block groundwater in shallow contaminated sites, and provide an effective risk control method for blocking pollution migration caused by groundwater hydrodynamics during the window period of soil risk control or remediation caused by contaminated site investigation and risk assessment;

[0019] 2. The tubular water guide device adopts a special pipe body structure. The bottom of the pipe body has no holes for water conduction, while the upper part of the pipe body has holes for water seepage. With the function of the first filter layer to prevent impurities and the second filter layer to disperse water, it is conducive to the entry of water into the pipe body, achieving water blocking and export, thereby effectively improving the drainage effect;

[0020] 3. The method of the present invention determines the water conduction influence range of the tubular water conduction device according to the groundwater flow direction, soil type of the contaminated site, and the buried depth of the tubular water conduction device, and then determines whether to increase the tubular water conduction device according to whether the water conduction influence range can be covered, so as to achieve full coverage of the contaminated site by the tubular water conduction device and effectively enhance the barrier effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the arrangement of tubular water guide devices when the groundwater flows in a groove facing the groove and the length of the longer tubular water guide device in the groove adjacent to the groove is greater than the following influence range;

[0022] Figure 2 The schematic diagram of the arrangement of the tubular water guide device is when the groundwater flows in two grooves facing each other and the distance from the intersection of the two grooves to the intersection of the diagonal grooves is greater than the following influence range;

[0023] Figure 3It is a structural schematic diagram of a tubular water guide device;

[0024] Figure 4 It is a structural schematic diagram of the distance between the tubular water guide device and the edge of the contaminated site;

[0025] Figure 5 This is a schematic plan view of the arrangement of the tubular water guide device in Example 10;

[0026] In the figure: 1- tubular water guide device, 101- pipe body, 102- first filter layer, 103- second filter layer, 104- water guide hole, 2- polluted site, 3- edge of polluted site. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the embodiments and drawings, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention.

[0028] Example 1

[0029] The method of this embodiment for blocking the migration of pollutants from the shallow contaminated site due to the dynamic effect of groundwater is that the contaminated soil layer of the contaminated site is higher than the groundwater layer, trenches are dug around the contaminated site, and the depth is dug to 1 meter below the contaminated soil layer and not reaching the groundwater layer, and the tubular water guide device 1 is placed in the trench, and then the trench is backfilled, and the groundwater flows to the corresponding tubular water guide device 1 facing it and is discharged independently, and the remaining tubular water guide devices 1 are connected to each other and discharged externally.

[0030] Example 2

[0031] As attached Figure 3 As shown, the method for blocking the migration of pollutants in shallow contaminated sites under the action of groundwater dynamics in this embodiment is based on Example 1, wherein the tubular water guide device 1 includes a pipe body 101, a first filter layer 102, and a second filter layer 103. The pipe body 101 is a DN80 PVC pipe. The pipe wall relative to the area from one-third of the diameter of the pipe body 101 to the edge of the pipe body 101 is a solid pipe wall, and the remaining pipe wall positions are uniformly distributed with water guide holes 104 with a pore size of 3mm. The first filter layer 102 is wrapped outside the pipe body 101, and the second filter layer 103 is wrapped outside the first filter layer 102; the first filter layer 102 is a filter screen, using 400g / cm 3 Nylon mesh, the second filter layer 103 is a 20 cm thick gravel layer, the gravel diameter is 2-5 cm; the inclination angle between the tubular water guide device 1 and the horizontal plane is 4°.

[0032] Example 3

[0033] As attached Figure 3 ~Attached Figure 4As shown, the method of blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics in this embodiment is based on Example 2, and the tubular water-guiding device 1 corresponding to the groundwater flow direction is located outside the contaminated site, and the distance between the tubular water-guiding device 1 and the edge of the contaminated site is 0.5m; in addition, the inclination angle between the tubular water-guiding device 1 and the horizontal plane is 5°.

[0034] Example 4

[0035] As attached Figure 1 , Attachment Figure 3 ~Attached Figure 4 As shown, the soil type of the contaminated site in this embodiment is sandy soil. The method of this embodiment for blocking the migration of pollutants in the shallow contaminated site under the action of groundwater dynamics is based on Example 3, wherein the tubular water guide device 1 is buried at a depth of 2m and the impact range is 10m; when the groundwater flows in a direction facing a corresponding groove, the length of the longer tubular water guide device 1 in the adjacent groove of the groove is 12m, which is greater than the impact range, and a groove is dug at a position running through the middle of the contaminated site with a spacing of 10m. The groove in the middle of the contaminated site is perpendicular to the groundwater flow direction, and the groove in the middle of the contaminated site is connected with the adjacent groove, so that the corresponding tubular water guide device is connected; in addition, the inclination angle between the tubular water guide device 1 and the horizontal plane is 6°, and the distance between the tubular water guide device 1 and the edge of the contaminated site is 0.4m.

[0036] Example 5

[0037] As attached Figure 2 , Attachment Figure 3 ~Attached Figure 4 As shown, the soil type of the contaminated site in this embodiment is clay. The method of this embodiment for blocking the migration of pollutants from the shallow contaminated site under the action of groundwater dynamics is based on Example 3, wherein the tubular water guide device 1 is buried at a depth of 3m and the impact range is 4m; the groundwater flow direction faces two corresponding grooves, and the distance from the intersection of the two grooves to the intersection of the diagonal grooves is 8m, which is greater than the impact range. A groove is dug through the middle of the contaminated site with a spacing of 4m. The groove in the middle of the contaminated site is perpendicular to the groundwater flow direction, and the groove in the middle of the contaminated site is connected with the adjacent groove, so that the corresponding tubular water guide device is connected; in addition, the tubular water guide device 1 is 0.6m away from the edge of the contaminated site.

[0038] Example 6

[0039] The soil type of the contaminated site in this embodiment is loam. The method of this embodiment to block the migration of pollutants from the shallow contaminated site under the action of groundwater dynamics is based on Example 3, wherein the tubular water guide device 1 is buried at a depth of 2m and the impact range is 7.5m; when the groundwater flows in a direction facing a corresponding groove, the longer tubular water guide device 1 in the adjacent groove of the groove is 12m long, which is greater than the impact range. A groove is dug at a position running through the middle of the contaminated site with a spacing of 7.5m. The groove in the middle of the contaminated site is perpendicular to the groundwater flow direction, and the groove in the middle of the contaminated site is connected to the adjacent groove.

[0040] Example 7

[0041] The method of blocking the migration of pollutants from shallow contaminated sites due to groundwater dynamics in this embodiment is based on Example 6, and also includes cleaning the pollutants accumulated on the surface of the contaminated site before digging the trench, if there are pollutants accumulated on the surface of the contaminated site.

[0042] Example 8

[0043] The method of this embodiment to block the migration of pollutants from shallow contaminated sites due to the dynamic action of groundwater is based on Example 7, burying an impermeable concrete enclosure outside the contaminated site and laying an impermeable membrane on the surface of the impermeable concrete enclosure; regularly cleaning the pollutants remaining on the inner and outer surfaces of the enclosure.

[0044] Example 9

[0045] The method of blocking the migration of pollutants from shallow contaminated sites due to the dynamic action of groundwater in this embodiment is based on Example 8. The groundwater flows to the corresponding tubular water-conducting device 1 in the opposite direction and discharges clean water independently. The other interconnected tubular water-conducting devices 1 are connected to the wastewater collection tank through an external delivery pipeline. Lime and PAC flocculant are added to the wastewater in the wastewater collection tank, and the wastewater is treated by stirring and sedimentation, and is discharged after meeting the standards.

[0046] Example 10

[0047] The solid waste dump of a company in Lancang was built in December 2012, and the project was put into trial production in February 2014. In 2017, due to the impact on the surrounding environment during the production process of the enterprise, it stopped production since 2017. From April 20 to December 16, 2021, more than 10,000 tons of hazardous waste in the solid waste dump were successively transferred to a company in Yunnan for disposal. According to the investigation, the soil layer of the dump is 1.5 meters deep and the groundwater is polluted. At present, no hazardous waste is piled up in the solid waste dump.

[0048] During the transportation and disposal of hazardous waste from the solid waste landfill, the anti-seepage measures, hardened ground, some enclosures and ceilings in the landfill were damaged, which may have a certain degree of impact on the soil and groundwater in the landfill. In April and June 2022, an ecological environment monitoring station conducted supervisory monitoring of the groundwater of the solid waste landfill, the upstream river of the factory area, and the downstream river of the factory area. The monitoring results showed that the lead, zinc, cadmium, iron and manganese in the groundwater exceeded the standard (GB / T 14848 Class III standard). At present, no hazardous waste is stacked in the solid waste landfill, and the conditions for landfill acceptance and cancellation have been met. However, the groundwater in the landfill area is abundant, and the salt in the original landfill has infiltrated into the soil and groundwater. Due to long-term sunshine, there is salt return on the soil surface of the landfill and yellow groundwater infiltration.

[0049] The soil texture of the solid waste dump is clay. There is shallow groundwater in the solid waste dump, and the groundwater flows from the north to the south of the solid waste dump. In order to prevent the further spread of pollution in the solid waste dump and successfully pass the acceptance, the method of the present invention is used for rectification. The specific process is as follows:

[0050] Dig trenches around the solid waste dump with a depth of 2.5m, place the tubular water guiding device 1 in the trench, and then backfill the trench. The groundwater flows to the corresponding tubular water guiding device 1 on the opposite side and is drained independently. The tubular water guiding device to which the groundwater flows is located outside the contaminated site, and the distance between the tubular water guiding device and the edge of the contaminated site is 0.5m. The water discharged from the tubular water guiding device 1 is collected separately. If the pollution does not meet the standard after detection, it can be used as clean water. The remaining tubular water guiding devices 1 are interconnected and connected to the wastewater collection tank (located in the southwest direction) through an external discharge pipe. Quicklime, polyferric sulfate and polyaluminium chloride (PAC) are added to the wastewater collection pool; because the groundwater flows in a corresponding groove, the length of the longer tubular water guide device 1 in the adjacent groove of the groove is 50m, which is greater than the affected range of 3.5m. A groove is dug in the middle of the contaminated site with a spacing of 3.5m. The groove in the middle of the contaminated site is perpendicular to the groundwater flow direction, and the groove in the middle of the contaminated site is connected with the adjacent groove, so that the corresponding tubular water guide device is connected; the schematic diagram of the layout of the tubular water guide device is attached Figure 5 As shown;

[0051] The tubular water guide device 1 includes a tube body 101, a first filter layer 102, and a second filter layer 103. The tube body 101 is a DN90 PVC tube. The tube wall from one-third of the diameter of the tube body 101 to the edge of the tube body 101 is a solid tube wall. The remaining tube wall positions are uniformly distributed with water guide holes 104 with a pore size of 3 mm. The first filter layer 102 is wrapped outside the tube body 101, and the second filter layer 103 is wrapped outside the first filter layer 102; the first filter layer 102 is a filter screen, using 400g / cm 3 Nylon mesh, the second filter layer 103 is a 25 cm thick gravel layer, the gravel diameter is 2~5 cm;

[0052] After the construction is completed, the tubular water guide device 1 drains water, during which the groundwater flows to the corresponding tubular water guide device 1 in front and discharges clean water, which is directly discharged after testing; the sewage discharged by the other tubular water guide devices 1 flows by gravity into the wastewater collection pool on the southwest side of the site for stirring treatment. After static sedimentation, sampling and testing are carried out to meet the maximum allowable emission concentration of the first category of pollutants in the "Comprehensive Sewage Discharge Standard" (GB978-1996) and the maximum allowable emission concentration of the second category of pollutants. After the first standard, it is discharged; 7 days later, it is detected that the lead, zinc, cadmium, iron and manganese in the groundwater outside the solid waste landfill are not exceeded, and there is no salt return on the soil surface of the landfill and no yellow groundwater infiltration, which effectively controls the outward migration of pollutants from the solid waste landfill; as a temporary risk control plan, the present invention operates until the end of the window period of pollution site investigation and risk assessment, and the next step of pollution control is carried out according to the investigation and assessment results.

Claims

1. A method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics, characterized by: The contaminated soil layer of the contaminated site is higher than the groundwater layer. A trench is dug around the contaminated site to a depth below the contaminated soil layer. A tubular water guide device (1) is placed in the trench. The trench is then backfilled. Groundwater flows to the corresponding tubular water guide device (1) facing the trench and is discharged independently. The remaining tubular water guide devices (1) are interconnected and discharged externally. The tubular water guide device (1) corresponding to the groundwater flow direction is located outside the contaminated site, and the distance between the tubular water guide device (1) and the edge of the contaminated site is 0.4-0.6 m; If the groundwater flows in a direction facing a corresponding groove, and the length of the longer tubular water guide device (1) in the groove adjacent to the groove is greater than the following influence range, then a plurality of grooves parallel to each other and with equal spacing are dug in the contaminated site, and the spacing is equal to the value of the influence range. The plurality of grooves parallel to each other and with equal spacing are perpendicular to the groundwater flow direction, and the tubular water guide device (1) is set. The groove in the contaminated site is connected to the groove at the edge of the corresponding contaminated site, so that the corresponding tubular water guide device (1) is connected; If the groundwater flows in the direction facing the two corresponding grooves, and the distance from the intersection of the two grooves to the intersection of the diagonal grooves is greater than the following impact range, a plurality of grooves parallel to each other and with equal spacing are dug in the contaminated site, and the spacing is equal to the value of the impact range. The plurality of grooves parallel to each other and with equal spacing are perpendicular to the groundwater flow direction, and a tubular water guide device (1) is provided. The grooves in the contaminated site are connected to the corresponding grooves at the edge of the contaminated site, so that the corresponding tubular water guide devices (1) are connected; Determine the scope of impact specifically: If the soil type of the contaminated site is sandy, the impact range of the tubular water guide device is 8m when it is 1m above the ground. The impact range increases by 2m for every 1m deeper the tubular water guide device is from the ground. If the soil type of the contaminated site is loam, the impact range of the tubular water guide device is 6m when it is 1m above the ground. The impact range increases by 1.5m for every 1m deeper the tubular water guide device is from the ground. If the soil type of the contaminated site is clay, the impact range of the tubular water guide device is 2m when it is 1m above the ground. The impact range increases by 1m for every 1m deeper the tubular water guide device is from the ground.

2. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 1, characterized in that: The tubular water-conducting device (1) comprises a tube body (101), a first filter layer (102), and a second filter layer (103); the tube wall from one-third of the diameter of the tube body (101) to the edge of the tube body (101) is a solid tube wall, and the remaining tube wall positions are uniformly provided with water-conducting through holes (104) with a hole diameter of 3 to 5 cm; the first filter layer (102) is wrapped around the outside of the tube body (101), and the second filter layer (103) is wrapped around the outside of the first filter layer (102); the first filter layer (102) is a filter screen, and the second filter layer (103) is a 20 to 30 cm thick gravel layer, and the gravel diameter is 2 to 5 cm.

3. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 2, characterized in that: The pipe body (101) is a PVC pipe or a PPR pipe with a diameter not less than DN80.

4. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 1, characterized in that: The inclination angle between the tubular water guiding device (1) and the horizontal plane is 4-6°.

5. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 1, characterized in that: Before digging trenches, if pollutants have accumulated on the surface of the contaminated site, the pollutants accumulated on the surface of the contaminated site should be cleaned up first.

6. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 1, characterized in that: Bury impermeable concrete enclosures outside the contaminated site and lay anti-seepage membranes on the surface of the impermeable concrete enclosures.

7. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 6, characterized in that: Regularly clean the remaining pollutants on the inner and outer surfaces of the enclosure.

8. The method for blocking the migration of pollutants from shallow contaminated sites under the action of groundwater dynamics according to claim 1, 2 or 4, characterized in that: The groundwater flows to the corresponding tubular water guide device (1) to independently discharge clean water, and the other interconnected tubular water guide devices (1) are connected to the wastewater collection pool through an external delivery pipeline, and wastewater treatment agents are added to the wastewater in the wastewater collection pool. After treatment, the wastewater is discharged after meeting the standards.

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