JP5682250B2 - Contamination purification method to suppress secondary pollution on site - Google Patents

Description

  The present invention relates to a pollution purification method for suppressing secondary contamination in a site by contaminated soil to be purified.

  On-site processing is known in which contaminated soil and contaminated water contaminated with pollutants are purified on the site to be purified. This on-site treatment is recommended as an environmentally friendly treatment such that the soil after purification can be used for backfilling.

  In this on-site treatment, it is necessary to install a soil cleaning facility that cleans and purifies contaminated soil, and a temporary soil storage facility that temporarily stores contaminated soil and purified soil. (Contamination of non-contaminated areas by pollutants contained in contaminated soil) is a concern. And, in the “Guidelines on Investigation and Measures Based on the Soil Contamination Countermeasures Law” issued in July 2010, if the purification equipment is installed on the site, the purification equipment will be installed after the purification treatment is completed. It was indicated that it was necessary to confirm that there was no secondary contamination at the site.

  However, the surface soil under the equipment can be collected only after the purification equipment is removed, and it takes several weeks to analyze the collected soil. For this reason, even if the work is completed, an additional period of about one month is required until a complete action report can be submitted. In addition, soil surveys after the removal of equipment may be affected by natural causes of contamination and dispersion. In this case, although it is after equipment removal, the contamination purification process will be needed again.

  Here, Patent Document 1 discloses a soil purification facility in which a water shielding sheet is laid at the bottom of a bioyard and a temporary storage site for contaminated soil. By providing the water-impervious sheet of Patent Document 1 at the installation location of the purification equipment, it is considered that secondary contamination at the installation location of the purification equipment can be suppressed and the above-described problems can be solved.

JP 20048941 A

  However, the water shielding sheet of Patent Document 1 is provided for the purpose of collecting contaminated water. This can be understood from the fact that a water-permeable crushed stone layer is provided on the water-impervious sheet and is continuously laid in the groove at the location of the water collecting groove. For this reason, merely providing this water shielding sheet can suppress the secondary contamination after the water shielding sheet is provided, but there is no guarantee about the exclusion of the influence of local variations. Therefore, after removing the equipment, the soil must be collected and analyzed, and the problem of requiring an additional period and the problem of recontamination processing cannot be solved.

  This invention is made | formed in view of such a situation, The objective is to propose the pollution purification construction method which can ensure easily that it is non-polluting about the protection area in a site.

In order to solve the above-described problems, the present invention provides an excavation and removal process for excavating and removing contaminated soil contaminated with a pollutant from a site to be subjected to pollution purification, and a backfilling process for backfilling the excavated portion of the site with healthy soil. In accordance with the contamination purification method for purifying the site, the site is divided into a plurality of areas, a contamination determination step for determining the degree of contamination for each area, and the degree of contamination for each area A protective area selecting step for selecting a non-polluted protected area that is protected from secondary contamination by the contaminated soil excavated from the area to be purified, and a protective layer for preventing the penetration of the pollutants, coercive after the protective layer forming step of forming on the surface of the protected area is performed prior to the excavation and removal process, the excavation removed contaminated soil in the excavation and removal step the protective layer is formed The contaminated soil temporary location step of temporarily placing the contaminated soil temporary shelter provided in the area, and performs before the backfill process.

  According to the present invention, prior to the excavation and removal process, the contamination determination process, the protection area selection process, and the protection layer formation process are performed, and the surface of the non-contamination protection area selected according to the degree of contamination A protective layer that prevents penetration is formed. Since the secondary contamination of the protected area by the contaminated soil excavated in the excavation and removal process is suppressed by this protective layer, it can be easily guaranteed that the protected area in the site is non-contaminated.

  In the present invention, the protective layer includes a double-layer water-proof sheet that is divided into a number of airtight compartments, and applies a negative pressure to the compartment and monitors the degree of vacuum due to the negative pressure. When the degree of vacuum reduction exceeds a set value, the damage monitoring process for determining that the waterproof sheet has been damaged is completed after the backfill process is completed after the waterproof sheet is laid. It is preferable to carry out over the period until. In this way, the presence or absence of damage to the protective layer can be easily monitored over a long period of time.

  In the present invention, in the protective layer forming step, after removing the surface soil of the protective area selected in the protective area selecting step, spread the healthy soil in the range where the surface soil is removed, and on the surface side of the healthy soil It is preferable to lay the water shielding sheet. If it does in this way, the fault which receives the influence by the contamination by a natural cause and the dispersion | variation by the soil investigation after equipment removal can be suppressed.

  In the present invention, in the protection area selecting step, it is preferable that an area determined as non-contaminated among the plurality of areas is selected as the protection area. If it does in this way, the construction period of purification work can be shortened.

  In the present invention, in the protection area selecting step, an area that is less contaminated among the plurality of areas than the other areas, and is uncontaminated by being backfilled with healthy soil after excavation and removal of the contaminated soil. The protective area is preferably selected. If it does in this way, even if the whole site is contaminated, it can be guaranteed that there is no secondary contamination in the protection area in the site.

  In the present invention, the equipment installation process for installing the purification equipment used for the purification of the contaminated soil on the protection area is performed after the protection layer forming process and before the excavation removal process. It is preferable. The purification facility is at least one of a soil cleaning facility for cleaning and purifying the contaminated soil and a soil temporary storage facility for temporarily placing the contaminated soil or the healthy soil used in the backfilling step. preferable. If it does in this way, since the purification equipment is installed on the non-contaminated protection area, the protection area can be protected from the secondary pollution caused by the purification equipment.

  According to the present invention, it is possible to ensure that the protected area in the site is non-polluted.

It is a figure explaining the field used as the object of pollution purification. It is a flowchart explaining the procedure of a pollution purification method. It is a figure explaining the state which divided the site for pollution purification into a plurality of areas. It is a figure explaining the contamination degree for every area. It is a figure explaining the non-contamination area of the magnitude | size which can install the installation for purification | cleaning. It is a figure explaining the protection area selected as the non-contamination area. It is a figure explaining laying of a water-impervious sheet and asphalt. It is a figure explaining the breakage monitoring system of a impermeable sheet. It is a figure explaining the state which installed the equipment for a purification | cleaning and a channel | path. It is a figure explaining the spot of the state which is performing the soil purification process. It is a figure explaining the state which removed the purification equipment. It is a figure explaining the state which removed the water shielding sheet of the protection area.

  Embodiments of the present invention will be described below with reference to the drawings. In the site shown in FIG. 1, the site 1 to be subjected to pollution purification is divided into a plurality of areas. For the sake of convenience, in the following description, virtual lines extending in the vertical direction and having different horizontal positions are represented by symbols Y1 to Y14, and virtual lines having different vertical positions and extending in the horizontal direction are represented by X1 to X9. And Therefore, the site 1 is divided into a plurality of areas with the virtual lines Y1 to Y14 and the virtual lines X1 to X9 as boundaries.

  In the illustrated site, soil contamination is confirmed in the areas A to D of the site 1. The area B is composed of seven areas B1 to B7, and the area D is composed of two areas D1 and D2. Moreover, the purification plant 2 is installed in the upper left and right center in FIG. In addition, a clarified soil temporary storage 3 for stocking the purified soil is installed almost at the center of the site 1, and a backfill temporary storage yard 4 is installed adjacent to the purified soil temporary storage 3. Furthermore, an asphalt-carrying roadway 5 is formed so as to surround the outer periphery of the clarified soil temporary storage site 3 and the backfill soil temporary storage site 4 and to connect the contaminated areas A to D and the purification plant 2.

  In the pollution purification method of the present embodiment, the site 1 is purified by excavating and removing the contaminated soil contaminated with the pollutant from the contaminated areas A to D of the site 1 and refilling the excavated portion with healthy soil.

  The outline will be described. First, the contaminated soil is excavated and removed from the contaminated areas A to D, and the contaminated soil is transported along the roadway 5 to the purification plant 2. Then, the contaminated soil is washed and purified by the purification plant 2. As this purification plant 2, for example, the soil purification system “R Cubic MINI” (registered trademark) of Obayashi Corporation is preferably used. In this soil remediation system, the contaminated soil is classified into a sand portion from which the contaminant has been washed away and a fine particle portion to which the contaminant has adhered. And the sand is reused for backfilling as purified soil, and the fine grain is discharged as a dehydrated cake by a filter press. Further, the water used in the cleaning is reused after the contaminants are removed.

  The purified soil purified by the purification plant 2 is temporarily placed in the purified soil temporary storage site 3 for a period until the inspection confirmation is completed, and the purified soil (that is, healthy soil) for which the inspection confirmation is completed is used as backfill soil. Temporarily placed in the reclaimed soil temporary storage 4. Then, the backfilling soil is backfilled in the contaminated areas A to D from which the contaminated soil has been excavated and removed, thereby completing the purification of the contaminated areas A to D.

  And the contamination purification method of this embodiment is the purification equipment before installing the purification equipment such as the purification plant 2, the purification soil temporary storage site 3, and the backfilling temporary storage site 4 (that is, before excavation and removal of the contaminated soil). This is characterized in that the area in which is installed is selected as a protection area, and a protective layer for preventing the penetration of contaminants is formed on the surface of the protection area. The protected area means an uncontaminated area that is protected from secondary contamination by contaminated soil excavated from the contaminated area to be purified. Hereinafter, the details of the contamination purification method will be described focusing on this point.

  As shown in the flowchart of FIG. 2, in this pollution purification method, the site 1 to be purified is first partitioned into a plurality of areas (S1). For example, as shown in FIG. 2, site 1 is partitioned into a plurality of areas by virtual lines Y1 to Y14 and virtual lines X1 to X9. In addition, the space | interval of adjacent virtual lines Y1-Y14 and the space | interval of virtual lines X1-X9 are defined equally, for example, is 10 m. Each area is a unit for excavation and backfilling. That is, determination of the degree of contamination, excavation of contaminated soil, and backfilling with backfill soil are performed for each area.

  If the area is divided into a plurality of areas, the degree of contamination is determined for each area (S2). That is, chemical analysis is performed for each area, and the type and concentration of contaminants are measured. At this time, the kind and concentration of the pollutant are measured several times while changing the depth of the soil. FIG. 4 schematically shows the determination result of the degree of contamination. As described above, the areas A to D are all contaminated areas contaminated with the pollutants. Of these areas A to D, area A and area B5 are areas having a higher degree of contamination than other contaminated areas.

  If the degree of contamination is determined for each area, it is determined whether or not there is a non-contaminated area large enough to install the purification equipment (S3). In the example shown in FIG. 5, the equipment for purification (the purification plant 2, the purification soil temporary storage site 3, and the backfilling temporary storage site 4) is installed in the range surrounded by the virtual lines X1 and X7 and the virtual lines Y5 and Y13. There is a non-contaminated area E of a possible size. For this reason, it is determined that there is a non-contaminated area that is large enough to install the purification equipment.

  If it is determined in step S3 that there is a non-contaminated area E, a protection area is selected in the non-contaminated area E (S4). In this embodiment, as shown in FIG. 6, the 1st protection area E1 in which the purification plant 2 is installed, the 2nd protection area E2 in which the purification soil temporary storage place 3 is installed, and the backfill soil temporary storage place 4 are installed. The third protected area E3 is selected.

  Next, as shown in FIG. 7, the water shielding sheet 11 is laid in the selected protection areas E1 to E3 (S5). This water shielding sheet 11 constitutes a protective layer for the protective areas E1 to E3 together with the asphalt 12 covering the surface, and protects the protective areas E1 to E3 from secondary contamination by contaminated soil excavated in the contaminated areas A to D. Protect. As shown in FIG. 7A, when laying the water shielding sheet 11, first, the surface soil of the selected protection areas E1 to E3 is removed. Next, as shown in FIG. 7B, healthy soil is spread over the area from which the surface soil has been removed, and as shown in FIG. 7C, the water shielding sheet 11 is laid on the surface side of the healthy soil. Furthermore, as shown in FIG.7 (d), the asphalt 12 is laid in the state which covers the water-impervious sheet 11 (S6).

  Here, it is preferable to use a sheet that can detect the presence or absence of damage to the water-impervious sheet 11. This is because by showing the detection result that there is no damage to the water-impervious sheet 11, it can be indirectly proved that there is no secondary contamination of the protected area by the pollutant. As a damage monitoring system having such a water shielding sheet 11, for example, “T & OH System” (registered trademark) of Obayashi Corporation is preferably used.

  As shown in FIGS. 7C and 7D, the water shielding sheet 11 used in this breakage monitoring system is such that the middle layer mat 13a (protective material) is an upper surface by a double sheet composed of an upper layer sheet 13b and a lower layer sheet 13c. It is produced by joining a plurality of bag structures 13 sandwiched between the side and the lower surface side. That is, the water shielding sheet 11 has a double structure in which the interior is divided into a number of compartments (bag structures 13) that are airtight. The middle layer mat 13a is made of a material having air permeability and water permeability such as a nonwoven fabric, and the upper layer sheet 13b and the lower layer sheet 13c are made of a flexible sheet material having water shielding properties such as a soft synthetic resin or a rubber sheet. ing. A management hose 14 is embedded in the middle layer mat 13a. This management hose 14 is provided for each bag structure 13. When the presence or absence of damage to the water-impervious sheet 11 is detected, the control hose 14 is in a reduced pressure state, and when the damaged bag structure 13 is stopped, the control hose 14 is stopped. Water material is delivered.

  The management hose 14 is pulled out of the water shielding sheet 11 and connected to the monitoring facility. As shown in FIG. 8, the monitoring facility includes an individual negative pressure sensor 15 and an electric valve 16 provided in the middle of each management hose 14, and an upstream side (bag structure body) of the individual negative pressure sensor 15 in each management hose 14. 13), a connection portion 17 with a valve to which a supply hose (not shown) for supplying a water stop material is connected, a suction pipe 18 to which an end of each management hose 14 is connected, and a suction A vacuum gauge 19 for measuring and displaying the internal pressure of the pipe 18, a common negative pressure sensor 20 provided in the middle of the suction pipe 18, a vacuum pump 21 provided at the end of the suction pipe 18, and the suction pipe 18 The drain tank 22 provided upstream of the vacuum pump 21 is electrically connected to the negative pressure sensors 15, 20, the electric valves 16, and the vacuum pump 21, and the negative pressure sensors 15, 20. Depending on the detection result by And a control unit 23 for controlling the vacuum pump 21 and solenoid valve Te.

  If the asphalt 12 is laid, the damage monitoring process by the damage monitoring system is started (S7). In this case, the control unit 23 opens each electric valve 16 and starts the operation of the vacuum pump 21. Thereafter, based on the detection signals of the negative pressure sensors 15 and 20, the control unit 23 reaches a predetermined degree of vacuum (a degree of vacuum sufficient for determining that there is no leakage) inside each management hose 14 and the suction pipe 18. Under the condition, the operation of the vacuum pump 21 is stopped, and the detection signals of the negative pressure sensors 15 and 20 are monitored. As described above, since the end portion of each management hose 14 is embedded in the middle layer 13a of the bag structure 13, the inside of the suction pipe 18 can be made to have a predetermined degree of vacuum inside the bag structure 13 ( It corresponds to applying a negative pressure in the compartment), and monitoring the detection signals of the respective negative pressure sensors 15 and 20 corresponds to monitoring the degree of vacuum of the bag structure 13. And if the vacuum state is maintained, it will be judged that there is no damage of the water-impervious sheet 11.

  On the other hand, when the vacuum state can no longer be maintained (when the degree of decrease in the degree of vacuum exceeds the set value), the control unit 23 determines that the water shielding sheet 11 is damaged and detects each of the individual negative pressure sensors 15. Based on the result, it is determined from which management hose 14 air or the like has flowed. Then, the control part 23 interrupts | blocks the electric valve 16 corresponding to the management hose 14 into which air etc. flowed in, and alert | reports the management hose 14. FIG. Along with this notification, the worker connects the supply hose to the connection portion 17 with valve provided in the management hose 14 to be notified, and pumps the water stop material toward the bag structure 13. Thereby, the water-stopping material is filled in the damaged bag structure 13 and the damage of the bag structure 13 is repaired.

  In addition, a supply hose may be connected to all the connection parts 17 with a valve beforehand, and you may make it perform the filling of a water stop material by the control part 23 automatically. In addition, as the water-stopping material, for example, a cement-based solidified material such as cement or mortar, or a resin-based solidified material such as urethane resin, superabsorbent resin, epoxy resin, or polyester resin can be used.

  Next, a purification facility is installed on the protection areas E1 to E3 (S8). In the present embodiment, as shown in FIG. 9, the purification plant 2 is installed in the first protection area E1, the purification soil temporary storage site 3 is installed in the second protection area E2, and the backfill temporary soil is installed in the third protection area E3. Yard 4 is installed. In addition, asphalt is laid in a place where the vehicle passes, and a roadway 5 is provided, and an iron plate 6 is laid on a vehicle turning point in the roadway 5 to prevent the roadway 5 from being damaged.

  If the purification facilities 2 to 4 are installed, the contaminated soil is purified (S9). As shown in FIG. 10, in this purification process, the contaminated soil in the contaminated areas A to D is excavated and removed, and temporarily placed in the contaminated soil temporary storage place 7 provided in the first protection area E1. Then, the contaminated soil temporarily placed in the contaminated soil temporary storage site 7 is purified by the purification plant 2. The purified soil purified by the purification plant 2 is stocked in the purified soil temporary storage place 3 over a period until the confirmation inspection is completed. The purified soil whose purification has been confirmed is stocked in the backfill temporary storage site 4 as backfill soil (healthy soil) and then used for backfilling the contaminated areas A to D after excavation.

  In the example of FIG. 10, the contaminated areas A and B are in a state where the contaminated soil has been excavated and removed, and the contaminated soil excavated last is temporarily placed in the contaminated soil temporary storage place 7. The purified soil excavated from the contaminated areas A and B is temporarily placed in the purified soil temporary storage place 3, and the backfilled soil is temporarily placed in the backfill soil temporary storage place 4. Further, the contaminated areas C and D are backfilled with backfill soil.

  If purification is completed for all the contaminated areas A to D, the purification facilities 2 to 4 are disassembled and removed (S10). Thereby, as shown in FIG. 11, the protection areas E1-E3 become further ground.

  If the purification facilities 2 to 4 have been removed, a non-contamination confirmation process is performed on the protection areas E1 to E3 (S11). This confirmation process is performed, for example, by submitting a monitoring result by a damage monitoring system. That is, if the water-impervious sheet 11 is not damaged over the purification work period, it can be estimated that the protection areas E1 to E3 are non-polluted. For this reason, the analysis work for confirming that the protection areas E1 to E3 are not secondarily contaminated can be omitted. Even if an analysis operation is performed, the surface soil in the protection areas E1 to E3 is replaced with healthy soil, and thus no contamination is detected.

  Even when the water shielding sheet 11 is damaged, the asphalt 12 can prevent the infiltration of contaminants. Moreover, since a quick response | compatibility is possible by the water stop process with respect to the water shielding sheet 11, in many cases, secondary pollution can be stopped with the layer of the healthy soil laid under the water shielding sheet 11. FIG. In this case, since the secondary contamination can be purified by replacing the healthy soil, the purification work can be performed in a short period of time. Further, since the breakage point of the water shielding sheet 11 can be specified by the breakage monitoring system, it is possible to narrow down the location of the secondary contamination, and the purification work for the secondary contamination in the protection areas E1 to E3 can be performed in a short period of time. it can.

  Next, a process when it is determined in step S3 described above that there is no non-contaminated area having a required size will be described with reference to the flowchart of FIG.

  In this case, first, an area where purification equipment can be installed and the degree of contamination is relatively small is selected from a plurality of areas (S21). For example, the area indicated by symbol E in FIG. If an area is selected, the contaminated soil is excavated and removed from the selected area, and then backfilled with healthy soil for purification. And the area shown with the code | symbol E1-E3 in FIG. 6 is selected as a protection area (S22). If the protection areas E1 to E3 are selected, the water shielding sheet 11 is laid in the protection areas E1 to E3 (S23). In this case, since it is backfilled with healthy soil, it is only necessary to lay the water shielding sheet 11 on the surface of the healthy soil. Since the subsequent processing is the same as the processing described above, description thereof is omitted.

  By performing the above processing, even if the entire site 1 is contaminated and there is no non-contaminated area for installing the purification facilities 2 to 4, secondary protection is performed on the protection areas E1 to E3 in the site. Can guarantee that there is no.

  In addition, the purification process of the contaminated soil of step S9 mentioned above is the excavation removal process which excavates and removes the contaminated soil contaminated with the pollutant from the site 1 which is the target of the pollution purification, and the excavation site of the site 1 is a healthy soil. This corresponds to a backfilling process. Moreover, the partition process of step S1 and the determination process of the contamination degree of step S2 correspond to the contamination determination process of dividing the site 1 into a plurality of areas and determining the contamination degree for each area. Moreover, the size determination process of the non-contaminated area in step S3 and the protection area selection process in step S4 correspond to a protection area selection process in which a protection area is selected according to the degree of contamination for each area. Similarly, the area selection process in step S21 and the purification and area selection process in step S22 correspond to the protection area selection process. In addition, the water shielding sheet 11 laying process in step S5 and step S23 and the asphalt laying process in step S6 correspond to a protective layer forming process in which a protective layer that prevents penetration of contaminants is formed on the surface of the protective area. Moreover, the installation process of step S8 is corresponded to the installation process of installing the purification equipment used for purification of contaminated soil on a protection area.

  As described above, according to the pollution purification method of the present embodiment, prior to excavation of the contaminated area, the degree of contamination of the site 1 is determined for each area, and it is non-contaminated and can be installed with a purification facility. This area is selected as the protective areas E1 to E3, and protective layers (water-proof sheet 11 and asphalt 12) for preventing the penetration of contaminants are formed on the surface. By this protective layer, secondary contamination of the protected areas E1 to E3 due to excavated contaminated soil is suppressed, and it can be ensured that the protected areas E1 to E3 are non-polluted after the purification work is completed.

  Further, in this pollution purification method, in the damage monitoring process of step S7, a negative pressure is applied to the inside (inside the compartment) of the bag structure 13 and the degree of vacuum due to this negative pressure is monitored, and the degree of vacuum reduction is a set value Since it is determined that the water-impervious sheet 11 is damaged when it exceeds the upper limit, it is possible to easily monitor whether or not the water-impervious sheet 11 (protective layer) is damaged over a long period of time.

  Further, in this pollution purification method, after removing the surface soil from the non-contaminated protected area, the soil is spread over the area where the surface soil is removed, and the water shielding sheet 11 is laid on the surface side of the healthy soil. Yes. If it does in this way, since the surface soil is replaced by the healthy soil, it is possible to suppress problems caused by natural causes of contamination and variations due to soil surveys after the equipment removal.

  By the way, the description regarding the above embodiment is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and purpose of the present invention, and the present invention naturally includes equivalents thereof. For example, you may comprise as follows.

  Although the protection area in the above-described embodiment is the installation position of the purification equipment, it is not limited to this. Any area that should be protected from secondary contamination by excavated contaminated soil can be a protected area. For example, an area where the roadway 5 is laid may be selected as a protection area.

  Moreover, although the above-mentioned embodiment illustrated the on-site process which purifies contaminated soil on-site, it is not limited to this. For example, the present invention can be applied even when contaminated soil is processed at a processing plant away from the site. In this case, the area where the contaminated soil temporary storage place 7 for temporarily storing the contaminated soil to be loaded on the vehicle is selected as the protection area.

  In addition, regarding the protective layer, the two-layer structure of the water-impervious sheet 11 and the asphalt 12 is used in the above-described embodiment, but is not limited to this configuration. For example, you may comprise only asphalt 12. In short, any layer that prevents the penetration of contaminants may be used.

DESCRIPTION OF SYMBOLS 1 Site 2 Purification plant 3 Temporary soil temporary storage 4 Backfill temporary storage 5 Road 6 Iron plate 7 Contaminated soil temporary storage 11 Water shielding sheet 12 Asphalt 13 Bag structure 13a Middle layer mat 13b Upper layer sheet 13c Lower layer sheet 14 Management hose 15 Individual Negative pressure sensor 16 Electric valve 17 Connecting part 18 with valve 18 Suction pipe 19 Vacuum gauge 20 Common negative pressure sensor 21 Vacuum pump 22 Drain tank 23 Control part X1-X9 Virtual line Y1-Y14 Virtual line A-D Contaminated area E Non-contaminated area E1-E3 Protected area

Claims (7)

The site is purified by performing an excavation and removal step of excavating and removing the contaminated soil contaminated with the pollutant from the site to be purified and a backfilling step of backfilling the excavated portion of the site with healthy soil. Contamination purification method,
A contamination determination step of dividing the site into a plurality of areas and determining the degree of contamination for each area,
According to the degree of contamination for each area, a protection area selection step of selecting a non-contamination protection area that is protected from secondary contamination by the contaminated soil excavated from the area to be purified;
Prior to the excavation and removal step, the protective layer forming step of forming a protective layer for preventing the penetration of the contaminants on the surface of the protective area ,
The contaminated soil temporary placement step of temporarily placing the contaminated soil excavated and removed in the excavation removal step in the contaminated soil temporary storage site provided in the protection area after the formation of the protective layer is performed before the backfilling step. Contamination purification method characterized by performing. The protective layer includes a double-layer water-proof sheet divided into a number of compartments whose inside is airtight,
A damage monitoring process in which a negative pressure is applied to the compartment and the degree of vacuum due to the negative pressure is monitored, and when the degree of decrease in the degree of vacuum exceeds a set value, it is determined that the waterproof sheet has been damaged. The contamination purification method according to claim 1, wherein the contamination purification method is performed over a period from when the water shielding sheet is laid to when the backfilling process is completed.   In the protective layer forming step, after removing the surface soil of the protective area selected in the protective area selecting step, spread the healthy soil in the range where the surface soil is removed, and the water shielding sheet on the surface side of the healthy soil The contamination purification method according to claim 2, wherein:   The contamination purification method according to any one of claims 1 to 3, wherein, in the protection area selection step, an area determined as non-contamination among the plurality of areas is selected as the protection area.   In the protection area selecting step, an area that is less contaminated among the plurality of areas and is uncontaminated by being backfilled with healthy soil after excavation and removal of the contaminated soil is selected as the protection area. The contamination purification method according to claim 1 or 2, wherein the contamination purification method is selected.   A facility installation step for installing the purification equipment used for purification of the contaminated soil on the protection area is performed after the protective layer formation step and before the excavation removal step, The contamination purification method according to any one of claims 1 to 5.   The purification facility is at least one of a soil cleaning facility that cleans and purifies the contaminated soil, and a soil temporary facility that temporarily stores the contaminated soil or healthy soil used in the backfilling process. The contamination purification method according to claim 6.

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