A risk control system for in-situ integrated remediation of built environment under soil vapor intrusion

Abstract

The application relates to the technical field of contaminated site remediation, and discloses an in-situ integrated remediation risk management and control system for preventing soil vapor intrusion in a built environment and a use method thereof. The system comprises a longitudinal four-layer structure and a double-screen pipe injection and extraction well. The four-layer structure comprises, from top to bottom, a surface barrier layer, a gravel layer, a biological reaction layer and a water-bearing layer remediation and slow-release reagent dosing layer. The double-screen pipe injection and extraction well is provided with two sections of screen pipes, the first section of which is located in the gravel layer for aeration, and the second section of which is located in the water-bearing layer for injection and extraction. Through the cooperation of the longitudinal four-layer structure and the double-screen pipe injection and extraction well, the integrated management and control of the aeration zone and the saturated zone is realized, the surface barrier layer blocks the vertical migration, the biological reaction layer strengthens the degradation, and the water-bearing layer reduces the source, so that the vapor intrusion prevention and control effect is significantly improved. The use method of the application realizes the whole-chain accurate management and control of the contaminated site risk through four stages of system layout, active remediation, slow-release control and operation and maintenance monitoring.

Description

Technical Field

[0001] This application relates to the field of contaminated site remediation and risk management technology, and more specifically, it relates to an in-situ integrated remediation risk management system for preventing soil vapor intrusion in the built environment. Background Technology

[0002] In my country's urban renewal and land development processes, contaminated sites such as oil refineries, pesticide plants, and chemical plants have been redeveloped and reused. However, in recent years, the diffusion of volatile and semi-volatile organic compounds (VOCs) from the original sites or surrounding contaminated soil and groundwater via soil vapor has repeatedly triggered public concerns about vapor intrusion into sensitive land uses such as residential areas and schools. In built environments, due to the obstruction of building foundations, load-bearing limitations, and spatial constraints, the remediation of site pollution sources is extremely difficult. Volatile pollutants can infiltrate buildings through building foundations and joints, seriously threatening human health.

[0003] Existing technologies have many shortcomings. For example, the remediation system disclosed in patent CN114393019A is not specifically applied to existing underground pollution conditions in buildings. Regarding barrier control, the fluidized solidified soil in patent CN116332611B is only used for engineering backfilling and does not address targeted sealing of vapor intrusion; the barrier layer in patent CN114800237A uses a single membrane material and does not design targeted sealing solutions for joints. In terms of remediation systems, the combined vadose zone-saturation zone remediation system in patent CN115674298A lacks an integrated structural design and has poor synergy. Regarding filler applications, the zeolite filler in patent CN117534199B does not achieve solid waste resource utilization; the biological fillers in patents CN116873659A and CN113617818B are costly and lack rigid load-bearing capacity. In terms of well design, existing injection and extraction wells have single functions and do not achieve multi-functional integration.

[0004] In summary, existing technologies generally suffer from problems such as asynchronous control of the vadose zone and saturation zone, single function of injection and extraction wells, poor compatibility between the load-bearing and ventilation of the bioreactor layer, low utilization rate of solid waste resources, and insufficient control of weak links in steam intrusion. These technologies cannot meet the risk management requirements of "in-situ, integrated, and full-chain" for contaminated sites under the building foundation. Summary of the Invention

[0005] To achieve efficient, coordinated, and low-cost remediation and risk management of contaminated sites beneath building foundations, this application provides an in-situ integrated remediation risk management system for preventing soil vapor intrusion in built environments and its application method.

[0006] Firstly, this application provides an integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment, employing the following technical solution: An in-situ integrated remediation risk management system for preventing soil vapor intrusion in the built environment includes a vertical four-layer structure and dual-screen injection wells installed on the exterior of the building. The vertical four-layer structure, from top to bottom, consists of: The surface barrier layer is laid under the building's foundation to block the vertical migration of soil vapor. The gravel layer is set below the surface barrier layer and is used for gas extraction to supply oxygen to the lower layer. The bioreactor layer is located below the gravel layer and is laid out using a grid method. The grid cells are filled with composite fillers for degrading volatile pollutants. The aquifer remediation and slow-release agent dosing layer is located within the groundwater aquifer and is used for active remediation and slow-release control of pollutants. The well body of the dual-screen injection well is equipped with two screen sections: the first screen section is located in the gravel layer and is used to introduce air into the bioreactor layer or extract residual gas; the second screen section is located in the groundwater aquifer and is used to extract contaminated groundwater, inject leaching agents, or inject slow-release agents.

[0007] By adopting the above technical solutions, the surface barrier layer achieves dual protection through area coverage and joint sealing. The composite structure of two layers of fabric and one membrane with concrete in the main area has high tensile strength and low permeability, effectively resisting shear damage caused by uneven foundation settlement and ensuring the integrity of the large-area barrier. For the joints of the building slab and wall corners, fluidized solidified soil is used for targeted sealing. Utilizing its high fluidity and micro-expansion after solidification, it can adaptively fill complex-shaped gaps and completely block the channels for vapor migration. The combination of these two methods solves the problem of traditional single materials being prone to failure at joints and significantly reduces the risk of vapor intrusion.

[0008] Preferably, the main area of ​​the surface barrier layer is laid with a composite of two layers of cloth and one membrane and concrete, and the joints of the building base plate and the corner joints are targeted and sealed with fluidized solidified soil.

[0009] By adopting the above technical solution, the selection of the particle size and thickness of the gravel layer, as well as the design of the aperture of the first section of the screen tube, together a highly efficient and low-resistance gas distribution layer is constructed. The 20-50mm gravel forms a stable support framework and continuous void channels, and the 30-40cm thickness ensures uniform diffusion of gas in the horizontal direction, avoiding local short circuits. The aperture of the first section of the screen tube is 2-5mm, which not only ensures smooth airflow, but also effectively prevents fine gravel particles from entering the well casing and causing blockage. This not only provides a uniform and sufficient oxygen supply for the upper bioreactor layer, but also creates excellent gas guiding conditions for the extraction of residual gas in the lower layer.

[0010] Preferably, the crushed stone layer is laid with crushed stone with a particle size of 20-50mm and a thickness of 30-40cm; the first section of screen tube is laid in the crushed stone layer and its pore size is 2-5mm.

[0011] By adopting the above technical solution, firstly, a grid method of 1m×1m×1m or 2m×2m×1m is used for the layout, and the crushed stone layer is used for segmentation, which effectively prevents the porosity of the filler from decreasing due to gravity compaction and ensures long-term ventilation. Secondly, coal gangue and straw are mixed in a volume ratio of 3:1 in the composite filler. The coal gangue is used to build a rigid skeleton to provide load-bearing capacity, and the straw is used as a slow-release carbon source to provide long-term nutrition for microorganisms. The fly ash content of 10-15% can adjust the pH value of the filler and fill some micropores, so that the porosity is controlled at 30-40%. This range not only meets the air and moisture exchange space required for microbial growth, but also ensures sufficient compressive strength to meet the load-bearing requirements under the building foundation.

[0012] Preferably, the grid unit size of the bioreactor layer is 1m×1m×1m or 2m×2m×1m, and the grids are separated by a layer of crushed stone; the composite filler is a mixture of coal gangue, fly ash and straw, wherein the volume ratio of coal gangue to straw is 3:1, the fly ash content is 10-15% of the total volume of the composite filler, and the porosity of the composite filler is controlled at 30-40%.

[0013] By adopting the above technical solution, the three-stage particle size distribution of coal gangue significantly optimizes the packing structure of the bioreactor layer. Coarse particles serve as the main skeleton, bearing the load and forming macroscopic gas-conducting channels; medium particles fill the gaps between coarse particles, increasing the packing density and improving overall stability; fine particles further fill the tiny voids and provide a larger specific surface area for microbial attachment. The gradation design enables the composite packing to achieve higher packing density and compressive strength while maintaining a suitable porosity of 30-40%, effectively avoiding packing settling and clogging problems during use.

[0014] Preferably, the coal gangue is produced by a three-stage particle size distribution consisting of coarse particles of 20-50 mm, medium particles of 5-20 mm, and fine particles of 1-5 mm.

[0015] By adopting the above technical solution, nutrient solution and moisture regulation pipes and micro-negative pressure extraction branch pipes are added to each grid unit of the bioreactor layer, enabling precise control of the microbial degradation process. The nutrient solution and moisture regulation pipes can replenish water and nutrients such as nitrogen and phosphorus in zones and quantities according to the pollutant concentration and microbial activity requirements, ensuring maximum degradation efficiency. The micro-negative pressure extraction branch pipes are connected to the first section of the sieve tubes, enabling proactive and timely extraction of residual gases generated during biodegradation, preventing their accumulation within the grid and the formation of new vapor sources, fundamentally eliminating the risk of secondary migration.

[0016] Preferably, each grid unit of the bioreactor layer is further provided with nutrient solution and moisture regulating pipes, as well as a micro-negative pressure exhaust branch pipe; the exhaust branch pipe is connected to the first section of the sieve pipe.

[0017] By adopting the above technical solution, the second section of the screen pipe is located in the groundwater aquifer, and its aperture is designed to be 1-3mm, which precisely matches the particle size range of the aquifer gravel medium. This aperture can not only ensure the flow capacity when pumping out contaminated groundwater or injecting leaching / slow-release agents, but also effectively intercept most of the formation particles in the aquifer, preventing fine sand from entering the well pipe and causing well blockage or equipment wear. This extends the effective service life of the pumping and injection well in the aquifer, reduces the maintenance frequency and cost, and provides a reliable downhole channel guarantee for active repair and long-term slow-release control.

[0018] Preferably, the second section of the screen tube is located within the groundwater aquifer, and its aperture is 1-3 mm.

[0019] By adopting the above technical solution, the bidirectional pump enables switching between extraction and injection functions; the gas / liquid flow meter provides real-time operating data to determine changes in formation permeability and the diffusion range of the reagent; and the valves are used to independently control the opening and closing of the first and second screen tubes and the flow distribution. This complete set of components allows operators to dynamically adjust the ventilation rate, reagent dosage, and extraction / injection mode based on on-site monitoring data, upgrading the system from "experience-based operation" to "data-driven intelligent management and control."

[0020] Preferably, the dual-screen injection well is connected to a bidirectional pump, a gas flow meter, a liquid flow meter, and valves for regulating the delivery of gas or liquid.

[0021] By adopting the above technical solution, the aquifer is extracted or leached in situ through the second-stage screen tube, significantly reducing the quality of pollutants at the source. Simultaneously, air is introduced into the bioreactor layer through the first-stage screen tube, creating an aerobic environment within the vadose zone, activating and enhancing the degradation capacity of indigenous microorganisms for residual soil gases. Secondly, this application provides a method for using an integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment, employing the following technical solution: A method for using an integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment includes the following steps: System deployment phase: Construct double-screen pipe injection wells outside the building, and sequentially lay a surface barrier layer, a crushed stone layer, and a grid-based bioreactor layer under the building's foundation slab; Active repair and control phase: The pumping well is activated, and the aquifer is actively repaired through the second screen pipe, while air is simultaneously introduced into the bioreactor layer through the first screen pipe; Slow-release control phase: After the concentration of pollutants in the aquifer drops to the target value, slow-release agents are injected through the second screen tube to form a slow-release reaction zone, while retaining the ventilation and extraction functions of the first screen tube; Operation and maintenance monitoring phase: Regularly monitor system operating parameters and pollutant concentrations, and adjust operating strategies accordingly.

[0022] By adopting the above technical solutions, the system deployment phase completed the integrated construction of the four-layer vertical structure and the dual-screen injection wells, laying the material foundation for subsequent operation. In the active remediation and control phase, the dual-screen pipes worked collaboratively to simultaneously reduce aquifer pollutants and enhance biodegradation in the vadose zone, achieving gas-liquid co-control and source reduction. In the slow-release control phase, after pollution standards were met, a seamless switch to a low-cost slow-release mode was implemented. Slow-release agents were injected to form an underground reaction zone, continuously inhibiting the secondary release of residual pollutants while retaining the ventilation and extraction functions of the first-stage screen pipes to maintain the long-term activity of the bioreaction layer. In the operation and maintenance monitoring phase, operating parameters were dynamically adjusted through data feedback to ensure the system is always in optimal working condition. These four interconnected and smoothly transitioning phases address the pain points of existing technologies where remediation and control are separated, and where there is a lack of continuous inhibition measures after active remediation. This provides a complete solution for the long-term, safe, and economical risk management of contaminated sites in the built environment.

[0023] Preferably, the active remediation and control phase includes extracting contaminated groundwater through a second-stage screen tube for off-site treatment, or injecting leaching agents for in-situ leaching.

[0024] By adopting the above-mentioned technical solutions, in-situ rinsing avoids the extraction, transportation, and surface treatment of contaminated groundwater. Especially for clay layers or aquifers with poor permeability, hydraulic fracturing and chemical diffusion can deliver the chemicals more evenly to the core area of ​​the contamination plume, achieving in-situ chemical oxidation / reduction. This method complements extraction treatment and can be flexibly selected or combined according to the site's hydrogeological conditions and pollutant characteristics, further enhancing the system's versatility for different types of contaminated sites.

[0025] In summary, this application has the following beneficial effects: 1. This application achieves integrated and coordinated management of the vadose zone and saturation zone by constructing a vertical four-layer structure and a double-screen injection well. The surface barrier layer blocks vertical migration, the bio-reaction layer enhances degradation, the aquifer repair layer reduces the amount of vapor at the source, and the double-screen well achieves gas-liquid linkage, which significantly improves the prevention and control effect of steam intrusion.

[0026] 2. In this application, coal gangue, fly ash and straw are preferred as composite fillers. Through three-stage particle gradation and grid method, while ensuring rigid bearing capacity, solid waste resource utilization, porosity optimization and microbial activity maintenance are realized, reducing costs and improving system stability.

[0027] 3. The application method of this application achieves precise control of the risk of contaminated sites in the whole chain and in stages through a smooth transition of four stages: system deployment, active remediation, slow release control and operation and maintenance monitoring, from source reduction to long-term suppression. It is particularly suitable for complex pollution conditions in built environments. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments. Example

[0029] Example 1 This example focuses on a school cafeteria in Beijing (building area 1000m²). 2 The site is contaminated with petroleum hydrocarbons and chlorinated hydrocarbons (tetrachloroethylene, trichloroethylene) in the lower part of the building. The concentration of pollutants in the groundwater ranges from 3 to 40 mg / L, and there is an odor in the room.

[0030] The four-layer vertical structure, from top to bottom, consists of: The surface barrier layer is laid beneath the building's foundation slab. The main area utilizes a composite layer of C25 concrete and two layers of fabric and one layer of film, with a concrete thickness of 10cm and an HDPE film thickness of 1.2mm. Joints in the building's foundation slab and wall corners are sealed using a targeted application of fluidized solidified soil, with a curing agent dosage of 12%, resulting in a permeability coefficient of 8.5 × 10⁻⁶ after curing. -8 cm / s; The crushed stone layer is set below the surface barrier layer, and is made of limestone crushed stone with a particle size of 20 to 40 mm and a thickness of 30 cm. The bioreactor layer is located below the crushed stone layer and is laid out using a grid method. The grid unit size is 1m×1m×1m, and the grids are separated by a 15cm wide crushed stone layer. Each grid unit is filled with a composite filler, which is a mixture of coal gangue, fly ash, and straw. The volume ratio of coal gangue to straw is 3:1, and the fly ash content is 10% of the total volume of the composite filler. The coal gangue adopts a three-stage particle size distribution: coarse particles with a diameter of 20-40mm, medium particles with a diameter of 5-20mm, and fine particles with a diameter of 1-5mm, with a volume ratio of 1:4:5. The measured porosity of the composite filler is 35%. Each grid unit is also equipped with PE material nutrient solution and moisture regulating pipes with an opening rate of 5%, as well as a 40mm diameter micro-negative pressure exhaust branch pipe, which is connected to the first section of screen pipe.

[0031] The aquifer remediation and slow-release agent application layer is located within the groundwater aquifer, without additional filling materials. Active remediation and slow-release control are achieved through subsequently injected slow-release agents. The slow-release agent is a compound agent composed of rhamnolipids, hydrogen peroxide, ammonium dihydrogen phosphate, and ammonium chloride.

[0032] The double-screen injection wells are located outside the building's perimeter wall, with a total of 8 wells, spaced 6 meters apart and 8 meters deep. Each well contains two sections of screen pipe. The first section of the screen tube is located within the gravel layer, at a depth of 2-2.3m, with a pore size of 2mm, and is made of HDPE. It is used to introduce air into the bioreactor layer or extract residual gas.

[0033] The second section of the screen tube is located within the groundwater aquifer at a depth of 6-8m, with a pore size of 1.5mm. It is used for extracting contaminated groundwater and injecting leaching agents or slow-release agents. The leaching agent is a 1% (v / v) ethanol solution, and the slow-release agent is a slow-release microbial agent.

[0034] The dual-screen injection well is also connected to a bidirectional pump, a gas flow meter, a liquid flow meter, and valves. The flow rate adjustment range of the bidirectional pump is 0.3-3m³. 3 / h is used for precise control of gas or liquid transport.

[0035] The usage method of the above system includes the following steps: The system deployment phase will take 25 days. Dual-screen injection wells will be constructed outside the building, and a surface barrier layer, a crushed stone layer, and a grid-based bioreactor layer will be laid sequentially beneath the building's foundation slab. Small-scale machinery will be used during construction to avoid disrupting the school's normal operations with large equipment.

[0036] The active repair and control phase will last 45 days. The bidirectional pumps of the injection and extraction wells will be started, and a leaching agent (1% ethanol solution by volume) will be injected into the aquifer through the second-stage screen pipe, simultaneously at a flow rate of 1.2m. 3 Contaminated groundwater is extracted at a rate of / h for off-site treatment. It passes through the first section of screen pipe at a rate of 0.5m... 3 / (m 2 Air is introduced into the bioreactor layer at a rate of h, and the humidity of the bioreactor layer is controlled at 60-65% through nutrient solution and water regulation pipes. During operation, an alternating operation mode of induced aeration and micro-negative pressure extraction is adopted: when the north injection well is performing micro-negative pressure extraction, the south injection well opens the induced aeration valve and stops extraction; when the south injection well is performing micro-negative pressure extraction, the north injection well opens the induced aeration valve and stops extraction; the east and west injection wells are operated in the same alternating manner.

[0037] The controlled-release phase lasts 120 days. Once the concentration of chlorinated hydrocarbons in the aquifer has decreased to below 2 mg / L, a controlled-release microbial agent will be injected through the second-stage screen tube at a dosage of 1.5 kg / m³.3 The aquifer forms a slow-release reaction zone. The active repair equipment is shut down, but the low-intensity ventilation and extraction functions of the first-stage screen tube are retained, with the ventilation rate adjusted to 0.2m. 3 / (m 2 ·h).

[0038] During the operation and maintenance monitoring phase, system operating parameters, including gas flow rate and pressure, were monitored every 20 days. Simultaneously, pollutant concentrations in downstream monitoring wells were monitored, and operating strategies were dynamically adjusted based on the monitoring data. Monitoring results showed that the degradation efficiency of chlorinated hydrocarbons in the bioreactor layer remained consistently above 85%.

[0039] Example 2

[0040] The difference between Example 2 and Example 1 is that the application site is an ordinary residential building, the grid unit size of the bioreactor layer is 2m×2m×1m, the fly ash content is 15% of the total volume of the composite filler, and the measured porosity of the composite filler is 38%.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that the joints of the surface barrier layer are not sealed with fluidized solidified soil, but are covered with two layers of cloth and one film of the same material overlapping.

[0043] Example 4

[0044] The difference between Example 4 and Example 1 is that the coal gangue in the composite filler does not use a three-stage particle size distribution, but instead uses single-size crushed stone with a particle size of 10 to 30 mm.

[0045] Example 5

[0046] The difference between Example 5 and Example 1 is that the bioreactor layer is not laid out using a grid method, but rather the composite filler is filled in a monolithic large volume. Comparative Example

[0047] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no surface barrier layer is provided, and the building base plate is in direct contact with the crushed stone layer.

[0048] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no bioreactor layer is set up, and the aquifer is directly below the gravel layer.

[0049] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the dual-screen injection well only has a screen pipe section located in the aquifer, and does not have a first screen pipe section located in the gravel layer, so it cannot actively ventilate the vadose zone. Performance testing

[0050] Vapor intrusion risk reduction rate: After 180 days of system operation, five sampling points were set up in the building's indoor space to monitor the total concentration of chlorinated hydrocarbons in the indoor air, using tetrachloroethylene as a representative pollutant for calculation. The vapor intrusion risk reduction rate was calculated using the following formula: indoor chlorinated hydrocarbon concentration before system operation minus the indoor chlorinated hydrocarbon concentration after 180 days of operation, divided by the indoor chlorinated hydrocarbon concentration before system operation, and then multiplied by 100%. The indoor chlorinated hydrocarbon concentration before system operation was 0.35 mg / m³. 3 .

[0051] Groundwater pollutant remediation effect: After 180 days of system operation, groundwater monitoring well samples were collected from the site, and the total concentration of chlorinated hydrocarbons was determined in accordance with the "Determination of Volatile Organic Compounds in Water by Purge-Trap / Gas Chromatography-Mass Spectrometry" (HJ 639-2012).

[0052] Pollutant removal effect of the vadose zone: After the system has been running for 180 days, composite packing samples at different depths of the surface, middle and bottom layers of the bioreactor layer were collected. The total amount of chlorinated hydrocarbons adsorbed and degraded in the packing was measured, and the average removal rate of the vadose zone was calculated.

[0053] Bioreactor packing performance: After 360 days of system operation, composite packing samples of the bioreactor were obtained by drilling, and the rate of decrease in porosity compared to the initial porosity was detected. At the same time, the number of microorganisms in the packing was detected, expressed as phospholipid fatty acid (PLFA) biomass, in nmol / g.

[0054] Table 1 Performance test results after 180 days of system operation Example 1 99.1 0.05 89.2 Example 2 98.7 0.06 88.5 Example 3 85.4 0.06 88.9 Example 4 95.1 0.07 85.3 Example 5 91.3 0.06 80.6 Comparative Example 1 44.6 0.08 89.5 Comparative Example 2 31.4 0.09 —— Comparative Example 3 63.8 0.08 54.7 Table 2. Performance test results of the bioreactor packing material after 360 days of system operation. Example 1 7.8 128.3 Example 2 8.5 121.6 Example 3 11.9 109.4 Example 4 17.6 90.2 Example 5 24.1 82.7 Comparative Example 1 —— —— Comparative Example 2 —— —— Comparative Example 3 14.8 71.5 As can be seen from Table 1 and Examples 1-2, the in-situ integrated remediation risk management system for preventing soil vapor intrusion in the constructed environment described in Examples 1-2 of this application has excellent vapor intrusion prevention effect, groundwater remediation capacity, and vadose zone pollutant removal efficiency. After 180 days of operation, the indoor vapor intrusion risk reduction rate reached 99.1% and 98.7%, respectively, the residual concentration of chlorinated hydrocarbons in groundwater was as low as 0.05-0.06 mg / L, and the average removal rate of chlorinated hydrocarbons in the vadose zone was as high as 88.5-89.2%. This is thanks to the synergistic effect of the system's four-layer vertical structure and the dual-screen injection wells: the surface barrier layer achieves large-area isolation through a composite paving of two layers of cloth and one membrane with concrete, while targeted sealing at the joints is achieved using fluidized solidified soil, completely cutting off the vertical migration channels of soil vapor; the bioreactor layer uses a grid layout and a composite filler of coal gangue, fly ash, and straw, providing rigid bearing capacity while creating a suitable environment for aerobic microbial degradation; the dual-screen injection wells supply oxygen to the bioreactor layer by aerating the gravel layer through the first screen pipe, and actively repair the aquifer through the second screen pipe, achieving integrated and coordinated management of the vadose zone and saturation zone.

[0055] As can be seen from Table 1, Example 1, and Example 3, in Example 3, the joints of the surface barrier layer were not targeted with fluidized solidified soil, but were covered with two layers of fabric and one membrane of the same material. The risk reduction rate of vapor intrusion decreased from 99.1% to 85.4%. This indicates that the joints of the building floor slab and the corner joints are weak points for vapor intrusion. Ordinary overlapping methods are difficult to form a complete seal. Fluidized solidified soil, with its high fluidity and micro-expansion after solidification, can adaptively fill gaps of complex shapes, thereby completely blocking the vapor migration channels and significantly improving the barrier effect.

[0056] As can be seen from Tables 1 and 2, as well as Examples 1 and 4, in Example 4, the coal gangue used in the composite packing did not adopt a three-stage particle size distribution, but instead used only single-size crushed stone with a particle size of 10-30mm. After 180 days of operation, the average removal rate of chlorinated hydrocarbons in the vadose zone decreased from 89.2% to 85.3%. After 360 days of operation, the porosity reduction rate of the packing increased from 7.8% to 17.6%, and the PLFA biomass decreased from 128.3 nmol / g to 90.2 nmol / g. This is because the single-size packing lacks the mutual support and filling of coarse and fine particles, and under long-term load-bearing, particle rearrangement and compaction are prone to occur, leading to a rapid decrease in porosity and affecting gas diffusion and microbial activity. In contrast, in the three-stage particle size distribution, coarse particles act as the skeleton to bear the load, while medium and fine particles fill the gaps, maintaining a suitable porosity and improving compressive stability, thereby maintaining long-term biodegradation efficiency.

[0057] As can be seen from Tables 1 and 2, as well as Examples 1 and 5, the bioreactor layer in Example 5 did not use a grid method for layout. Instead, the composite packing material was filled in a monolithic, large-volume manner. After 180 days of operation, the average removal rate of chlorinated hydrocarbons in the vadose zone decreased from 89.2% to 80.6%. After 360 days of operation, the porosity reduction rate increased from 7.8% to 24.1%, and the PLFA biomass decreased from 128.3 nmol / g to 82.7 nmol / g. This is because, under the gravity compaction effect, the porosity of the deep packing material was significantly reduced in the monolithic filling, which led to the obstruction of oxygen and nutrient transport and the easy formation of anaerobic dead zones in some areas. In contrast, the grid method used a gravel layer to divide the large-volume packing material into independent small units, effectively preventing the overall settling and compaction of the packing material and ensuring good aeration and water permeability and microbial activity in each grid unit.

[0058] As can be seen from Table 1 and Comparative Example 1, in Comparative Example 1, without a surface barrier layer, the building slab is in direct contact with the gravel layer, and the risk reduction rate of vapor intrusion drops sharply from 99.1% to 44.6%. This indicates that without a surface barrier layer, soil vapor can penetrate the gravel layer and the building slab and directly enter the room, resulting in an extremely high risk of vapor intrusion. The surface barrier layer of this application, as the first line of defense, has a dual protection mechanism of surface coverage and seam sealing, which is crucial for preventing vapor intrusion.

[0059] As can be seen from Table 1 and Comparative Example 2, without a bioreactor layer, the aquifer lies directly below the gravel layer in Comparative Example 2, resulting in a vapor intrusion risk reduction rate of only 31.4%. Chlorinated hydrocarbons in the vadose zone cannot be effectively removed. This indicates that without a bioreactor layer, rising soil vapor lacks effective in-situ interception and degradation methods. Even if aquifer remediation achieves some effect, pollutants remaining in the vadose zone can still continuously migrate into the room. The bioreactor layer in this application, as a key layer connecting the upper and lower layers, not only receives oxygen from the gravel layer but also actively degrades rising soil vapor, achieving in-situ reduction of pollutants in the vadose zone.

[0060] As can be seen from Tables 1-2 and Comparative Example 3, the dual-screen injection well in Comparative Example 3 only has a screen section located within the aquifer, lacking a first screen section located within the gravel layer. Therefore, it cannot actively ventilate the vadose zone, resulting in a steam intrusion risk reduction rate of only 63.8% and an average removal rate of chlorinated hydrocarbons in the vadose zone of only 54.7%. After 360 days of operation, the PLFA biomass in the bioreactor layer was 71.5 nmol / g, far lower than the 128.3 nmol / g in Example 1. This indicates that without active ventilation, the oxygen supply in the bioreactor layer is insufficient, severely inhibiting the activity of aerobic microorganisms and significantly reducing degradation efficiency. The dual-screen design of this application achieves active ventilation and micro-negative pressure extraction of the vadose zone through the first screen section, providing sufficient electron acceptors for aerobic degradation and timely removing residual gas, thereby maintaining the long-term and efficient degradation capacity of the bioreactor layer.

[0061] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment, characterized in that, Includes a four-story longitudinal structure and double-screen injection wells installed on the exterior of the building: The vertical four-layer structure, from top to bottom, consists of: The surface barrier layer is laid under the building's foundation to block the vertical migration of soil vapor. The gravel layer is set below the surface barrier layer and is used for gas extraction to supply oxygen to the lower layer. The bioreactor layer is located below the gravel layer and is laid out using a grid method. The grid cells are filled with composite fillers for degrading volatile pollutants. The aquifer remediation and slow-release agent dosing layer is located within the groundwater aquifer and is used for active remediation and slow-release control of pollutants. The well body of the dual-screen injection well is equipped with two screen sections: the first screen section is located in the gravel layer and is used to introduce air into the bioreactor layer or extract residual gas; the second screen section is located in the groundwater aquifer and is used to extract contaminated groundwater, inject leaching agents, or inject slow-release agents.

2. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, The main area of ​​the surface barrier layer is laid with a composite of two layers of cloth and one membrane and concrete. The joints of the building base plate and the corner joints are sealed with fluidized solidified soil.

3. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, The crushed stone layer is made of crushed stone with a particle size of 20-50mm and a thickness of 30-40cm; the first section of screen tube is laid in the crushed stone layer and its pore size is 2-5mm.

4. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, The grid unit size of the bioreactor layer is 1m×1m×1m or 2m×2m×1m, and the grids are separated by a layer of crushed stone. The composite filler is a mixture of coal gangue, fly ash and straw, wherein the volume ratio of coal gangue to straw is 3:1, the fly ash content is 10-15% of the total volume of the composite filler, and the porosity of the composite filler is controlled at 30-40%.

5. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 4, characterized in that, The coal gangue is produced using a three-stage particle size distribution: coarse particles of 20-50 mm, medium particles of 5-20 mm, and fine particles of 1-5 mm.

6. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, Each grid unit of the bioreactor layer is also equipped with nutrient solution and moisture regulation pipes, as well as a micro-negative pressure exhaust branch pipe; the exhaust branch pipe is connected to the first section of the sieve pipe.

7. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, The second section of the screen tube is located within the groundwater aquifer, and its aperture is 1-3 mm.

8. The in-situ integrated remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 1, characterized in that, The dual-screen injection well is connected to a bidirectional pump, a gas flow meter, a liquid flow meter, and valves for regulating the delivery of gas or liquid.

9. A method for using an integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment, based on any one of claims 1-8, characterized in that, Includes the following steps: System deployment phase: Construct double-screen pipe injection wells outside the building, and sequentially lay a surface barrier layer, a crushed stone layer, and a grid-based bioreactor layer under the building's foundation slab; Active repair and control phase: The pumping well is activated, and the aquifer is actively repaired through the second screen pipe, while air is simultaneously introduced into the bioreactor layer through the first screen pipe; Slow-release control phase: After the concentration of pollutants in the aquifer drops to the target value, slow-release agents are injected through the second screen tube to form a slow-release reaction zone, while retaining the ventilation and extraction functions of the first screen tube; Operation and maintenance monitoring phase: Regularly monitor system operating parameters and pollutant concentrations, and adjust operating strategies accordingly.

10. The method of using the integrated in-situ remediation risk management system for preventing soil vapor intrusion in a built environment according to claim 9, characterized in that, The active remediation and control phase includes off-site treatment by extracting contaminated groundwater through the second-stage screen tube, or in-situ leaching by injecting leaching agents.