Pollution risk investigation method for soil in waste chemical land parcel

Abstract

The invention discloses a pollution risk investigation method for soil in a waste chemical land parcel. The method comprises the following steps: S1, preliminarily listing pollutants; s2, delimiting a pollution range for the first time; s3, point distribution detection; s4, correcting the model; s5, delimiting a pollution range for the second time; s6, point distribution detection; s7, judging the pollution risk; according to the method, data collection and model simulation are carried out on the waste chemical land parcel, the problem that in the prior art, due to the fact that sampling and detection analysis are high in cost and inaccurate in point distribution in soil investigation, evaluation on the land parcel is inaccurate can be solved, point distribution setting can be reduced, the distribution condition of pollutants can be obtained more accurately, and the evaluation accuracy of the land parcel is improved. And risk assessment investigation can be carried out on the waste chemical land parcels.

Description

Technical Field

[0001] The present invention relates to the technical field of land risk investigation, and in particular to a method for investigating the pollution risk of soil in abandoned chemical industry plots. Background Art

[0002] With the acceleration of urbanization and industrialization, environmental issues are becoming increasingly important, especially in land use projects. Due to insufficient understanding of soil pollution, the soil environment is polluted during use. Many enterprises have moved out of the city or permanently retired, but the soil and groundwater at the sites of these polluting enterprises may be polluted to varying degrees during the original production process. During the redevelopment and utilization process, the soil and groundwater pollution problems are exposed. Therefore, it is particularly important to conduct environmental investigations, risk assessments, restoration and governance for retired enterprise sites, especially before the land function change of polluting enterprise retired sites, otherwise there will be ecological health risks, affecting the urban environment and the health of its residents.

[0003] In the existing technology, soil sample collection is difficult due to the difficulty in soil sample collection, the wide distribution of soil and the changeable geographical environment, and the complex underground structure and pollutant distribution of abandoned chemical sites. In addition, there are many types of pollutants that may exist in chemical sites, including heavy metals, organic pollutants, etc. The properties and hazards of these pollutants vary, which increases the difficulty of analysis. Although the existing soil pollution investigation technology has made certain progress, in some cases, the accuracy of the investigation results may be limited due to improper selection of sampling points, inaccurate analysis methods or insufficient data analysis. In addition, soil pollution investigations require a lot of manpower, material and financial resources, including the costs of sampling tools, laboratory equipment, analytical reagents, as well as personnel training, on-site surveys and other expenses. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for investigating the pollution risk of soil in abandoned chemical industry sites.

[0005] A method for investigating the pollution risk of soil in abandoned chemical industry plots comprises the following steps:

[0006] S1. Preliminary list of pollutants;

[0007] Collect historical data of abandoned chemical sites, and list various pollutants based on the historical data; the historical data include production processes, various pollutants involved and the location of each pollutant, stratum conditions and hydrogeological information;

[0008] S2. Determine the pollution scope once;

[0009] Based on historical data, establish a process diffusion model; the process diffusion model includes a production process module, a groundwater flow module, and a solute transport module; the input of the process diffusion model is multiple pollutants, and the output is the pollutant emission points, leakage-prone points, and pollutant concentration distribution. The positions where the pollutant concentrations on the abandoned chemical industrial plot exceed the concentration threshold are designated as the primary simulated pollution range; the multiple pollutants include raw materials, intermediate products, and final products in the production process;

[0010] Among them, the concentration threshold is determined according to the land use of the abandoned chemical industrial plot; that is, the concentration threshold refers to the pollutant concentration screening value specified according to the land use, which is taken from the implementation standard of the land use. For example, if the land use is construction land, the pollutant concentration screening value refers to "Soil Environmental Quality - Risk Control Standard for Soil Pollution of Construction Land (Trial)" (GB 36600-2018). If the land use is agricultural land, the pollutant concentration screening value refers to "Risk Control Standard for Soil Pollution of Agricultural Land (Trial)";

[0011] S3. Layout points for detection;

[0012] On the plot within the primary simulated pollution range, conduct dense point layout, and on the other areas of the abandoned chemical industrial plot except the primary simulated pollution range, conduct general point layout. Then, collect samples and detect them at the dense points and general points to obtain the concentration detection values of multiple pollutants; among them, the samples include soil samples and groundwater samples;

[0013] S4. Model calibration;

[0014] Use the concentration detection values of each pollutant in the multiple pollutants detected in S3 to calibrate the process diffusion model to obtain the calibrated process diffusion model;

[0015] S5. Redefine the pollution range for the second time;

[0016] Use the calibrated process diffusion model to determine the pollutant concentrations at the emission points and leakage-prone points, and designate the positions where the pollutant concentrations at the emission points and leakage-prone points exceed the concentration threshold as the secondary simulated pollution range;

[0017] S6. Layout points for detection;

[0018] On the plot within the secondary simulated pollution range, conduct dense point layout, and on the other areas of the abandoned chemical industrial plot except the secondary simulated pollution range, conduct general point layout. Then, collect samples and detect them at the dense points and general points to obtain the concentrations of multiple pollutants;

[0019] S7. Judge the pollution risk;

[0020] Judge whether the detection values of pollutants in the samples detected by S3 and S6 exceed the concentration threshold. If the detection value of any pollutant in S3 and S6 exceeds the concentration threshold, it indicates that there is a pollution risk and a health risk assessment is required. If neither exceeds the concentration threshold, it indicates that there is no risk in this plot.

[0021] Description: By collecting data and conducting model simulations on abandoned chemical industrial plots through the above methods, it is possible to solve the problems in the existing technology of large costs for sampling and testing analysis in soil surveys and inaccurate plot assessments caused by inaccurate sampling points. By delimiting the scope and respectively conducting encrypted and general sampling point settings for sampling, the setting of sampling points can be reduced. At the same time, after calibrating the model, the model can more accurately reflect the distribution of pollutants, facilitating the risk assessment and investigation of abandoned chemical industrial plots.

[0022] Furthermore, the plot uses include: residential land, public management and public service land, commercial service land, industrial and mining storage land, transportation land, water conservancy facility land, agricultural land, and green space and square land.

[0023] Description: The above plot uses are the current common uses.

[0024] Furthermore, the method for establishing a process diffusion model based on the data of the historical materials includes:

[0025] Obtain multiple groups of the data of the historical materials;

[0026] According to the data of the production process and the law of conservation of mass of substances, establish a production process module for simulating the material flow and transformation during the production process; the input of the production process module is the raw material substances and the emission parameters used to describe pollutant emissions, and the output is the intermediate product or final product and the pollutant emission points and easy leakage points;

[0027] Based on the formation conditions, hydrogeological information, and the finite difference method or finite element method, establish a groundwater flow module for simulating the flow path and velocity of groundwater; the input of the groundwater flow module is the production process raw material or intermediate product or final product, formation conditions and hydrogeological information, and the diffusion parameters used to describe the diffusion of pollutants in groundwater, and the output is the concentration of the production process raw material or intermediate product or final product in groundwater;

[0028] According to the physical and chemical properties of the soil, establish a solute transport module for simulating the migration and diffusion of pollutants in the soil and groundwater; the input of the solute transport module is the physical and chemical properties of the soil and the diffusion parameters used to describe the diffusion of pollutants in the soil, and the output of the solute transport module is the concentration distribution of pollutants in the soil;

[0029] Among them, the production process module, the groundwater flow module, and the solute transport module are connected in sequence, and the production process module is connected to the solute transport module.

[0030] Explanation: Through the above method, a process diffusion model can be established. Through the production process module, the abandoned chemical production model can be restored and pollution diffusion simulation can be carried out to obtain the sewage discharge points and emissions. Through the groundwater flow module and the solute transport module, the distribution of pollutant concentrations can be obtained, thereby realizing the simulation of the model.

[0031] Furthermore, the data of the production process includes process flow information; the formation conditions and hydrogeological information include formation thickness, rock type, porosity, permeability, saturation, groundwater level, groundwater flow direction and velocity; the physical and chemical properties of the soil include soil organic matter content and soil pH value.

[0032] Explanation:

[0033] Furthermore, in S3 and S6, the grid point density of the dense grid points is 1m×1m to 5m×5m, and the grid point density of the general grid points is 6m×6m to 15×15m.

[0034] Furthermore, the method for calibrating the process diffusion model using the concentrations of various pollutants obtained by the dense sampling and general sampling in S4 includes:

[0035] When the concentration detection value of the pollutant obtained in S3 is greater than the output value of the process diffusion model, increase the emission parameters in the production process module, or decrease the diffusion parameters in the groundwater flow module and the solute transport module;

[0036] When the concentration detection value of the pollutant obtained in S3 is less than the output value of the process diffusion model, decrease the emission parameters in the production process module, or increase the diffusion parameters in the groundwater flow module and the solute transport module.

[0037] Furthermore, the easily leakable points in the production process include: pipe joints, valves, seals of pumps or compressors, openings and seals of storage tanks and containers, sampling points, and instrument interfaces.

[0038] The beneficial effects of the present invention are:

[0039] By collecting data and conducting model simulations on abandoned chemical industrial sites through the above methods, the present invention can solve the problems in the prior art that the costs of sampling and testing analysis in soil surveys are relatively high, and inaccurate site layout leads to inaccurate assessment of the sites. By delimiting the scope and separately conducting encrypted and general site layout for sampling, the setting of site layout can be reduced. At the same time, after calibrating the model, the model can more accurately reflect the distribution of pollutants, so as to facilitate the risk assessment survey of abandoned chemical industrial sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flowchart of the method for investigating the pollution risk of soil in an abandoned chemical industrial site according to an embodiment of the present invention;

[0041] Figure 2 is a schematic diagram of the detection results of a part of the abandoned chemical industrial site according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] To further elaborate on the methods adopted and the effects achieved by the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with experiments.

[0043] Due to the difficulty in collecting soil samples, the wide distribution of soil and the diverse geographical environments, abandoned chemical industrial sites often have complex underground structures and pollutant distributions, making it difficult to collect soil samples; moreover, there are a wide variety of pollutants that may exist in chemical industrial sites, including heavy metals, organic pollutants, etc. The properties and hazards of these pollutants are different, increasing the difficulty of analysis; although the existing soil pollution investigation technologies have made certain progress, in some cases, due to improper selection of sampling points, inaccurate analysis methods or insufficient data analysis, etc., the accuracy of the investigation results may be limited; in addition, soil pollution investigation requires a large amount of manpower, material resources and financial resources, including the costs of sampling tools, laboratory equipment, analysis reagents, etc., as well as the costs of personnel training, on-site investigation, etc.

[0044] Embodiment 1: A method for investigating the pollution risk of soil in an abandoned chemical industrial site, comprising the following steps:

[0045] S1. Initially list pollutants;

[0046] Collect the historical data of the abandoned chemical industrial site, and list various pollutants according to the historical data; the historical data includes production processes, various pollutants involved, the location of each pollutant, stratum conditions and hydrogeological information;

[0047] The on-site data collection for a plot of land in a certain city is as follows: The original enterprise on this plot was a chemical enterprise engaged in the storage of petroleum products, with a risk of soil pollution. This plot is planned to be changed into a park green space. The plot was originally used for the storage and sale of petroleum products, and there were a total of 13 horizontal tanks. Among them, 9 horizontal tanks were distributed in Plot 1 and 4 horizontal tanks were distributed in Plot 2, which were used to store ethylene tar and C9. At present, all the storage structures on the plot have been demolished and the plot is idle. The future planning of the plot is for park green space, belonging to the second type of land. Pollution identification: According to the information obtained from historical use changes, on-site inspections, and personnel interviews, this plot was used for carbon black production before 2008; from 2009 to 2019, it was used for the storage and sale of ethylene tar and C9. At the end of July 2020, all the storage tanks on the plot were demolished and the plot was idle. The key pollutants focused on in this investigation are organic pollutants such as petroleum hydrocarbons (C6 - C9), petroleum hydrocarbons (C10 - C40), volatile organic compounds (VOCs) such as benzene series, semi-volatile organic pollutants (SVOCs) such as polycyclic aromatic hydrocarbons, and heavy metal pollutants (arsenic) generated by coal combustion. Therefore, the preliminary list of pollutants includes organic pollutants such as petroleum hydrocarbons (C6 - C9), petroleum hydrocarbons (C10 - C40), volatile organic compounds (VOCs) such as benzene series, semi-volatile organic pollutants (SVOCs) such as polycyclic aromatic hydrocarbons, and heavy metal pollutants (arsenic) generated by coal combustion.

[0048] In addition, the location, area, current use, and planned use of the plot are as follows:

[0049] From 2009 to 2019, it was mainly used for the storage and sale of petroleum products (C9 and ethylene tar); at the end of July 2020, the demolition of the plot began. At present, the demolition of the storage tank structures on the plot is completed and the plot is idle; a certain area of the plot was originally used for the storage of petroleum products, with a total of 13 horizontal tanks. Among them, 9 horizontal tanks were distributed in a certain area of Plot 1 and 4 horizontal tanks were distributed in a certain area of Plot 2, which were used to store ethylene tar and C9. At present, all the storage structures on the plot have been demolished and the plot is idle. According to the "Overall Plan of a Certain District (2014 - 2030)", the future planned use of this plot is park green space (G1), belonging to the second type of land in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB 36600 - 2018).

[0050] By querying literature and other materials, ethylene tar is the product of high-temperature condensation of raw materials and products during the steam cracking of ethylene cracking raw materials. Its chemical composition is extremely complex. Among them, the contents of indene, methylindene and their homologues, naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, as well as anthracene, acenaphthene, phenanthrene and other components are relatively high, and they are all important raw materials for organic chemical synthesis. C9 is obtained by polymerization of the fraction containing nine-carbon-atom aromatics in the by-products after the catalytic reforming and cracking of petroleum in the presence of an acidic catalyst. Its main components include isopropylbenzene, n-propylbenzene, ethyltoluene, indene, mesitylene, pseudocumene, sym-trimethylbenzene, etc. Therefore, the pollutants that this investigation will focus on include volatile organic compounds such as petroleum hydrocarbons and benzene series, and semi-volatile organic compounds such as polycyclic aromatic hydrocarbons.

[0051] The topography, geomorphology, geology and soil types of the investigated plot and its surrounding areas are as follows:

[0052] A certain district is located in the northwest of a certain city, north of the Yangtze River. Its north, west and south are connected with the low mountains and hills of Anhui Province. The terrain within the district is undulating and the geomorphic types are diverse, forming a geomorphic complex with interlaced distribution of low mountains, hills, hillocks and plain alluvial lands. According to the geomorphic characteristics, a certain district can be divided into three major geomorphic types, namely low mountain and hilly areas, hillock areas and plain areas. Among them, the area of low mountain and hilly areas accounts for 23.6% of the total area of the district, the area of hillock areas accounts for 45.4% of the total area of the district, and the area of plain areas accounts for 31% of the total area of the district. The elevation difference in the low mountain and hilly areas is relatively large, the terrain is steep, the highest altitude is 442m, and hillocks extend on both sides of the low mountains and hills, with undulating terrain, an altitude of 20m - 50m, and gullies are well developed under the erosion of running water. The plains are regularly interlaced among the low mountains and hills. The Chuhe River valley plain is located between the northern hills of Liuhe and the Laoshan Mountains, and the southern side of the Laoshan Mountains is the Yangtze River alluvial plain and alluvial lands. The terrain in the plain area is low and flat, with an altitude of about 10m.

[0053] The investigated plot is located in a certain district on the north bank of the Yangtze River and belongs to the hillock area.

[0054] The geological strata and lithology are as follows:

[0055] The Quaternary strata in a certain area are mainly distributed in the hillock areas and plain areas, and the lithology varies greatly. The Quaternary is more developed in the Yangtze River plain and the Chuhe River plain, mainly composed of Holocene sediments (clay, soft soil, sandy soil). The Quaternary thickness in the Yangtze River alluvial plain is relatively large, generally 40 - 80m, and the thickness of Quaternary sediments in the Chuhe River plain area is generally less than 50m. Affected by tectonic uplift and subsidence movements, the middle and lower Pleistocene sediments are missing in most areas. The hillock areas are mainly composed of the middle and upper Pleistocene (clay), and the Holocene (clay) is locally distributed in the depressions, with a small formation thickness, generally about 10 - 30m.

[0056] The bedrock generally outcrops on the surface in the low mountain and hilly areas, while it is buried beneath the Quaternary strata in the tableland and plain areas. In the Pukou area, the bedrock depth is generally less than 40m. Along the Yangtze River, the bedrock depth is 40 - 60m. The deepest part is located in the area of Shengliwei Farm in Pukou, exceeding 90m. In the Liuhe area, the bedrock depth in the areas of Xiongzhou and Hengliang is greater than 40m, reaching a maximum of 60 - 70m, and the rest is less than 40m.

[0057] The bedrock hidden beneath the Quaternary loose strata in a certain area mainly consists of Cretaceous volcanic rocks, Pukou Formation and Chishan Formation, with the lithology mainly being sandstone and sandy mudstone. The bedrock outcropping in Laoshan and Yeshan in Liuhe is mainly composed of dolomite, siliceous mudstone, shale of the Paleozoic, Dengying Formation, Huangxu Formation, Hetang Formation, Guanyintai Formation of the Neoproterozoic, and breccia and tuff of the Cretaceous Xihuanshan Formation.

[0058] The strata in the area where the surveyed plot is located are not fully developed, mainly the upper Pleistocene. The middle and lower parts of the Pleistocene are missing in most areas. The middle and upper Pleistocene mainly outcrop at the foot of the low mountains and hills, and the Holocene is distributed in local depressions. The strata thickness is small, generally 10 - 30m. The geological characteristics are manifested as Holocene clay.

[0059] The hydrogeological conditions are as follows:

[0060] According to the water-bearing medium, a certain area is divided into three types of water-bearing rock formations, namely the pore aquifer group of loose rocks, the fissure aquifer group of carbonate rocks, and the fissure aquifer group of bedrock.

[0061] Groundwater distribution and its water-richness characteristics

[0062] (1) Pore water of loose rocks

[0063] The pore aquifer group is composed of Cenozoic loose sediments and is widely distributed in the tableland and alluvial plain areas. Pore phreatic water is distributed in the shallow part of the river valley floodplain, the edge of the floodplain, and the hillock terrace areas, belonging to the weak pore water-bearing rock group of loose rocks. It is generally buried less than 5m below the surface. The lithology is mainly interbedded silty clay, silt and fine sand, and thin gravel-bearing sand layers are commonly found in the middle and lower parts of the hillock valleys. Pore slightly confined water is mainly distributed in the Yangtze River floodplain and the Chuhe River floodplain.

[0064] ① Pore water in the Yangtze River floodplain

[0065] It is mainly stored in the loose sediments and underlying sandy soil of the Yangtze River floodplain, with a thickness generally of 20 - 40m and a maximum of 75m. The permeability coefficient of the aquifer can reach 20 - 30m / d, and the transmissivity coefficient reaches 600 - 900m2 / d. The groundwater level is generally buried 1 - 3m, with rich to extremely rich water volume. The single-well yield is generally 800 - 1400m3 / d, and the maximum can reach 3000m3 / d.

[0066] ② Pore water in the Chuhe River floodplain

[0067] The thickness of the loose sediments in the Chuzhe floodplain is generally 30 - 40m, and the thickness of the sand layer is about 10m. The aquifer is divided into upper and lower sections. In the upper section, there are interbeds of silty sand, silt, and silty clay. In the lower section, there are medium - coarse sand with gravel. The water volume is rich to relatively rich. The daily yield of a single well is generally 500 - 1000m3 / d, and in the marginal area of the floodplain, it is 100 - 500m3 / d. The buried depth of the static water level is generally 2 - 4m. Near Pucheng in Pukou and Liucheng Town, affected by exploitation, the water level burial depth is 15 - 20m.

[0068] ③Pore water in Liuhe area and pore water in basalt cavities

[0069] In the northern and eastern parts of Liuhe, the aquifer group is composed of gravel layers of the Yuhuatai Formation of the Miocene and basalt of the Fangshan Formation. The cumulative thickness is generally 30 - 50m, with strong water - rich property and abundant water volume. Due to the large topographic undulation, the water level is affected by the mountain terrain and local exploitation, and the burial depth is 5 - 40m.

[0070] The sediments of the ancient Chuzhe floodplain are mainly gravels of the Yuhuatai Formation of the Miocene, which is a groundwater - rich area. The top plate of the aquifer is mostly deeper than 30m, the sediment thickness is 50 - 60m, and the thickest part is more than 80m (at Fangshan Forest Farm). The daily yield of a single well is 100 - 1000m3 / d. The influence of exploitation on the water level burial depth is obvious. The exploitation intensity is relatively large in the Liucheng area and Lingyan Mountain area of Liuhe. The water level burial depth is 16 - 17m (elevation about - 12m). For the rest of the areas, the water level burial depth varies greatly affected by the terrain height, generally less than 15m.

[0071] ④Pore water in hilly land (undulating plain)

[0072] It is distributed in the periphery of low mountains and hills, in most areas except for the areas where pore water is distributed in the Yangtze River, Chuzhe floodplain, and Liuhe River valley floodplain. The lithology is mainly clayey soil. There are thin layers of silt and silty sand in the marginal area of the floodplain. Xiashu soil is mostly distributed in the areas with higher terrain, and gravels are distributed at the bottom of local gully valleys in hilly land. The water - rich property is weak, and the daily yield of a single well is generally less than 100m3 / d.

[0073] (2) Karst fissure water in carbonate rocks

[0074] The karst fissure water in carbonate rocks in a certain area is mainly distributed in the Laoshan area of Pukou District. Secondly, there is also a small amount of distribution in Yeshan in the northeast of Liuhe. Karst develops shallowly in Laoshan. Well - known karst caves include Tianjing Cave, Long Cave, Big Guanyin Cave, and Zushi Cave, etc. The general outcrop position of the karst caves is relatively high, and most of them are filled with mud. The development of karst is mainly controlled by faults. The water volume is relatively large along the fault zone, up to 500 - 1000m3 / d, and relatively small otherwise. Most of the rock layers in Laoshan incline towards the NW, and generally, the water volume is larger on the NW side and smaller on the SE slope.

[0075] (3) Bedrock fissure water

[0076] The clastic rock aquifer group in a certain area is mainly distributed along the line from the periphery of the main body of Laoshan in Pukou to Yeshan in Liuhe. The groundwater is mainly stored in the bedrock structural fissures of the Chishan Formation and Pukou Formation of the Cretaceous System. Its water-richness is affected by various factors, and the water volume is relatively poor. The volcanic clastic rock aquifer group is only locally distributed around Yeshan Town in Liuhe District, and the water volume is poor.

[0077] Groundwater recharge, runoff, and discharge relationship

[0078] In a certain area, the terrain fluctuates greatly. The geomorphic types include low mountains and hills, tablelands, plains, etc. The terrain structure is complex, and there are various types of groundwater. The recharge of groundwater includes infiltration of atmospheric precipitation, infiltration of surface water, infiltration of irrigation water, and lateral runoff recharge from outside the region. Among them, the infiltration of atmospheric precipitation is the main recharge source. During the rainy season, surface water also has a certain recharge effect in a short period. The unconfined aquifer adjusts the discontinuous atmospheric precipitation into groundwater runoff in time, and part of the water volume is replenished to the (micro) confined water in the form of leakage infiltration. Evaporation in situ, spring overflow, discharge into surface water bodies, and artificial exploitation are the main discharge ways of groundwater.

[0079] Soil type

[0080] The soil types in a certain area are yellow-brown soil, yellow-cinnamon soil, fluvo-aquic soil, and paddy soil, accounting for 2.0%, 23.5%, 0.6%, and 74.0% of the total area respectively. Due to the complex geomorphology and parent material types, and the long agricultural history with profound human activities. Therefore, in addition to the zonal soils dominated by soil zonal laws, there are also large areas of azonal soils dominated by soil regional laws, and the two form a certain combination in spatial distribution. The main soil types in a certain area are yellow-cinnamon soil and paddy soil. Yellow-cinnamon soil is mainly distributed in Longwang Mountain and Lingyan Mountain, and some soils along the western Yangtze River coast are also yellow-cinnamon soil. The other areas in a certain area are basically paddy soil. Soil erosion is mainly divided into water erosion, wind erosion, and freeze-thaw erosion. The area is mainly affected by water erosion, and the soil erosion degree is relatively light. Only 4.4% of the area is slightly eroded by water, and the rest are slightly eroded.

[0081] The soil in the area where the surveyed plot is located is mainly paddy soil.

[0082] In summary, through the collection of historical data of the site investigation, on-site inspection, personnel interviews, and field sampling and analysis, the content of soil pollutants in the plot exceeds the screening values of soil pollution risks for second-class construction land specified in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB36600 - 2018), and various pollutant indicators in the groundwater exceed the standard limits of Class IV water in GB / T14848 - 2017. This plot belongs to a contaminated plot. It is necessary to carry out the next-stage human health risk assessment work on this plot.

[0083] In a certain area, within Plot 1, there is a storage tank area and a fire pool. The storage tank area includes 9 horizontal tanks, and the other areas are idle lands. In a certain area, Plot 2 has a storage tank area and an office area, with 4 horizontal tanks in the storage tank area. The aerial drone photos of the plots show traces of demolition in the areas where the horizontal tanks are located on the plots.

[0084] This plot has been successively engaged in the production of carbon black, and the storage and sales of ethylene tar and C9. The following separately introduces the production process conditions of the two land use histories.

[0085] (1) Carbon black production process: Since the carbon black factory has a relatively long production history, after extensive inquiries and data collection, no relevant information on its production process was obtained. Through literature and website searches, relevant information on carbon black production was found. The raw materials and auxiliary materials for carbon black production include coal tar and ethylene tar, and the energy fuel is coal. The specific production process is described as follows: The fuel oil pump is sent to mix and burn with the air preheated to 850 °C by the main air blower in the combustion section, generating a high-temperature combustion gas stream of about 1900 °C. The raw material oil is pumped to the on-line raw material oil preheater, preheated to 180 °C and then radially sprayed into the throat section of the reaction furnace, where it mixes with the high-temperature combustion gas stream and rapidly cracks to produce carbon black flue gas. In the quenching section of the reaction furnace, water is directly sprayed into the high-temperature carbon black flue gas to rapidly reduce its temperature and terminate the reaction. The carbon black flue gas generated in the reaction furnace preheats the air through the air preheater and the raw material oil through the oil preheater, and then enters the main cyclone separator and the main bag filter to collect the carbon black. The collected carbon black is pulverized and then sent to the collection cyclone separator by the air delivery blower. The carbon black-containing flue gas coming out of the collection cyclone separator returns to the main bag filter, and the collected carbon black enters the powder storage tank. The tail gas discharged from the main bag filter is pressurized by the tail gas pressurizing blower, and a part of it enters the tail gas combustion furnace for combustion as the heat source of the dryer, and most of it is sent to the tail gas boiler as fuel. The powdered carbon black is granulated by a wet granulator, enters rotary drying, and then through lifting, screening, and magnetic separation, is stored in the product storage tank. The finished product is packaged and stored in the warehouse. The flue gas for drying the wet carbon black is pumped by the exhaust blower to the exhaust bag filter, and the filtered carbon black enters the air delivery system, and the gas is discharged into the atmosphere through the chimney. (2) Ethylene tar and C9 storage process: During the use of this plot, only the storage and transportation of petroleum products are involved, and the production of petroleum products is not involved. The storage and transportation of petroleum products on this plot adopt mechanical filling. This process theoretically only involves the unorganized emission of organic waste gas, but the long-term corrosion of the tank body by petroleum products may cause the phenomenon of "running, leaking, dripping, and overflowing" of ethylene tar and C9 in the tank body. Potential pollution sources and migration pathways of the plot: There are two production histories on this plot in the past, namely carbon black production and the storage of ethylene tar and C9. The potential pollution sources in the plot include the running, leaking, dripping, and overflowing during carbon black production and the storage of ethylene tar and C9. (1) During the carbon black production period, the raw materials and auxiliary materials are coal tar and ethylene tar, and the energy fuel is coal. The long-term storage of coal tar and ethylene tar tanks may cause the leakage of raw materials and auxiliary materials due to corrosion; the flue gas generated by the high-temperature combustion of coal tar and ethylene tar will release polycyclic aromatic hydrocarbons and petroleum hydrocarbon pollutants; the flue gas generated during the combustion of coal as a heating fuel contains polycyclic aromatic hydrocarbons and heavy metals, and the flue gas particles migrate to the soil through sedimentation. (2) During the storage period of ethylene tar and C9, dripping may occur when the incoming and outgoing transport vehicles fill ethylene tar and C9, and leakage of ethylene tar and C9 may occur if the valve is not closed in time during the unloading process, which will all affect the soil and groundwater environment.In addition, the horizontal storage tank has been in use for a long time, and leakage occurs due to the corrosion of the tank body by petroleum products, which will also have a great impact on the surrounding soil environment. Therefore, there is a certain risk of soil pollution in this plot. Considering the on-site investigation, there is tar on the exposed ground in the storage tank area of the plot, and there is a small amount of water with abnormal color on the ground. There are obvious pollution traces in the plot, and further investigation and analysis are required. To sum up, there are two production histories in the history of the plot. Before 2007 - 2008, it was used by a carbon black factory, using coal tar and ethylene tar as raw materials and auxiliary materials, and producing through high-temperature heating by coal combustion; from 2009 to 2019, it was used by a certain XX Co., Ltd. for storing and selling ethylene tar and carbon nine. In July 2020, the demolition of 13 storage tank structures in the plot was completed, and the plot was left idle. The potential pollution sources in the plot include the spills and leaks during carbon black production and the storage of ethylene tar and carbon nine. Therefore, this investigation will focus on organic pollutants such as petroleum hydrocarbons (C6 - C9), petroleum hydrocarbons (C10 - C40), volatile organic compounds (VOCs) such as benzene series, semi-volatile organic pollutants (SVOCs) such as polycyclic aromatic hydrocarbons, and heavy metal pollutants (arsenic) generated by coal combustion.

[0086] Hydrogeological information of the plot:

[0087] Stratum properties of the plot: During the preliminary investigation stage, no hydrogeological exploration was carried out on this plot. The stratum information refers to the geological exploration report "Geotechnical Engineering Investigation Report of 120,000 Tons / Year Pyrolytic Carbon Nine Comprehensive Utilization Device of a Certain Co., Ltd." (March 2014) which is 930 m southwest of this plot. There is no river between the plot in a certain area and the cited geological exploration.

[0088] According to the description in the geological exploration report, the site strata from top to bottom are as follows: Layer 0A miscellaneous fill (Qml): variegated, mainly composed of broken bricks and stones with a small amount of cohesive soil, and locally concrete floor. The filling age is generally 1 - 5 years, and the uniformity is poor. Layer 0B plain fill (Qml): mainly silty clay, brownish yellow to yellowish brown, with a small amount of broken bricks and stones and plant rhizomes. The filling age is generally 1 - 5 years. It was not compacted during filling, with a loose structure and large differences in compactness, generally in a plastic state. Layer 0C plain fill (Qml): mainly silty clay, brownish yellow to yellowish brown, locally containing weathered rock blocks and broken bricks and stones. The filling age is more than 10 years. It was not strictly stratified and rolled during filling, with large differences in compactness, generally in a plastic state. Layer 1A, silty clay (Q4al), yellowish brown to brownish yellow, with a small amount of grayish white kaolin streaks, containing iron oxide, plastic, medium compressibility. Layer 2A, silty clay (Q3al), yellowish brown to brownish yellow, with ferromanganese spots and grayish white kaolin lumps, containing iron oxide, hard plastic, locally plastic, medium compressibility. Layer 2B0, silty clay (Q3al), brownish yellow to light yellow, containing iron oxide, with uniform soil quality, plastic, locally soft plastic, medium compressibility. Layer 2B, silty clay (Q3al), brownish yellow, containing iron oxide, with uniform soil quality, plastic, locally hard plastic, medium compressibility.

[0089] Layer 2C, silty clay (Q3al), brownish yellow to brownish yellow, with ferromanganese nodules and grayish white kaolin lumps, containing iron oxide, hard plastic, locally hard plastic, medium compressibility. Layer 3, silty clay (Qal), reddish brown, locally brownish yellow, formed by weathered residual deposits of bedrock, with ferromanganese nodules and weathered rock debris, hard plastic, locally hard plastic, medium compressibility. Layer 4A, strongly weathered mudstone (K): reddish brown, with developed fissures, the core recovery rate is about 70%, the rock core is relatively broken, in a fragmented state, easily broken by hammering, extremely easy to soften when encountering water, belonging to extremely soft rock. Layer 4B, moderately weathered mudstone (K): reddish brown, with slightly developed fissures, the core recovery rate is generally 80 - 90%,

[0090] the rock core is relatively broken, in a short columnar state, can be broken by hammering, easy to soften when encountering water, belonging to extremely soft rock.

[0091] Distribution and flow direction of groundwater: The groundwater belongs to perched water, mainly stored in the upper soil layers such as 0A, 0B, 0C, and 1A. The recharge source is mainly atmospheric precipitation, and the discharge methods are evaporation and seepage. The triangular well - hole method is used to determine the groundwater flow direction, that is, based on the natural groundwater levels of each monitoring well, the equipotential lines are drawn by interpolation method. The direction perpendicular to the equipotential lines and from high water level to low water level is the groundwater flow direction. By exploring the groundwater depth at 5 well points in 3 plots, it is found that the groundwater flow direction in the plot is from southwest to northeast.

[0092] S2. Demarcate the pollution range once;

[0093] Based on historical data, a process diffusion model is established; the process diffusion model includes a production process module, a groundwater flow module, and a solute transport module; the input of the process diffusion model is various pollutants, and the output is the pollutant emission points, the leakage-prone points, and the pollutant concentration distribution. The positions where the pollutant concentration on the abandoned chemical industrial site exceeds the concentration threshold are demarcated as the primary simulated pollution range; the various pollutants include raw materials, intermediate products, and final products in the production process;

[0094] Among them, the concentration threshold is determined according to the land use of the abandoned chemical industrial site; that is, the concentration threshold refers to the pollutant concentration screening value stipulated according to the land use, which is taken from the implementation standard of the land use. For example, if the land use is construction land, the pollutant concentration screening value refers to the "Soil Pollution Risk Control Standard for Construction Land (Trial) (GB36600—2018)". If the land use is agricultural land, the pollutant concentration screening value refers to the "Soil Pollution Risk Control Standard for Agricultural Land (Trial)". In this embodiment, the "Soil Pollution Risk Control Standard for Construction Land (Trial) (GB36600—2018)" is referred to;

[0095] The leakage-prone points in the production process include: pipe joints, valves, seals of pumps or compressors, openings and seals of storage tanks and containers, sampling points, and instrument interfaces;

[0096] The method for establishing the process diffusion model based on the historical data includes:

[0097] Obtain multiple sets of the historical data;

[0098] According to the data of the production process and the material mass conservation, establish a production process module for simulating the material flow and transformation in the production process; the input of the production process module is the raw material and the emission parameters used to describe the pollutant emission, and the output is the intermediate product or the final product, and the pollutant emission points and the leakage-prone points;

[0099] Based on the formation conditions, hydrogeological information, and the finite difference method or the finite element method, establish a groundwater flow module for simulating the flow path and velocity of groundwater; the input of the groundwater flow module is the raw material, intermediate product, or final product of the production process, the formation conditions and hydrogeological information, and the diffusion parameters used to describe the diffusion of pollutants in groundwater, and the output is the concentration of the raw material, intermediate product, or final product of the production process in groundwater;

[0100] According to the physical and chemical properties of the soil, establish a solute transport module for simulating the migration and diffusion of pollutants in the soil and groundwater; the input of the solute transport module is the physical and chemical properties of the soil and the diffusion parameters used to describe the diffusion of pollutants in the soil, and the output of the solute transport module is the pollutant concentration distribution in the soil;

[0101] Among them, the production process module, the groundwater flow module, and the solute transport module are connected in sequence, and the production process module is connected to the solute transport module.

[0102] Exemplarily, establishing a production process model and a groundwater flow model usually involves various methods and software tools, which can help simulate and analyze complex environmental and engineering problems. The following are the common methods and software used when establishing these models:

[0103] Production process module: Aspen Plus software (which can be used to simulate and optimize chemical production processes); ProII software (suitable for simulating and analyzing production processes in the chemical, petroleum, and natural gas industries); -SuperPro Designer software (used to simulate and design production processes, including cost estimation and economic analysis).

[0104] Groundwater flow module and solute transport module: The Finite Difference Method (FDM) can discretize continuous partial differential equations into difference equations and is suitable for regular grids; the Finite Element Method (FEM) can approximately solve partial differential equations by dividing a continuous domain into finite elements and is suitable for irregular shapes and boundary conditions. The MODFLOW simulation software can be used to establish two-dimensional or three-dimensional models; the GMS (Groundwater Modeling System) modeling software.

[0105] The data of the production process includes process flow information; the formation conditions and hydrogeological information include formation thickness, rock type, porosity, permeability, saturation, groundwater level, groundwater flow direction and velocity; the physical and chemical properties of the soil include soil organic matter content and soil pH value.

[0106] S3. Layout points for detection;

[0107] On the plots within the scope of the first simulation pollution, dense layout points are carried out, and on the plots of other areas of the abandoned chemical industrial plot except the scope of the first simulation pollution, general layout points are carried out. Then, samples are collected and detected at the dense layout points and general layout points, and the concentration detection values of various pollutants are obtained through detection; among them, the samples include soil samples and groundwater samples; the layout density of the dense layout points is 1m×1m to 5m×5m, and the layout density of the general layout points is 6m×6m to 15×15m;

[0108] Exemplarily, for soil site layout: Based on the analysis of the data collected in the early stage, combined with the on-site inspection and personnel interviews, the site layout and sampling work are carried out. According to the plane layout within the plot and the suspected pollution traces found during the on-site inspection, a certain area of the plot is divided into a key concern area and a general concern area. The key concern area is the storage tank area and the adjacent areas nearby, and the general concern area includes the fire water tank, the office and living area, the road, and the open space. Since the floor areas of Plot 1 and Plot 2 in a certain area are both small, less than 1000 m 2 , the site layout refers to the relevant site layout requirements in the "Technical Guidelines for Soil Environmental Investigation and Assessment of Construction Land" (No. 72 of the Ministry of Environmental Protection). In the preliminary investigation stage, when the plot area ≤ 5000 m 2 , the number of soil sampling points is not less than 3; when the plot area > 5000 m 2 , the number of soil sampling points is not less than 6, and it can be appropriately increased according to the actual situation.

[0109] Sampling depth: According to the engineering investigation report of a certain limited liability company, which is 930 m away from this plot, the soil layer distribution of the plot and its surrounding areas is roughly known as follows: the fill soil layer, with a thickness of 0.3 - 2.8 m; the silty clay layer, with a thickness of 0.4 - 10.1 m; the strongly weathered mudstone layer, with a thickness of 0.3 - 1.9 m; the moderately weathered mudstone layer, not penetrated. By analyzing the soil layer distribution of the plot and its surrounding areas, it can be seen that the silty clay layer is relatively thick and can better block the downward migration of pollutants. Therefore, the initial soil drilling depth is set to 6 m, drilling to the silty clay layer. According to the "Technical Guidelines for Monitoring of Soil Pollution Risk Control and Remediation of Construction Land" (HJ25.2 - 2019), the vertical layer division of the surface soil and the underlying soil should be determined by comprehensively considering factors such as the pollutant migration situation, the damage of structures and pipelines, and the soil characteristics. The sampling depth should deduct the thickness of the non-soil hardened layer on the ground surface. In principle, surface soil samples of 0 - 0.5 m should be collected, and the soil sampling interval of 0.5 - 6 m should not exceed 2 m; at least one soil sample should be collected from different soil layers with different properties. When the thickness of the same soil layer is large or obvious pollution traces appear, additional sampling points should be added at this layer according to the actual situation. When sampling, for the sensory indicators such as the color and smell of the soil at different depths, and the on-site rapid detection data, determine whether to increase the sampling depth or stop sampling, and the maximum depth should reach the depth where there is no pollution.

[0110] The samples sent to the laboratory are as follows:

[0111] (1) At least one sample of the topsoil, i.e., 0 - 0.5 m, shall be taken and sent to the laboratory for subsequent assessment of the risks of oral ingestion and skin contact by humans and animals (if necessary). (2) When vertical variations occur in the soil layer properties, at least one soil sample of different soil properties shall be sent to the laboratory. According to the cited engineering investigation report, the strata of the plot are roughly divided into three geological layers, namely fill soil, silty clay, strongly weathered mudstone, and moderately weathered mudstone. (3) During on-site drilling and sampling, samples with abnormal soil color and / or soil odor shall be sent to the laboratory. (4) During on-site rapid testing, soil samples with higher rapid test data shall be sent to the laboratory. In summary, at least 2 - 5 soil samples shall be selected from each borehole and sent to the laboratory.

[0112] Combined with the groundwater flow direction and water level, as well as the soil layout, the groundwater monitoring wells within the plot are arranged in the original plot storage tank area. The groundwater monitoring targets the most vulnerable phreatic aquifer. According to the actual on-site situation, one groundwater monitoring well (W1) with a depth of 6 m is arranged in Plot 1 of a certain area. The groundwater depth of this plot is 0.61 m. Since the characteristic pollutants in this plot involve LNAPL pollutants (petroleum hydrocarbons), the screen opening position should be above the groundwater level. Therefore, the screen depth of the groundwater monitoring well is 0.5 - 6.0 m.

[0113] S4. Model calibration;

[0114] Using the concentration detection values of each pollutant among the multiple pollutants obtained by S3 detection, calibrate the process diffusion model to obtain the calibrated process diffusion model;

[0115] The method for calibrating the process diffusion model using the concentrations of multiple pollutants obtained by the encrypted sampling and general sampling includes:

[0116] When the monitoring value of the pollutant sample obtained by S3 detection is greater than the output value of the process diffusion model, increase the emission parameters in the production process module, or decrease the diffusion parameters in the groundwater flow module and solute transport module;

[0117] When the monitoring value of the pollutant sample obtained by S3 detection is less than the output value of the process diffusion model, decrease the emission parameters in the production process module, or increase the diffusion parameters in the groundwater flow module and solute transport module.

[0118] Exemplarily, the emission parameters and diffusion parameters can be adjusted through sensitivity analysis and optimization algorithms; Sensitivity analysis; By performing sensitivity analysis on each parameter, increase and decrease the parameter values respectively, and observe the changes in the model output. We found that the emission rate has a greater impact on the model output, so we focus more on adjusting the emission rate.

[0119] S5. Redefine the pollution range for the second time;

[0120] Using the calibrated process diffusion model, determine the pollutant concentration diffusion range between the emission point and the leakage-prone point, and define the positions where the pollutant concentration in the emission point and the leakage-prone point exceeds the concentration threshold as the secondary simulated pollution range;

[0121] S6. Layout points for detection;

[0122] On the plots within the secondary simulated pollution range, conduct dense point layout, and on the other plot areas outside the secondary simulated pollution range in the abandoned chemical industrial plot, conduct general point layout. Then, collect samples and detect them at the dense points and general points to obtain the concentrations of various pollutants;

[0123] Specifically, the results of the point layout monitoring in S3 - S6 are as follows:

[0124] A total of 10 soil borehole sampling points (including 1 control point) and 4 groundwater monitoring wells (including 1 control point) were sampled on the surveyed plot. A total of 41 soil samples (including 5 parallel samples) and 6 groundwater samples (including 2 parallel samples) were sent for inspection respectively. (1) Results of the soil pollution status survey: The pollutants detected in the soil within the plot include 6 heavy metals, 26 VOCs (mainly benzene series and chlorinated hydrocarbons), 15 SVOCs (mainly polycyclic aromatic hydrocarbons), petroleum hydrocarbons (C10 - C40), and petroleum hydrocarbons (C6 - C9). Comparing with the risk screening values for the second type of land in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB36600 - 2018), the petroleum hydrocarbons (C10 - C40) (8070 mg / kg) and naphthalene (477.5 mg / kg) in the soil at a depth of 1 m at the 1A02 point in the storage tank area within Plot 1 exceeded the screening values for the second type of land, and the multiples exceeding the concentration threshold were 0.8 times and 5.8 times respectively; the 2,4,6 - trichlorophenol (138 mg / kg) in the soil at a depth of 0.5 m at the 1A02 - 3 point exceeded the screening values for the second type of land, and the multiple exceeding the concentration threshold was 0.07 times. The detected indicators in the soil at other points did not exceed the concentration threshold. The pollutants exceeding the concentration threshold were caused by the plot being used as a storage area for petroleum products in the early stage, improper environmental management measures, and the corrosion of petroleum products on the storage tanks, which easily led to the leakage and migration of petroleum products in the tanks to the soil over a long time.

[0125] (2) Investigation results of groundwater pollution: Pollutants detected in the groundwater within the plot include 8 metals, 29 VOCs (mainly benzene series and chlorinated hydrocarbons), and 15 SVOCs (including phenols, polycyclic aromatic hydrocarbons, and esters). Comparing with the Class IV standard limits of the "Groundwater Quality Standard" (GB / T 14848-2017), the indicators of the groundwater within Plot 1 that exceed the concentration threshold include color, odor and taste, total hardness, anionic surfactant, volatile phenol, permanganate index, iron, manganese, dichloromethane, benzene, 1,2-dichloroethane, toluene, styrene, chlorobenzene, 2,4,6-trichlorophenol, and naphthalene. The concentration of petroleum hydrocarbons (C10-C40) exceeds the screening value for the second type of land use in the Shanghai local standard, and the maximum multiple exceeding the concentration threshold is 33.3 times; the concentration of petroleum exceeds the Class IV standard limits in the "Surface Water Environment Quality Standard" (GB 3838-2002), and the multiple exceeding the concentration threshold is 51.6 times. It can be seen that the groundwater within Plot 1 is severely polluted, and the main pollutants in the groundwater are benzene series, chlorinated hydrocarbons, petroleum hydrocarbons, 2,4,6-trichlorophenol, and naphthalene. There is a good correlation between the pollutants detected in the plot and the pollutants exceeding the concentration threshold and the historical land use of the plot.

[0126] Types and indicators of pollutants detected: Based on the identification of factors such as the odor of samples, XRF, and PID detection results on-site, and referring to the previous on-site investigation, the on-site pollution identification conclusion of the plot, and the characteristic pollutants of surrounding enterprises, the samples are tested.

[0127] Basis for setting detection indicators:

[0128] (1) According to the requirements of the "Soil Environmental Quality Risk Control Standard for Soil Pollution of Construction Land (Trial)" (GB 36600-2018), the soil detection indicators include 45 mandatory items.

[0129] (2) According to the "Groundwater Quality Standard" (GB / T 14848-2017), the groundwater monitoring indicators include some conventional indicators in Table 1 of the standard (excluding microbial indicators and radioactive indicators).

[0130] (3) Based on the analysis of the collected data, the possible characteristic pollutants in the plot are determined. This plot is mainly engaged in the storage, dilution, transportation, and sales of ethylene tar and carbon nine. Therefore, the types of volatile organic pollutants and semi-volatile organic pollutants will be appropriately increased in this detection, and petroleum hydrocarbons (C10-C40) will be added as mandatory items for soil and groundwater.

[0131] The detection indicators for this time are divided into the following categories:

[0132] (1) Soil sample detection indicators: For the collected soil samples, the soil detection indicators include pH, 7 heavy metals and inorganic substances, 62 volatile organic pollutants, 62 semi-volatile organic pollutants, and petroleum hydrocarbons (C10-C40), totaling 133 kinds. (2) Groundwater sample detection indicators: Petroleum hydrocarbons (C10-C40);

[0133] Others: Zinc, aluminum, sodium, iron, manganese, chloride, ammonia nitrogen, oxygen consumption, chloride, visible substances, sulfide, sulfate (SO42-), odor and taste, turbidity, volatile phenol, total hardness (calculated as CaCO3), chromaticity, total dissolved solids, anionic surfactant, petroleum. For the collected groundwater samples, the groundwater detection indicators include pH value, 7 heavy metals, petroleum hydrocarbons (C10-C40), petroleum, 18 conventional water quality indicators, 55 volatile organic pollutants, and 61 semi-volatile organic pollutants, totaling 144 kinds.

[0134] Groundwater sampling: Sampling well washing is carried out 24 hours after well construction and washing. Slowly lower the bailer into the well until it is completely immersed in the water body. Slowly and evenly lift the well pipe. After the well washing effluent reaches 3 times, measure the effluent water quality. If each parameter meets Table 4.3-3, if the requirements still cannot be met after the well washing reaches 5 times the volume, the well washing can be ended.

[0135] Place them in different sample bottles according to different analysis indicators. The water sample should fill the sample bottle. When covering the cap, push it horizontally along the bottle mouth to remove the surface bubbles and then tighten the cap to ensure that the water body in the sample bottle is full without bubbles. Stick a label on the sample bottle body, indicating information such as sample number, sampling date, and sampler. Immediately place it in a refrigerator at 0-4°C for storage after the sample preparation is completed, and send it to the laboratory for analysis within 48 hours.

[0136] Considering the sensitivity of volatile organic compounds in the water sample, the bottling sequence is as follows: (i) For volatile organic compounds, select a 40 mL brown glass bottle as the sampling container. The effluent rate generally does not exceed 100 mL / min to prevent the generation of bubbles. When the water sample overflows the sample bottle to form a convex surface, tighten the bottle cap, invert the sample bottle to ensure that there are no bubbles in the bottle, and collect parallel duplicate samples; (ii) For semi-volatile organic compounds, select a 1000 mL brown glass bottle. Let the water sample overflow the sample bottle and tighten the bottle cap; (iii) For heavy metals, select a 500 mL polyethylene bottle for sampling. When the water sample is significantly turbid during the collection of metal samples, it needs to be filtered with a 0.45 μm filter membrane.

[0137] On-site rapid detection: On-site rapid detection mainly uses portable detection instruments to conduct on-line monitoring of on-site soil samples. The detection indicators include volatile organic compounds and heavy metals. As one of the auxiliary means for on-site judgment of pollution conditions, rapid detection has the characteristics of being rapid and simple. According to the rapid detection results, the soil pollution situation on-site can be roughly judged, and it can be used as the basis for adjusting the positions and depths of monitoring wells during the sampling process. According to the on-site rapid detection results, the heavy metal contents in the investigated plot do not exceed the screening values for soil pollution risks of the second type of land use in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB36600-2018). The maximum PID value is 114.6, which appears in the 1m soil sample at Point 1A02. The soil between 1m and 2m at Points 1A01 and 1A02 has a pungent smell. These two points are both located in the horizontal tank area within Plot 1 of a certain area, indicating that this plot may be contaminated by volatile organic pollutants.

[0138] S7. Judge the pollution risk;

[0139] Judge whether the detection values of pollutants in the samples detected in S3 and S6 exceed the concentration threshold. If the detection value of any pollutant in S3 and S6 exceeds the concentration threshold, it indicates that there is a pollution risk and a health risk assessment is required. If none of them exceed the concentration threshold, it indicates that there is no risk in this plot.

[0140] The land uses of the said plot include: residential land, public management and public service land, commercial service land, industrial and mining storage land, transportation land, water conservancy facility land, agricultural land, and green space and square land.

[0141] The method for judging whether the pollutants sampled and detected in S3 and S6 exceed the concentration threshold according to the land use of the abandoned chemical industrial plot is as follows: According to the land use of the abandoned chemical industrial plot, find the screening values of various pollutants in the standard, compare the detection values of the pollutants obtained from the sampling detection with the said screening values. If the detection value is less than or equal to the screening value, the concentration of the said pollutant does not exceed the concentration threshold. If the detection value is greater than the screening value, the concentration of the said pollutant exceeds the concentration threshold; estimate the pollutant emissions by calculating the amounts of input and output materials; use the finite difference method or the finite element method or other numerical methods to solve the groundwater flow equation. In this embodiment, the finite element method is selected.

[0142] Investigation conclusion: As Figure 2 shown, the investigated plot of this project is divided into Plot 1 of a certain area and Plot 2 of a certain area. The future planned use is park green space (G1). A total of 10 soil borehole sampling points (including 1 control point) and 4 groundwater monitoring wells (including 1 control point) were sampled in this project. A total of 41 soil samples (including 5 parallel samples) and 6 groundwater samples (including 2 parallel samples) were sent for inspection. The test results show that:

[0143] (1) Pollutants detected in the soil within a certain area plot include 6 heavy metals, 26 VOCs (mainly benzene series and chlorinated hydrocarbons), 15 SVOCs (mainly polycyclic aromatic hydrocarbons), petroleum hydrocarbons (C10 - C40), and petroleum hydrocarbons (C6 - C9). Comparing with the risk screening values for the second type of land use in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB 36600 - 2018), in the soil at a depth of 1 m at the 1A02 point in the storage tank area within a certain area plot 1, the petroleum hydrocarbons (C10 - C40) (8070 mg / kg) and naphthalene (477.5 mg / kg) exceed the screening values for the second type of land use, and the multiples of the exceeded concentration thresholds are 0.8 times and 5.8 times respectively; in the soil at a depth of 0.5 m at the 1A02 - 3 point, 2,4,6 - trichlorophenol (138 mg / kg) exceeds the screening values for the second type of land use, and the multiple of the exceeded concentration threshold is 0.07 times. The detected indicators in the soil at other points do not exceed the concentration threshold. The pollutants exceeding the concentration threshold are caused by the improper environmental management measures in the early stage when the certain area plot was used as a storage area for petroleum products, and the corrosion of petroleum products on the storage tanks, which is likely to cause leakage of petroleum products in the tanks and migration to the soil over a long time.

[0144] (2) Pollutants detected in the groundwater within the plot include 8 metals, 29 VOCs (mainly benzene series and chlorinated hydrocarbons), and 15 SVOCs (including phenols, polycyclic aromatic hydrocarbons, and esters). Comparing with the standard limits of Class Ⅳ water in the "Groundwater Quality Standard" (GB / T 14848 - 2017), the indicators exceeding the concentration threshold in the groundwater within a certain area plot 1 include color, odor and taste, total hardness, anionic surfactant, volatile phenol, permanganate index, iron, manganese, dichloromethane, benzene, 1,2 - dichloroethane, toluene, styrene, chlorobenzene, 2,4,6 - trichlorophenol, and naphthalene. The concentration of petroleum hydrocarbons (C10 - C40) exceeds the screening values for the second type of land use in the Shanghai local standard, and the highest multiple of the exceeded concentration threshold is 33.3 times; the concentration of petroleum exceeds the standard limits of Class Ⅳ water in the "Surface Water Environmental Quality Standard" (GB 3838 - 2002), and the multiple of the exceeded concentration threshold is 51.6 times. It can be seen that the groundwater within a certain area plot 1 is seriously polluted, and the main pollutants in the groundwater are benzene series, chlorinated hydrocarbons, petroleum hydrocarbons, 2,4,6 - trichlorophenol, and naphthalene. There is a good correlation between the detected pollutants and the pollutants exceeding the concentration threshold within the plot and the land use history.

[0145] (3) Through the collection of historical data, on - site investigation, personnel interviews, and field sampling and analysis during the site investigation, the content of soil pollutants exceeds the risk screening values for soil pollution of the second type of construction land specified in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB 36600 - 2018), and the concentration of pollutants in the groundwater also exceeds the corresponding standard limits. Therefore, a certain area plot belongs to a contaminated plot.

[0146] In summary, the content of pollutants in the soil within the plot is compared with the pollutant screening values for the second type of land in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Construction Land (Trial)" (GB36600-2018). The maximum concentration of the detected pollutants exceeds the screening value, and the pollutants exceeding the screening value need to be regarded as the concerned pollutants to initiate the risk assessment process. Multiple pollutant indicators in the groundwater samples within the plot exceed the limit values for Class IV water in GB / T14848-2017, and the pollutants exceeding the standard limit values need to be regarded as the concerned pollutants to initiate the risk assessment process.

Claims

1. A method for investigating soil pollution risk in abandoned chemical industry plots, characterized in that: The following steps are involved: S1. Preliminary list of pollutants; Collect historical data of abandoned chemical sites, and list various pollutants based on the historical data; the historical data include production processes, various pollutants involved and the location of each pollutant, stratum conditions and hydrogeological information; S2. Determine the pollution scope once; Based on the data of historical data, a process diffusion model is established; the process diffusion model includes a production process module, a groundwater flow module and a solute transport module; the input of the process diffusion model is a variety of pollutants, and the output is pollutant emission points and leakage points and pollutant concentration distribution, and the location where the pollutant concentration on the abandoned chemical site exceeds the concentration threshold is defined as a simulated pollution range; the various pollutants include raw materials, intermediate products and final products in the production process; Wherein, the concentration threshold is determined according to the land use of the abandoned chemical land; S3, point detection; The encrypted points are arranged on the plots within the scope of the primary simulated pollution, and the general points are arranged on the plots in other areas of the abandoned chemical plots except the scope of the primary simulated pollution, and then samples are collected and tested at the encrypted points and the general points to obtain the concentration detection values ​​of multiple pollutants; wherein the samples include soil samples and groundwater samples; S4, model calibration; Using S3 detection to obtain a concentration detection value of each of the multiple pollutants, calibrating the process diffusion model to obtain a calibrated process diffusion model; S5. Secondary delineation of the pollution scope; The corrected process diffusion model is used to determine the pollutant concentrations at the emission points and the leakage points, and the locations where the pollutant concentrations at the emission points and the leakage points exceed the concentration threshold are defined as the secondary simulation pollution range; S6, point detection; The encrypted points are arranged on the plots within the secondary simulated pollution range, and the general points are arranged on the plots in other areas of the abandoned chemical plots except the secondary simulated pollution range, and then samples are collected and tested at the encrypted points and the general points to obtain the concentrations of multiple pollutants; S7. Determine pollution risk; Determine whether the detection values ​​of pollutants in the samples tested by S3 and S6 exceed the concentration threshold. If the detection value of any pollutant in S3 and S6 exceeds the concentration threshold, it means that there is a pollution risk and a health risk assessment is required. If neither exceeds the concentration threshold, it means that there is no risk for the land.

2. The method for investigating soil pollution risk in abandoned chemical industry plots according to claim 1, characterized in that: The uses of the land include: residential land, public administration and public service land, commercial service land, industrial and mining storage land, transportation land, water conservancy facilities land, agricultural land, as well as green space and square land.

3. The method for investigating soil pollution risk in abandoned chemical industry plots according to claim 1, characterized in that: The method for establishing a process diffusion model based on the data of the historical data includes: Obtaining data of multiple sets of the historical data; According to the production process data and the conservation of material mass, a production process module is established to simulate the material flow and transformation in the production process; the input of the production process module is the raw material and the emission parameters used to describe the pollutant emission, and the output is the intermediate product or the final product and the pollutant emission point and the leakage point; Based on formation conditions, hydrogeological information, and finite difference method or finite element method, a groundwater flow module for simulating the flow path and velocity of groundwater is established; the input of the groundwater flow module is production process raw materials or intermediate products or final products, formation conditions and hydrogeological information, and diffusion parameters for describing the diffusion of pollutants in groundwater, and the output is the concentration of production process raw materials or intermediate products or final products in groundwater; According to the physical and chemical properties of soil, a solute transport module is established to simulate the migration and diffusion of pollutants in soil and groundwater. The input of the solute transport module is the physical and chemical properties of soil and the diffusion parameters used to describe the diffusion of pollutants in soil. The output of the solute transport module is the distribution of pollutant concentration in soil. Wherein, the production process module, the groundwater flow module and the solute transport module are connected in sequence, and the production process module is connected to the solute transport module.

4. The method for investigating soil pollution risk in abandoned chemical industry land according to claim 3, characterized in that: The data of the production process includes process flow information; the formation conditions and hydrogeological information include formation thickness, rock type, porosity, permeability, saturation, groundwater level, groundwater flow direction and speed; the physical and chemical properties of the soil include soil organic matter content and soil pH value.

5. The method for investigating soil pollution risk in abandoned chemical sites according to claim 3, characterized in that: In S3 and S6, the density of the encrypted distribution points is 1m×1m to 5m×5m, and the density of the general distribution points is 6m×6m to 15×15m.

6. The method for investigating soil pollution risk in abandoned chemical industry land according to claim 3, characterized in that: The method for correcting the process diffusion model in S4 includes: When the concentration detection value of the pollutant obtained in S3 is greater than the output value of the process diffusion model, the emission parameter in the production process module is increased, or the diffusion parameter in the groundwater flow module and the solute transport module is decreased; When the pollutant concentration detection value obtained in S3 is less than the output value of the process diffusion model, the emission parameters in the production process module are reduced, or the diffusion parameters in the groundwater flow module and the solute transport module are increased.

7. The method for investigating soil pollution risk in abandoned chemical industry land according to claim 1, characterized in that: The leak-prone points in the production process include: pipeline connections, valves, pump or compressor seals, tank and container openings, seals, sampling points and instrument interfaces.

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