Test method for obtaining threshold permeability coefficient and distribution coefficient of uncalibrated pollutant soil

Abstract

The invention discloses an acquisition test method for calculating an uncalibrated pollutant soil threshold permeability coefficient and a distribution coefficient, and belongs to the field of soil threshold calculation. According to the method, a sampling point is selected on a site, an annular groove is dug to fix a soil column so as to collect permeability coefficient determination samples, and meanwhile distribution coefficient samples are collected at multiple points on the periphery of the sampling point. When the permeability coefficient is measured, a Markov bottle is used for supplying water and calculation is performed according to the Darcy law; a static adsorption test is carried out on the distribution coefficient, and the fixed proportion of the pollutant solutions with different concentrations in the soil is measured, so that the distribution coefficient is obtained. The method solves the problems that a traditional soil column sampling structure is damaged and the representativeness of a distribution coefficient sample is insufficient, the permeability coefficient and the distribution coefficient can be accurately obtained, a reliable basis is provided for calculating a soil threshold value for protecting underground water, and the method is suitable for risk assessment of uncalibrated new pollutants in a chemical field.

Description

Technical Field

[0001] The present invention belongs to the field of soil threshold calculation, and in particular relates to a test method for obtaining the soil threshold permeability coefficient and distribution coefficient of uncalibrated pollutants. Background Art

[0002] Groundwater plays a crucial role in my country's economic and social development. Soil has a certain capacity to accommodate and immobilize pollutants. Establishing soil thresholds based on the goal of protecting the safe use of groundwater plays a crucial role in understanding and preventing groundwater pollution risks.

[0003] my country's current research on soil thresholds for groundwater protection is still in its infancy. For uncalibrated new pollutants with a high detection rate in chemical sites, such as pesticides (such as chlorpyrifos, triclosan, methyl parathion, dichlorvos), perfluorinated compounds (such as PFOA, PFOS, PFBS), and antibiotics (carbamazepine, oxytetracycline, ciprofloxacin), their toxicological indicators are unclear, their potential hazards are great, and there is no relevant soil threshold guidance, making it impossible to conduct effective risk assessment of groundwater pollution in chemical sites, which restricts the remediation and sustainable use of chemical sites.

[0004] The migration of pollutants into groundwater is influenced by numerous factors, including the nature of the pollutants, soil composition and physical and chemical properties, and site hydrogeological conditions. The soil permeability coefficient and the distribution coefficient of pollutants in the soil are essential key parameters for calculating the soil threshold for groundwater protection. Currently, the permeability coefficient is primarily determined through soil column leaching experiments, using Darcy's law. However, during the sampling process, the soil columns are difficult to fix and easily disperse, requiring recompaction in the laboratory before conducting leaching experiments. This alters the soil pore structure and results in significant deviations in the obtained soil permeability coefficient. Furthermore, the soil distribution on a site is uneven, so the distribution coefficient samples obtained using traditional fixed-point sampling methods are less representative of the site. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a test method for obtaining the threshold permeability coefficient and distribution coefficient of soil for uncalibrated pollutants. The method can fully fix the soil column that needs to be leached, retain the pore structure of the soil column, avoid the operation of breaking up and re-compacting, and improve the accuracy of obtaining the soil permeability coefficient. During the soil sample collection process, the distribution coefficient sample can be collected simultaneously, providing a reliable basis for calculating the soil threshold for protecting groundwater.

[0006] The specific technical solution adopted in the present invention is:

[0007] A test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil, comprising the following steps:

[0008] S1. Select sampling points within the site where the pollutants have not been calibrated;

[0009] S2. Dig a soil column at the sampling point and collect a sample for measuring the permeability coefficient;

[0010] S3. Take several points on the circumference within a radius r around the sampling point as samples for determination of the distribution coefficient;

[0011] S4. Measure the permeability coefficient and distribution coefficient of the collected samples respectively.

[0012] The method for collecting samples for the determination of permeability coefficient is as follows: an annular groove is dug around the sampling point, and the core of the annular groove is the soil column to be sampled. After the annular groove is dug to the designed depth, a nylon mesh is wrapped around the side wall of the soil column. After the wrapping is completed, polyurethane foam is evenly sprayed on the nylon mesh. When the polyurethane foam has not yet completely solidified, the sampling glass tube is put on the outside of the soil column. The polyurethane foam expands and fills the space between the soil column and the glass tube. After the polyurethane foam solidifies, the soil column is shoveled off from the bottom, and the complete soil column is fixed in the sampling glass tube to complete the collection of the measurement sample.

[0013] After the annular groove is excavated, the loose soil and debris at the top of the soil column formed in the core are cleaned, and the loose soil blocks on the side walls of the soil column are cut until the diameter of the soil column reaches a predetermined size.

[0014] The length of the glass tube is greater than the length of the soil column to be sampled. After the soil column is cut off, the glass tube is inverted and the soil column is cleaned until the soil column reaches a predetermined length. Quartz sand and gravel of different diameters are laid in the cleaned cavity in turn. Nylon mesh cut into sheets is used to fill the remaining space to form a filter layer and a sealing plug is inserted into the end of the glass tube so that the sealing plug abuts the filter layer. The glass tube is turned over so that the top surface of the soil column faces upward, a nylon mesh is laid on the top surface of the soil column to form a filter layer, and a sealing plug is inserted. A water pipe that passes through the plug body is provided in the middle of the sealing plug.

[0015] The diameter of the quartz sand is 1-2 mm and the diameter of the gravel is 4-5 mm, and the aperture of the nylon mesh is smaller than the diameter of the gravel.

[0016] The test method for the permeability coefficient is to use a Malchnitz flask to supply water from the bottom of the soil column to saturate the soil column, change the position of the water inlet and outlet, and change the water supply from top to bottom. The Malchnitz flask is adjusted to a set height and fixed. The water output of the soil column is recorded at fixed time intervals until the flow rate difference is less than 5% for three consecutive times, and the permeability coefficient is calculated using Darcy's law.

[0017] The outer diameter of the annular groove is r, and the value range of r is 0.5-1.5m. The method for collecting samples for determining the distribution coefficient is as follows: several points are selected on the outer circumference of the annular groove, and the side wall surface of the annular groove corresponding to the point is scraped from bottom to top along the vertical direction using a sampling tube to scrape soil samples. Each point is scraped at least 3 times, and samples at different points are respectively encapsulated in different sampling tubes.

[0018] The test method for the distribution coefficient is as follows: the sample soil obtained by sampling is dried and sieved to separate impurities, 2 g of the soil to be tested is placed in a test tube, 20 mL of pollutant solution with different initial mass concentrations is added respectively, and the initial mass concentration of the pollutant solution is set to 5, 10, 20, 40, 50, 60, 80, and 100 mg / L. The sample is oscillated at a constant temperature of 25° C. for 48 hours and then allowed to stand for at least 1 hour. The oscillation frequency is 200 r / min. After standing, the supernatant is taken into a centrifuge tube and centrifuged for 10 minutes. The centrifuge speed is 3000 r / min. After centrifugation, it is filtered through a 0.45 μm filter membrane. After standing, 1 mL of the supernatant is taken to test the pollutant concentration. The solid phase adsorption amount of the uncalibrated pollutant fixed in the soil can be obtained by comparing it with the initial concentration of the pollutant solution. The ratio of this value to the liquid phase concentration in the solution is the distribution coefficient.

[0019] The beneficial effects of the present invention are:

[0020] This method uses an annular groove excavation and a nylon mesh and polyurethane foam to secure the soil column, avoiding the traditional method of breaking up the soil and recompacting it. This method fully preserves the original pore structure of the soil column, making the obtained permeability coefficient more accurate to the actual site conditions and reducing measurement deviations caused by soil structural damage. The distribution coefficient samples are collected at multiple points around the permeability coefficient sampling point, covering the spatial distribution differences of the site soil. Compared with traditional single-point sampling, the samples better reflect the regional soil characteristics and improve the reliability of the distribution coefficient data. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments:

[0022] The present invention is a test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil, comprising the following steps:

[0023] S1. Select sampling points within the site where the pollutants have not been calibrated;

[0024] S2. Dig a soil column at the sampling point and collect a sample for measuring the permeability coefficient;

[0025] S3. Take several points on the circumference within a radius r around the sampling point as samples for determination of the distribution coefficient;

[0026] S4. Measure the permeability coefficient and distribution coefficient of the collected samples respectively.

[0027] The present invention completes the sampling of permeability coefficient and distribution coefficient at the same time by setting comprehensive sampling points. Since the distribution coefficient is closely related to the soil composition, by sampling at multiple points, conducting separate tests and taking the average value in the later stage, the test results can be expanded from the sampling point to the surface of the annular groove centered on the sampling point, thereby improving the representativeness of the sample.

[0028] Furthermore, the method for collecting samples for measuring the permeability coefficient of the present invention is as follows: an annular groove is excavated around the sampling point, the core of the annular groove is the soil column to be sampled, and after the annular groove is excavated to the designed depth, a nylon mesh is wrapped around the side wall of the soil column. After the wrapping is completed, the nylon mesh is evenly sprayed with polyurethane foam glue, and when the polyurethane foam glue has not yet completely solidified, the sampling glass tube is put on the outside of the soil column, and the polyurethane foam glue expands and fills the space between the soil column and the glass tube. After the polyurethane foam glue solidifies, the soil column is shoveled off from the lower end, and the complete soil column is fixed in the sampling glass tube to complete the collection of the measurement sample.

[0029] The design depth of a single annular trough is 50-80cm. Depending on the degree of pollutant penetration, after removing the surface soil column from the previous annular trough, the bottom of the previous annular trough can be dug deeper to form a second soil column and package it separately. This cycle will be repeated until the total sampling depth reaches the potential groundwater diffusion depth in the area where the site is located.

[0030] The soil column is further wrapped with nylon mesh, and the nylon mesh can be bundled with a rolling belt, so that the nylon mesh can be stably hung on the outside of the soil column, and at the same time restrain the soil column to prevent it from loosening. At the same time, the nylon mesh plays a bearing role for the sprayed polyurethane foam. On the one hand, the polyurethane foam penetrates into the nylon mesh and directly contacts the soil to form a direct seal on the side wall of the soil column, and at the same time fills the pores on the side wall between the nylon mesh and the soil column. With the nylon mesh as the skeleton, the constraint on the soil column is further improved to prevent it from spreading and protect the original soil structure of the soil column.

[0031] Since the situation of uncalibrated new pollutants in chemical sites is relatively complicated, in order to avoid excessive interference of polyurethane foam on potential uncalibrated new pollutants, the side walls of the soil column can be wrapped with plastic wrap before wrapping the nylon mesh. Then, by wrapping the nylon mesh and spraying polyurethane foam, the polyurethane foam penetrates between the nylon mesh and the plastic wrap, which has the effect of pushing and fixing the plastic wrap with the help of the nylon mesh, so that the plastic wrap is in full contact with the soil column, hindering the formation of water flow channels on the side walls of the soil column to avoid the formation of fluid short circuits, making the permeability coefficient measurement results more accurate.

[0032] Furthermore, after the annular groove is excavated, loose soil and debris are removed from the top of the soil column formed in the core, and loose soil blocks on the side walls of the soil column are cut until the diameter of the soil column reaches a predetermined size. The length of the glass tube is greater than the length of the soil column to be sampled. After the soil column is cut, the glass tube is inverted and the soil column is cleaned until the soil column reaches the predetermined length. Quartz sand and gravel of different diameters are then laid in the cleaned cavity. Nylon mesh cut into sheets is used to fill the remaining space to form a filter layer, and a sealing plug is inserted into the end of the glass tube so that the sealing plug abuts the filter layer. The glass tube is flipped so that the top surface of the soil column faces upward, nylon mesh is laid on the top surface of the soil column to form a filter layer, and a sealing plug is inserted. A water pipe is provided in the middle of each sealing plug that passes through the plug body. The diameter of the quartz sand is 1-2 mm, and the gravel is 4-5 mm. The pore size of the nylon mesh is smaller than the diameter of the gravel. The test method for the permeability coefficient is to use a Malchnitz flask to supply water from the bottom of the soil column to saturate the soil column, swap the positions of the water inlet and outlet, and change the water supply from top to bottom. The Malchnitz flask is adjusted to a set height and fixed, wherein the set height is that the height of the Malchnitz flask water outlet is about 3-5 cm higher than the height of the soil column. The water output of the soil column is recorded at fixed time intervals, wherein the fixed time interval is 10-15 minutes, and the test ends when the flow rate difference is less than 5% for three consecutive times. The permeability coefficient is calculated using Darcy's law.

[0033] This method forms support for the lower end of the soil column by laying quartz sand and gravel at the bottom of the soil column, preventing the soil column from collapsing and scattering after it reaches a water-saturated state. At the same time, the filter layer blocks the outflow of soil particles from the bottom, preventing inaccurate water output records.

[0034] Furthermore, the outer diameter of the annular groove is r, with a value of r ranging from 0.5 to 1.5 m, preferably 1 m. The method for collecting samples for determining the distribution coefficient is to select several points on the outer circumference of the annular groove, and scrape soil samples from the sidewall surface of the annular groove corresponding to these points vertically from bottom to top using a sampling tube. Each point is scraped at least three times, and samples from different points are respectively encapsulated in different sampling tubes. Each sampling point sample is individually encapsulated and measured to obtain data on the single-point distribution coefficient. By taking the average or median value, the soil distribution coefficient within the annular groove can be more accurately obtained. Multiple sets of data can also be used to analyze the spatial coefficient of variation of the site soil, providing data support for further analysis of groundwater contamination distribution.

[0035] The test method for the distribution coefficient is as follows: drying the sample soil obtained by sampling, sieving to separate impurities, taking 2g of the soil to be tested into a group and placing it in a test tube, adding 20mL of pollutant solution with different initial mass concentrations, respectively, the initial mass concentration of the pollutant solution is set to 5, 10, 20, 40, 50, 60, 80, and 100 mg / L, oscillating at a constant temperature of 25°C for 48 hours and then standing for at least 1 hour, the oscillation frequency is 200r / min, after standing, taking the supernatant into a centrifuge tube and centrifuging for 10 minutes, the centrifuge speed is 3000r / min, after centrifugation, passing through a 0.45μm filter membrane, taking 1mL of the supernatant after standing to test the pollutant concentration, and comparing it with the initial concentration of the pollutant solution to know the solid phase adsorption amount of the uncalibrated pollutant fixed in the soil, and the ratio of this value to the liquid phase concentration in the solution is the distribution coefficient.

Claims

1. A test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil, characterized by: The following steps are included: S1. Select sampling points within the target site for uncalibrated pollutants; S2. Dig a soil column at the sampling point and collect a sample for measuring the permeability coefficient; S3. Take several points on the circumference within a radius r around the sampling point as samples for determination of the distribution coefficient; S4. Measure the permeability coefficient and distribution coefficient of the collected samples respectively.

2. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 1, characterized in that: The method for collecting samples for the determination of the permeability coefficient is as follows: an annular groove is dug around the sampling point, and the core of the annular groove is the soil column to be sampled. After the annular groove is dug to the designed depth, a nylon mesh is wrapped around the side wall of the soil column. After the wrapping is completed, polyurethane foam is evenly sprayed on the nylon mesh. When the polyurethane foam has not yet completely solidified, the sampling glass tube is put on the outside of the soil column. The polyurethane foam expands and fills the space between the soil column and the glass tube. After the polyurethane foam solidifies, the soil column is shoveled off from the lower end, and the complete soil column is fixed in the sampling glass tube to complete the collection of the measurement sample.

3. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 2, characterized in that: After the annular groove is excavated, the loose soil and debris at the top of the soil column formed in the core are cleaned, and the loose soil blocks on the side walls of the soil column are cut until the diameter of the soil column reaches a predetermined size.

4. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 2, characterized in that: The length of the glass tube is greater than the length of the soil column to be sampled. After the soil column is cut off, the glass tube is inverted and the soil column is cleaned until the soil column reaches a predetermined length. Quartz sand and gravel of different diameters are laid in the cleaned cavity in turn. Nylon mesh cut into sheets is used to fill the remaining space to form a filter layer and a sealing plug is inserted into the end of the glass tube so that the sealing plug abuts the filter layer. The glass tube is turned over so that the top surface of the soil column faces upward, a nylon mesh is laid on the top surface of the soil column to form a filter layer, and a sealing plug is inserted. A water pipe that passes through the plug body is provided in the middle of the sealing plug.

5. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 4, characterized in that: The diameter of the quartz sand is 1-2 mm and the diameter of the gravel is 4-5 mm, and the aperture of the nylon mesh is smaller than the diameter of the gravel.

6. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 1, characterized in that: The test method for the permeability coefficient is to use a Malchnitz flask to supply water from the bottom of the soil column to saturate the soil column, change the position of the water inlet and outlet, and change the water supply from top to bottom. The Malchnitz flask is adjusted to a set height and fixed. The water output of the soil column is recorded at fixed time intervals until the flow rate difference is less than 5% for three consecutive times, and the permeability coefficient is calculated using Darcy's law.

7. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 2, characterized in that: The outer diameter of the annular groove is r, and the value range of r is 0.5-1.5m. The method for collecting samples for determining the distribution coefficient is as follows: several points are selected on the outer circumference of the annular groove, and the side wall surface of the annular groove corresponding to the point is scraped from bottom to top along the vertical direction using a sampling tube to scrape soil samples. Each point is scraped at least 3 times, and samples at different points are respectively encapsulated in different sampling tubes.

8. The test method for obtaining the threshold permeability coefficient and distribution coefficient of uncalibrated pollutants in soil according to claim 1, characterized in that: The test method for the distribution coefficient is as follows: drying the sample soil obtained by sampling, sieving to separate impurities, taking 2g of the soil to be tested into a group and placing it in a test tube, adding 20mL of pollutant solution with different initial mass concentrations, respectively, the initial mass concentration of the pollutant solution is set to 5, 10, 20, 40, 50, 60, 80, and 100 mg / L, oscillating at a constant temperature of 25°C for 48 hours and then standing for at least 1 hour, the oscillation frequency is 200r / min, after standing, taking the supernatant into a centrifuge tube and centrifuging for 10 minutes, the centrifuge speed is 3000r / min, after centrifugation, passing through a 0.45μm filter membrane, taking 1mL of the supernatant after standing to test the pollutant concentration, and comparing it with the initial concentration of the pollutant solution to know the solid phase adsorption amount of the uncalibrated pollutant fixed in the soil, and the ratio of this value to the liquid phase concentration in the solution is the distribution coefficient.