What are the methods for soil pollution investigation?

At present, soil pollution in China is divided into two major areas, namely farmland soil pollution and urban relocation factory soil pollution. This article first explains the investigation of relocation factory soil pollution (i.e. contaminated sites). In 2014, China has issued relevant guidelines for the investigation, monitoring, and evaluation of contaminated sites. The official explanation of relevant professional terms can be found in the relevant guidelines: "Technical Guidelines for Site Environmental Investigation" and "Technical Guidelines for Site Environmental Monitoring". Here are some site pollution investigation methods.

1 Drilling method

That is, monitoring wells are established in the investigation area to obtain groundwater samples at different depths, and soil sampling at specified depths can be carried out during the well construction process. This method is the most widely used. The tools currently used for drilling are triple drilling and Geoprobe drilling rigs. Geoprobe has a small body and is easy to operate. It is particularly advantageous for taking soil samples containing volatile organic compounds. After development, Geoprobe can not only take soil and groundwater samples, but also improve Geoprobe to take soil gas, obtain the hydraulic conductivity coefficient of the aquifer, test the geological structure of the profile, and test the total volatile organic compound concentration at a specified depth during the drilling process. However, it also has disadvantages: sampling depth limitation; monitoring well mouth is small. As far as we know, soil sampling depth can reach 20m underground, and the well mouth diameter is about 5-10cm. If the water content of the site is small, it cannot meet the requirements of the pumping experiment. The triple drill can reach the specified depth (can reach below 100m in certain areas), and the specified well monitoring well can also be obtained by using different drill bits, but because water needs to be added during drilling, cross contamination may occur when taking soil samples, and it is impossible to obtain a good original soil sample.

The samples taken out by drilling can be analyzed to obtain accurate pollutant concentration data, but the cost of drilling is high. If you want to obtain detailed distribution of soil and groundwater pollutants on the site, you need to drill more wells, which increases the cost of the survey. Therefore, geophysical exploration methods have been developed in recent years.

2 Geophysical Exploration (Geophysical Exploration)

Experience shows that effective geophysical methods include resistivity, geological radar, electromagnetic wave method, seismic reflection and refraction wave method, natural gamma logging, magnetic method, etc. Among them, resistivity/conductivity method, electromagnetic method, geological radar, etc. can directly detect abnormal conditions caused by the presence of pollutants. Although seismic reflection and refraction wave method, natural gamma logging and magnetic method cannot directly detect the specific range of pollutants, they can detect underground structures and find out where pollutants may exist, providing a strong basis for successfully surveying the scope of pollution. The most commonly used method for site investigation is high-density resistivity method. It is to derive the range of soil that may be contaminated by the fact that the resistivity of contaminated soil is lower than that of normal soil, especially for the detection of non-aqueous liquids.

3. High-density resistivity method

In actual site surveys, geophysical exploration can be combined with drilling methods. Drilling and sampling can be performed in high-pollution areas determined by geophysical exploration to determine the pollution concentration and provide a data basis for remediation.