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At present, soil pollution in China is divided into two parts, namely farmland soil pollution and urban relocation factory soil pollution. This paper first introduces the investigation of soil pollution (i.e. contaminated site) in the relocated factory. In 2014, China issued relevant guidelines for the investigation, monitoring and evaluation of contaminated sites. For the official explanation of relevant terms, please refer to the relevant Guidelines: Technical Guidelines for Site Environmental Investigation and Technical Guidelines for Site Environmental Monitoring. The following will introduce some site contamination investigation methods.

1. Drilling method

That is, monitoring Wells are set up in the survey area to obtain groundwater samples at different depths, and soil samples at specified depths can be taken during well construction. The method is the most widely used, and currently the tools used for drilling are the triple rig and the Geoprobe rig. Geoprobe has a small body and is easy to operate, which is especially advantageous for taking soil samples containing volatile organic compounds. After development, Geoprobe can not only take soil and groundwater samples, but also take soil gas and obtain aquifer hydraulic conductivity. Test the geologic structure of the profile and test the total volatile organic compounds concentration at the specified depth during drilling. But it also has some disadvantages: sampling depth limit; The monitoring well head is small. As far as is known, the depth of soil sampling can reach 20m underground, and the diameter of well head is about 5-10cm. If the water content of the site is small, it cannot meet the requirements of pumping experiment. Triples can be drilled to specified depths (up to 100m in certain areas), and designated monitoring Wells can be obtained by using different drill bits. However, due to the need to add water during drilling, cross-contamination may occur during soil sample collection, and good undisturbed soil samples may not be obtained.

Geoprobe

Accurate pollutant concentration data can be obtained through analysis of the samples taken by drilling method. However, the cost of drilling is high. In order to obtain the detailed distribution of pollutants in soil and groundwater at the site, it needs to be drilled with infill Wells, which increases the investigation cost. Therefore, geophysical prospecting methods have been developed in recent years.

2 Geophysical Exploration (geophysical method)

Experience shows that the effective geophysical exploration methods include resistivity method, geological radar method, electromagnetic wave method, seismic reflection refraction wave method, natural gamma logging, magnetic method, etc. Among them, resistivity/conductivity method, electromagnetic method, geological radar and other methods can directly detect the abnormal situation caused by the presence of pollutants. Seismic reflection refraction wave method, natural gamma logging and magnetic method can not directly detect the specific range of pollutants, but can detect the underground structure, and identify the possible existence of pollutants. It provides a strong basis for the successful survey of pollution scope. The most commonly used method for site investigation is high density resistivity. It is to obtain the possible contaminated soil range through the electrical resistivity of contaminated soil is lower than that of normal soil, especially for the detection of non-aqueous liquid.

3.High density resistivity method

In the actual site investigation, the geophysical method and drilling method can be combined to determine the concentration of pollution in the high-pollution area determined by the geophysical method.