Sampling point of soil environmental monitoring

1. Simple random

The monitoring unit is divided into grids, and each grid has a number. After determining the sample number of sampling points, randomly select the samples with the specified sample number, and the grid number corresponding to the sample number is the sampling point. Random numbers can be obtained by rolling dice, drawing lots and looking up a random number table.

2. Random grouping

According to the collected data, if there are obvious soil types in the monitoring area, the area can be divided into several blocks, with uniform pollutants in each block and obvious differences between blocks. Take each block as a monitoring unit, and then randomly distribute points in each monitoring unit. On the premise of correct block distribution, the representativeness of block distribution is better than simple random distribution. If the block distribution is incorrect, the effect of block distribution may be counterproductive.

3. The system is random

The monitoring area is divided into several parts with equal area (grid division), and a sampling point is arranged in each grid, which is called system random distribution. If the content of soil pollutants in the region changes greatly, the representativeness of samples collected by random distribution system is better than that of simple random distribution.

Number of distribution points

The number of soil monitoring points should meet the basic requirements of sample size, that is, the number of samples calculated by mean square deviation, absolute deviation, coefficient of variation and relative deviation is the lower limit of sample size, and the number of soil points in actual work should be determined according to the purpose, accuracy and environmental conditions of the investigation area.

Generally, each monitoring unit is required to have at least 3 points.

According to the different precision of regional soil environment investigation, the grid spacing points can be selected as 2.5km, 5km, 10km, 20km and 40km, and the number of grid nodes in the region is the number of soil sampling points.

Sample collection

Sample collection is usually carried out in three stages:

Pre-sampling: according to the background data and field investigation results, a certain number of samples are collected for analysis and determination, which is used to preliminarily verify the spatial heterogeneity of pollutants, judge the degree of soil pollution, and provide a basis for making a monitoring plan (selecting distribution methods and determining monitoring items and sample numbers). Pre-sampling can be carried out at the same time as field investigation.

Formal sampling: according to the monitoring plan, carry out on-site sampling.

Supplementary sampling: after the formal sampling test, it is found that the layout of sampling points does not meet the overall design requirements, and additional sampling points need to be added for supplementary sampling.

Small area soil pollution investigation and sudden soil pollution accident investigation can be directly sampled.

Sample circulation

At the sampling site, samples must be checked with the sample registration form, sample labels and sampling records one by one, and then classified and packaged.

Strictly prevent the loss, confusion and pollution of samples during transportation. Photosensitive samples should be stored away from light.

The soil samples are sent to the laboratory by special personnel, and the sample sender and the sample receiver check and verify the samples at the same time, and sign the sample handover form for confirmation. Sample handover forms will be kept by both parties for future reference.

Sample preservation

According to the sample name, number and particle size.

Samples of unstable components, such as easily decomposed or volatile components, should be transported at low temperature and sent to the laboratory for analysis and testing as soon as possible. The test project needs fresh soil samples. After collection, it should be stored in a sealable polyethylene or glass container, protected from light, at a temperature below 4℃, and the samples should be put into the container. Avoid using containers made of materials that contain components to be tested or interfere with the test to store samples. Soil samples used to determine organic pollutants should be stored in glass containers.

Retained sample

The retained samples are stored in the sample library. The remaining samples after analysis and sampling are also handed over to the sample library for preservation after all data are reported. After analysis, the remaining samples are generally kept for half a year, and the remaining samples are generally kept for 2 years. Special, rare, arbitration and controversial samples should generally be kept permanently.