Note: 1 - most appropriate method; 2 - appropriate method; 3 - more appropriate method; 4 - inappropriate method。
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Figure 3. 4
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Figure 3. 4 soil survey site approach
Among them, the system grid dot method is one of the simple, operational and most appropriate. The system gridd points range is determined by: the presence of non-balanced point sources of contamination at the site (united states epa methodology) would be appropriate to determine the spacing of survey points using the probability capture source method; to determine the average scale of visible sources at the site on the basis of large-scale ground-scale survey measurements; and to establish a table of probability values for a capture source such as 94 per cent (i. E. 6 per cent error rate) based on the site survey accuracy requirements, to reverse the length of the square grid of the site。
The number of sampling sites for soil contamination routes at contaminated sites should be determined by the size of the site, the nature of the source, the type of soil on the site, the extent of contamination. In general, the number of soil sampling sites should be laid at no less than 2-3 sources per source。
3. 4. 1. 2 location of preliminary sampling sites for soil environmental survey
1 several potentially more polluting plots may be selected for monitoring as soil pollutant identification, based on the functionality of use and contamination characteristics of the site. In principle, monitoring points should select the centre of the plot or areas with apparent contamination, such as production workshops, sewage lines, waste dumps, etc。
For sites that are more evenly contaminated (including the type and level of contamination) and sites that have been severely damaged (including demolition, historical alteration) the site may be sampled at the centre of each plot using a systematic random dotage based on its shape。
The number and depth of monitoring points should be determined by the findings of the site area, the type of contamination and the different functional areas used。
For each monitored plot, the vertical orientation of the surface and deep soils should be defined by taking into account such factors as the transport of pollutants, constructions and pipelines, and soil characteristics. The depth of the sample should be reduced by the thickness of the non-soil scrutinization layer of the surface, and in principle it is recommended that the spacing of the samples at the depth of 3 m be 0. 5 m, at the intervals of 3 to 6 m, at the intervals of 1 m, 6 m and 2 m for groundwater samples, depending on the circumstances。
In general, the depth of sampling of deep soils should be determined on the basis of site environmental findings and on-site conditions, with maximum depth until uncontaminated。
Soil samples are divided into surface and deep soil. The depth of sampling of deep soils should take into account the depth at which the contaminants may be released and transported (e. G., deep underground pipes and storage tanks), the nature of the contaminants, the soil's mass and perforation, groundwater table and backfilling. On-site detection equipment can be used to determine sampling depth. When taking samples containing volatile contaminants, disturbances in the samples should be minimized and their equalisation prohibited. After taking soil samples, suitable containers should be selected for preservation, depending on, inter alia, the physical nature of the contamination. Soil samples containing mercury or organic pollutants should be stored and transported at temperatures below 4°c, with reference to hj 25. 2。
Soil sampling should be recorded on site, including, inter alia, the name and number of the sample, meteorological conditions, the timing of the sample, the location of the sample, the depth of the sample, the sample's location, the colour and smell of the sample, the results of the field test and the sampler。
3. 4. 1. 3 the following needs attention in soil sampling sites:
When site contamination is localized and hotspots (contaminated plots identified in the first and second stages of preliminary sampling) are clearly distributed, a diagnostic site method should be used to conduct intensive sampling in and around the contaminated hotspots, which should be slightly larger than the perceived contamination. When the range of defined hotspot areas is larger, smaller grid units can also be used, using grid-encrypted locations in and around hotspots. In non-hot spots, a small number of sampling sites should be set up at random to minimize miscalculation. The number of random spots shall not be less than 5 per cent of the total number of places。
If soil is to be sampled, it may be divided into a grid of 1 to 9 equal areas, depending on the level of contamination and area of each monitored plot, and sampled at each grid centre, making a mixed sample of the same layer of soil (except for sites contaminated by volatile organic matter)。
The placement of deep sampling sites should be determined on the basis of the vertical distribution patterns of contaminants revealed by preliminary sampling, in accordance with the requirements of the initial sampling phase of contamination and the technical guidelines for site environmental monitoring (hj 25. 2)。
Where detailed sampling does not meet the requirements for risk assessment or for site remediation, one or more additional samplings should be conducted using a diagnostic placement method until there is sufficient data to delineate the remediation. When necessary, surveys of soil gas, site populations and flora and fauna can be conducted to conduct deeper risk assessments。
3. 4. 1. 4 geophysical survey techniques for deep soil pollution investigation
Geophysical methods involved in site surveys of contamination include geological radar, high-density electrical resistance, integrated well detection techniques, etc. In practice, a variety of search methods are often required to conduct site surveys, and the range of applications and characteristics of commonly used search methods are shown in table 3. 7。
Table 3. 7 scope and characteristics of application of commonly used tracing methods
