The Nature and Survey of Soil Pollution - Environmental Geomechanics - page 333

documents and on exchanges with former workers) together with a site inspection
and investigation of the site environment. A first survey with some borings,
samplings and analysis is carried out.
− The simplified hazard evaluation which is conducted based on a
methodological grid (www.fasp.info). The site may be classified in one of the three
following categories:
- Class 1: Sites presenting some hazards that make a detailed diagnosis
compulsory. This diagnosis will result in a detailed hazard evaluation . Grades are
given for around 30 parameters within the scheme source → environment → target .
Examples of parameters are: contaminant solubility, permeability of the soil layers,
distance to the target, intensity of existing impacts (if any), etc. The site is then
classified accordingly.
- Class 2: Sites with limited impact or hazard only requiring monitoring with
some regular analyses.
- Class 3: Sites than can be considered normal with no particular further
attention required.
The detailed diagnosis includes standard in situ investigation methods (borings,
piezometers and laboratory characterization) and more sophisticated in situ
investigation methods that will be detailed at a later stage together with laboratory
analyses of contaminated soils (see [BRG 01] for more details).
The conclusions of the detailed hazard evaluation help us estimate whether
hazards are acceptable or not and, consequently, if remediation works are to be
planned, according to techniques that are described in Chapter 15.
12.3.1. Sampling strategy
The precise and detailed determination of the stratigraphy and hydrogeology of a
contaminated site, together with that of the extent of contamination, ideally requires
an excessive number of sampling points. The density of the sampling plan depends
on the size and topography of the site, the probable position of the contamination
and the required degree of precision.
Different sampling strategies can be adopted according to various models that
define the number and localization of sampling. The strategies most often referred to
in the literature and that are described here are based on systematic regular sampling
and random sampling. Other strategies include targeted sampling, random stratified
sampling, systematic unaligned sampling and fish bone sampling (see [FER 92,
JEW 93, KEI 91]).