Guidelines on remediation of contaminated sites
Appendix 4.8
Geological assessment
During soil boring, soil samples are normally taken at intervals of 50 cm and from any strata that may occur in between these intervals. At the same time, the drilling foreman will note down his observations on the soil boring and prepare a preliminary description of the extracted soil strata and a record of stratum boundaries. The actual geological assessment of the soil samples is carried out with due reference to this information and the specific type of contamination in each individual case. This assessment sees the samples being classified on the basis of a description of soil type (lithology), geological period and formation environment. The geological assessment is supported and supplemented by information from existing information from soil borings in the area, geological literature and topographical/geological maps. The main outline of the assessment is shown in Table 1.
Table 1
Main outline of sample description. The quality of samples and the purpose of the
sample description determines the degree of details and consequently the scope of the
assessment..
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The geological assessment may include:
 | An overall designation, written in capitals in the lithologic log, stating the dominant component of the sample, e.g. GRAVEL or SAND. Secondary component contents of the sample are written in lower-case letters in the lithologic log, e.g. clayey and/or silty, etc. |
| The degree of hardening is used e.g. to separate calcareous deposits into limestone and limestone rock, where the latter is characterised by being so hard that the sample can only be scratched using a knife. In hard rock, groundwater movement will occur in fissures. It must be noted that fissures in limestone rock will only be registered during geological assessment if block or core samples of rock are available. |
| The main component and secondary components, along with any fissuring, determines the permeability properties of the sample, properties influencing water movement in the strata. |
| Signs or layers of fill, e.g. brick or slag etc. |
| In many cases, the colour of the sample will reflect the oxidation-reduction (redox) conditions of the strata; which may influence the mobility of the contamination. In addition to this, colour/redox conditions, when seen in relation with the surrounding strata, can often provide an impression of the type and degree of contamination. |
| Based on the above description and the background information, classification of the soil samples is concluded by an assessment of the geological period and formation environment of the samples. The assessments of samples are presented in lithologic logs showing the stratification of the soil borings. |
Jointly, these records make it possible to correlate the geological information in a geological model which is in accordance with and related to the geological surroundings of the site.
Within the investigation site, the lithologic log provide information on geological and hydrogeological conditions as an aid for trial pumping etc. In addition to this, the records can also provide valuable information on conditions of geochemistry and dispersion with reference to contamination.